Freescale Semiconductor MC68HC908MR32 User Manual

MC68HC908MR32  
MC68HC908MR16  
Data Sheet  
M68HC08  
Microcontrollers  
MC68HC908MR32  
Rev. 6.1  
07/2005  
freescale.com  
MC68HC908MR32  
MC68HC908MR16  
Data Sheet  
To provide the most up-to-date information, the revision of our documents on the World Wide Web will be  
the most current. Your printed copy may be an earlier revision. To verify you have the latest information  
available, refer to:  
Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc.  
This product incorporates SuperFlash® technology licensed from SST.  
© Freescale Semiconductor, Inc., 2005. All rights reserved.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
3
Revision History  
The following revision history table summarizes changes contained in this document. For your  
convenience, the page number designators have been linked to the appropriate location.  
Revision History  
Revision  
Level  
Page  
Number(s)  
Date  
Description  
Figure 2-1. MC68HC908MR32 Memory Map — Added FLASH Block Protect  
Register (FLBPR) at address location $FF7E  
29  
August,  
2001  
3.0  
Figure A-1. MC68HC908MR16 Memory Map — Added FLASH Block Protect  
Register (FLBPR) at address location $FF7E  
306  
October,  
2001  
4.0  
5.0  
3.3.3 Conversion Time — Reworked equations and text for clarity.  
50  
Figure 18-8. Monitor Mode Circuit — PTA7 and connecting circuitry added  
279  
281  
Table 18-2. Monitor Mode Signal Requirements and Options — Switch locations  
added to column headings for clarity  
December,  
2001  
Section 16. Timer Interface A (TIMA) — Timer discrepancies corrected throughout  
this section.  
233  
255  
Section 17. Timer Interface B (TIMB) — Timer discrepancies corrected throughout  
this section.  
Reformatted to meet current publication standards  
Throughout  
2.8.2 FLASH Page Erase Operation — Procedure reworked for clarity  
2.8.3 FLASH Mass Erase Operation — Procedure reworked for clarity  
2.8.4 FLASH Program Operation — Procedure reworked for clarity  
Figure 14-14. SIM Break Status Register (SBSR) — Clarified definition of SBSW bit.  
42  
42  
November,  
2003  
43  
6.0  
6.1  
207  
19.5 DC Electrical Characteristics — Corrected maximum value for monitor mode  
entry voltage (on IRQ)  
291  
292  
19.6 FLASH Memory Characteristics — Updated table entries  
July,  
2005  
Updated to meet Freescale identity guidelines.  
Throughout  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
4
Freescale Semiconductor  
 
List of Chapters  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
5
List of Chapters  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
6
Freescale Semiconductor  
Table of Contents  
Power Supply Pins (VDD and VSS). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22  
CGM Power Supply Pins (VDDA and VSSAD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22  
Analog Power Supply Pins (VDDAD and VSSAD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23  
ADC Voltage Decoupling Capacitor Pin (VREFH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23  
ADC Voltage Reference Low Pin (VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
7
Table of Contents  
Analog-to-Digital Converter (ADC)  
ADC Analog Power Pin (VDDAD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50  
ADC Analog Ground Pin (VSSAD). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50  
ADC Voltage Reference Low Pin (VREFL) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50  
VREFH and VREFL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
8
Freescale Semiconductor  
PLL Analog Power Pin (VDDA) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
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Table of Contents  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
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Freescale Semiconductor  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
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Table of Contents  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
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Freescale Semiconductor  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
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Table of Contents  
VSS (Clock Ground) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
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Freescale Semiconductor  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
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Table of Contents  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
16  
Freescale Semiconductor  
Chapter 1  
General Description  
1.1 Introduction  
The MC68HC908MR32 is a member of the low-cost, high-performance M68HC08 Family of 8-bit  
microcontroller units (MCUs). All MCUs in the family use the enhanced M68HC08 central processor unit  
(CPU08) and are available with a variety of modules, memory sizes and types, and package types.  
The information contained in this document pertains to the MC68HC908MR16 with the exceptions shown  
1.2 Features  
Features include:  
High-performance M68HC08 architecture  
Fully upward-compatible object code with M6805, M146805, and M68HC05 Families  
8-MHz internal bus frequency  
On-chip FLASH memory with in-circuit programming capabilities of FLASH program memory:  
MC68HC908MR32 — 32 Kbytes  
MC68HC908MR16 — 16 Kbytes  
On-chip programming firmware for use with host personal computer  
FLASH data security(1)  
768 bytes of on-chip random-access memory (RAM)  
12-bit, 6-channel center-aligned or edge-aligned pulse-width modulator (PWMMC)  
Serial peripheral interface module (SPI)  
Serial communications interface module (SCI)  
16-bit, 4-channel timer interface module (TIMA)  
16-bit, 2-channel timer interface module (TIMB)  
Clock generator module (CGM)  
Low-voltage inhibit (LVI) module with software selectable trip points  
10-bit, 10-channel analog-to-digital converter (ADC)  
System protection features:  
Optional computer operating properly (COP) reset  
Low-voltage detection with optional reset  
Illegal opcode or address detection with optional reset  
Fault detection with optional PWM disabling  
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for  
unauthorized users.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
17  
     
General Description  
Available packages:  
64-pin plastic quad flat pack (QFP)  
56-pin shrink dual in-line package (SDIP)  
Low-power design, fully static with wait mode  
Master reset pin (RST) and power-on reset (POR)  
Stop mode as an option  
Break module (BRK) supports setting the in-circuit simulator (ICS) single break point  
Features of the CPU08 include:  
Enhanced M68HC05 programming model  
Extensive loop control functions  
16 addressing modes (eight more than the M68HC05)  
16-bit index register and stack pointer  
Memory-to-memory data transfers  
Fast 8 × 8 multiply instruction  
Fast 16/8 divide instruction  
Binary-coded decimal (BCD) instructions  
Optimization for controller applications  
C language support  
1.3 MCU Block Diagram  
Figure 1-1 shows the structure of the MC68HC908MR32.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
18  
Freescale Semiconductor  
 
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
PTC1/ATD9(1)  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
USER FLASH VECTOR SPACE — 46 BYTES  
PTC0/ATD8  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDAD  
(3)  
VSSAD  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 1-1. MCU Block Diagram  
 
General Description  
1.4 Pin Assignments  
Figure 1-2 shows the 64-pin QFP pin assignments and Figure 1-3 shows the 56-pin SDIP pin  
assignments.  
PTB2/ATD2  
PTB3/ATD3  
PTB4/ATD4  
PTB5/ATD5  
PTB6/ATD6  
PTB7/ATD7  
PTC0/ATD8  
PTC1/ATD9  
VDDAD  
IRQ  
1
48  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO  
PTF2/MOSI  
PTF1/SS  
2
47  
46  
45  
44  
43  
42  
41  
40  
39  
38  
37  
36  
35  
34  
3
4
5
6
PTF0/SPSCK  
VSS  
7
8
VDD  
9
VSSAD  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B  
PTE1/TCH0B  
10  
11  
12  
13  
14  
15  
VREFL  
VREFH  
PTC2  
PTC3  
PTC4  
PTC5  
16  
33  
Figure 1-2. 64-Pin QFP Pin Assignments  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
20  
Freescale Semiconductor  
   
Pin Assignments  
PTA2  
PTA3  
PTA1  
1
56  
55  
54  
53  
52  
51  
50  
49  
48  
47  
46  
45  
44  
43  
42  
41  
40  
39  
38  
37  
36  
35  
34  
33  
32  
31  
30  
29  
PTA0  
2
PTA4  
VSSA  
3
PTA5  
OSC2  
4
PTA6  
OSC1  
5
PTA7  
CGMXFC  
VDDA  
6
PTB0/ATD0  
PTB1/ATD1  
PTB2/ATD2  
PTB3/ATD3  
PTB4/ATD4  
PTB5/ATD5  
PTB6/ATD5  
PTB7/ATD7  
PTC0/ATD8  
VDDAD  
7
RST  
8
IRQ  
9
PTF5/TxD  
PTF4/RxD  
VSS  
10  
11  
12  
13  
14  
15  
16  
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
VDD  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
NC  
VSSAD/VREFL  
VREFH  
PTC2  
PTC3  
PWM6  
PTC4  
PWM5  
PTC5  
PWMGND  
PWM4  
PTC6  
PTD0/FAULT1  
PTD1/FAULT2  
PTD2/FAULT3  
PTD3/FAULT4  
PTD4/IS1  
PWM3  
PWM2  
PWM1  
PTD6/IS3  
PTD5/IS2  
Note:  
PTC1, PTE0, PTE1, PTE2, PTF0, PTF1, PTF2, and PTF3  
are removed from this package.  
Figure 1-3. 56-Pin SDIP Pin Assignments  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
21  
 
General Description  
1.4.1 Power Supply Pins (V and V )  
DD  
SS  
VDD and VSS are the power supply and ground pins. The MCU operates from a single power supply.  
Fast signal transitions on MCU pins place high, short-duration current demands on the power supply. To  
prevent noise problems, take special care to provide power supply bypassing at the MCU as Figure 1-4  
shows. Place the C1 bypass capacitor as close to the MCU as possible. Use a high-frequency-response  
ceramic capacitor for C1. C2 is an optional bulk current bypass capacitor for use in applications that  
require the port pins to source high-current levels.  
MCU  
VDD  
VSS  
C1  
0.1 µF  
+
C2  
1–10 µF  
VDD  
Note: Component values shown represent typical applications.  
Figure 1-4. Power Supply Bypassing  
1.4.2 Oscillator Pins (OSC1 and OSC2)  
The OSC1 and OSC2 pins are the connections for the on-chip oscillator circuit. For more detailed  
1.4.3 External Reset Pin (RST)  
A logic 0 on the RST pin forces the MCU to a known startup state. RST is bidirectional, allowing a reset  
of the entire system. It is driven low when any internal reset source is asserted. See Chapter 14 System  
1.4.4 External Interrupt Pin (IRQ)  
IRQ is an asynchronous external interrupt pin. See Chapter 8 External Interrupt (IRQ).  
1.4.5 CGM Power Supply Pins (V  
and V  
)
DDA  
SSAD  
VDDA and VSSAD are the power supply pins for the analog portion of the clock generator module (CGM).  
Decoupling of these pins should be per the digital supply. See Chapter 4 Clock Generator Module (CGM).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
22  
Freescale Semiconductor  
           
Pin Assignments  
1.4.6 External Filter Capacitor Pin (CGMXFC)  
CGMXFC is an external filter capacitor connection for the CGM. See Chapter 4 Clock Generator Module  
(CGM).  
1.4.7 Analog Power Supply Pins (V  
and V  
)
SSAD  
DDAD  
VDDAD and VSSAD are the power supply pins for the analog-to-digital converter. Decoupling of these pins  
should be per the digital supply. See Chapter 3 Analog-to-Digital Converter (ADC).  
1.4.8 ADC Voltage Decoupling Capacitor Pin (V  
)
REFH  
VREFH is the power supply for setting the reference voltage. Connect the VREFH pin to the same voltage  
1.4.9 ADC Voltage Reference Low Pin (V  
)
REFL  
VREFL is the lower reference supply for the ADC. Connect the VREFL pin to the same voltage potential as  
1.4.10 Port A Input/Output (I/O) Pins (PTA7–PTA0)  
PTA7–PTA0 are general-purpose bidirectional input/output (I/O) port pins. See Chapter 10 Input/Output  
1.4.11 Port B I/O Pins (PTB7/ATD7–PTB0/ATD0)  
Port B is an 8-bit special function port that shares all eight pins with the analog-to-digital converter (ADC).  
1.4.12 Port C I/O Pins (PTC6–PTC2 and PTC1/ATD9–PTC0/ATD8)  
PTC6–PTC2 are general-purpose bidirectional I/O port pins Chapter 10 Input/Output (I/O) Ports  
(PORTS). PTC1/ATD9–PTC0/ATD8 are special function port pins that are shared with the  
analog-to-digital converter (ADC). See Chapter 3 Analog-to-Digital Converter (ADC) and Chapter 10  
1.4.13 Port D Input-Only Pins (PTD6/IS3–PTD4/IS1 and PTD3/FAULT4–PTD0/FAULT1)  
PTD6/IS3–PTD4/IS1 are special function input-only port pins that also serve as current sensing pins for  
the pulse-width modulator module (PWMMC). PTD3/FAULT4–PTD0/FAULT1 are special function port  
pins that also serve as fault pins for the PWMMC. See Chapter 12 Pulse-Width Modulator for Motor  
1.4.14 PWM Pins (PWM6–PWM1)  
PWM6–PWM1 are dedicated pins used for the outputs of the pulse-width modulator module (PWMMC).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
23  
                 
General Description  
1.4.15 PWM Ground Pin (PWMGND)  
PWMGND is the ground pin for the pulse-width modulator module (PWMMC). This dedicated ground pin  
is used as the ground for the six high-current PWM pins. See Chapter 12 Pulse-Width Modulator for Motor  
1.4.16 Port E I/O Pins (PTE7/TCH3A–PTE3/TCLKA and PTE2/TCH1B–PTE0/TCLKB)  
Port E is an 8-bit special function port that shares its pins with the two timer interface modules (TIMA and  
1.4.17 Port F I/O Pins (PTF5/TxD–PTF4/RxD and PTF3/MISO–PTF0/SPSCK)  
Port F is a 6-bit special function port that shares two of its pins with the serial communications interface  
module (SCI) and four of its pins with the serial peripheral interface module (SPI). See Chapter 15 Serial  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
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Freescale Semiconductor  
     
Chapter 2  
Memory  
2.1 Introduction  
The central processor unit (CPU08) can address 64 Kbytes of memory space. The memory map, shown  
in Figure 2-1, includes:  
32 Kbytes of FLASH  
768 bytes of random-access memory (RAM)  
46 bytes of user-defined vectors  
240 bytes of monitor read-only memory (ROM)  
2.2 Unimplemented Memory Locations  
Some addresses are unimplemented. Accessing an unimplemented address can cause an illegal address  
reset. In the memory map and in the input/output (I/O) register summary, unimplemented addresses are  
shaded.  
Some I/O bits are read only; the write function is unimplemented. Writing to a read-only I/O bit has no  
effect on microcontroller unit (MCU) operation. In register figures, the write function of read-only bits is  
shaded.  
Similarly, some I/O bits are write only; the read function is unimplemented. Reading of write-only I/O bits  
has no effect on MCU operation. In register figures, the read function of write-only bits is shaded.  
2.3 Reserved Memory Locations  
Some addresses are reserved. Writing to a reserved address can have unpredictable effects on MCU  
operation. In the memory map (Figure 2-1) and in the I/O register summary (Figure 2-2) reserved  
addresses are marked with the word reserved.  
Some I/O bits are reserved. Writing to a reserved bit can have unpredictable effects on MCU operation.  
In register figures, reserved bits are marked with the letter R.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
25  
       
Memory  
2.4 I/O Section  
Addresses $0000–$005F, shown in Figure 2-2, contain most of the control, status, and data registers.  
Additional I/O registers have these addresses:  
$FE00, SIM break status register (SBSR)  
$FE01, SIM reset status register (SRSR)  
$FE03, SIM break flag control register (SBFCR)  
$FE07, FLASH control register (FLCR)  
$FE0C, Break address register high (BRKH)  
$FE0D, Break address register low (BRKL)  
$FE0E, Break status and control register (BRKSCR)  
$FE0F, LVI status and control register (LVISCR)  
$FF7E, FLASH block protect register (FLBPR)  
$FFFF, COP control register (COPCTL)  
2.5 Memory Map  
Figure 2-1 shows the memory map for the MC68HC908MR32 while the memory map for the  
MC68HC908MR16 is shown in Appendix A MC68HC908MR16  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
26  
Freescale Semiconductor  
   
Memory Map  
$0000  
$005F  
I/O REGISTERS — 96 BYTES  
RAM — 768 BYTES  
$0060  
$035F  
$0360  
$7FFF  
UNIMPLEMENTED — 31,904 BYTES  
FLASH — 32,256 BYTES  
$8000  
$FDFF  
$FE00  
$FE01  
SIM BREAK STATUS REGISTER (SBSR)  
SIM RESET STATUS REGISTER (SRSR)  
RESERVED  
$FE02  
$FE03  
SIM BREAK FLAG CONTROL REGISTER (SBFCR)  
RESERVED  
$FE04  
$FE05  
$FE06  
$FE07  
$FE08  
RESERVED  
RESERVED  
RESERVED  
FLASH CONTROL REGISTER (FLCR)  
UNIMPLEMENTED  
$FE09  
$FE0A  
$FE0B  
$FE0C  
$FE0D  
$FE0E  
$FE0F  
UNIMPLEMENTED  
UNIMPLEMENTED  
SIM BREAK ADDRESS REGISTER HIGH (BRKH)  
SIM BREAK ADDRESS REGISTER LOW (BRKL)  
SIM BREAK FLAG CONTROL REGISTER (SBFCR)  
LVI STATUS AND CONTROL REGISTER (LVISCR)  
$FE10  
$FEFF  
MONITOR ROM — 240 BYTES  
$FF00  
$FF7D  
UNIMPLEMENTED — 126 BYTES  
FLASH BLOCK PROTECT REGISTER (FLBPR)  
UNIMPLEMENTED — 83 BYTES  
$FF7E  
$FF7F  
$FFD1  
$FFD2  
$FFFF  
VECTORS — 46 BYTES  
Figure 2-1. MC68HC908MR32 Memory Map  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
27  
 
Memory  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
(PTA) Write:  
Port A Data Register  
PTA7  
PTA6  
PTA5  
PTA4  
PTA3  
PTA2  
PTA1  
PTA0  
$0000  
Reset:  
Read:  
Unaffected by reset  
PTB4 PTB3  
Unaffected by reset  
PTC4 PTC3  
Unaffected by reset  
Port B Data Register  
PTB7  
PTB6  
PTC6  
PTB5  
PTC5  
PTB2  
PTC2  
PTB1  
PTC1  
PTB0  
PTC0  
$0001  
$0002  
$0003  
$0004  
$0005  
(PTB) Write:  
Reset:  
Read:  
0
Port C Data Register  
(PTC) Write:  
R
Reset:  
Read:  
0
PTD6  
R
PTD5  
R
PTD4  
R
PTD3  
R
PTD2  
R
PTD1  
R
PTD0  
R
Port D Data Register  
(PTD) Write:  
R
Reset:  
Read:  
Unaffected by reset  
Data Direction Register A  
DDRA7 DDRA6  
DDRA5  
DDRA4  
DDRA3  
DDRA2  
DDRA1 DDRA0  
(DDRA) Write:  
Reset:  
Read:  
0
0
0
DDRB5  
0
0
DDRB4  
0
0
DDRB3  
0
0
DDRB2  
0
0
0
Data Direction Register B  
DDRB7 DDRB6  
DDRB1 DDRB0  
(DDRB) Write:  
Reset:  
Read:  
0
0
0
DDRC6  
0
0
0
Data Direction Register C  
DDRC5  
0
DDRC4  
0
DDRC3  
0
DDRC2  
0
DDRC1 DDRC0  
$0006  
$0007  
(DDRC) Write:  
R
0
Reset:  
0
0
Unimplemented  
Read:  
Port E Data Register  
PTE7  
PTE6  
PTE5  
PTF5  
PTE4  
PTE3  
PTE2  
PTF2  
PTE1  
PTF1  
PTE0  
PTF0  
$0008  
$0009  
(PTE) Write:  
Reset:  
Read:  
Unaffected by reset  
PTF4 PTF3  
Unaffected by reset  
0
0
Port F Data Register  
(PTF) Write:  
R
R
Reset:  
$000A  
$000B  
Unimplemented  
Unimplemented  
Read:  
Data Direction Register E  
DDRE7 DDRE6  
DDRE5  
DDRE4  
0
DDRE3  
0
DDRE2  
DDRE1 DDRE0  
$000C  
(DDRE) Write:  
Reset:  
Read:  
0
0
0
0
0
DDRF5  
0
0
DDRF2  
0
0
DDRF1  
0
0
DDRF0  
0
Data Direction Register F  
DDRF4  
DDRF3  
$000D  
(DDRF) Write:  
R
R
Reset:  
0
0
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 1 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
28  
Freescale Semiconductor  
 
Memory Map  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read: TOF  
0
TRST  
0
0
R
TIMA Status/Control Register  
TOIE  
TSTOP  
PS2  
PS1  
PS0  
$000E  
(TASC) Write:  
0
0
TIMA Counter Register High  
Reset:  
0
Bit 14  
R
1
Bit 13  
R
0
0
Bit 10  
R
0
Bit 9  
R
0
Bit 8  
R
Read: Bit 15  
Bit 12  
R
Bit 11  
R
$000F  
$0010  
$0011  
$0012  
$0013  
$0014  
$0015  
$0016  
$0017  
$0018  
$0019  
(TACNTH) Write:  
R
0
Reset:  
0
0
0
0
0
0
0
Read: Bit 7  
Bit 6  
R
Bit 5  
R
Bit 4  
R
Bit 3  
R
Bit 2  
R
Bit 1  
R
Bit 0  
R
TIMA Counter Register Low  
(TACNTL) Write:  
R
0
Reset:  
Read:  
0
0
0
0
0
0
0
TIMA Counter Modulo  
Bit 15  
1
14  
1
13  
1
12  
1
11  
1
10  
1
9
1
Bit 8  
1
Register High (TAMODH) Write:  
Reset:  
Read:  
TIMA Counter Modulo  
Register Low (TAMODL) Write:  
Bit 7  
Bit 6  
1
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Reset:  
1
Read: CH0F  
TIMA Channel 0 Status/Control  
CH0IE  
0
MS0B  
0
MS0A  
0
ELS0B  
0
ELS0A  
0
TOV0 CH0MAX  
Register (TASC0) Write:  
0
0
Reset:  
Read:  
0
0
TIMA Channel 0 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TACH0H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMA Channel 0 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TACH0L) Write:  
Reset:  
Read: CH1F  
0
R
0
TIMA Channel 1 Status/Control  
CH1IE  
0
MS1A  
0
ELS1B  
0
ELS1A  
0
TOV1 CH1MAX  
Register (TASC1) Write:  
0
0
Reset:  
Read:  
0
0
TIMA Channel 1 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TACH1H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMA Channel 1 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TACH1L) Write:  
Reset:  
Read: CH2F  
TIMA Channel 2 Status/Control  
CH2IE  
MS2B  
0
MS2A  
ELS2B  
ELS2A  
0
TOV2 CH2MAX  
Register (TASC2) Write:  
0
0
Reset:  
0
0
0
0
0
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 2 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
29  
Memory  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
TIMA Channel 2 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
$001A  
$001B  
$001C  
$001D  
$001E  
$001F  
$0020  
$0021  
$0022  
$0023  
$0024  
$0025  
(TACH2H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMA Channel 2 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TACH2L) Write:  
Reset:  
Read: CH3F  
0
R
0
TIMA Channel 3 Status/Control  
CH3IE  
0
MS3A  
0
ELS3B  
0
ELS3A  
0
TOV3 CH3MAX  
Register (TASC3) Write:  
0
0
Reset:  
Read:  
0
0
TIMA Channel 3 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TACH3H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMA Channel 3 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TACH3L) Write:  
Reset:  
Read:  
Configuration Register  
EDGE BOTNEG TOPNEG  
INDEP  
LVIRST  
1
LVIPWR STOPE  
COPD  
(CONFIG) Write:  
Reset:  
0
DISX  
0
0
DISY  
0
0
0
PWMF  
0
1
ISENS0  
0
0
LDOK  
0
0
Read:  
PWM Control Register 1  
PWMINT  
ISENS1  
0
PWMEN  
(PCTL1) Write:  
Reset:  
Read:  
0
0
0
PRSC0  
0
PWM Control Register 2  
LDFQ1  
0
LDFQ0  
0
IPOL1  
0
IPOL2  
0
IPOL3  
0
PRSC1  
0
(PCTL2) Write:  
Reset:  
Read:  
0
Fault Control Register  
FINT4 FMODE4  
FINT3  
FMODE3  
FINT2  
FMODE2  
FINT1 FMODE1  
(FCR) Write:  
Reset:  
Read: FPIN4  
(FSR) Write:  
0
0
0
0
0
0
0
0
FFLAG4  
FPIN3  
FFLAG3  
FPIN2  
FFLAG2  
FPIN1  
FFLAG1  
Fault Status Register  
Reset:  
Read:  
U
0
0
U
0
DT5  
U
0
DT3  
U
0
DT1  
0
FTACK4  
0
DT6  
DT4  
DT2  
Fault Acknowledge Register  
(FTACK) Write:  
FTACK3  
0
FTACK2  
0
FTACK1  
0
Reset:  
Read:  
0
0
0
OUT6  
0
0
0
OUT2  
0
PWM Output Control Register  
OUTCTL  
OUT5  
OUT4  
OUT3  
0
OUT1  
(PWMOUT) Write:  
Reset:  
0
0
0
0
0
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 3 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
30  
Freescale Semiconductor  
Memory Map  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
0
0
0
0
Bit 11  
Bit 10  
Bit 9  
Bit 8  
PWM Counter Register High  
$0026  
(PCNTH) Write:  
Reset:  
0
0
0
0
0
0
0
0
Read: Bit 7  
(PCNTL) Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Bit 0  
PWM Counter Register Low  
$0027  
$0028  
$0029  
$002A  
$002B  
$002C  
$002D  
$002E  
$002F  
$0030  
Reset:  
Read:  
0
0
0
0
0
0
0
0
0
Bit 11  
X
0
Bit 10  
X
0
Bit 9  
X
0
Bit 8  
X
PWM Counter Modulo Register  
High (PMODH) Write:  
Reset:  
0
Bit 7  
X
0
Bit 6  
X
0
Bit 5  
X
0
Bit 4  
X
Read:  
PWM Counter Modulo Register  
Bit 3  
X
Bit 2  
X
Bit 1  
X
Bit 0  
X
Low (PMODL) Write:  
Reset:  
Read:  
PWM 1 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL1H) Write:  
Reset:  
Read:  
PWM 1 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL1L) Write:  
Reset:  
Read:  
PWM 2 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL2H) Write:  
Reset:  
Read:  
PWM 2 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL2L) Write:  
Reset:  
Read:  
PWM 3 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL3H) Write:  
Reset:  
Read:  
PWM 3 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL3L) Write:  
Reset:  
Read:  
PWM 4 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL4H) Write:  
Reset:  
Read:  
PWM 4 Value Register Low  
Bit 7  
Bit 6  
Bit 5  
0
Bit 4  
Bit 3  
Bit 2  
0
Bit 1  
Bit 0  
$0031  
(PVAL4L) Write:  
Reset:  
0
0
0
0
0
0
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 4 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
31  
Memory  
Addr.  
Register Name  
Bit 7  
Bit 15  
0
6
Bit 14  
0
5
Bit 13  
0
4
Bit 12  
0
3
Bit 11  
0
2
Bit 10  
0
1
Bit 9  
0
Bit 0  
Bit 8  
0
Read:  
PWM 5 Value Register High  
$0032  
$0033  
$0034  
$0035  
$0036  
$0037  
$0038  
$0039  
$003A  
$003B  
$003C  
(PMVAL5H) Write:  
Reset:  
Read:  
PWM 5 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL5L) Write:  
Reset:  
Read:  
PWM 6 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL6H) Write:  
Reset:  
Read:  
PWM 6 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PMVAL6L) Write:  
Reset:  
Read:  
Dead-Time Write-Once  
Register (DEADTM) Write:  
Bit 7  
1
Bit 6  
1
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Reset:  
Read:  
PWM Disable Mapping  
Write-Once Register (DISMAP) Write:  
Bit 7  
1
Bit 6  
1
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Reset:  
Read:  
SCI Control Register 1  
LOOPS  
0
ENSCI  
0
TXINV  
0
M
WAKE  
0
ILTY  
0
PEN  
0
PTY  
0
(SCC1) Write:  
Reset:  
0
Read:  
SCI Control Register 2  
SCTIE  
TCIE  
0
SCRIE  
ILIE  
TE  
RE  
0
RWU  
0
SBK  
0
(SCC2) Write:  
Reset:  
0
R8  
R
0
0
0
0
0
Read:  
SCI Control Register 3  
T8  
ORIE  
NEIE  
FEIE  
PEIE  
(SCC3) Write:  
Reset:  
R
R
U
U
TC  
R
0
0
0
OR  
R
0
NF  
R
0
FE  
R
0
PE  
R
Read: SCTE  
SCRF  
R
IDLE  
R
SCI Status Register 1  
(SCS1) Write:  
R
1
Reset:  
Read:  
1
0
0
0
0
0
0
0
0
0
0
0
0
BKF  
R
RPF  
R
SCI Status Register 2  
(SCS2) Write:  
R
R
R
R
R
R
Reset:  
Read:  
0
0
0
0
0
0
0
0
R7  
T7  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
R0  
T0  
SCI Data Register  
$003D  
(SCDR) Write:  
Reset:  
Unaffected by reset  
Bold = Buffered  
U = Unaffected X = Indeterminate  
R
= Reserved  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 5 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
32  
Freescale Semiconductor  
Memory Map  
Addr.  
Register Name  
Bit 7  
6
0
5
4
3
0
2
1
Bit 0  
SCR0  
0
Read:  
0
R
0
SCI Baud Rate Register  
SCP1  
SCP0  
SCR2  
SCR1  
0
$003E  
(SCBR) Write:  
R
0
R
Reset:  
Read:  
0
0
0
0
0
0
0
0
0
IRQF  
IRQ Status/Control Register  
IMASK1 MODE1  
$003F  
$0040  
$0041  
$0042  
$0043  
$0044  
$0045  
$0046  
(ISCR) Write:  
R
0
R
0
R
0
R
0
ACK1  
0
Reset:  
0
0
0
Read: COCO  
ADC Status and Control  
Register (ADSCR) Write:  
AIEN  
ADCO  
ADCH4  
ADCH3  
ADCH2  
ADCH1 ADCH0  
R
0
Reset:  
0
0
0
0
1
0
1
0
1
0
1
AD9  
R
1
AD8  
R
Read:  
0
ADC Data Register High  
Right Justified Mode (ADRH) Write:  
R
R
R
R
R
R
Reset:  
Unaffected by reset  
Read: AD7  
AD6  
R
AD5  
R
AD4  
R
AD3  
R
AD2  
R
AD1  
R
AD0  
R
ADC Data Register Low  
Right Justified Mode (ADRL) Write:  
R
Reset:  
Unaffected by reset  
Read:  
0
R
0
ADC Clock Register  
ADIV2  
ADIV1  
ADIV0  
0
ADICLK  
0
MODE1  
0
MODE0  
1
0
0
(ADCLK) Write:  
Reset:  
0
SPRIE  
0
0
Read:  
SPI Control Register  
R
0
SPMSTR  
CPOL  
CPHA  
SPWOM  
0
SPE  
0
SPTIE  
0
(SPCR) Write:  
Reset:  
1
OVRF  
R
0
MODF  
R
1
SPTE  
R
Read: SPRF  
SPI Status and Control  
Register (SPSCR) Write:  
ERRIE  
MODFEN  
SPR1  
SPR0  
R
0
Reset:  
0
0
0
1
0
0
0
Read:  
R7  
T7  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
R0  
T0  
SPI Data Register  
(SPDR) Write:  
Reset:  
Unaffected by reset  
$0047  
Unimplemented  
$0050  
Read: TOF  
0
TRST  
0
0
TIMB Status/Control Register  
TOIE  
TSTOP  
PS2  
PS1  
PS0  
$0051  
$0052  
(TBSC) Write:  
0
0
R
Reset:  
0
1
Bit 13  
R
0
0
Bit 10  
R
0
Bit 9  
R
0
Bit 8  
R
Read: Bit 15  
Bit 14  
Bit 12  
R
Bit 11  
TIMB Counter Register High  
(TBCNTH) Write:  
R
0
R
R
0
Reset:  
0
0
0
0
0
0
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 6 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
33  
Memory  
Addr.  
Register Name  
Bit 7  
6
Bit 6  
R
5
Bit 5  
R
4
Bit 4  
R
3
Bit 3  
R
2
Bit 2  
R
1
Bit 1  
R
Bit 0  
Bit 0  
R
Read: Bit 7  
TIMB Counter Register Low  
$0053  
$0054  
$0055  
$0056  
$0057  
$0058  
$0059  
$005A  
$005B  
$005C  
$005D  
(TBCNTL) Write:  
R
0
Reset:  
Read:  
0
0
0
0
0
0
0
TIMB Counter Modulo Register  
Bit 15  
1
Bit 14  
1
Bit 13  
1
Bit 12  
1
Bit 11  
1
Bit 10  
1
Bit 9  
1
Bit 8  
1
High (TBMODH) Write:  
Reset:  
Read:  
TIMB Counter Modulo Register  
Bit 7  
Bit 6  
1
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Low (TBMODL) Write:  
Reset:  
1
Read: CH0F  
TIMB Channel 0 Status/Control  
CH0IE  
0
MS0B  
0
MS0A  
0
ELS0B  
0
ELS0A  
0
TOV0 CH0MAX  
Register (TBSC0) Write:  
0
0
Reset:  
Read:  
0
0
TIMB Channel 0 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TBCH0H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMB Channel 0 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TBCH0L) Write:  
Reset:  
Read: CH1F  
0
R
0
TIMB Channel 1 Status/Control  
CH1IE  
0
MS1A  
0
ELS1B  
0
ELS1A  
0
TOV1 CH1MAX  
Register (TBSC1) Write:  
0
0
Reset:  
Read:  
0
0
TIMB Channel 1 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TBCH1H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
TIMB Channel 1 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TBCH1L) Write:  
Reset:  
Read:  
Indeterminate after reset  
PLLF  
1
1
R
1
1
R
1
1
R
1
PLL Control Register  
PLLIE  
PLLON  
BCS  
(PCTL) Write:  
R
R
Reset:  
Read:  
0
AUTO  
0
0
LOCK  
R
1
ACQ  
0
0
XLD  
0
1
0
0
0
0
PLL Bandwidth Control  
Register (PBWC) Write:  
Reset:  
R
0
R
0
R
0
R
0
0
Read:  
PLL Programming Register  
MUL7  
0
MUL6  
1
MUL5  
1
MUL4  
0
VRS7  
0
VRS6  
1
VRS5  
1
VRS4  
0
$005E  
$005F  
(PPG) Write:  
Reset:  
Unimplemented  
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 7 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
34  
Freescale Semiconductor  
Memory Map  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
SIM Break Status Register  
R
R
R
R
R
R
BW  
R
$FE00  
(SBSR) Write:  
Reset:  
Read: POR  
0
LVI  
R
PIN  
R
COP  
R
ILOP  
ILAD  
R
MENRST  
0
R
0
SIM Reset Status Register  
$FE01  
$FE03  
(SRSR) Write:  
R
1
R
0
R
0
Reset:  
Read:  
0
0
0
0
SIM Break Flag Control  
BCFE  
R
R
R
R
R
R
R
Register (SBFCR) Write:  
Reset:  
0
0
FLASH Control Register Read:  
(FLCR)  
0
0
0
0
0
0
HVEN  
0
MASS  
0
ERASE  
0
PGM  
0
Write:  
$FE08  
Reset:  
0
Read:  
Break Address Register High  
Bit 15  
0
14  
13  
0
12  
0
11  
0
10  
0
9
0
1
Bit 8  
0
$FE0C  
$FE0D  
$FE0E  
$FE0F  
$FF7E  
(BRKH) Write:  
Reset:  
0
Read:  
Break Address Register Low  
Bit 7  
0
6
0
5
4
3
2
Bit 0  
(BRKL) Write:  
Reset:  
0
0
0
0
0
0
0
0
0
0
0
0
Read:  
Break Status and Control  
Register (BRKSCR) Write:  
BRKE  
BRKA  
Reset:  
0
0
0
0
TRPSEL  
0
0
0
0
0
0
0
0
0
0
0
Read: LVIOUT  
LVI Status and Control Register  
(LVISCR) Write:  
R
0
R
0
R
0
R
0
R
0
R
0
R
0
Reset:  
Read:  
FLASH Block Protect Register  
BPR7  
0
BPR6  
0
BPR5  
0
BPR4  
0
BPR3  
0
BPR2  
0
BPR1  
0
BPR0  
0
(FLBPR) Write:  
Reset:  
Read:  
Low byte of reset vector  
Clear COP counter  
Unaffected by reset  
COP Control Register  
$FFFF  
(COPCTL) Write:  
Reset:  
U = Unaffected X = Indeterminate  
R
= Reserved  
Bold  
= Buffered  
= Unimplemented  
Figure 2-2. Control, Status, and Data Registers Summary (Sheet 8 of 8)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
35  
Memory  
Table 2-1 is a list of vector locations.  
Table 2-1. Vector Addresses  
Address  
$FFD2  
$FFD3  
$FFD4  
$FFD5  
$FFD6  
$FFD7  
$FFD8  
Vector  
SCI transmit vector (high)  
SCI transmit vector (low)  
SCI receive vector (high)  
SCI receive vector (low)  
SCI error vector (high)  
SCI error vector (low)  
(1)  
SPI transmit vector (high)  
(1)  
$FFD9  
$FFDA  
SPI transmit vector (low)  
SPI receive vector (high)  
(1)  
(1)  
$FFDB  
$FFDC  
$FFDD  
$FFDE  
$FFDF  
$FFE0  
$FFE1  
$FFE2  
$FFE3  
$FFE4  
$FFE5  
$FFE6  
$FFE7  
$FFE8  
$FFE9  
$FFEA  
$FFEB  
$FFEC  
$FFED  
SPI receive vector (low)  
A/D vector (high)  
A/D vector (low)  
TIMB overflow vector (high)  
TIMB overflow vector (low)  
TIMB channel 1 vector (high)  
TIMB channel 1 vector (low)  
TIMB channel 0 vector (high)  
TIMB channel 0 vector (low)  
TIMA overflow vector (high)  
TIMA overflow vector (low)  
TIMA channel 3 vector (high)  
TIMA channel 3 vector (low)  
TIMA channel 2 vector (high)  
TIMA channel 2 vector (low)  
TIMA channel 1 vector (high)  
TIMA channel 1 vector (low)  
TIMA channel 0 vector (high)  
TIMA channel 0 vector (low)  
1. The SPI module is not available in the 56-pin SDIP package.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
36  
Freescale Semiconductor  
 
Monitor ROM  
Table 2-1. Vector Addresses (Continued)  
Address  
$FFEE  
$FFEF  
$FFF0  
$FFF1  
$FFF2  
$FFF3  
$FFF4  
$FFF5  
$FFF6  
$FFF7  
$FFF8  
$FFF9  
$FFFA  
$FFFB  
$FFFC  
$FFFD  
$FFFE  
$FFFF  
Vector  
PWMMC vector (high)  
PWMMC vector (low)  
FAULT 4 (high)  
FAULT 4 (low)  
FAULT 3 (high)  
FAULT 3 (low)  
FAULT 2 (high)  
FAULT 2 (low)  
FAULT 1 (high)  
FAULT 1 (low)  
PLL vector (high)  
PLL vector (low)  
IRQ vector (high)  
IRQ vector (low)  
SWI vector (high)  
SWI vector (low)  
Reset vector (high)  
Reset vector (low)  
2.6 Monitor ROM  
The 240 bytes at addresses $FE10–$FEFF are reserved ROM addresses that contain the instructions for  
2.7 Random-Access Memory (RAM)  
Addresses $0060–$035F are RAM locations. The location of the stack RAM is programmable. The 16-bit  
stack pointer allows the stack to be anywhere in the 64-Kbyte memory space.  
NOTE  
For correct operation, the stack pointer must point only to RAM locations.  
Within page zero are 160 bytes of RAM. Because the location of the stack RAM is programmable, all page  
zero RAM locations can be used for input/output (I/O) control and user data or code. When the stack  
pointer is moved from its reset location at $00FF, direct addressing mode instructions can access  
efficiently all page zero RAM locations. Page zero RAM, therefore, provides ideal locations for frequently  
accessed global variables.  
Before processing an interrupt, the central processor unit (CPU) uses five bytes of the stack to save the  
contents of the CPU registers.  
NOTE  
For M68HC05 and M1468HC05 compatibility, the H register is not stacked.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
37  
   
Memory  
During a subroutine call, the CPU uses two bytes of the stack to store the return address. The stack  
pointer decrements during pushes and increments during pulls.  
NOTE  
Be careful when using nested subroutines. The CPU may overwrite data in  
the RAM during a subroutine or during the interrupt stacking operation.  
2.8 FLASH Memory (FLASH)  
The FLASH memory is an array of 32,256 bytes with an additional 46 bytes of user vectors and one byte  
of block protection.  
NOTE  
An erased bit reads as a 1 and a programmed bit reads as a 0.  
Program and erase operations are facilitated through control bits in a memory mapped register. Details  
for these operations appear later in this section.  
Memory in the FLASH array is organized into two rows per page. The page size is 128 bytes per page.  
The minimum erase page size is 128 bytes. Programming is performed on a row basis, 64 bytes at a time.  
The address ranges for the user memory and vectors are:  
$8000–$FDFF, user memory  
$FF7E, block protect register (FLBPR)  
$FE08, FLASH control register (FLCR)  
$FFD2–$FFFF, reserved for user-defined interrupt and reset vectors  
Programming tools are available from Freescale. Contact a local Freescale representative for more  
information.  
NOTE  
A security feature prevents viewing of the FLASH contents.(1)  
2.8.1 FLASH Control Register  
The FLASH control register (FLCR) controls FLASH program and erase operations.  
Address:  
$FE08  
Bit 7  
0
6
0
5
0
4
0
3
HVEN  
0
2
MASS  
0
1
ERASE  
0
Bit 0  
PGM  
0
Read:  
Write:  
Reset:  
0
0
0
0
= Unimplemented  
Figure 2-3. FLASH Control Register (FLCR)  
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for  
unauthorized users.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
38  
Freescale Semiconductor  
     
FLASH Memory (FLASH)  
HVEN — High-Voltage Enable Bit  
This read/write bit enables the charge pump to drive high voltages for program and erase operations  
in the array. HVEN can only be set if either PGM = 1 or ERASE = 1 and the proper sequence for  
program or erase is followed.  
1 = High voltage enabled to array and charge pump on  
0 = High voltage disabled to array and charge pump off  
MASS — Mass Erase Control Bit  
Setting this read/write bit configures the 32-Kbyte FLASH array for mass erase operation. Mass erase  
is disabled if any FLASH block is protected  
1 = MASS erase operation selected  
0 = MASS erase operation unselected  
ERASE — Erase Control Bit  
This read/write bit configures the memory for erase operation. ERASE is interlocked with the PGM bit  
such that both bits cannot be equal to 1 or set to 1 at the same time.  
1 = Erase operation selected  
0 = Erase operation unselected  
PGM — Program Control Bit  
This read/write bit configures the memory for program operation. PGM is interlocked with the ERASE  
bit such that both bits cannot be equal to 1 or set to 1 at the same time.  
1 = Program operation selected  
0 = Program operation unselected  
2.8.2 FLASH Page Erase Operation  
Use this step-by-step procedure to erase a page (128 bytes) of FLASH memory.  
1. Set the ERASE bit and clear the MASS bit in the FLASH control register.  
2. Read the FLASH block protect register.  
3. Write any data to any FLASH location within the address range of the block to be erased.  
4. Wait for a time, tNVS (minimum 10 µs).  
5. Set the HVEN bit.  
6. Wait for a time, tErase (minimum 1 ms or 4 ms).  
7. Clear the ERASE bit.  
8. Wait for a time, tNVH (minimum 5 µs).  
9. Clear the HVEN bit.  
10. After time, tRCV (typical 1 µs), the memory can be accessed in read mode again.  
NOTE  
Programming and erasing of FLASH locations cannot be performed by  
code being executed from the FLASH memory. While these operations  
must be performed in the order shown, other unrelated operations may  
occur between the steps.  
In applications that require more than 1000 program/erase cycles, use the 4 ms page erase specification  
to get improved long-term reliability. Any application can use this 4 ms page erase specification. However,  
in applications where a FLASH location will be erased and reprogrammed less than 1000 times, and  
speed is important, use the 1 ms page erase specification to get a shorter cycle time.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
39  
 
Memory  
2.8.3 FLASH Mass Erase Operation  
Use this step-by-step procedure to erase the entire FLASH memory.  
1. Set both the ERASE bit and the MASS bit in the FLASH control register.  
2. Read the FLASH block protect register.  
3. Write any data to any FLASH address(1) within the FLASH memory address range.  
4. Wait for a time, tNVS (minimum 10 µs).  
5. Set the HVEN bit.  
6. Wait for a time, tMErase (minimum 4 ms).  
7. Clear the ERASE and MASS bits.  
NOTE  
Mass erase is disabled whenever any block is protected (FLBPR does not  
equal $FF).  
8. Wait for a time, tNVHL (minimum 100 µs).  
9. Clear the HVEN bit.  
10. After time, tRCV (typical 1 µs), the memory can be accessed in read mode again.  
NOTE  
Programming and erasing of FLASH locations cannot be performed by  
code being executed from the FLASH memory. While these operations  
must be performed in the order shown, other unrelated operations may  
occur between the steps.  
1. When in monitor mode, with security sequence failed (see 18.3.2 Security), write to the FLASH block protect register instead  
of any FLASH address.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
40  
Freescale Semiconductor  
 
FLASH Memory (FLASH)  
2.8.4 FLASH Program Operation  
Use the following step-by-step procedure to program a row of FLASH memory. Figure 2-4 shows a  
flowchart of the programming algorithm.  
NOTE  
Only bytes which are currently $FF may be programmed.  
1. Set the PGM bit. This configures the memory for program operation and enables the latching of  
address and data for programming.  
2. Read the FLASH block protect register.  
3. Write any data to any FLASH location within the address range desired.  
4. Wait for a time, tNVS (minimum 10 µs).  
5. Set the HVEN bit.  
6. Wait for a time, tPGS (minimum 5 µs).  
7. Write data to the FLASH address being programmed(1).  
8. Wait for time, tPROG (minimum 30 µs).  
9. Repeat step 7 and 8 until all desired bytes within the row are programmed.  
10. Clear the PGM bit(1).  
11. Wait for time, tNVH (minimum 5 µs).  
12. Clear the HVEN bit.  
13. After time, tRCV (typical 1 µs), the memory can be accessed in read mode again.  
NOTE  
The COP register at location $FFFF should not be written between steps  
5-12, when the HVEN bit is set. Since this register is located at a valid  
FLASH address, unpredictable behavior may occur if this location is written  
while HVEN is set.  
This program sequence is repeated throughout the memory until all data is programmed.  
NOTE  
Programming and erasing of FLASH locations cannot be performed by  
code being executed from the FLASH memory. While these operations  
must be performed in the order shown, other unrelated operations may  
occur between the steps. Do not exceed tPROG maximum, see 19.6 FLASH  
1. The time between each FLASH address change, or the time between the last FLASH address programmed to clearing PGM  
bit, must not exceed the maximum programming time, t  
maximum.  
PROG  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
41  
 
Memory  
1
2
3
ALGORITHM FOR PROGRAMMING  
A ROW (64 BYTES) OF FLASH MEMORY  
SET PGM BIT  
READ THE FLASH BLOCK PROTECT REGISTER  
WRITE ANY DATA TO ANY FLASH ADDRESS  
WITHIN THE ROW ADDRESS RANGE DESIRED  
4
5
6
WAIT FOR A TIME, tNVS  
SET HVEN BIT  
WAIT FOR A TIME, tPGS  
7
8
WRITE DATA TO THE FLASH ADDRESS  
TO BE PROGRAMMED  
WAIT FOR A TIME, tPROG  
COMPLETED  
YES  
PROGRAMMING  
THIS ROW?  
NO  
10  
CLEAR PGM BIT  
WAIT FOR A TIME, tNVH  
CLEAR HVEN BIT  
11  
12  
Note:  
The time between each FLASH address change (step 7 to step 7), or  
the time between the last FLASH address programmed  
to clearing PGM bit (step 7 to step 10)  
must not exceed the maximum programming  
13  
WAIT FOR A TIME, tRCV  
END OF PROGRAMMING  
time, t  
max.  
PROG  
This row program algorithm assumes the row/s  
to be programmed are initially erased.  
Figure 2-4. FLASH Programming Flowchart  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
42  
Freescale Semiconductor  
 
FLASH Memory (FLASH)  
2.8.5 FLASH Block Protection  
Due to the ability of the on-board charge pump to erase and program the FLASH memory in the target  
application, provision is made for protecting a block of memory from unintentional erase or program  
operations due to system malfunction. This protection is done by using a FLASH block protect register  
(FLBPR).  
The FLBPR determines the range of the FLASH memory which is to be protected. The range of the  
protected area starts from a location defined by FLBPR and ends at the bottom of the FLASH memory  
($FFFF). When the memory is protected, the HVEN bit cannot be set in either ERASE or PROGRAM  
operations.  
NOTE  
In performing a program or erase operation, the FLASH block protect  
register must be read after setting the PGM or ERASE bit and before  
asserting the HVEN bit  
When the FLBPR is programmed with all 0s, the entire memory is protected from being programmed and  
erased. When all the bits are erased (all 1s), the entire memory is accessible for program and erase.  
When bits within the FLBPR are programmed, they lock a block of memory, whose address ranges are  
shown in 2.8.6 FLASH Block Protect Register. Once the FLBPR is programmed with a value other than  
$FF, any erase or program of the FLBPR or the protected block of FLASH memory is prohibited. Mass  
erase is disabled whenever any block is protected (FLBPR does not equal $FF). The FLBPR itself can be  
erased or programmed only with an external voltage, VTST, present on the IRQ pin. This voltage also  
allows entry from reset into the monitor mode.  
2.8.6 FLASH Block Protect Register  
The FLASH block protect register (FLBPR) is implemented as a byte within the FLASH memory, and  
therefore can be written only during a programming sequence of the FLASH memory. The value in this  
register determines the starting location of the protected range within the FLASH memory.  
Address:  
$FF7E  
Bit 7  
6
BPR6  
0
5
BPR5  
0
4
BPR4  
0
3
BPR3  
0
2
BPR2  
0
1
BPR1  
0
Bit 0  
BPR0  
0
Read:  
Write:  
Reset:  
BPR7  
0
U = Unaffected by reset. Initial value from factory is 1.  
Write to this register by a programming sequence to the FLASH memory.  
Figure 2-5. FLASH Block Protect Register (FLBPR)  
BPR[7:0] — FLASH Block Protect Bits  
These eight bits represent bits [14:7] of a 16-bit memory address. Bit 15 is 1 and bits [6:0] are 0s.  
The resultant 16-bit address is used for specifying the start address of the FLASH memory for block  
protection. The FLASH is protected from this start address to the end of FLASH memory at $FFFF.  
With this mechanism, the protect start address can be XX00 and XX80 (128 bytes page boundaries)  
within the FLASH memory.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
43  
     
Memory  
16-BIT MEMORY ADDRESS  
START ADDRESS OF FLASH  
BLOCK PROTECT  
0
0
0
0
0
0
0
FLBPR VALUE  
1
Figure 2-6. FLASH Block Protect Start Address  
Refer to Table 2-2 for examples of the protect start address.  
Table 2-2. Examples of Protect Start Address  
BPR[7:0]  
$00  
Start of Address of Protect Range  
The entire FLASH memory is protected.  
$8080 (1000 0000 1000 0000)  
$8100 (1000 0001 0000 0000)  
and so on...  
$01 (0000 0001)  
$02 (0000 0010)  
$FE (1111 1110)  
$FF00 (1111 1111 0000 0000)  
$FF  
The entire FLASH memory is not protected.  
Note: The end address of the protected range is always $FFFF.  
2.8.7 Wait Mode  
Putting the MCU into wait mode while the FLASH is in read mode does not affect the operation of the  
FLASH memory directly, but there will not be any memory activity since the CPU is inactive.  
The WAIT instruction should not be executed while performing a program or erase operation on the  
FLASH. Otherwise, the operation will discontinue, and the FLASH will be on standby mode.  
2.8.8 Stop Mode  
Putting the MCU into stop mode while the FLASH is in read mode does not affect the operation of the  
FLASH memory directly, but there will not be any memory activity since the CPU is inactive.  
The STOP instruction should not be executed while performing a program or erase operation on the  
FLASH, otherwise the operation will discontinue, and the FLASH will be on standby mode  
NOTE  
Standby mode is the power-saving mode of the FLASH module in which all  
internal control signals to the FLASH are inactive and the current  
consumption of the FLASH is at a minimum.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
44  
Freescale Semiconductor  
     
Chapter 3  
Analog-to-Digital Converter (ADC)  
3.1 Introduction  
This section describes the 10-bit analog-to-digital converter (ADC).  
3.2 Features  
Features of the ADC module include:  
10 channels with multiplexed input  
Linear successive approximation  
10-bit resolution, 8-bit accuracy  
Single or continuous conversion  
Conversion complete flag or conversion complete interrupt  
Selectable ADC clock  
Left or right justified result  
Left justified sign data mode  
High impedance buffered ADC input  
3.3 Functional Description  
Ten ADC channels are available for sampling external sources at pins PTC1/ATD9:PTC0/ATD8 and  
PTB7/ATD7:PTB0/ATD0. To achieve the best possible accuracy, these pins are implemented as  
input-only pins when the analog-to-digital (A/D) feature is enabled. An analog multiplexer allows the single  
ADC to select one of the 10 ADC channels as ADC voltage IN (ADCVIN). ADCVIN is converted by the  
successive approximation algorithm. When the conversion is completed, the ADC places the result in the  
ADC data register (ADRH and ADRL) and sets a flag or generates an interrupt. See Figure 3-2.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
45  
         
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
PTC1/ATD9(1)  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
USER FLASH VECTOR SPACE — 46 BYTES  
PTC0/ATD8  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 3-1. Block Diagram Highlighting ADC Block and Pins  
Functional Description  
INTERNAL  
DATA BUS  
PTB/Cx  
ADC CHANNEL x  
READ PTB/PTC  
DISABLE  
ADC DATA REGISTERS  
CONVERSION  
COMPLETE  
ADC VOLTAGE IN  
ADVIN  
INTERRUPT  
LOGIC  
CHANNEL  
SELECT  
ADC  
ADCH[4:0]  
AIEN  
COCO  
ADC CLOCK  
CGMXCLK  
CLOCK  
GENERATOR  
BUS CLOCK  
ADIV[2:0]  
ADICLK  
Figure 3-2. ADC Block Diagram  
3.3.1 ADC Port I/O Pins  
PTC1/ATD9:PTC0/ATD8 and PTB7/ATD7:PTB0/ATD0 are general-purpose I/O pins that are shared with  
the ADC channels.  
The channel select bits define which ADC channel/port pin will be used as the input signal. The ADC  
overrides the port logic when that port is selected by the ADC multiplexer. The remaining ADC  
channels/port pins are controlled by the port logic and can be used as general-purpose input/output (I/O)  
pins. Writes to the port register or DDR will not have any effect on the port pin that is selected by the ADC.  
Read of a port pin which is in use by the ADC will return a 0.  
3.3.2 Voltage Conversion  
When the input voltage to the ADC equals VREFH, the ADC converts the signal to $3FF (full scale). If the  
input voltage equals VREFL, the ADC converts it to $000. Input voltages between VREFH and VREFL are  
straight-line linear conversions. All other input voltages will result in $3FF if greater than VREFH and $000  
if less than VREFL  
.
NOTE  
Input voltage should not exceed the analog supply voltages. See  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
47  
     
Analog-to-Digital Converter (ADC)  
3.3.3 Conversion Time  
Conversion starts after a write to the ADSCR. A conversion is between 16 and 17 ADC clock cycles,  
therefore:  
16 to17 ADC Cycles  
Conversion time =  
ADC Frequency  
Number of Bus Cycles = Conversion Time x CPU Bus Frequency  
The ADC conversion time is determined by the clock source chosen and the divide ratio selected. The  
clock source is either the bus clock or CGMXCLK and is selectable by ADICLK located in the ADC clock  
register. For example, if CGMXCLK is 4 MHz and is selected as the ADC input clock source, the ADC  
input clock divide-by-4 prescale is selected and the CPU bus frequency is 8 MHz:  
16 to 17 ADC Cycles  
Conversion Time =  
= 16 to 17 µs  
4 MHz/4  
Number of bus cycles = 16 µs x 8 MHz = 128 to 136 cycles  
NOTE  
The ADC frequency must be between fADIC minimum and fADIC maximum  
to meet A/D specifications. See 19.13 Analog-to-Digital Converter (ADC)  
Since an ADC cycle may be comprised of several bus cycles (eight, 136 minus 128, in the previous  
example) and the start of a conversion is initiated by a bus cycle write to the ADSCR, from zero to eight  
additional bus cycles may occur before the start of the initial ADC cycle. This results in a fractional ADC  
cycle and is represented as the 17th cycle.  
3.3.4 Continuous Conversion  
In continuous conversion mode, the ADC data registers ADRH and ADRL will be filled with new data after  
each conversion. Data from the previous conversion will be overwritten whether that data has been read  
or not. Conversions will continue until the ADCO bit is cleared. The COCO bit is set after each conversion  
and will stay set until the next read of the ADC data register.  
When a conversion is in process and the ADSCR is written, the current conversion data should be  
discarded to prevent an incorrect reading.  
3.3.5 Result Justification  
The conversion result may be formatted in four different ways:  
1. Left justified  
2. Right justified  
3. Left Justified sign data mode  
4. 8-bit truncation mode  
All four of these modes are controlled using MODE0 and MODE1 bits located in the ADC clock register  
(ADCR).  
Left justification will place the eight most significant bits (MSB) in the corresponding ADC data register  
high, ADRH. This may be useful if the result is to be treated as an 8-bit result where the two least  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
48  
Freescale Semiconductor  
     
Functional Description  
significant bits (LSB), located in the ADC data register low, ADRL, can be ignored. However, ADRL must  
be read after ADRH or else the interlocking will prevent all new conversions from being stored.  
Right justification will place only the two MSBs in the corresponding ADC data register high, ADRH, and  
the eight LSBs in ADC data register low, ADRL. This mode of operation typically is used when a 10-bit  
unsigned result is desired.  
Left justified sign data mode is similar to left justified mode with one exception. The MSB of the 10-bit  
result, AD9 located in ADRH, is complemented. This mode of operation is useful when a result,  
represented as a signed magnitude from mid-scale, is needed. Finally, 8-bit truncation mode will place  
the eight MSBs in ADC data register low, ADRL. The two LSBs are dropped. This mode of operation is  
used when compatibility with 8-bit ADC designs are required. No interlocking between ADRH and ADRL  
is present.  
NOTE  
Quantization error is affected when only the most significant eight bits are  
used as a result. See Figure 3-3.  
8-BIT 10-BIT  
RESULT RESULT  
IDEAL 8-BIT CHARACTERISTIC  
WITH QUANTIZATION = 1/2  
10-BIT TRUNCATED  
TO 8-BIT RESULT  
003  
00B  
00A  
IDEAL 10-BIT CHARACTERISTIC  
WITH QUANTIZATION = 1/2  
009  
008  
007  
006  
005  
004  
003  
002  
001  
000  
002  
001  
000  
WHEN TRUNCATION IS USED,  
ERROR FROM IDEAL 8-BIT = 3/8 LSB  
DUE TO NON-IDEAL QUANTIZATION.  
INPUT VOLTAGE  
1/2  
2 1/2  
4 1/2  
6 1/2  
8 1/2  
REPRESENTED AS 10-BIT  
9 1/2  
INPUT VOLTAGE  
1 1/2  
3 1/2  
5 1/2  
7 1/2  
1/2  
1 1/2  
2 1/2  
REPRESENTED AS 8-BIT  
Figure 3-3. 8-Bit Truncation Mode Error  
3.3.6 Monotonicity  
The conversion process is monotonic and has no missing codes.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
49  
   
Analog-to-Digital Converter (ADC)  
3.4 Interrupts  
When the AIEN bit is set, the ADC module is capable of generating a CPU interrupt after each ADC  
conversion. A CPU interrupt is generated if the COCO bit is at 0. The COCO bit is not used as a  
conversion complete flag when interrupts are enabled.  
3.5 Wait Mode  
The WAIT instruction can put the MCU in low power-consumption standby mode.  
The ADC continues normal operation during wait mode. Any enabled CPU interrupt request from the ADC  
can bring the MCU out of wait mode. If the ADC is not required to bring the MCU out of wait mode, power  
down the ADC by setting ADCH[4:0] in the ADC status and control register before executing the WAIT  
instruction.  
3.6 I/O Signals  
The ADC module has 10 input signals that are shared with port B and port C.  
3.6.1 ADC Analog Power Pin (V  
)
DDAD  
The ADC analog portion uses VDDAD as its power pin. Connect the VDDAD pin to the same voltage  
potential as VDD. External filtering may be necessary to ensure clean VDDAD for good results.  
NOTE  
Route VDDAD carefully for maximum noise immunity and place bypass  
capacitors as close as possible to the package.  
3.6.2 ADC Analog Ground Pin (V  
)
SSAD  
The ADC analog portion uses VSSAD as its ground pin. Connect the VSSAD pin to the same voltage  
potential as VSS.  
3.6.3 ADC Voltage Reference Pin (V  
)
REFH  
VREFH is the power supply for setting the reference voltage VREFH. Connect the VREFH pin to the same  
voltage potential as VDDAD. There will be a finite current associated with VREFH. See Chapter 19 Electrical  
NOTE  
Route VREFH carefully for maximum noise immunity and place bypass  
capacitors as close as possible to the package.  
3.6.4 ADC Voltage Reference Low Pin (V  
)
REFL  
VREFL is the lower reference supply for the ADC. Connect the VREFL pin to the same voltage potential as  
VSSAD. A finite current will be associated with VREFL. See Chapter 19 Electrical Specifications.  
NOTE  
In the 56-pin shrink dual in-line package (SDIP), VREFL and VSSAD are tied  
together.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
50  
Freescale Semiconductor  
             
I/O Registers  
3.6.5 ADC Voltage In (ADVIN)  
ADVIN is the input voltage signal from one of the 10 ADC channels to the ADC module.  
3.6.6 ADC External Connections  
This section describes the ADC external connections: VREFH and VREFL, ANx, and grounding.  
3.6.6.1 VREFH and VREFL  
Both ac and dc current are drawn through the VREFH and VREFL loop. The AC current is in the form of  
current spikes required to supply charge to the capacitor array at each successive approximation step.  
The current flows through the internal resistor string. The best external component to meet both these  
current demands is a capacitor in the 0.01 µF to 1 µF range with good high frequency characteristics. This  
capacitor is connected between VREFH and VREFL and must be placed as close as possible to the  
package pins. Resistance in the path is not recommended because the dc current will cause a voltage  
drop which could result in conversion errors.  
3.6.6.2 ANx  
Empirical data shows that capacitors from the analog inputs to VREFL improve ADC performance. 0.01-µF  
and 0.1-µF capacitors with good high-frequency characteristics are sufficient. These capacitors must be  
placed as close as possible to the package pins.  
3.6.6.3 Grounding  
In cases where separate power supplies are used for analog and digital power, the ground connection  
between these supplies should be at the VSSAD pin. This should be the only ground connection between  
these supplies if possible. The VSSA pin makes a good single point ground location. Connect the VREFL  
pin to the same potential as VSSAD at the single point ground location.  
3.7 I/O Registers  
These I/O registers control and monitor operation of the ADC:  
ADC status and control register, ADSCR  
ADC data registers, ADRH and ARDL  
ADC clock register, ADCLK  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
51  
           
Analog-to-Digital Converter (ADC)  
3.7.1 ADC Status and Control Register  
This section describes the function of the ADC status and control register (ADSCR). Writing ADSCR  
aborts the current conversion and initiates a new conversion.  
Address: $0040  
Bit 7  
6
5
ADCO  
0
4
ADCH4  
1
3
ADCH3  
1
2
ADCH2  
1
1
ADCH1  
1
Bit 0  
ADCH0  
1
Read:  
Write:  
Reset:  
COCO  
AIEN  
R
0
0
R
= Reserved  
Figure 3-4. ADC Status and Control Register (ADSCR)  
COCO — Conversions Complete Bit  
In non-interrupt mode (AIEN = 0), COCO is a read-only bit that is set at the end of each conversion.  
COCO will stay set until cleared by a read of the ADC data register. Reset clears this bit.  
In interrupt mode (AIEN = 1), COCO is a read-only bit that is not set at the end of a conversion. It  
always reads as a 0.  
1 = Conversion completed (AIEN = 0)  
0 = Conversion not completed (AIEN = 0) or CPU interrupt enabled  
(AIEN = 1)  
NOTE  
The write function of the COCO bit is reserved. When writing to the ADSCR  
register, always have a 0 in the COCO bit position.  
AIEN — ADC Interrupt Enable Bit  
When this bit is set, an interrupt is generated at the end of an ADC conversion. The interrupt signal is  
cleared when the data register is read or the status/control register is written. Reset clears the AIEN bit.  
1 = ADC interrupt enabled  
0 = ADC interrupt disabled  
ADCO — ADC Continuous Conversion Bit  
When set, the ADC will convert samples continuously and update the ADR register at the end of each  
conversion. Only one conversion is allowed when this bit is cleared. Reset clears the ADCO bit.  
1 = Continuous ADC conversion  
0 = One ADC conversion  
ADCH[4:0] — ADC Channel Select Bits  
ADCH4, ADCH3, ADCH2, ADCH1, and ADCH0 form a 5-bit field which is used to select one of 10 ADC  
channels. The ADC channels are detailed in Table 3-1.  
NOTE  
Take care to prevent switching noise from corrupting the analog signal  
when simultaneously using a port pin as both an analog and digital input.  
The ADC subsystem is turned off when the channel select bits are all set to 1. This feature allows for  
reduced power consumption for the MCU when the ADC is not used.  
NOTE  
Recovery from the disabled state requires one conversion cycle to stabilize.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
52  
Freescale Semiconductor  
   
I/O Registers  
The voltage levels supplied from internal reference nodes as specified in Table 3-1 are used to verify  
the operation of the ADC both in production test and for user applications.  
Table 3-1. Mux Channel Select  
ADCH4  
ADCH3  
ADCH2  
ADCH1  
ADCH0  
Input Select  
PTB0/ATD0  
PTB1/ATD1  
PTB2/ATD2  
PTB3/ATD3  
PTB4/ATD4  
PTB5/ATD5  
PTB6/ATD6  
PTB7/ATD7  
PTC0/ATD8  
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
0
1
0
1
0
1
0
1
0
1
(1)  
PTC1/ATD9  
(2)  
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
1
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
0
0
Unused  
Ø
Ø
Ø
Ø
Ø
Ø
(2)  
Unused  
(3)  
1
1
0
1
1
Reserved  
(2)  
1
1
1
1
1
1
1
1
1
1
1
1
0
0
1
1
0
1
0
1
Unused  
V
REFH  
V
REFL  
ADC power off  
1. ATD9 is not available in the 56-pin SDIP package.  
2. Used for factory testing.  
3. If any unused channels are selected, the resulting ADC conversion will be unknown.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
53  
 
Analog-to-Digital Converter (ADC)  
3.7.2 ADC Data Register High  
In left justified mode, this 8-bit result register holds the eight MSBs of the 10-bit result. This register is  
updated each time an ADC single channel conversion completes. Reading ADRH latches the contents of  
ADRL until ADRL is read. Until ADRL is read, all subsequent ADC results will be lost.  
Address:  
$0041  
Bit 7  
AD9  
R
6
AD8  
R
5
AD7  
R
4
AD6  
R
3
AD5  
R
2
AD4  
R
1
AD3  
R
Bit 0  
AD2  
R
Read:  
Write:  
Reset:  
Unaffected by reset  
R
= Reserved  
Figure 3-5. ADC Data Register High (ADRH) Left Justified Mode  
In right justified mode, this 8-bit result register holds the two MSBs of the 10-bit result. All other bits read  
as 0. This register is updated each time a single channel ADC conversion completes. Reading ADRH  
latches the contents of ADRL until ADRL is read. Until ADRL is read, all subsequent ADC results will be  
lost.  
Address:  
$0041  
Bit 7  
0
6
0
5
0
4
0
3
0
2
0
1
AD9  
R
Bit 0  
AD8  
R
Read:  
Write:  
Reset:  
R
R
R
R
R
R
Unaffected by reset  
R
= Reserved  
Figure 3-6. ADC Data Register High (ADRH) Right Justified Mode  
3.7.3 ADC Data Register Low  
In left justified mode, this 8-bit result register holds the two LSBs of the 10-bit result. All other bits read as  
0. This register is updated each time a single channel ADC conversion completes. Reading ADRH latches  
the contents of ADRL until ADRL is read. Until ADRL is read, all subsequent ADC results will be lost.  
Address:  
$0042  
Bit 7  
AD1  
R
6
AD0  
R
5
0
4
0
3
0
2
0
1
0
Bit 0  
0
Read:  
Write:  
Reset:  
R
R
R
R
R
R
Unaffected by reset  
R
= Reserved  
Figure 3-7. ADC Data Register Low (ADRL) Left Justified Mode  
In right justified mode, this 8-bit result register holds the eight LSBs of the 10-bit result. This register is  
updated each time an ADC conversion completes. Reading ADRH latches the contents of ADRL until  
ADRL is read. Until ADRL is read, all subsequent ADC results will be lost.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
54  
Freescale Semiconductor  
       
I/O Registers  
Address:  
$0042  
Bit 7  
AD7  
R
6
AD6  
R
5
AD5  
R
4
AD4  
R
3
AD3  
R
2
AD2  
R
1
AD1  
R
Bit 0  
AD0  
R
Read:  
Write:  
Reset:  
Unaffected by reset  
R
= Reserved  
Figure 3-8. ADC Data Register Low (ADRL) Right Justified Mode  
In 8-bit mode, this 8-bit result register holds the eight MSBs of the 10-bit result. This register is updated  
each time an ADC conversion completes. In 8-bit mode, this register contains no interlocking with ADRH.  
Address:  
$0042  
Bit 7  
AD9  
R
6
AD8  
R
5
AD7  
R
4
AD6  
R
3
AD5  
R
2
AD4  
R
1
AD3  
R
Bit 0  
AD2  
R
Read:  
Write:  
Reset:  
Unaffected by reset  
R
= Reserved  
Figure 3-9. ADC Data Register Low (ADRL) 8-Bit Mode  
3.7.4 ADC Clock Register  
This register selects the clock frequency for the ADC, selecting between modes of operation.  
Address:  
$0043  
Bit 7  
6
5
ADIV0  
0
4
ADICLK  
0
3
MODE1  
0
2
MODE0  
1
1
0
0
Bit 0  
0
Read:  
Write:  
Reset:  
ADIV2  
ADIV1  
R
0
0
0
R
= Reserved  
Figure 3-10. ADC Clock Register (ADCLK)  
ADIV2:ADIV0 — ADC Clock Prescaler Bits  
ADIV2, ADIV1, and ADIV0 form a 3-bit field which selects the divide ratio used by the ADC to generate  
the internal ADC clock. Table 3-2 shows the available clock configurations.  
Table 3-2. ADC Clock Divide Ratio  
ADIV2  
ADIV1  
ADIV0  
ADC Clock Rate  
ADC input clock ÷ 1  
ADC input clock ÷ 2  
ADC input clock ÷ 4  
ADC input clock ÷ 8  
ADC input clock ÷ 16  
0
0
0
0
1
0
0
1
1
X
0
1
0
1
X
X = don’t care  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
55  
     
Analog-to-Digital Converter (ADC)  
ADICLK — ADC Input Clock Select Bit  
ADICLK selects either bus clock or CGMXCLK as the input clock source to generate the internal ADC  
clock. Reset selects CGMXCLK as the ADC clock source.  
If the external clock (CGMXCLK) is equal to or greater than 1 MHz, CGMXCLK can be used as the  
clock source for the ADC. If CGMXCLK is less than 1 MHz, use the PLL-generated bus clock as the  
clock source. As long as the internal ADC clock is at fADIC, correct operation can be guaranteed. See  
1 = Internal bus clock  
0 = External clock, CGMXCLK  
CGMXCLK or bus frequency  
fADIC  
=
ADIV[2:0]  
MODE1:MODE0 — Modes of Result Justification Bits  
MODE1:MODE0 selects among four modes of operation. The manner in which the ADC conversion  
results will be placed in the ADC data registers is controlled by these modes of operation. Reset returns  
right-justified mode.  
00 = 8-bit truncation mode  
01 = Right justified mode  
10 = Left justified mode  
11 = Left justified sign data mode  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
56  
Freescale Semiconductor  
Chapter 4  
Clock Generator Module (CGM)  
4.1 Introduction  
This section describes the clock generator module (CGM, version A). The CGM generates the crystal  
clock signal, CGMXCLK, which operates at the frequency of the crystal. The CGM also generates the  
base clock signal, CGMOUT, from which the system integration module (SIM) derives the system clocks.  
CGMOUT is based on either the crystal clock divided by two or the phase-locked loop (PLL) clock,  
CGMVCLK, divided by two. The PLL is a frequency generator designed for use with crystals or ceramic  
resonators. The PLL can generate an 8-MHz bus frequency without using a 32-MHz external clock.  
4.2 Features  
Features of the CGM include:  
PLL with output frequency in integer multiples of the crystal reference  
Programmable hardware voltage-controlled oscillator (VCO) for low-jitter operation  
Automatic bandwidth control mode for low-jitter operation  
Automatic frequency lock detector  
Central processor unit (CPU) interrupt on entry or exit from locked condition  
4.3 Functional Description  
The CGM consists of three major submodules:  
1. Crystal oscillator circuit — The crystal oscillator circuit generates the constant crystal frequency  
clock, CGMXCLK.  
2. Phase-locked loop (PLL) — The PLL generates the programmable VCO frequency clock,  
CGMVCLK.  
3. Base clock selector circuit — This software-controlled circuit selects either CGMXCLK divided by  
two or the VCO clock, CGMVCLK, divided by two as the base clock, CGMOUT. The SIM derives  
the system clocks from CGMOUT.  
Figure 4-1 shows the structure of the CGM.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
57  
         
Clock Generator Module (CGM)  
CRYSTAL OSCILLATOR  
OSC2  
CGMXCLK  
CGMOUT  
TO SIM  
TO SIM  
CLOCK  
SELECT  
CIRCUIT  
OSC1  
A
B
÷ 2  
S*  
*WHEN S = 1, CGMOUT = B  
SIMOSCEN  
CGMRDV  
CGMRCLK  
BCS  
USER MODE  
VDDA  
CGMXFC  
VSS  
PTC2  
VRS[7:4]  
MONITOR MODE  
VOLTAGE  
CONTROLLED  
OSCILLATOR  
PHASE  
DETECTOR  
LOOP  
FILTER  
PLL ANALOG  
CGMINT  
LOCK  
DETECTOR  
BANDWIDTH  
CONTROL  
INTERRUPT  
CONTROL  
LOCK  
AUTO  
ACQ  
PLLIE  
PLLF  
MUL[7:4]  
CGMVDV  
CGMVCLK  
FREQUENCY  
DIVIDER  
Figure 4-1. CGM Block Diagram  
Addr.  
Register Name  
Bit 7  
PLLIE  
0
6
PLLF  
R
5
PLLON  
1
4
BCS  
0
3
2
1
1
1
Bit 0  
Read:  
1
R
1
1
R
1
PLL Control Register  
(PCTL) Write:  
$005C  
R
1
R
1
Reset:  
Read:  
0
LOCK  
R
0
0
0
0
PLL Bandwidth Control Register  
AUTO  
0
ACQ  
0
XLD  
0
$005D  
$005E  
(PBWC) Write:  
R
0
R
0
R
0
R
0
Reset:  
Read:  
0
PLL Programming Register  
MUL7  
MUL6  
MUL5  
1
MUL4  
0
VRS7  
0
VRS6  
1
VRS5  
1
VRS4  
0
(PPG) Write:  
Reset:  
0
1
R
= Reserved  
Figure 4-2. CGM I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
58  
Freescale Semiconductor  
   
Functional Description  
4.3.1 Crystal Oscillator Circuit  
The crystal oscillator circuit consists of an inverting amplifier and an external crystal. The OSC1 pin is the  
input to the amplifier and the OSC2 pin is the output. The SIMOSCEN signal from the system integration  
module (SIM) enables the crystal oscillator circuit.  
The CGMXCLK signal is the output of the crystal oscillator circuit and runs at a rate equal to the crystal  
frequency. CGMXCLK is then buffered to produce CGMRCLK, the PLL reference clock.  
CGMXCLK can be used by other modules which require precise timing for operation. The duty cycle of  
CGMXCLK is not guaranteed to be 50 percent and depends on external factors, including the crystal and  
related external components.  
An externally generated clock also can feed the OSC1 pin of the crystal oscillator circuit. Connect the  
external clock to the OSC1 pin and let the OSC2 pin float.  
4.3.2 Phase-Locked Loop Circuit (PLL)  
The PLL is a frequency generator that can operate in either acquisition mode or tracking mode, depending  
on the accuracy of the output frequency. The PLL can change between acquisition and tracking modes  
either automatically or manually.  
4.3.2.1 PLL Circuits  
The PLL consists of these circuits:  
Voltage-controlled oscillator (VCO)  
Modulo VCO frequency divider  
Phase detector  
Loop filter  
Lock detector  
The operating range of the VCO is programmable for a wide range of frequencies and for maximum  
immunity to external noise, including supply and CGMXFC noise. The VCO frequency is bound to a range  
from roughly one-half to twice the center-of-range frequency, fVRS. Modulating the voltage on the  
CGMXFC pin changes the frequency within this range. By design, fVRS is equal to the nominal  
center-of-range frequency, fNOM, (4.9152 MHz) times a linear factor, L or (L) fNOM  
CGMRCLK is the PLL reference clock, a buffered version of CGMXCLK. CGMRCLK runs at a frequency,  
RCLK, and is fed to the PLL through a buffer. The buffer output is the final reference clock, CGMRDV,  
running at a frequency, fRDV = fRCLK  
.
f
.
The VCO’s output clock, CGMVCLK, running at a frequency, fVCLK, is fed back through a programmable  
modulo divider. The modulo divider reduces the VCO clock by a factor, N. The divider’s output is the VCO  
feedback clock, CGMVDV, running at a frequency, fVDV = fVCLK/N. (See 4.3.2.4 Programming the PLL for  
more information.)  
The phase detector then compares the VCO feedback clock, CGMVDV, with the final reference clock,  
CGMRDV. A correction pulse is generated based on the phase difference between the two signals. The  
loop filter then slightly alters the dc voltage on the external capacitor connected to CGMXFC based on  
the width and direction of the correction pulse. The filter can make fast or slow corrections depending on  
its mode, described in 4.3.2.2 Acquisition and Tracking Modes. The value of the external capacitor and  
the reference frequency determines the speed of the corrections and the stability of the PLL.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
59  
     
Clock Generator Module (CGM)  
The lock detector compares the frequencies of the VCO feedback clock, CGMVDV, and the final  
reference clock, CGMRDV. Therefore, the speed of the lock detector is directly proportional to the final  
reference frequency, fRDV. The circuit determines the mode of the PLL and the lock condition based on  
this comparison.  
4.3.2.2 Acquisition and Tracking Modes  
The PLL filter is manually or automatically configurable into one of two operating modes:  
1. Acquisition mode — In acquisition mode, the filter can make large frequency corrections to the  
VCO. This mode is used at PLL startup or when the PLL has suffered a severe noise hit and the  
VCO frequency is far off the desired frequency. When in acquisition mode, the ACQ bit is clear in  
the PLL bandwidth control register. See 4.5.2 PLL Bandwidth Control Register.  
2. Tracking mode — In tracking mode, the filter makes only small corrections to the frequency of the  
VCO. PLL jitter is much lower in tracking mode, but the response to noise is also slower. The PLL  
enters tracking mode when the VCO frequency is nearly correct, such as when the PLL is selected  
as the base clock source. See 4.3.3 Base Clock Selector Circuit. The PLL is automatically in  
tracking mode when not in acquisition mode or when the ACQ bit is set.  
4.3.2.3 Manual and Automatic PLL Bandwidth Modes  
The PLL can change the bandwidth or operational mode of the loop filter manually or automatically.  
In automatic bandwidth control mode (AUTO = 1), the lock detector automatically switches between  
acquisition and tracking modes. Automatic bandwidth control mode also is used to determine when the  
VCO clock, CGMVCLK, is safe to use as the source for the base clock, CGMOUT. See 4.5.2 PLL  
Bandwidth Control Register. If PLL interrupts are enabled, the software can wait for a PLL interrupt  
request and then check the LOCK bit. If interrupts are disabled, software can poll the LOCK bit  
continuously (during PLL startup, usually) or at periodic intervals. In either case, when the LOCK bit is set,  
the VCO clock is safe to use as the source for the base clock. See 4.3.3 Base Clock Selector Circuit. If  
the VCO is selected as the source for the base clock and the LOCK bit is clear, the PLL has suffered a  
severe noise hit and the software must take appropriate action, depending on the application. See 4.6  
Interrupts for information and precautions on using interrupts.  
These conditions apply when the PLL is in automatic bandwidth control mode:  
The ACQ bit (see 4.5.2 PLL Bandwidth Control Register) is a read-only indicator of the mode of the  
filter. For more information, see 4.3.2.2 Acquisition and Tracking Modes.  
The ACQ bit is set when the VCO frequency is within a certain tolerance, TRK, and is cleared when  
the VCO frequency is out of a certain tolerance, UNT. For more information, see 4.8  
The LOCK bit is a read-only indicator of the locked state of the PLL.  
The LOCK bit is set when the VCO frequency is within a certain tolerance, Lock, and is cleared  
when the VCO frequency is out of a certain tolerance, UNL. For more information, see 4.8  
CPU interrupts can occur if enabled (PLLIE = 1) when the PLL’s lock condition changes, toggling  
the LOCK bit. For more information, see 4.5.1 PLL Control Register.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
60  
Freescale Semiconductor  
   
Functional Description  
The PLL also may operate in manual mode (AUTO = 0). Manual mode is used by systems that do not  
require an indicator of the lock condition for proper operation. Such systems typically operate well below  
f
BUSMAX and require fast startup. These conditions apply when in manual mode:  
ACQ is a writable control bit that controls the mode of the filter. Before turning on the PLL in manual  
mode, the ACQ bit must be clear.  
Before entering tracking mode (ACQ = 1), software must wait a given time, tACQ (see 4.8  
Acquisition/Lock Time Specifications), after turning on the PLL by setting PLLON in the PLL control  
register (PCTL).  
Software must wait a given time, tAL, after entering tracking mode before selecting the PLL as the  
clock source to CGMOUT (BCS = 1).  
The LOCK bit is disabled.  
CPU interrupts from the CGM are disabled.  
4.3.2.4 Programming the PLL  
Use this 9-step procedure to program the PLL. Table 4-1 lists the variables used and their meaning.  
Table 4-1. Variable Definitions  
Variable  
Definition  
Desired bus clock frequency  
f
BUSDES  
f
Desired VCO clock frequency  
Chosen reference crystal frequency  
Calculated VCO clock frequency  
Calculated bus clock frequency  
Nominal VCO center frequency  
Shifted FCO center frequency  
VCLKDES  
f
RCLK  
f
VCLK  
f
BUS  
f
NOM  
f
VRS  
1. Choose the desired bus frequency, fBUSDES  
Example: fBUSDES = 8 MHz  
.
2. Calculate the desired VCO frequency, fVCLKDES  
.
f
VCLKDES = 4 x fBUSDES  
Example: fVCLKDES = 4 x 8 MHz = 32 MHz  
3. Using a reference frequency, fRCLK, equal to the crystal frequency, calculate the VCO frequency  
multiplier, N. Round the result to the nearest integer.  
fVCLKDES  
N =  
fRCLK  
32 MHz  
4 MHz  
Example: N =  
= 8 MHz  
4. Calculate the VCO frequency, fVCLK  
.
fVCLK = N x fRCLK  
Example: fVCLK = 8 x 4 MHz = 32 MHz  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
61  
   
Clock Generator Module (CGM)  
5. Calculate the bus frequency, fBUS, and compare fBUS with fBUSDES  
fVCLK  
.
fBUS  
=
4
32 MHz  
4 MHz  
Example: N =  
= 8 MHz  
6. If the calculated fBUS is not within the tolerance limits of the application, select another fBUSDES or  
another fRCLK  
.
7. Using the value 4.9152 MHz for fNOM, calculate the VCO linear range multiplier, L. The linear range  
multiplier controls the frequency range of the PLL.  
fVCLK  
fNOM  
)
(
L = round  
32 MHz  
4.9152 MHz  
Example: L =  
= 7 MHz  
8. Calculate the VCO center-of-range frequency, fVRS. The center-or-range frequency is the midpoint  
between the minimum and maximum frequencies attainable by the PLL.  
f
VRS = L x fNOM  
Example: fVRS = 7 x 4.9152 MHz = 34.4 MHz  
For proper operation,  
fNOM  
fVRS – fVCLK | ≤  
2
CAUTION  
Exceeding the recommended maximum bus frequency or VCO frequency can crash the MCU.  
9. Program the PLL registers accordingly:  
a. In the upper four bits of the PLL programming register (PPG), program the binary equivalent  
of N.  
b. In the lower four bits of the PLL programming register (PPG), program the binary equivalent  
of L.  
4.3.2.5 Special Programming Exceptions  
The programming method described in 4.3.2.4 Programming the PLL does not account for possible  
exceptions. A value of 0 for N or L is meaningless when used in the equations given. To account for these  
exceptions:  
A 0 value for N is interpreted exactly the same as a value of 1.  
A 0 value for L disables the PLL and prevents its selection as the source for the base clock. See  
4.3.3 Base Clock Selector Circuit  
This circuit is used to select either the crystal clock, CGMXCLK, or the VCO clock, CGMVCLK, as the  
source of the base clock, CGMOUT. The two input clocks go through a transition control circuit that waits  
up to three CGMXCLK cycles and three CGMVCLK cycles to change from one clock source to the other.  
During this time, CGMOUT is held in stasis. The output of the transition control circuit is then divided by  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
62  
Freescale Semiconductor  
   
Functional Description  
two to correct the duty cycle. Therefore, the bus clock frequency, which is one-half of the base clock  
frequency, is one-fourth the frequency of the selected clock (CGMXCLK or CGMVCLK).  
The BCS bit in the PLL control register (PCTL) selects which clock drives CGMOUT. The VCO clock  
cannot be selected as the base clock source if the PLL is not turned on. The PLL cannot be turned off if  
the VCO clock is selected. The PLL cannot be turned on or off simultaneously with the selection or  
deselection of the VCO clock. The VCO clock also cannot be selected as the base clock source if the  
factor L is programmed to a 0. This value would set up a condition inconsistent with the operation of the  
PLL, so that the PLL would be disabled and the crystal clock would be forced as the source of the base  
clock.  
4.3.4 CGM External Connections  
In its typical configuration, the CGM requires seven external components. Five of these are for the crystal  
oscillator and two are for the PLL.  
The crystal oscillator is normally connected in a Pierce oscillator configuration, as shown in Figure 4-3.  
Figure 4-3 shows only the logical representation of the internal components and may not represent actual  
circuitry.  
SIMOSCEN  
CGMXCLK  
OSC1  
OSC2  
RS*  
VSS  
CGMXFC  
CF  
VDDA  
VDD  
CBYP  
RB  
X1  
*RS can be 0 (shorted) when used with  
higher frequency crystals. Refer to  
manufacturer’s data.  
C1  
C2  
Figure 4-3. CGM External Connections  
The oscillator configuration uses five components:  
1. Crystal, X1  
2. Fixed capacitor, C1  
3. Tuning capacitor, C2 (can also be a fixed capacitor)  
4. Feedback resistor, RB  
5. Series resistor, RS (optional)  
The series resistor (RS) is included in the diagram to follow strict Pierce oscillator guidelines and may not  
be required for all ranges of operation, especially with high-frequency crystals. Refer to the crystal  
manufacturer’s data for more information.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
63  
   
Clock Generator Module (CGM)  
Figure 4-3 also shows the external components for the PLL:  
Bypass capacitor, CBYP  
Filter capacitor, CF  
NOTE  
Routing should be done with great care to minimize signal cross talk and  
noise. (See 4.8 Acquisition/Lock Time Specifications for routing information  
and more information on the filter capacitor’s value and its effects on PLL  
performance.)  
4.4 I/O Signals  
This section describes the CGM input/output (I/O) signals.  
4.4.1 Crystal Amplifier Input Pin (OSC1)  
The OSC1 pin is an input to the crystal oscillator amplifier.  
4.4.2 Crystal Amplifier Output Pin (OSC2)  
The OSC2 pin is the output of the crystal oscillator inverting amplifier.  
4.4.3 External Filter Capacitor Pin (CGMXFC)  
The CGMXFC pin is required by the loop filter to filter out phase corrections. A small external capacitor is  
connected to this pin.  
NOTE  
To prevent noise problems, CF should be placed as close to the CGMXFC  
pin as possible, with minimum routing distances and no routing of other  
signals across the CF connection.  
4.4.4 PLL Analog Power Pin (V  
)
DDA  
VDDA is a power pin used by the analog portions of the PLL. Connect the VDDA pin to the same voltage  
potential as the VDD pin.  
NOTE  
Route VDDA carefully for maximum noise immunity and place bypass  
capacitors as close as possible to the package.  
4.4.5 Oscillator Enable Signal (SIMOSCEN)  
The SIMOSCEN signal comes from the system integration module (SIM) and enables the oscillator and  
PLL.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
64  
Freescale Semiconductor  
           
CGM Registers  
4.4.6 Crystal Output Frequency Signal (CGMXCLK)  
CGMXCLK is the crystal oscillator output signal. It runs at the full speed of the crystal (fXCLK) and comes  
directly from the crystal oscillator circuit. Figure 4-3 shows only the logical relation of CGMXCLK to OSC1  
and OSC2 and may not represent the actual circuitry. The duty cycle of CGMXCLK is unknown and may  
depend on the crystal and other external factors. Also, the frequency and amplitude of CGMXCLK can be  
unstable at startup.  
4.4.7 CGM Base Clock Output (CGMOUT)  
CGMOUT is the clock output of the CGM. This signal goes to the SIM, which generates the MCU clocks.  
CGMOUT is a 50 percent duty cycle clock running at twice the bus frequency. CGMOUT is software  
programmable to be either the oscillator output, CGMXCLK, divided by two or the VCO clock, CGMVCLK,  
divided by two.  
4.4.8 CGM CPU Interrupt (CGMINT)  
CGMINT is the interrupt signal generated by the PLL lock detector.  
4.5 CGM Registers  
These registers control and monitor operation of the CGM:  
PLL control register (PCTL) — see 4.5.1 PLL Control Register  
PLL bandwidth control register (PBWC) — see 4.5.2 PLL Bandwidth Control Register  
PLL programming register (PPG) — see 4.5.3 PLL Programming Register  
Figure 4-4 is a summary of the CGM registers.  
Addr.  
Register Name  
Bit 7  
PLLIE  
0
6
PLLF  
R
5
PLLON  
1
4
BCS  
0
3
1
2
1
1
1
Bit 0  
Read:  
PLL Control Register  
(PCTL) Write:  
1
R
1
$005C  
R
1
R
1
R
1
Reset:  
Read:  
0
LOCK  
R
0
0
0
0
PLL Bandwidth Control Register  
AUTO  
0
ACQ  
0
XLD  
0
$005D  
$005E  
Notes:  
(PBWC) Write:  
R
0
R
0
R
0
R
0
Reset:  
Read:  
0
PLL Programming Register  
MUL7  
MUL6  
MUL5  
1
MUL4  
0
VRS7  
0
VRS6  
1
VRS5  
1
VRS4  
0
(PPG) Write:  
Reset:  
0
1
= Reserved  
R
1. When AUTO = 0, PLLIE is forced to logic 0 and is read-only.  
2. When AUTO = 0, PLLF and LOCK read as logic 0.  
3. When AUTO = 1, ACQ is read-only.  
4. When PLLON = 0 or VRS[7:4] = $0, BCS is forced to logic 0 and is read-only.  
5. When PLLON = 1, the PLL programming register is read-only.  
6. When BCS = 1, PLLON is forced set and is read-only.  
Figure 4-4. CGM I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
65  
         
Clock Generator Module (CGM)  
4.5.1 PLL Control Register  
The PLL control register (PCTL) contains the interrupt enable and flag bits, the on/off switch, and the base  
clock selector bit.  
Address:  
$005C  
Bit 7  
6
5
PLLON  
1
4
BCS  
0
3
1
2
1
1
1
Bit 0  
1
Read:  
Write:  
Reset:  
PLLF  
PLLIE  
R
R
1
R
1
R
1
R
0
0
1
= Reserved  
R
Figure 4-5. PLL Control Register (PCTL)  
PLLIE — PLL Interrupt Enable Bit  
This read/write bit enables the PLL to generate an interrupt request when the LOCK bit toggles, setting  
the PLL flag, PLLF. When the AUTO bit in the PLL bandwidth control register (PBWC) is clear, PLLIE  
cannot be written and reads as logic 0. Reset clears the PLLIE bit.  
1 = PLL interrupts enabled  
0 = PLL interrupts disabled  
PLLF — PLL Interrupt Flag  
This read-only bit is set whenever the LOCK bit toggles. PLLF generates an interrupt request if the  
PLLIE bit also is set. PLLF always reads as logic 0 when the AUTO bit in the PLL bandwidth control  
register (PBWC) is clear. Clear the PLLF bit by reading the PLL control register. Reset clears the PLLF  
bit.  
1 = Change in lock condition  
0 = No change in lock condition  
NOTE  
Do not inadvertently clear the PLLF bit. Any read or read-modify-write  
operation on the PLL control register clears the PLLF bit.  
PLLON — PLL On Bit  
This read/write bit activates the PLL and enables the VCO clock, CGMVCLK. PLLON cannot be  
cleared if the VCO clock is driving the base clock, CGMOUT (BCS = 1). See 4.3.3 Base Clock Selector  
Circuit. Reset sets this bit so that the loop can stabilize as the MCU is powering up.  
1 = PLL on  
0 = PLL off  
BCS — Base Clock Select Bit  
This read/write bit selects either the crystal oscillator output, CGMXCLK, or the VCO clock,  
CGMVCLK, as the source of the CGM output, CGMOUT. CGMOUT frequency is one-half the  
frequency of the selected clock. BCS cannot be set while the PLLON bit is clear. After toggling BCS,  
it may take up to three CGMXCLK and three CGMVCLK cycles to complete the transition from one  
source clock to the other. During the transition, CGMOUT is held in stasis. See 4.3.3 Base Clock  
Selector Circuit. Reset clears the BCS bit.  
1 = CGMVCLK divided by two drives CGMOUT  
0 = CGMXCLK divided by two drives CGMOUT  
NOTE  
PLLON and BCS have built-in protection that prevents the base clock  
selector circuit from selecting the VCO clock as the source of the base clock  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
66  
Freescale Semiconductor  
     
CGM Registers  
if the PLL is off. Therefore, PLLON cannot be cleared when BCS is set, and  
BCS cannot be set when PLLON is clear. If the PLL is off (PLLON = 0),  
selecting CGMVCLK requires two writes to the PLL control register. See  
PCTL[3:0] — Unimplemented Bits  
These bits provide no function and always read as logic 1s.  
4.5.2 PLL Bandwidth Control Register  
The PLL bandwidth control register (PBWC):  
Selects automatic or manual (software-controlled) bandwidth control mode  
Indicates when the PLL is locked  
In automatic bandwidth control mode, indicates when the PLL is in acquisition or tracking mode  
In manual operation, forces the PLL into acquisition or tracking mode  
Address: $005D  
Bit 7  
6
5
ACQ  
0
4
XLD  
0
3
0
2
0
1
0
Bit 0  
0
Read:  
Write:  
Reset:  
LOCK  
AUTO  
R
R
0
R
0
R
0
R
0
0
0
= Reserved  
R
Figure 4-6. PLL Bandwidth Control Register (PBWC)  
AUTO — Automatic Bandwidth Control Bit  
This read/write bit selects automatic or manual bandwidth control. When initializing the PLL for manual  
operation (AUTO = 0), clear the ACQ bit before turning on the PLL. Reset clears the AUTO bit.  
1 = Automatic bandwidth control  
0 = Manual bandwidth control  
LOCK — Lock Indicator Bit  
When the AUTO bit is set, LOCK is a read-only bit that becomes set when the VCO clock, CGMVCLK,  
is locked (running at the programmed frequency). When the AUTO bit is clear, LOCK reads as logic 0  
and has no meaning. Reset clears the LOCK bit.  
1 = VCO frequency correct or locked  
0 = VCO frequency incorrect or unlocked  
ACQ — Acquisition Mode Bit  
When the AUTO bit is set, ACQ is a read-only bit that indicates whether the PLL is in acquisition mode  
or tracking mode. When the AUTO bit is clear, ACQ is a read/write bit that controls whether the PLL is  
in acquisition or tracking mode.  
In automatic bandwidth control mode (AUTO = 1), the last-written value from manual operation is  
stored in a temporary location and is recovered when manual operation resumes. Reset clears this bit,  
enabling acquisition mode.  
1 = Tracking mode  
0 = Acquisition mode  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
67  
     
Clock Generator Module (CGM)  
XLD — Crystal Loss Detect Bit  
When the VCO output, CGMVCLK, is driving CGMOUT, this read/write bit can indicate whether the  
crystal reference frequency is active or not. To check the status of the crystal reference, follow these  
steps:  
1. Write a logic 1 to XLD.  
2. Wait N × 4 cycles. (N is the VCO frequency multiplier.)  
3. Read XLD.  
The crystal loss detect function works only when the BCS bit is set, selecting CGMVCLK to drive  
CGMOUT. When BCS is clear, XLD always reads as logic 0.  
1 = Crystal reference is not active.  
0 = Crystal reference is active.  
PBWC[3:0] — Reserved for Test  
These bits enable test functions not available in user mode. To ensure software portability from  
development systems to user applications, software should write 0s to PBWC[3:0] whenever writing to  
PBWC.  
4.5.3 PLL Programming Register  
The PLL programming register (PPG) contains the programming information for the modulo feedback  
divider and the programming information for the hardware configuration of the VCO.  
Address: $005E  
Bit 7  
MUL7  
0
6
MUL6  
1
5
MUL5  
1
4
MUL4  
0
3
VRS7  
0
2
VRS6  
1
1
VRS5  
1
Bit 0  
VRS4  
0
Read:  
Write:  
Reset:  
Figure 4-7. PLL Programming Register (PPG)  
MUL[7:4] — Multiplier Select Bits  
These read/write bits control the modulo feedback divider that selects the VCO frequency multiplier,  
N. See 4.3.2.1 PLL Circuits and 4.3.2.4 Programming the PLL. A value of $0 in the multiplier select bits  
configures the modulo feedback divider the same as a value of $1. Reset initializes these bits to $6 to  
give a default multiply value of 6.  
Table 4-2. VCO Frequency Multiplier (N) Selection  
MUL7:MUL6:MUL5:MUL4  
VCO Frequency Multiplier (N)  
0000  
0001  
0010  
0011  
1
1
2
3
1101  
1110  
1111  
13  
14  
15  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
68  
Freescale Semiconductor  
     
Interrupts  
NOTE  
The multiplier select bits have built-in protection that prevents them from  
being written when the PLL is on (PLLON = 1).  
VRS[7:4] — VCO Range Select Bits  
These read/write bits control the hardware center-of-range linear multiplier L, which controls the  
hardware center-of-range frequency fVRS. See 4.3.2.1 PLL Circuits, 4.3.2.4 Programming the PLL and  
4.5.1 PLL Control Register. VRS[7:4] cannot be written when the PLLON bit in the PLL control register  
(PCTL) is set. See 4.3.2.5 Special Programming Exceptions. A value of $0 in the VCO range select  
bits disables the PLL and clears the BCS bit in the PCTL. See 4.3.3 Base Clock Selector Circuit and  
Reset initializes the bits to $6 to give a default range multiply value of 6.  
NOTE  
The VCO range select bits have built-in protection that prevents them from  
being written when the PLL is on (PLLON = 1) and prevents selection of the  
VCO clock as the source of the base clock (BCS = 1) if the VCO range  
select bits are all clear.  
The VCO range select bits must be programmed correctly. Incorrect  
programming may result in failure of the PLL to achieve lock.  
4.6 Interrupts  
When the AUTO bit is set in the PLL bandwidth control register (PBWC), the PLL can generate a CPU  
interrupt request every time the LOCK bit changes state. The PLLIE bit in the PLL control register (PCTL)  
enables CPU interrupts from the PLL. PLLF, the interrupt flag in the PCTL, becomes set whether  
interrupts are enabled or not. When the AUTO bit is clear, CPU interrupts from the PLL are disabled and  
PLLF reads as logic 0.  
Software should read the LOCK bit after a PLL interrupt request to see if the request was due to an entry  
into lock or an exit from lock. When the PLL enters lock, the VCO clock, CGMVCLK, divided by two can  
be selected as the CGMOUT source by setting BCS in the PCTL. When the PLL exits lock, the VCO clock  
frequency is corrupt, and appropriate precautions should be taken. If the application is not  
frequency-sensitive, interrupts should be disabled to prevent PLL interrupt service routines from impeding  
software performance or from exceeding stack limitations.  
NOTE  
Software can select the CGMVCLK divided by two as the CGMOUT source  
even if the PLL is not locked (LOCK = 0). Therefore, software should make  
sure the PLL is locked before setting the BCS bit.  
4.7 Wait Mode  
The WAIT instruction puts the MCU in low power-consumption standby mode.  
The WAIT instruction does not affect the CGM. Before entering wait mode, software can disengage and  
turn off the PLL by clearing the BCS and PLLON bits in the PLL control register (PCTL). Less  
power-sensitive applications can disengage the PLL without turning it off. Applications that require the  
PLL to wake the MCU from wait mode also can deselect the PLL output without turning off the PLL.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
69  
   
Clock Generator Module (CGM)  
4.8 Acquisition/Lock Time Specifications  
The acquisition and lock times of the PLL are, in many applications, the most critical PLL design  
parameters. Proper design and use of the PLL ensures the highest stability and lowest acquisition/lock  
times.  
4.8.1 Acquisition/Lock Time Definitions  
Typical control systems refer to the acquisition time or lock time as the reaction time, within specified  
tolerances, of the system to a step input. In a PLL, the step input occurs when the PLL is turned on or  
when it suffers a noise hit. The tolerance is usually specified as a percent of the step input or when the  
output settles to the desired value plus or minus a percent of the frequency change. Therefore, the  
reaction time is constant in this definition, regardless of the size of the step input. For example, consider  
a system with a 5 percent acquisition time tolerance. If a command instructs the system to change from  
0 Hz to 1 MHz, the acquisition time is the time taken for the frequency to reach 1 MHz 50 kHz.  
Fifty kHz = 5% of the 1-MHz step input. If the system is operating at 1 MHz and suffers a –100-kHz noise  
hit, the acquisition time is the time taken to return from 900 kHz to 1 MHz 5 kHz. Five kHz = 5% of the  
100-kHz step input.  
Other systems refer to acquisition and lock times as the time the system takes to reduce the error between  
the actual output and the desired output to within specified tolerances. Therefore, the acquisition or lock  
time varies according to the original error in the output. Minor errors may not even be registered. Typical  
PLL applications prefer to use this definition because the system requires the output frequency to be  
within a certain tolerance of the desired frequency regardless of the size of the initial error.  
The discrepancy in these definitions makes it difficult to specify an acquisition or lock time for a typical  
PLL. Therefore, the definitions for acquisition and lock times for this module are:  
Acquisition time, tACQ, is the time the PLL takes to reduce the error between the actual output  
frequency and the desired output frequency to less than the tracking mode entry tolerance, TRK  
.
Acquisition time is based on an initial frequency error, (fDES – fORIG)/fDES, of not more than 100  
percent. In automatic bandwidth control mode (see 4.3.2.3 Manual and Automatic PLL Bandwidth  
Modes), acquisition time expires when the ACQ bit becomes set in the PLL bandwidth control  
register (PBWC).  
Lock time, tLock, is the time the PLL takes to reduce the error between the actual output frequency  
and the desired output frequency to less than the lock mode entry tolerance, Lock. Lock time is  
based on an initial frequency error, (fDES – fORIG)/fDES, of not more than 100 percent. In automatic  
bandwidth control mode, lock time expires when the LOCK bit becomes set in the PLL bandwidth  
Obviously, the acquisition and lock times can vary according to how large the frequency error is and may  
be shorter or longer in many cases.  
4.8.2 Parametric Influences on Reaction Time  
Acquisition and lock times are designed to be as short as possible while still providing the highest possible  
stability. These reaction times are not constant, however. Many factors directly and indirectly affect the  
acquisition time.  
The most critical parameter which affects the reaction times of the PLL is the reference frequency, fRDV  
.
This frequency is the input to the phase detector and controls how often the PLL makes corrections. For  
stability, the corrections must be small compared to the desired frequency, so several corrections are  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
70  
Freescale Semiconductor  
     
Acquisition/Lock Time Specifications  
required to reduce the frequency error. Therefore, the slower the reference the longer it takes to make  
these corrections. This parameter is also under user control via the choice of crystal frequency, fXCLK  
.
Another critical parameter is the external filter capacitor. The PLL modifies the voltage on the VCO by  
adding or subtracting charge from this capacitor. Therefore, the rate at which the voltage changes for a  
given frequency error (thus change in charge) is proportional to the capacitor size. The size of the  
capacitor also is related to the stability of the PLL. If the capacitor is too small, the PLL cannot make small  
enough adjustments to the voltage and the system cannot lock. If the capacitor is too large, the PLL may  
not be able to adjust the voltage in a reasonable time. See 4.8.3 Choosing a Filter Capacitor.  
Also important is the operating voltage potential applied to VDDA. The power supply potential alters the  
characteristics of the PLL. A fixed value is best. Variable supplies, such as batteries, are acceptable if  
they vary within a known range at very slow speeds. Noise on the power supply is not acceptable,  
because it causes small frequency errors which continually change the acquisition time of the PLL.  
Temperature and processing also can affect acquisition time because the electrical characteristics of the  
PLL change. The part operates as specified as long as these influences stay within the specified limits.  
External factors, however, can cause drastic changes in the operation of the PLL. These factors include  
noise injected into the PLL through the filter capacitor filter, capacitor leakage, stray impedances on the  
circuit board, and even humidity or circuit board contamination.  
4.8.3 Choosing a Filter Capacitor  
As described in 4.8.2 Parametric Influences on Reaction Time, the external filter capacitor, CF, is critical  
to the stability and reaction time of the PLL. The PLL is also dependent on reference frequency and supply  
voltage. The value of the capacitor must, therefore, be chosen with supply potential and reference  
frequency in mind. For proper operation, the external filter capacitor must be chosen according to this  
equation:  
V
DDA  
--------------  
C
= C  
FACT  
F
f
RDV  
For acceptable values of CFACT, see 4.8 Acquisition/Lock Time Specifications. For the value of VDDA  
,
choose the voltage potential at which the MCU is operating. If the power supply is variable, choose a value  
near the middle of the range of possible supply values.  
This equation does not always yield a commonly available capacitor size, so round to the nearest  
available size. If the value is between two different sizes, choose the higher value for better stability.  
Choosing the lower size may seem attractive for acquisition time improvement, but the PLL can become  
unstable. Also, always choose a capacitor with a tight tolerance ( 20 percent or better) and low  
dissipation.  
4.8.4 Reaction Time Calculation  
The actual acquisition and lock times can be calculated using the equations here. These equations yield  
nominal values under these conditions:  
Correct selection of filter capacitor, CF, see 4.8.3 Choosing a Filter Capacitor  
Room temperature operation  
Negligible external leakage on CGMXFC  
Negligible noise  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
71  
   
Clock Generator Module (CGM)  
The K factor in the equations is derived from internal PLL parameters. KACQ is the K factor when the PLL  
is configured in acquisition mode, and KTRK is the K factor when the PLL is configured in tracking mode.  
V
8
DDA  
-------------- --------------  
t
=
ACQ  
f
K
RDV  
ACQ  
V
4
DDA  
-------------- -------------  
t
=
AL  
f
K
RDV  
TRK  
t
= t  
+ t  
ACQ AL  
Lock  
NOTE  
The inverse proportionality between the lock time and the reference  
frequency.  
In automatic bandwidth control mode, the acquisition and lock times are quantized into units based on the  
reference frequency. See 4.3.2.3 Manual and Automatic PLL Bandwidth Modes A certain number of clock  
cycles, nACQ, is required to ascertain that the PLL is within the tracking mode entry tolerance, TRK  
,
before exiting acquisition mode. A certain number of clock cycles, nTRK, is required to ascertain that the  
PLL is within the lock mode entry tolerance, Lock. Therefore, the acquisition time, tACQ, is an integer  
multiple of nACQ RDV, and the acquisition to lock time, tAL, is an integer multiple of nTRK/fRDV. Also, since  
/f  
the average frequency over the entire measurement period must be within the specified tolerance, the  
total time usually is longer than tLock as calculated in the previous example.  
In manual mode, it is usually necessary to wait considerably longer than tLock before selecting the PLL  
Influences on Reaction Time may slow the lock time considerably.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
72  
Freescale Semiconductor  
Chapter 5  
Configuration Register (CONFIG)  
5.1 Introduction  
This section describes the configuration register (CONFIG). This register contains bits that configure  
these options:  
Resets caused by the low-voltage inhibit (LVI) module  
Power to the LVI module  
Computer operating properly (COP) module  
Top-side pulse-width modulator (PWM) polarity  
Bottom-side PWM polarity  
Edge-aligned versus center-aligned PWMs  
Six independent PWMs versus three complementary PWM pairs  
5.2 Functional Description  
The configuration register (CONFIG) is used in the initialization of various options. The configuration  
register can be written once after each reset. All of the configuration register bits are cleared during reset.  
Since the various options affect the operation of the microcontroller unit (MCU), it is recommended that  
this register be written immediately after reset. The configuration register is located at $001F and may be  
read at anytime.  
NOTE  
On a FLASH device, the options are one-time writeable by the user after  
each reset. The registers are not in the FLASH memory but are special  
registers containing one-time writeable latches after each reset. Upon a  
reset, the configuration register defaults to predetermined settings as  
shown in Figure 5-1.  
If the LVI module and the LVI reset signal are enabled, a reset occurs when  
VDD falls to a voltage, VLVRx, and remains at or below that level for at least  
nine consecutive central processor unit (CPU) cycles. Once an LVI reset  
occurs, the MCU remains in reset until VDD rises to a voltage, VLVRX  
.
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
73  
         
Configuration Register (CONFIG)  
5.3 Configuration Register  
Address:  
$001F  
Bit 7  
6
5
4
INDEP  
0
3
LVIRST  
1
2
LVIPWR  
1
1
STOPE  
0
Bit 0  
COPD  
0
Read:  
Write:  
Reset:  
EDGE  
0
BOTNEG TOPNEG  
0
0
Figure 5-1. Configuration Register (CONFIG)  
EDGE — Edge-Align Enable Bit  
EDGE determines if the motor control PWM will operate in edge-aligned mode or center-aligned mode.  
1 = Edge-aligned mode enabled  
0 = Center-aligned mode enabled  
BOTNEG — Bottom-Side PWM Polarity Bit  
BOTNEG determines if the bottom-side PWMs will have positive or negative polarity. See Chapter 12  
1 = Negative polarity  
0 = Positive polarity  
TOPNEG — Top-Side PWM Polarity Bit  
TOPNEG determines if the top-side PWMs will have positive or negative polarity. See Chapter 12  
1 = Negative polarity  
0 = Positive polarity  
INDEP — Independent Mode Enable Bit  
INDEP determines if the motor control PWMs will be six independent PWMs or three complementary  
1 = Six independent PWMs  
0 = Three complementary PWM pairs  
LVIRST — LVI Reset Enable Bit  
LVIRST enables the reset signal from the LVI module. See  
1 = LVI module resets enabled  
0 = LVI module resets disabled  
LVIPWR — LVI Power Enable Bit  
LVIPWR enables the LVI module. Chapter 9 Low-Voltage Inhibit (LVI)  
1 = LVI module power enabled  
0 = LVI module power disabled  
STOPE — Stop Enable Bit  
Writing a 0 or a 1 to bit 1 has no effect on MCU operation. Bit 1 operates the same as the other bits  
within this write-once register operate.  
1 = STOP mode enabled  
0 = STOP mode disabled  
COPD — COP Disable Bit  
1 = COP module disabled  
0 = COP module enabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
74  
Freescale Semiconductor  
     
Chapter 6  
Computer Operating Properly (COP)  
6.1 Introduction  
This section describes the computer operating properly module, a free-running counter that generates a  
reset if allowed to overflow. The computer operating properly (COP) module helps software recover from  
runaway code. Prevent a COP reset by periodically clearing the COP counter.  
6.2 Functional Description  
Figure 6-1 shows the structure of the COP module. A summary of the input/output (I/O) register is shown  
in Figure 6-2.  
SIM  
SIM RESET CIRCUIT  
13-BIT SIM COUNTER  
CGMXCLK  
SIM RESET STATUS REGISTER  
INTERNAL RESET SOURCES(1)  
RESET VECTOR FETCH  
COPCTL WRITE  
COP MODULE  
6-BIT COP COUNTER  
COPD (FROM CONFIG)  
RESET  
CLEAR  
COP COUNTER  
COPCTL WRITE  
Figure 6-1. COP Block Diagram  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
75  
         
Computer Operating Properly (COP)  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
(COPCTL) Write:  
Low byte of reset vector  
Clear COP counter  
Unaffected by reset  
COP Control Register  
$FFFF  
Reset:  
Figure 6-2. COP I/O Register Summary  
The COP counter is a free-running, 6-bit counter preceded by the 13-bit system integration module (SIM)  
counter. If not cleared by software, the COP counter overflows and generates an asynchronous reset after  
218–24 CGMXCLK cycles. With a 4.9152-MHz crystal, the COP timeout period is 53.3 ms. Writing any  
value to location $FFFF before overflow occurs clears the COP counter and prevents reset.  
A COP reset pulls the RST pin low for 32 CGMXCLK cycles and sets the COP bit in the SIM reset status  
NOTE  
Place COP clearing instructions in the main program and not in an interrupt  
subroutine. Such an interrupt subroutine could keep the COP from  
generating a reset even while the main program is not working properly.  
6.3 I/O Signals  
This section describes the signals shown in Figure 6-1.  
6.3.1 CGMXCLK  
CGMXCLK is the crystal oscillator output signal. CGMXCLK frequency is equal to the crystal frequency.  
6.3.2 COPCTL Write  
Writing any value to the COP control register (COPCTL) (see 6.4 COP Control Register) clears the COP  
counter and clears bits 12–4 of the SIM counter. Reading the COP control register returns the reset  
vector.  
6.3.3 Power-On Reset  
The power-on reset (POR) circuit in the SIM clears the SIM counter 4096 CGMXCLK cycles after  
power-up.  
6.3.4 Internal Reset  
An internal reset clears the SIM counter and the COP counter.  
6.3.5 Reset Vector Fetch  
A reset vector fetch occurs when the vector address appears on the data bus. A reset vector fetch clears  
the SIM counter.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
76  
Freescale Semiconductor  
             
COP Control Register  
6.3.6 COPD (COP Disable)  
The COPD signal reflects the state of the COP disable bit (COPD) in the configuration register (CONFIG).  
6.4 COP Control Register  
The COP control register is located at address $FFFF and overlaps the reset vector. Writing any value to  
$FFFF clears the COP counter and starts a new timeout period. Reading location $FFFF returns the low  
byte of the reset vector.  
Address:  
$FFFF  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
Low byte of reset vector  
Clear COP counter  
Unaffected by reset  
Figure 6-3. COP Control Register (COPCTL)  
6.5 Interrupts  
The COP does not generate CPU interrupt requests.  
6.6 Monitor Mode  
The COP is disabled in monitor mode when VHI is present on the IRQ pin or on the RST pin.  
6.7 Wait Mode  
The WAIT instruction puts the MCU in low power-consumption standby mode.  
The COP continues to operate during wait mode.  
6.8 Stop Mode  
Stop mode turns off the CGMXCLK input to the COP and clears the COP prescaler. Service the COP  
immediately before entering or after exiting stop mode to ensure a full COP timeout period after entering  
or exiting stop mode.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
77  
               
Computer Operating Properly (COP)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
78  
Freescale Semiconductor  
Chapter 7  
Central Processor Unit (CPU)  
7.1 Introduction  
The M68HC08 CPU (central processor unit) is an enhanced and fully object-code-compatible version of  
the M68HC05 CPU. The CPU08 Reference Manual (document order number CPU08RM/AD) contains a  
description of the CPU instruction set, addressing modes, and architecture.  
7.2 Features  
Features of the CPU include:  
Object code fully upward-compatible with M68HC05 Family  
16-bit stack pointer with stack manipulation instructions  
16-bit index register with x-register manipulation instructions  
8-MHz CPU internal bus frequency  
64-Kbyte program/data memory space  
16 addressing modes  
Memory-to-memory data moves without using accumulator  
Fast 8-bit by 8-bit multiply and 16-bit by 8-bit divide instructions  
Enhanced binary-coded decimal (BCD) data handling  
Modular architecture with expandable internal bus definition for extension of addressing range  
beyond 64 Kbytes  
Low-power stop and wait modes  
7.3 CPU Registers  
Figure 7-1 shows the five CPU registers. CPU registers are not part of the memory map.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
79  
       
Central Processor Unit (CPU)  
7
0
0
0
0
ACCUMULATOR (A)  
15  
15  
15  
H
X
INDEX REGISTER (H:X)  
STACK POINTER (SP)  
PROGRAM COUNTER (PC)  
CONDITION CODE REGISTER (CCR)  
7
0
V
1
1
H
I
N
Z
C
CARRY/BORROW FLAG  
ZERO FLAG  
NEGATIVE FLAG  
INTERRUPT MASK  
HALF-CARRY FLAG  
TWO’S COMPLEMENT OVERFLOW FLAG  
Figure 7-1. CPU Registers  
7.3.1 Accumulator  
The accumulator is a general-purpose 8-bit register. The CPU uses the accumulator to hold operands and  
the results of arithmetic/logic operations.  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
Unaffected by reset  
Figure 7-2. Accumulator (A)  
7.3.2 Index Register  
The 16-bit index register allows indexed addressing of a 64-Kbyte memory space. H is the upper byte of  
the index register, and X is the lower byte. H:X is the concatenated 16-bit index register.  
In the indexed addressing modes, the CPU uses the contents of the index register to determine the  
conditional address of the operand.  
The index register can serve also as a temporary data storage location.  
Bit  
15 14 13 12 11 10  
Bit  
0
9
0
8
0
7
6
5
4
3
2
1
Read:  
Write:  
Reset:  
0
0
0
0
0
0
X
X
X
X
X
X
X
X
X = Indeterminate  
Figure 7-3. Index Register (H:X)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
80  
Freescale Semiconductor  
     
CPU Registers  
7.3.3 Stack Pointer  
The stack pointer is a 16-bit register that contains the address of the next location on the stack. During a  
reset, the stack pointer is preset to $00FF. The reset stack pointer (RSP) instruction sets the least  
significant byte to $FF and does not affect the most significant byte. The stack pointer decrements as data  
is pushed onto the stack and increments as data is pulled from the stack.  
In the stack pointer 8-bit offset and 16-bit offset addressing modes, the stack pointer can function as an  
index register to access data on the stack. The CPU uses the contents of the stack pointer to determine  
the conditional address of the operand.  
Bit  
15 14 13 12 11 10  
Bit  
0
9
8
7
6
5
4
3
2
1
Read:  
Write:  
Reset:  
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
Figure 7-4. Stack Pointer (SP)  
NOTE  
The location of the stack is arbitrary and may be relocated anywhere in  
random-access memory (RAM). Moving the SP out of page 0 ($0000 to  
$00FF) frees direct address (page 0) space. For correct operation, the  
stack pointer must point only to RAM locations.  
7.3.4 Program Counter  
The program counter is a 16-bit register that contains the address of the next instruction or operand to be  
fetched.  
Normally, the program counter automatically increments to the next sequential memory location every  
time an instruction or operand is fetched. Jump, branch, and interrupt operations load the program  
counter with an address other than that of the next sequential location.  
During reset, the program counter is loaded with the reset vector address located at $FFFE and $FFFF.  
The vector address is the address of the first instruction to be executed after exiting the reset state.  
Bit  
15 14 13 12 11 10  
Bit  
0
9
8
7
6
5
4
3
2
1
Read:  
Write:  
Reset:  
Loaded with vector from $FFFE and $FFFF  
Figure 7-5. Program Counter (PC)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
81  
   
Central Processor Unit (CPU)  
7.3.5 Condition Code Register  
The 8-bit condition code register contains the interrupt mask and five flags that indicate the results of the  
instruction just executed. Bits 6 and 5 are set permanently to 1. The following paragraphs describe the  
functions of the condition code register.  
Bit 7  
6
1
1
5
1
1
4
H
X
3
2
N
X
1
Z
X
Bit 0  
Read:  
Write:  
Reset:  
V
I
C
X
1
X
X = Indeterminate  
Figure 7-6. Condition Code Register (CCR)  
V — Overflow Flag  
The CPU sets the overflow flag when a two's complement overflow occurs. The signed branch  
instructions BGT, BGE, BLE, and BLT use the overflow flag.  
1 = Overflow  
0 = No overflow  
H — Half-Carry Flag  
The CPU sets the half-carry flag when a carry occurs between accumulator bits 3 and 4 during an  
add-without-carry (ADD) or add-with-carry (ADC) operation. The half-carry flag is required for  
binary-coded decimal (BCD) arithmetic operations. The DAA instruction uses the states of the H and  
C flags to determine the appropriate correction factor.  
1 = Carry between bits 3 and 4  
0 = No carry between bits 3 and 4  
I — Interrupt Mask  
When the interrupt mask is set, all maskable CPU interrupts are disabled. CPU interrupts are enabled  
when the interrupt mask is cleared. When a CPU interrupt occurs, the interrupt mask is set  
automatically after the CPU registers are saved on the stack, but before the interrupt vector is fetched.  
1 = Interrupts disabled  
0 = Interrupts enabled  
NOTE  
To maintain M6805 Family compatibility, the upper byte of the index  
register (H) is not stacked automatically. If the interrupt service routine  
modifies H, then the user must stack and unstack H using the PSHH and  
PULH instructions.  
After the I bit is cleared, the highest-priority interrupt request is serviced first.  
A return-from-interrupt (RTI) instruction pulls the CPU registers from the stack and restores the  
interrupt mask from the stack. After any reset, the interrupt mask is set and can be cleared only by the  
clear interrupt mask software instruction (CLI).  
N — Negative Flag  
The CPU sets the negative flag when an arithmetic operation, logic operation, or data manipulation  
produces a negative result, setting bit 7 of the result.  
1 = Negative result  
0 = Non-negative result  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
82  
Freescale Semiconductor  
 
Arithmetic/Logic Unit (ALU)  
Z — Zero Flag  
The CPU sets the zero flag when an arithmetic operation, logic operation, or data manipulation  
produces a result of $00.  
1 = Zero result  
0 = Non-zero result  
C — Carry/Borrow Flag  
The CPU sets the carry/borrow flag when an addition operation produces a carry out of bit 7 of the  
accumulator or when a subtraction operation requires a borrow. Some instructions — such as bit test  
and branch, shift, and rotate — also clear or set the carry/borrow flag.  
1 = Carry out of bit 7  
0 = No carry out of bit 7  
7.4 Arithmetic/Logic Unit (ALU)  
The ALU performs the arithmetic and logic operations defined by the instruction set.  
Refer to the CPU08 Reference Manual (document order number CPU08RM/AD) for a description of the  
instructions and addressing modes and more detail about the architecture of the CPU.  
7.5 Low-Power Modes  
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.  
7.5.1 Wait Mode  
The WAIT instruction:  
Clears the interrupt mask (I bit) in the condition code register, enabling interrupts. After exit from  
wait mode by interrupt, the I bit remains clear. After exit by reset, the I bit is set.  
Disables the CPU clock  
7.5.2 Stop Mode  
The STOP instruction:  
Clears the interrupt mask (I bit) in the condition code register, enabling external interrupts. After  
exit from stop mode by external interrupt, the I bit remains clear. After exit by reset, the I bit is set.  
Disables the CPU clock  
After exiting stop mode, the CPU clock begins running after the oscillator stabilization delay.  
7.6 CPU During Break Interrupts  
If a break module is present on the MCU, the CPU starts a break interrupt by:  
Loading the instruction register with the SWI instruction  
Loading the program counter with $FFFC:$FFFD or with $FEFC:$FEFD in monitor mode  
The break interrupt begins after completion of the CPU instruction in progress. If the break address  
register match occurs on the last cycle of a CPU instruction, the break interrupt begins immediately.  
A return-from-interrupt instruction (RTI) in the break routine ends the break interrupt and returns the MCU  
to normal operation if the break interrupt has been deasserted.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
83  
         
Central Processor Unit (CPU)  
7.7 Instruction Set Summary  
Table 7-1 provides a summary of the M68HC08 instruction set.  
Table 7-1. Instruction Set Summary (Sheet 1 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
ADC #opr  
IMM  
DIR  
EXT  
IX2  
A9 ii  
B9 dd  
C9 hh ll  
D9 ee ff  
E9 ff  
2
3
4
4
3
2
4
5
ADC opr  
ADC opr  
ADC opr,X  
ADC opr,X  
ADC ,X  
Add with Carry  
A (A) + (M) + (C)  
IX1  
IX  
SP1  
SP2  
F9  
ADC opr,SP  
ADC opr,SP  
9EE9 ff  
9ED9 ee ff  
ADD #opr  
ADD opr  
ADD opr  
ADD opr,X  
ADD opr,X  
ADD ,X  
ADD opr,SP  
ADD opr,SP  
IMM  
DIR  
EXT  
IX2  
AB ii  
BB dd  
CB hh ll  
DB ee ff  
EB ff  
FB  
9EEB ff  
9EDB ee ff  
2
3
4
4
3
2
4
5
Add without Carry  
A (A) + (M)  
IX1  
IX  
SP1  
SP2  
AIS #opr  
Add Immediate Value (Signed) to SP  
Add Immediate Value (Signed) to H:X  
– IMM  
– IMM  
A7 ii  
AF ii  
2
2
SP (SP) + (16 « M)  
AIX #opr  
H:X (H:X) + (16 « M)  
AND #opr  
AND opr  
IMM  
DIR  
EXT  
A4 ii  
B4 dd  
C4 hh ll  
D4 ee ff  
E4 ff  
2
3
4
4
3
2
4
5
AND opr  
AND opr,X  
AND opr,X  
AND ,X  
AND opr,SP  
AND opr,SP  
IX2  
Logical AND  
A (A) & (M)  
0
IX1  
IX  
F4  
SP1  
SP2  
9EE4 ff  
9ED4 ee ff  
ASL opr  
ASLA  
DIR  
INH  
38 dd  
48  
4
1
1
4
3
5
ASLX  
Arithmetic Shift Left  
(Same as LSL)  
INH  
58  
C
0
ASL opr,X  
ASL ,X  
IX1  
68 ff  
78  
b7  
b7  
b0  
b0  
IX  
ASL opr,SP  
SP1  
9E68 ff  
ASR opr  
ASRA  
ASRX  
ASR opr,X  
ASR opr,X  
ASR opr,SP  
DIR  
INH  
37 dd  
47  
4
1
1
4
3
5
INH  
57  
C
Arithmetic Shift Right  
IX1  
67 ff  
77  
IX  
SP1  
9E67 ff  
BCC rel  
Branch if Carry Bit Clear  
PC (PC) + 2 + rel ? (C) = 0  
– REL  
24 rr  
3
DIR (b0) 11 dd  
DIR (b1) 13 dd  
DIR (b2) 15 dd  
DIR (b3) 17 dd  
DIR (b4) 19 dd  
DIR (b5) 1B dd  
DIR (b6) 1D dd  
DIR (b7) 1F dd  
4
4
4
4
4
4
4
4
BCLR n, opr  
Clear Bit n in M  
Mn 0  
BCS rel  
Branch if Carry Bit Set (Same as BLO)  
Branch if Equal  
PC (PC) + 2 + rel ? (C) = 1  
PC (PC) + 2 + rel ? (Z) = 1  
– REL  
– REL  
25 rr  
27 rr  
3
3
BEQ rel  
Branch if Greater Than or Equal To  
(Signed Operands)  
BGE opr  
– REL  
– REL  
90 rr  
92 rr  
3
PC (PC) + 2 + rel ? (N V) = 0  
Branch if Greater Than (Signed  
Operands)  
BGT opr  
3
3
PC (PC) + 2 + rel ? (Z) | (N V) = 0  
BHCC rel  
BHCS rel  
BHI rel  
Branch if Half Carry Bit Clear  
Branch if Half Carry Bit Set  
Branch if Higher  
PC (PC) + 2 + rel ? (H) = 0  
PC (PC) + 2 + rel ? (H) = 1  
PC (PC) + 2 + rel ? (C) | (Z) = 0  
– REL  
– REL  
– REL  
28 rr  
29 rr  
22 rr  
3
3
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
84  
Freescale Semiconductor  
   
Instruction Set Summary  
Table 7-1. Instruction Set Summary (Sheet 2 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
Branch if Higher or Same  
(Same as BCC)  
BHS rel  
PC (PC) + 2 + rel ? (C) = 0  
– REL  
24 rr  
3
BIH rel  
Branch if IRQ Pin High  
Branch if IRQ Pin Low  
PC (PC) + 2 + rel ? IRQ = 1  
PC (PC) + 2 + rel ? IRQ = 0  
– REL  
– REL  
2F rr  
2E rr  
3
3
BIL rel  
BIT #opr  
BIT opr  
IMM  
DIR  
EXT  
A5 ii  
B5 dd  
C5 hh ll  
D5 ee ff  
E5 ff  
2
3
4
4
3
2
4
5
BIT opr  
BIT opr,X  
BIT opr,X  
BIT ,X  
BIT opr,SP  
BIT opr,SP  
IX2  
Bit Test  
(A) & (M)  
0
IX1  
IX  
F5  
SP1  
SP2  
9EE5 ff  
9ED5 ee ff  
Branch if Less Than or Equal To  
(Signed Operands)  
BLE opr  
– REL  
93 rr  
3
PC (PC) + 2 + rel ? (Z) | (N V) = 1  
BLO rel  
BLS rel  
BLT opr  
BMC rel  
BMI rel  
BMS rel  
BNE rel  
BPL rel  
BRA rel  
Branch if Lower (Same as BCS)  
Branch if Lower or Same  
Branch if Less Than (Signed Operands)  
Branch if Interrupt Mask Clear  
Branch if Minus  
PC (PC) + 2 + rel ? (C) = 1  
PC (PC) + 2 + rel ? (C) | (Z) = 1  
– REL  
– REL  
– REL  
– REL  
– REL  
– REL  
– REL  
– REL  
– REL  
25 rr  
23 rr  
91 rr  
2C rr  
2B rr  
2D rr  
26 rr  
2A rr  
20 rr  
3
3
3
3
3
3
3
3
3
PC (PC) + 2 + rel ? (N V) =1  
PC (PC) + 2 + rel ? (I) = 0  
PC (PC) + 2 + rel ? (N) = 1  
PC (PC) + 2 + rel ? (I) = 1  
PC (PC) + 2 + rel ? (Z) = 0  
PC (PC) + 2 + rel ? (N) = 0  
PC (PC) + 2 + rel  
Branch if Interrupt Mask Set  
Branch if Not Equal  
Branch if Plus  
Branch Always  
DIR (b0) 01 dd rr  
DIR (b1) 03 dd rr  
DIR (b2) 05 dd rr  
DIR (b3) 07 dd rr  
DIR (b4) 09 dd rr  
DIR (b5) 0B dd rr  
DIR (b6) 0D dd rr  
DIR (b7) 0F dd rr  
5
5
5
5
5
5
5
5
BRCLR n,opr,rel Branch if Bit n in M Clear  
PC (PC) + 3 + rel ? (Mn) = 0  
PC (PC) + 2  
BRN rel  
Branch Never  
– REL  
21 rr  
3
DIR (b0) 00 dd rr  
DIR (b1) 02 dd rr  
DIR (b2) 04 dd rr  
DIR (b3) 06 dd rr  
DIR (b4) 08 dd rr  
DIR (b5) 0A dd rr  
DIR (b6) 0C dd rr  
DIR (b7) 0E dd rr  
5
5
5
5
5
5
5
5
BRSET n,opr,rel Branch if Bit n in M Set  
PC (PC) + 3 + rel ? (Mn) = 1  
DIR (b0) 10 dd  
DIR (b1) 12 dd  
DIR (b2) 14 dd  
DIR (b3) 16 dd  
DIR (b4) 18 dd  
DIR (b5) 1A dd  
DIR (b6) 1C dd  
DIR (b7) 1E dd  
4
4
4
4
4
4
4
4
BSET n,opr  
Set Bit n in M  
Mn 1  
PC (PC) + 2; push (PCL)  
SP (SP) – 1; push (PCH)  
SP (SP) – 1  
BSR rel  
Branch to Subroutine  
– REL  
AD rr  
4
PC (PC) + rel  
CBEQ opr,rel  
PC (PC) + 3 + rel ? (A) – (M) = $00  
PC (PC) + 3 + rel ? (A) – (M) = $00  
PC (PC) + 3 + rel ? (X) – (M) = $00  
PC (PC) + 3 + rel ? (A) – (M) = $00  
PC (PC) + 2 + rel ? (A) – (M) = $00  
PC (PC) + 4 + rel ? (A) – (M) = $00  
DIR  
IMM  
31 dd rr  
41 ii rr  
51 ii rr  
61 ff rr  
71 rr  
5
4
4
5
4
6
CBEQA #opr,rel  
CBEQX #opr,rel  
CBEQ opr,X+,rel  
CBEQ X+,rel  
IMM  
Compare and Branch if Equal  
IX1+  
IX+  
SP1  
CBEQ opr,SP,rel  
9E61 ff rr  
CLC  
CLI  
Clear Carry Bit  
C 0  
I 0  
0
0 INH  
– INH  
98  
9A  
1
2
Clear Interrupt Mask  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
85  
Central Processor Unit (CPU)  
Table 7-1. Instruction Set Summary (Sheet 3 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
CLR opr  
CLRA  
M $00  
A $00  
X $00  
H $00  
M $00  
M $00  
M $00  
DIR  
INH  
INH  
3F dd  
4F  
3
1
1
1
3
2
4
CLRX  
5F  
CLRH  
Clear  
0
0
1
– INH  
IX1  
8C  
CLR opr,X  
CLR ,X  
6F ff  
7F  
IX  
SP1  
CLR opr,SP  
9E6F ff  
CMP #opr  
CMP opr  
CMP opr  
CMP opr,X  
CMP opr,X  
CMP ,X  
CMP opr,SP  
CMP opr,SP  
IMM  
DIR  
EXT  
A1 ii  
B1 dd  
C1 hh ll  
D1 ee ff  
E1 ff  
2
3
4
4
3
2
4
5
IX2  
Compare A with M  
(A) – (M)  
IX1  
IX  
F1  
SP1  
SP2  
9EE1 ff  
9ED1 ee ff  
COM opr  
COMA  
M (M) = $FF – (M)  
A (A) = $FF – (M)  
X (X) = $FF – (M)  
M (M) = $FF – (M)  
M (M) = $FF – (M)  
M (M) = $FF – (M)  
DIR  
INH  
33 dd  
43  
4
1
1
4
3
5
COMX  
INH  
53  
Complement (One’s Complement)  
Compare H:X with M  
0
1
COM opr,X  
COM ,X  
COM opr,SP  
IX1  
63 ff  
73  
9E63 ff  
IX  
SP1  
CPHX #opr  
CPHX opr  
IMM  
65 ii ii+1  
75 dd  
3
4
(H:X) – (M:M + 1)  
DIR  
CPX #opr  
CPX opr  
IMM  
DIR  
EXT  
A3 ii  
B3 dd  
C3 hh ll  
D3 ee ff  
E3 ff  
2
3
4
4
3
2
4
5
CPX opr  
CPX ,X  
IX2  
Compare X with M  
(X) – (M)  
(A)10  
CPX opr,X  
CPX opr,X  
CPX opr,SP  
CPX opr,SP  
IX1  
IX  
F3  
SP1  
SP2  
9EE3 ff  
9ED3 ee ff  
DAA  
Decimal Adjust A  
U –  
INH  
72  
2
A (A) – 1 or M (M) – 1 or X (X) – 1  
PC (PC) + 3 + rel ? (result) 0  
PC (PC) + 2 + rel ? (result) 0  
PC (PC) + 2 + rel ? (result) 0  
PC (PC) + 3 + rel ? (result) 0  
PC (PC) + 2 + rel ? (result) 0  
PC (PC) + 4 + rel ? (result) 0  
5
3
3
5
4
6
DBNZ opr,rel  
DBNZA rel  
DIR  
INH  
3B dd rr  
4B rr  
DBNZX rel  
Decrement and Branch if Not Zero  
– INH  
IX1  
5B rr  
DBNZ opr,X,rel  
DBNZ X,rel  
6B ff rr  
7B rr  
IX  
SP1  
DBNZ opr,SP,rel  
9E6B ff rr  
DEC opr  
DECA  
M (M) – 1  
A (A) – 1  
X (X) – 1  
M (M) – 1  
M (M) – 1  
M (M) – 1  
DIR  
INH  
3A dd  
4A  
4
1
1
4
3
5
DECX  
INH  
5A  
Decrement  
Divide  
DEC opr,X  
DEC ,X  
DEC opr,SP  
IX1  
6A ff  
7A  
9E6A ff  
IX  
SP1  
A (H:A)/(X)  
DIV  
INH  
52  
7
H Remainder  
EOR #opr  
EOR opr  
IMM  
DIR  
EXT  
A8 ii  
B8 dd  
C8 hh ll  
D8 ee ff  
E8 ff  
2
3
4
4
3
2
4
5
EOR opr  
EOR opr,X  
EOR opr,X  
EOR ,X  
EOR opr,SP  
EOR opr,SP  
IX2  
Exclusive OR M with A  
0
A (A M)  
IX1  
IX  
F8  
SP1  
SP2  
9EE8 ff  
9ED8 ee ff  
INC opr  
INCA  
M (M) + 1  
A (A) + 1  
X (X) + 1  
M (M) + 1  
M (M) + 1  
M (M) + 1  
DIR  
INH  
3C dd  
4C  
4
1
1
4
3
5
INCX  
INH  
5C  
Increment  
INC opr,X  
INC ,X  
IX1  
6C ff  
7C  
IX  
INC opr,SP  
SP1  
9E6C ff  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
86  
Freescale Semiconductor  
Instruction Set Summary  
Table 7-1. Instruction Set Summary (Sheet 4 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
JMP opr  
DIR  
BC dd  
CC hh ll  
DC ee ff  
EC ff  
2
3
4
3
2
JMP opr  
JMP opr,X  
JMP opr,X  
JMP ,X  
EXT  
Jump  
PC Jump Address  
– IX2  
IX1  
IX  
FC  
JSR opr  
JSR opr  
JSR opr,X  
JSR opr,X  
JSR ,X  
DIR  
EXT  
– IX2  
IX1  
BD dd  
CD hh ll  
DD ee ff  
ED ff  
4
5
6
5
4
PC (PC) + n (n = 1, 2, or 3)  
Push (PCL); SP (SP) – 1  
Push (PCH); SP (SP) – 1  
PC Unconditional Address  
Jump to Subroutine  
IX  
FD  
LDA #opr  
LDA opr  
IMM  
DIR  
EXT  
A6 ii  
B6 dd  
C6 hh ll  
D6 ee ff  
E6 ff  
2
3
4
4
3
2
4
5
LDA opr  
LDA opr,X  
LDA opr,X  
LDA ,X  
LDA opr,SP  
LDA opr,SP  
IX2  
Load A from M  
Load H:X from M  
Load X from M  
A (M)  
H:X ← (M:M + 1)  
X (M)  
0
0
0
IX1  
IX  
F6  
SP1  
SP2  
9EE6 ff  
9ED6 ee ff  
LDHX #opr  
LDHX opr  
IMM  
45 ii jj  
55 dd  
3
4
DIR  
LDX #opr  
LDX opr  
LDX opr  
LDX opr,X  
LDX opr,X  
LDX ,X  
LDX opr,SP  
LDX opr,SP  
IMM  
DIR  
EXT  
AE ii  
BE dd  
CE hh ll  
DE ee ff  
EE ff  
FE  
9EEE ff  
9EDE ee ff  
2
3
4
4
3
2
4
5
IX2  
IX1  
IX  
SP1  
SP2  
LSL opr  
LSLA  
DIR  
INH  
38 dd  
48  
4
1
1
4
3
5
LSLX  
Logical Shift Left  
(Same as ASL)  
INH  
58  
C
0
LSL opr,X  
LSL ,X  
LSL opr,SP  
IX1  
68 ff  
78  
9E68 ff  
b7  
b7  
b0  
b0  
IX  
SP1  
LSR opr  
LSRA  
DIR  
INH  
34 dd  
44  
4
1
1
4
3
5
LSRX  
INH  
54  
0
C
Logical Shift Right  
0
LSR opr,X  
LSR ,X  
IX1  
64 ff  
74  
IX  
LSR opr,SP  
SP1  
9E64 ff  
MOV opr,opr  
MOV opr,X+  
MOV #opr,opr  
MOV X+,opr  
DD  
4E dd dd  
5E dd  
5
4
4
4
(M)Destination (M)Source  
DIX+  
Move  
0
0
IMD  
IX+D  
6E ii dd  
7E dd  
H:X (H:X) + 1 (IX+D, DIX+)  
MUL  
Unsigned multiply  
X:A (X) × (A)  
0 INH  
42  
5
NEG opr  
NEGA  
DIR  
INH  
30 dd  
40  
4
1
1
4
3
5
M –(M) = $00 – (M)  
A –(A) = $00 – (A)  
X –(X) = $00 – (X)  
M –(M) = $00 – (M)  
M –(M) = $00 – (M)  
NEGX  
INH  
50  
Negate (Two’s Complement)  
NEG opr,X  
NEG ,X  
NEG opr,SP  
IX1  
60 ff  
70  
9E60 ff  
IX  
SP1  
NOP  
NSA  
No Operation  
Nibble Swap A  
None  
– INH  
– INH  
9D  
62  
1
3
A (A[3:0]:A[7:4])  
ORA #opr  
ORA opr  
IMM  
DIR  
EXT  
AA ii  
BA dd  
CA hh ll  
DA ee ff  
EA ff  
2
3
4
4
3
2
4
5
ORA opr  
ORA opr,X  
ORA opr,X  
ORA ,X  
ORA opr,SP  
ORA opr,SP  
IX2  
Inclusive OR A and M  
A (A) | (M)  
0
IX1  
IX  
FA  
SP1  
SP2  
9EEA ff  
9EDA ee ff  
PSHA  
PSHH  
PSHX  
Push A onto Stack  
Push H onto Stack  
Push X onto Stack  
Push (A); SP (SP) – 1  
Push (H); SP (SP) – 1  
Push (X); SP (SP) – 1  
– INH  
– INH  
– INH  
87  
8B  
89  
2
2
2
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
87  
Central Processor Unit (CPU)  
Table 7-1. Instruction Set Summary (Sheet 5 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
PULA  
PULH  
PULX  
Pull A from Stack  
Pull H from Stack  
Pull X from Stack  
SP (SP + 1); Pull (A)  
SP (SP + 1); Pull (H)  
SP (SP + 1); Pull (X)  
– INH  
– INH  
– INH  
86  
8A  
88  
2
2
2
ROL opr  
ROLA  
DIR  
INH  
39 dd  
49  
4
1
1
4
3
5
ROLX  
INH  
59  
C
Rotate Left through Carry  
Rotate Right through Carry  
ROL opr,X  
ROL ,X  
ROL opr,SP  
IX1  
69 ff  
79  
9E69 ff  
b7  
b0  
IX  
SP1  
ROR opr  
RORA  
DIR  
INH  
36 dd  
46  
4
1
1
4
3
5
RORX  
INH  
56  
C
ROR opr,X  
ROR ,X  
IX1  
66 ff  
76  
b7  
b0  
IX  
ROR opr,SP  
SP1  
9E66 ff  
RSP  
Reset Stack Pointer  
Return from Interrupt  
SP $FF  
– INH  
9C  
1
SP (SP) + 1; Pull (CCR)  
SP (SP) + 1; Pull (A)  
SP (SP) + 1; Pull (X)  
SP (SP) + 1; Pull (PCH)  
SP (SP) + 1; Pull (PCL)  
RTI  
INH  
80  
7
SP SP + 1; Pull (PCH)  
RTS  
Return from Subroutine  
Subtract with Carry  
– INH  
81  
4
SP SP + 1; Pull (PCL)  
SBC #opr  
SBC opr  
SBC opr  
SBC opr,X  
SBC opr,X  
SBC ,X  
SBC opr,SP  
SBC opr,SP  
IMM  
DIR  
EXT  
A2 ii  
B2 dd  
C2 hh ll  
D2 ee ff  
E2 ff  
2
3
4
4
3
2
4
5
IX2  
A (A) – (M) – (C)  
IX1  
IX  
SP1  
SP2  
F2  
9EE2 ff  
9ED2 ee ff  
SEC  
SEI  
Set Carry Bit  
C 1  
I 1  
1
1 INH  
– INH  
99  
9B  
1
2
Set Interrupt Mask  
STA opr  
DIR  
EXT  
IX2  
B7 dd  
C7 hh ll  
D7 ee ff  
E7 ff  
3
4
4
3
2
4
5
STA opr  
STA opr,X  
STA opr,X  
STA ,X  
STA opr,SP  
STA opr,SP  
Store A in M  
M (A)  
0
– IX1  
IX  
F7  
SP1  
SP2  
9EE7 ff  
9ED7 ee ff  
STHX opr  
Store H:X in M  
(M:M + 1) (H:X)  
0
0
– DIR  
35 dd  
4
Enable Interrupts, Stop Processing,  
Refer to MCU Documentation  
STOP  
I 0; Stop Processing  
– INH  
8E  
1
STX opr  
DIR  
EXT  
IX2  
BF dd  
CF hh ll  
DF ee ff  
EF ff  
3
4
4
3
2
4
5
STX opr  
STX opr,X  
STX opr,X  
STX ,X  
STX opr,SP  
STX opr,SP  
Store X in M  
M (X)  
0
– IX1  
IX  
FF  
SP1  
SP2  
9EEF ff  
9EDF ee ff  
SUB #opr  
SUB opr  
SUB opr  
SUB opr,X  
SUB opr,X  
SUB ,X  
SUB opr,SP  
SUB opr,SP  
IMM  
DIR  
EXT  
A0 ii  
B0 dd  
C0 hh ll  
D0 ee ff  
E0 ff  
2
3
4
4
3
2
4
5
IX2  
Subtract  
A (A) – (M)  
IX1  
IX  
F0  
SP1  
SP2  
9EE0 ff  
9ED0 ee ff  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
88  
Freescale Semiconductor  
Opcode Map  
Table 7-1. Instruction Set Summary (Sheet 6 of 6)  
Effect  
on CCR  
Source  
Form  
Operation  
Description  
V H I N Z C  
PC (PC) + 1; Push (PCL)  
SP (SP) – 1; Push (PCH)  
SP (SP) – 1; Push (X)  
SP (SP) – 1; Push (A)  
SWI  
Software Interrupt  
1
– INH  
83  
9
SP (SP) – 1; Push (CCR)  
SP (SP) – 1; I 1  
PCH Interrupt Vector High Byte  
PCL Interrupt Vector Low Byte  
TAP  
TAX  
TPA  
Transfer A to CCR  
Transfer A to X  
CCR (A)  
X (A)  
A (CCR)  
INH  
– INH  
– INH  
84  
97  
85  
2
1
1
Transfer CCR to A  
TST opr  
TSTA  
DIR  
INH  
3D dd  
4D  
3
1
1
3
2
4
TSTX  
INH  
5D  
Test for Negative or Zero  
(A) – $00 or (X) – $00 or (M) – $00  
0
TST opr,X  
TST ,X  
TST opr,SP  
IX1  
6D ff  
7D  
9E6D ff  
IX  
SP1  
TSX  
TXA  
TXS  
Transfer SP to H:X  
Transfer X to A  
H:X (SP) + 1  
A (X)  
(SP) (H:X) – 1  
– INH  
– INH  
– INH  
95  
9F  
94  
2
1
2
Transfer H:X to SP  
I bit 0; Inhibit CPU clocking  
WAIT  
Enable Interrupts; Wait for Interrupt  
0
– INH  
8F  
1
until interrupted  
A
Accumulator  
n
Any bit  
C
Carry/borrow bit  
opr Operand (one or two bytes)  
PC Program counter  
CCR  
dd  
Condition code register  
Direct address of operand  
Direct address of operand and relative offset of branch instruction  
Direct to direct addressing mode  
Direct addressing mode  
Direct to indexed with post increment addressing mode  
High and low bytes of offset in indexed, 16-bit offset addressing  
Extended addressing mode  
Offset byte in indexed, 8-bit offset addressing  
Half-carry bit  
Index register high byte  
PCH Program counter high byte  
PCL Program counter low byte  
REL Relative addressing mode  
rel  
rr  
SP1 Stack pointer, 8-bit offset addressing mode  
SP2 Stack pointer 16-bit offset addressing mode  
SP Stack pointer  
U
V
X
Z
&
|
dd rr  
DD  
DIR  
DIX+  
ee ff  
EXT  
ff  
Relative program counter offset byte  
Relative program counter offset byte  
H
H
Undefined  
Overflow bit  
Index register low byte  
Zero bit  
hh ll  
I
High and low bytes of operand address in extended addressing  
Interrupt mask  
Immediate operand byte  
Immediate source to direct destination addressing mode  
ii  
Logical AND  
Logical OR  
IMD  
IMM  
INH  
IX  
Immediate addressing mode  
Inherent addressing mode  
Indexed, no offset addressing mode  
Indexed, no offset, post increment addressing mode  
Logical EXCLUSIVE OR  
Contents of  
( )  
–( ) Negation (two’s complement)  
#
IX+  
Immediate value  
IX+D  
IX1  
IX1+  
IX2  
M
Indexed with post increment to direct addressing mode  
Indexed, 8-bit offset addressing mode  
Indexed, 8-bit offset, post increment addressing mode  
Indexed, 16-bit offset addressing mode  
Memory location  
«
?
Sign extend  
Loaded with  
If  
Concatenated with  
Set or cleared  
Not affected  
:
N
Negative bit  
7.8 Opcode Map  
See Table 7-2.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
89  
 
Table 7-2. Opcode Map  
Bit Manipulation Branch  
Read-Modify-Write  
Control  
Register/Memory  
DIR  
DIR  
REL  
DIR  
3
INH  
4
INH  
IX1  
SP1  
9E6  
IX  
7
INH  
INH  
IMM  
A
DIR  
B
EXT  
C
IX2  
SP2  
IX1  
E
SP1  
9EE  
IX  
F
MSB  
0
1
2
5
6
8
9
D
9ED  
LSB  
5
4
3
4
1
NEGA  
INH  
1
NEGX  
INH  
4
5
3
7
3
2
3
4
4
5
3
4
2
0
BRSET0 BSET0  
BRA  
NEG  
NEG  
NEG  
NEG  
RTI  
BGE  
SUB  
SUB  
SUB  
SUB  
SUB  
SUB  
SUB  
SUB  
3
DIR  
5
2
DIR  
4
2
2
2
2
2
2
2
2
REL 2 DIR  
1
1
2
IX1 3 SP1 1 IX  
5
1
1
INH  
2
2
2
2
1
1
REL 2 IMM 2 DIR  
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
EXT 3 IX2  
4
4
4
4
4
4
4
4
4
4
4
4
SP2 2 IX1  
3
3
3
3
3
3
3
3
3
3
3
3
SP1 1 IX  
3
BRN  
REL 3 DIR  
5
4
4
6
4
4
3
BLT  
2
3
4
4
5
3
4
2
1
2
BRCLR0 BCLR0  
CBEQ CBEQA CBEQX CBEQ  
CBEQ  
CBEQ  
RTS  
CMP  
CMP  
CMP  
CMP  
CMP  
CMP  
CMP  
CMP  
3
DIR  
5
2
DIR  
4
3
IMM 3 IMM 3 IX1+  
4
SP1 2 IX+  
INH  
REL 2 IMM 2 DIR  
EXT 3 IX2  
SP2 2 IX1  
SP1 1 IX  
3
5
7
3
2
DAA  
3
BGT  
2
SBC  
3
SBC  
4
SBC  
EXT 3 IX2  
4
CPX  
EXT 3 IX2  
4
AND  
EXT 3 IX2  
4
BIT  
EXT 3 IX2  
4
LDA  
EXT 3 IX2  
4
STA  
EXT 3 IX2  
4
EOR  
EXT 3 IX2  
4
ADC  
EXT 3 IX2  
4
ORA  
EXT 3 IX2  
4
ADD  
EXT 3 IX2  
3
JMP  
EXT 3 IX2  
5
JSR  
EXT 3 IX2  
4
LDX  
EXT 3 IX2  
4
STX  
EXT 3 IX2  
4
SBC  
5
SBC  
SP2 2 IX1  
5
CPX  
SP2 2 IX1  
5
AND  
SP2 2 IX1  
5
BIT  
SP2 2 IX1  
5
LDA  
SP2 2 IX1  
5
STA  
SP2 2 IX1  
5
EOR  
SP2 2 IX1  
5
ADC  
SP2 2 IX1  
3
SBC  
4
SBC  
SP1 1 IX  
4
CPX  
SP1 1 IX  
4
AND  
SP1 1 IX  
4
BIT  
SP1 1 IX  
4
LDA  
SP1 1 IX  
4
STA  
SP1 1 IX  
4
EOR  
SP1 1 IX  
4
ADC  
SP1 1 IX  
2
SBC  
BRSET1 BSET1  
BHI  
MUL  
INH  
DIV  
INH  
NSA  
3
DIR  
5
2
DIR  
4
REL  
1
1
1
2
2
3
2
2
2
2
2
INH  
1
INH  
3
REL 2 IMM 2 DIR  
3
BLS  
REL 2 DIR  
3
BCC  
REL 2 DIR  
3
BCS  
REL 2 DIR  
3
BNE  
REL 2 DIR  
4
1
1
4
COM  
IX1  
4
LSR  
IX1  
3
CPHX  
IMM  
4
ROR  
IX1  
4
ASR  
IX1  
4
LSL  
IX1  
4
ROL  
IX1  
4
DEC  
IX1  
5
9
3
BLE  
2
CPX  
3
CPX  
4
CPX  
3
CPX  
2
CPX  
3
BRCLR1 BCLR1  
COM  
COMA  
COMX  
COM  
COM  
SWI  
3
DIR  
5
2
DIR  
4
1
INH  
1
INH  
3
3
SP1 1 IX  
1
1
1
1
1
1
1
1
1
1
INH  
REL 2 IMM 2 DIR  
4
LSR  
1
LSRA  
INH  
1
LSRX  
INH  
5
LSR  
SP1 1 IX  
3
LSR  
2
2
2
AND  
IMM 2 DIR  
3
AND  
4
AND  
3
AND  
2
AND  
4
BRSET2 BSET2  
TAP  
TXS  
3
DIR  
5
2
DIR  
4
1
3
1
INH  
INH  
2
2
2
2
2
2
2
2
4
3
4
4
1
2
2
BIT  
3
BIT  
4
BIT  
3
BIT  
2
BIT  
5
BRCLR2 BCLR2  
STHX  
LDHX  
LDHX  
CPHX  
TPA  
TSX  
3
DIR  
5
2
DIR  
4
IMM 2 DIR  
2
DIR  
3
INH  
INH  
IMM 2 DIR  
4
ROR  
1
1
5
2
PULA  
INH  
2
PSHA  
INH  
2
PULX  
INH  
2
PSHX  
INH  
2
PULH  
INH  
2
PSHH  
INH  
1
CLRH  
INH  
2
LDA  
IMM 2 DIR  
2
AIS  
IMM 2 DIR  
2
EOR  
IMM 2 DIR  
2
ADC  
IMM 2 DIR  
2
ORA  
IMM 2 DIR  
2
ADD  
IMM 2 DIR  
3
LDA  
4
LDA  
3
LDA  
2
LDA  
6
BRSET3 BSET3  
RORA  
RORX  
ROR  
SP1 1 IX  
5
ASR  
SP1 1 IX  
5
LSL  
SP1 1 IX  
5
ROL  
SP1 1 IX  
ROR  
3
DIR  
5
2
DIR  
4
1
INH  
1
INH  
3
3
3
3
3
4
3
3
3
BEQ  
REL 2 DIR  
3
4
ASR  
1
ASRA  
INH  
1
LSLA  
INH  
1
ROLA  
INH  
1
DECA  
INH  
1
ASRX  
INH  
1
LSLX  
INH  
1
ROLX  
INH  
1
DECX  
INH  
3
ASR  
1
3
STA  
4
STA  
3
STA  
2
STA  
7
BRCLR3 BCLR3  
TAX  
3
DIR  
5
2
DIR  
4
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
INH  
4
LSL  
3
LSL  
1
3
EOR  
4
EOR  
3
EOR  
2
EOR  
8
BRSET4 BSET4 BHCC  
CLC  
3
DIR  
5
2
DIR  
4
2
REL 2 DIR  
3
INH  
4
ROL  
3
ROL  
1
3
ADC  
4
ADC  
3
ADC  
2
ADC  
9
BRCLR4 BCLR4 BHCS  
SEC  
3
DIR  
5
2
DIR  
4
2
2
2
2
2
2
2
REL 2 DIR  
INH  
3
BPL  
REL 2 DIR  
3
BMI  
REL 3 DIR  
4
DEC  
5
DEC  
SP1 1 IX  
3
DEC  
2
3
ORA  
4
ORA  
5
ORA  
SP2 2 IX1  
5
ADD  
SP2 2 IX1  
3
ORA  
4
ORA  
SP1 1 IX  
4
ADD  
SP1 1 IX  
2
ORA  
A
B
C
D
E
F
BRSET5 BSET5  
CLI  
3
DIR  
5
2
DIR  
4
INH  
5
3
3
5
6
4
2
3
ADD  
4
ADD  
3
ADD  
2
ADD  
BRCLR5 BCLR5  
DBNZ DBNZA DBNZX DBNZ  
DBNZ  
DBNZ  
SEI  
3
DIR  
5
2
DIR  
4
2
1
1
3
1
INH  
1
2
1
1
2
1
INH  
1
3
2
2
3
2
IX1  
4
SP1 2 IX  
INH  
3
4
INC  
5
INC  
SP1 1 IX  
4
TST  
SP1 1 IX  
3
INC  
1
2
JMP  
4
JMP  
3
JMP  
2
BRSET6 BSET6  
BMC  
INCA  
INCX  
INC  
RSP  
JMP  
3
DIR  
5
2
DIR  
4
REL 2 DIR  
INH  
1
INH  
1
IX1  
3
INH  
2
DIR  
4
2
2
IX1  
5
1
1
IX  
3
BMS  
3
TST  
2
TST  
1
4
BSR  
REL 2 DIR  
2
LDX  
IMM 2 DIR  
2
AIX  
IMM 2 DIR  
6
JSR  
4
JSR  
IX  
2
LDX  
BRCLR6 BCLR6  
TSTA  
TSTX  
TST  
NOP  
JSR  
JSR  
3
DIR  
5
2
DIR  
4
REL 2 DIR  
3
INH  
5
INH  
4
IX1  
4
INH  
2
2
2
IX1  
3
4
1
STOP  
INH  
1
WAIT  
INH  
3
LDX  
4
LDX  
5
LDX  
SP2 2 IX1  
5
STX  
SP2 2 IX1  
4
LDX  
SP1 1 IX  
4
STX  
SP1 1 IX  
BRSET7 BSET7  
BIL  
MOV  
MOV  
MOV  
MOV  
LDX  
*
1
TXA  
INH  
3
DIR  
5
2
DIR  
4
REL  
3
DD  
DIX+  
IMD  
3
2
IX+D  
1
1
4
4
3
3
3
CLR  
1
CLRA  
INH  
1
CLRX  
INH  
4
CLR  
SP1 1 IX  
2
CLR  
3
STX  
4
STX  
3
STX  
2
STX  
BRCLR7 BCLR7  
BIH  
CLR  
IX1  
3
DIR  
2
DIR  
REL 2 DIR  
3
1
INH Inherent  
REL Relative  
SP1 Stack Pointer, 8-Bit Offset  
SP2 Stack Pointer, 16-Bit Offset  
IX+ Indexed, No Offset with  
Post Increment  
IX1+ Indexed, 1-Byte Offset with  
Post Increment  
MSB  
LSB  
0
High Byte of Opcode in Hexadecimal  
Cycles  
IMM Immediate  
DIR Direct  
IX  
Indexed, No Offset  
IX1 Indexed, 8-Bit Offset  
IX2 Indexed, 16-Bit Offset  
IMD Immediate-Direct  
EXT Extended  
DD Direct-Direct  
IX+D Indexed-Direct DIX+ Direct-Indexed  
*Pre-byte for stack pointer indexed instructions  
5
Low Byte of Opcode in Hexadecimal  
0
BRSET0 Opcode Mnemonic  
DIR Number of Bytes / Addressing Mode  
3
 
Chapter 8  
External Interrupt (IRQ)  
8.1 Introduction  
This section describes the external interrupt (IRQ) module, which supports external interrupt functions.  
8.2 Features  
Features of the IRQ module include:  
A dedicated external interrupt pin, IRQ  
Hysteresis buffers  
8.3 Functional Description  
A logic 0 applied to any of the external interrupt pins can latch a CPU interrupt request. Figure 8-1 shows  
the structure of the IRQ module.  
ACK1  
VDD  
CLR  
D
Q
SYNCHRO-  
NIZER  
IRQ  
INTERRUPT  
REQUEST  
CK  
IRQ  
IRQ  
LATCH  
IMASK1  
MODE1  
TO MODE  
SELECT  
LOGIC  
HIGH  
VOLTAGE  
DETECT  
Figure 8-1. IRQ Module Block Diagram  
Addr.  
Register Name  
Bit 7  
0
6
5
0
4
0
3
IRQF  
0
2
0
1
Bit 0  
Read:  
Write:  
Reset:  
0
IRQ Status/Control Register  
(ISCR)  
IMASK1 MODE1  
$003F  
R
R
R
0
R
0
ACK1  
0
0
0
0
0
R
= Reserved  
Figure 8-2. IRQ I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
91  
           
External Interrupt (IRQ)  
Interrupt signals on the IRQ pin are latched into the IRQ1 latch. An interrupt latch remains set until one of  
the following actions occurs:  
Vector fetch — A vector fetch automatically generates an interrupt acknowledge signal that clears  
the latch that caused the vector fetch.  
Software clear — Software can clear an interrupt latch by writing to the appropriate acknowledge  
bit in the interrupt status and control register (ISCR). Writing a logic 1 to the ACK1 bit clears the  
IRQ1 latch.  
Reset — A reset automatically clears both interrupt latches.  
The external interrupt pins are falling-edge-triggered and are software-configurable to be both  
falling-edge and low-level-triggered. The MODE1 bit in the ISCR controls the triggering sensitivity of the  
IRQ pin.  
When the interrupt pin is edge-triggered only, the interrupt latch remains set until a vector fetch, software  
clear, or reset occurs.  
When the interrupt pin is both falling-edge and low-level-triggered, the interrupt latch remains set until  
both of these occur:  
Vector fetch, software clear, or reset  
Return of the interrupt pin to logic 1  
The vector fetch or software clear can occur before or after the interrupt pin returns to logic 1. As long as  
the pin is low, the interrupt request remains pending.  
When set, the IMASK1 bit in the ISCR masks all external interrupt requests. A latched interrupt request  
is not presented to the interrupt priority logic unless the IMASK bit is clear.  
NOTE  
The interrupt mask (I) in the condition code register (CCR) masks all  
interrupt requests, including external interrupt requests. (See Figure 8-3.)  
8.4 IRQ Pin  
A logic 0 on the IRQ pin can latch an interrupt request into the IRQ latch. A vector fetch, software clear,  
or reset clears the IRQ latch.  
If the MODE1 bit is set, the IRQ pin is both falling-edge-sensitive and low-level- sensitive. With MODE1  
set, both of these actions must occur to clear the IRQ1 latch:  
Vector fetch, software clear, or reset — A vector fetch generates an interrupt acknowledge signal  
to clear the latch. Software can generate the interrupt acknowledge signal by writing a logic 1 to  
the ACK1 bit in the interrupt status and control register (ISCR). The ACK1 bit is useful in  
applications that poll the IRQ pin and require software to clear the IRQ1 latch. Writing to the ACK1  
bit can also prevent spurious interrupts due to noise. Setting ACK1 does not affect subsequent  
transitions on the IRQ pin. A falling edge that occurs after writing to the ACK1 bit latches another  
interrupt request. If the IRQ1 mask bit, IMASK1, is clear, the CPU loads the program counter with  
the vector address at locations $FFFA and $FFFB.  
Return of the IRQ pin to logic 1 — As long as the IRQ pin is at logic 0, the IRQ1 latch remains set.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
92  
Freescale Semiconductor  
 
IRQ Pin  
FROM RESET  
YES  
I BIT SET?  
NO  
YES  
INTERRUPT?  
NO  
STACK CPU REGISTERS  
SET I BIT  
LOAD PC WITH INTERRUPT VECTOR  
FETCH NEXT  
INSTRUCTION  
YES  
SWI  
INSTRUCTION?  
NO  
YES  
RTI  
INSTRUCTION?  
UNSTACK CPU REGISTERS  
EXECUTE INSTRUCTION  
NO  
Figure 8-3. IRQ Interrupt Flowchart  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
93  
 
External Interrupt (IRQ)  
A logic 0 on the IRQ pin can latch an interrupt request into the IRQ latch. A vector fetch, software clear,  
or reset clears the IRQ latch.  
If the MODE1 bit is set, the IRQ pin is both falling-edge-sensitive and low-level- sensitive. With MODE1  
set, both of these actions must occur to clear the IRQ1 latch:  
Vector fetch, software clear, or reset — A vector fetch generates an interrupt acknowledge signal  
to clear the latch. Software can generate the interrupt acknowledge signal by writing a logic 1 to  
the ACK1 bit in the interrupt status and control register (ISCR). The ACK1 bit is useful in  
applications that poll the IRQ pin and require software to clear the IRQ1 latch. Writing to the ACK1  
bit can also prevent spurious interrupts due to noise. Setting ACK1 does not affect subsequent  
transitions on the IRQ pin. A falling edge that occurs after writing to the ACK1 bit latches another  
interrupt request. If the IRQ1 mask bit, IMASK1, is clear, the CPU loads the program counter with  
the vector address at locations $FFFA and $FFFB.  
Return of the IRQ pin to logic 1 — As long as the IRQ pin is at logic 0, the IRQ1 latch remains set.  
The vector fetch or software clear and the return of the IRQ pin to logic 1 can occur in any order. The  
interrupt request remains pending as long as the IRQ pin is at logic 0.  
If the MODE1 bit is clear, the IRQ pin is falling-edge-sensitive only. With MODE1 clear, a vector fetch or  
software clear immediately clears the IRQ1 latch.  
Use the branch if IRQ pin high (BIH) or branch if IRQ pin low (BIL) instruction to read the logic level on  
the IRQ pin.  
NOTE  
When using the level-sensitive interrupt trigger, avoid false interrupts by  
masking interrupt requests in the interrupt routine.  
8.5 IRQ Status and Control Register  
The IRQ status and control register (ISCR) has these functions:  
Clears the IRQ interrupt latch  
Masks IRQ interrupt requests  
Controls triggering sensitivity of the IRQ interrupt pin  
Address:  
$003F  
Bit 7  
0
6
5
0
4
0
3
IRQF  
0
2
0
1
IMASK1  
0
Bit 0  
MODE1  
0
Read:  
Write:  
Reset:  
0
R
R
R
0
R
0
ACK1  
0
0
0
R
= Reserved  
Figure 8-4. IRQ Status and Control Register (ISCR)  
ACK1 — IRQ Interrupt Request Acknowledge Bit  
Writing a logic 1 to this write-only bit clears the IRQ latch. ACK1 always reads as logic 0. Reset clears  
ACK1.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
94  
Freescale Semiconductor  
     
IRQ Status and Control Register  
IMASK1 — IRQ Interrupt Mask Bit  
Writing a logic 1 to this read/write bit disables IRQ interrupt requests. Reset clears IMASK1.  
1 = IRQ interrupt requests disabled  
0 = IRQ interrupt requests enabled  
MODE1 — IRQ Edge/Level Select Bit  
This read/write bit controls the triggering sensitivity of the IRQ pin. Reset clears MODE1.  
1 = IRQ interrupt requests on falling edges and low levels  
0 = IRQ interrupt requests on falling edges only  
IRQF — IRQ Flag  
This read-only bit acts as a status flag, indicating an IRQ event occurred.  
1 = External IRQ event occurred.  
0 = External IRQ event did not occur.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
95  
External Interrupt (IRQ)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
96  
Freescale Semiconductor  
Chapter 9  
Low-Voltage Inhibit (LVI)  
9.1 Introduction  
This section describes the low-voltage inhibit (LVI) module, which monitors the voltage on the VDD pin  
and can force a reset when the VDD voltage falls to the LVI trip voltage.  
9.2 Features  
Features of the LVI module include:  
Programmable LVI reset  
Programmable power consumption  
Digital filtering of VDD pin level  
Selectable LVI trip voltage  
9.3 Functional Description  
Figure 9-1 shows the structure of the LVI module. The LVI is enabled out of reset. The LVI module  
contains a bandgap reference circuit and comparator. The LVI power bit, LVIPWR, enables the LVI to  
monitor VDD voltage. The LVI reset bit, LVIRST, enables the LVI module to generate a reset when VDD  
falls below a voltage, VLVRX, and remains at or below that level for nine or more consecutive CGMXCLK.  
VLVRX and VLVHX are determined by the TRPSEL bit in the LVISCR (see Figure 9-2). LVIPWR and  
LVIRST are in the configuration register (CONFIG). See Chapter 5 Configuration Register (CONFIG).  
VDD  
LVIPWR  
FROM CONFIG  
FROM CONFIG  
CPU CLOCK  
LVIRST  
VDD  
DIGITAL FILTER  
VDD > LVItrip = 0  
VDD < LVItrip = 1  
LVI RESET  
LOW VDD  
DETECTOR  
TRPSEL  
ANLGTRIP  
LVIOUT  
FROM LVISCR  
Figure 9-1. LVI Module Block Diagram  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
97  
           
Low-Voltage Inhibit (LVI)  
Once an LVI reset occurs, the MCU remains in reset until VDD rises above a voltage, VLVRX + VLVHX  
VDD must be above VLVRX + VLVHX for only one CPU cycle to bring the MCU out of reset. See  
.
14.3.2.6 Low-Voltage Inhibit (LVI) Reset. The output of the comparator controls the state of the LVIOUT  
flag in the LVI status register (LVISCR).  
An LVI reset also drives the RST pin low to provide low-voltage protection to external peripheral devices.  
Addr.  
Register Name  
Bit 7  
6
5
TRPSEL  
0
4
0
3
0
2
0
1
0
Bit 0  
Read: LVIOUT  
0
0
R
0
LVI Status and Control Register  
$FE0F  
(LVISCR) Write:  
R
0
R
R
0
R
0
R
0
R
0
Reset:  
0
= Reserved  
R
Figure 9-2. LVI I/O Register Summary  
9.3.1 Polled LVI Operation  
In applications that can operate at VDD levels below VLVRX, software can monitor VDD by polling the  
LVIOUT bit. In the configuration register, the LVIPWR bit must be 1 to enable the LVI module, and the  
LVIRST bit must be 0 to disable LVI resets. See Chapter 5 Configuration Register (CONFIG). TRPSEL  
in the LVISCR selects VLVRX  
.
9.3.2 Forced Reset Operation  
In applications that require VDD to remain above VLVRX, enabling LVI resets allows the LVI module to  
reset the MCU when VDD falls to the VLVRX level and remains at or below that level for nine or more  
consecutive CPU cycles. In the CONFIG register, the LVIPWR and LVIRST bits must be 1s to enable the  
LVI module and to enable LVI resets. TRPSEL in the LVISCR selects VLVRX  
.
9.3.3 False Reset Protection  
The VDD pin level is digitally filtered to reduce false resets due to power supply noise. In order for the LVI  
module to reset the MCU, VDD must remain at or below VLVRX for nine or more consecutive CPU cycles.  
VDD must be above VLVRX + VLVHX for only one CPU cycle to bring the MCU out of reset. TRPSEL in the  
LVISCR selects VLVRX + VLVHX  
.
9.3.4 LVI Trip Selection  
The TRPSEL bit allows the user to chose between 5 percent and 10 percent tolerance when monitoring  
the supply voltage. The 10 percent option is enabled out of reset. Writing a 1 to TRPSEL will enable 5  
percent option.  
NOTE  
The microcontroller is guaranteed to operate at a minimum supply voltage.  
The trip point (VLVR1 or VLVR2) may be lower than this. See 19.5 DC  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
98  
Freescale Semiconductor  
         
LVI Status and Control Register  
9.4 LVI Status and Control Register  
The LVI status register (LVISCR) flags VDD voltages below the VLVRX level.  
Address:  
$FE0F  
Bit 7  
6
5
TRPSEL  
0
4
0
3
0
2
0
1
0
Bit 0  
0
Read: LVIOUT  
0
Write:  
R
0
R
R
0
R
0
R
0
R
0
R
Reset:  
0
0
= Reserved  
R
Figure 9-3. LVI Status and Control Register (LVISCR)  
LVIOUT — LVI Output Bit  
This read-only flag becomes set when the VDD voltage falls below the VLVRX voltage for 32 to 40  
Table 9-1. LVIOUT Bit Indication  
V
DD  
LVIOUT  
At Level:  
For Number of CGMXCLK Cycles:  
Any  
V
> V  
+ V  
0
DD  
LVRX LVHX  
V
V
V
< V  
< 32 CGMXCLK cycles  
Between 32 & 40 CGMXCLK cycles  
> 40 CGMXCLK cycles  
Any  
0
DD  
LVRX  
< V  
0 or 1  
1
DD  
DD  
LVRX  
LVRX  
LVRX  
< V  
V
< V < V  
+ V  
LVHX  
Previous value  
LVRX  
DD  
TRPSEL — LVI Trip Select Bit  
This bit selects the LVI trip point. Reset clears this bit.  
1 = 5 percent tolerance. The trip point and recovery point are determined by VLVR1 and VLVH1  
,
respectively.  
0 = 10 percent tolerance. The trip point and recovery point are determined by VLVR2 and VLVH2  
,
respectively.  
NOTE  
If LVIRST and LVIPWR are 0s, note that when changing the tolerance, LVI  
reset will be generated if the supply voltage is below the trip point.  
9.5 LVI Interrupts  
The LVI module does not generate interrupt requests.  
9.6 Wait Mode  
The WAIT instruction puts the MCU in low power-consumption standby mode.  
With the LVIPWR bit in the configuration register programmed to 1, the LVI module is active after a WAIT  
instruction.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
99  
           
Low-Voltage Inhibit (LVI)  
With the LVIRST bit in the configuration register programmed to 1, the LVI module can generate a reset  
and bring the MCU out of wait mode.  
9.7 Stop Mode  
If enabled, the LVI module remains active in stop mode. If enabled to generate resets, the LVI module  
can generate a reset and bring the MCU out of stop mode.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
100  
Freescale Semiconductor  
 
Chapter 10  
Input/Output (I/O) Ports (PORTS)  
10.1 Introduction  
Thirty-seven bidirectional input-output (I/O) pins and seven input pins form six parallel ports. All I/O pins  
are programmable as inputs or outputs.  
When using the 56-pin package version:  
Set the data direction register bits in DDRC such that bit 1 is written to a logic 1 (along with any  
other output bits on port C).  
Set the data direction register bits in DDRE such that bits 0, 1, and 2 are written to a logic 1 (along  
with any other output bits on port E).  
Set the data direction register bits in DDRF such that bits 0, 1, 2, and 3 are written to a logic 1 (along  
with any other output bits on port F).  
NOTE  
Connect any unused I/O pins to an appropriate logic level, either VDD or  
VSS. Although PWM6–PWM1 do not require termination for proper  
operation, termination reduces excess current consumption and the  
possibility of electrostatic damage.  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Port A Data Register  
(PTA)  
PTA7  
PTA6  
PTA5  
PTA4  
PTA3  
PTA2  
PTA1  
PTA0  
$0000  
Unaffected by reset  
PTB4 PTB3  
Unaffected by reset  
PTC4 PTC3  
Unaffected by reset  
Port B Data Register  
(PTB)  
PTB7  
PTB6  
PTC6  
PTB5  
PTC5  
PTB2  
PTC2  
PTB1  
PTC1  
PTB0  
PTC0  
$0001  
$0002  
$0003  
$0004  
0
Port C Data Register  
(PTC)  
R
0
PTD6  
R
PTD5  
R
PTD4  
R
PTD3  
R
PTD2  
R
PTD1  
R
PTD0  
R
Port D Data Register  
(PTD)  
R
Unaffected by reset  
Data Direction Register A  
(DDRA)  
DDRA7  
DDRA6  
DDRA5  
0
DDRA4  
0
DDRA3  
DDRA2  
0
DDRA1  
0
DDRA0  
0
0
0
0
R
= Reserved  
= Unimplemented  
Figure 10-1. I/O Port Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
101  
     
Input/Output (I/O) Ports (PORTS)  
Addr.  
Register Name  
Bit 7  
6
DDRB6  
0
5
DDRB5  
0
4
DDRB4  
0
3
DDRB3  
0
2
DDRB2  
0
1
DDRB1  
0
Bit 0  
DDRB0  
0
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Data Direction Register B  
(DDRB)  
DDRB7  
$0005  
0
0
Data Direction Register C  
(DDRC)  
DDRC6  
0
DDRC5  
0
DDRC4  
DDRC3  
DDRC2  
0
DDRC1  
0
DDRC0  
0
$0006  
$0007  
R
0
0
0
Unimplemented  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Port E Data Register  
(PTE)  
PTE7  
PTE6  
PTE5  
PTF5  
PTE4  
PTE3  
PTE2  
PTF2  
PTE1  
PTF1  
PTE0  
PTF0  
$0008  
$0009  
Unaffected by reset  
PTF4 PTF3  
Unaffected by reset  
0
0
Port F Data Register  
(PTF)  
R
R
$000A  
$000B  
Unimplemented  
Unimplemented  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Data Direction Register E  
(DDRE)  
DDRE7  
DDRE6  
DDRE5  
DDRE4  
DDRE3  
DDRE2  
DDRE1  
DDRE0  
$000C  
$000D  
0
0
0
0
0
DDRF5  
0
0
DDRF4  
0
0
DDRF3  
0
0
DDRF2  
0
0
DDRF1  
0
0
DDRF0  
0
Data Direction Register F  
(DDRF)  
R
R
R
= Reserved  
= Unimplemented  
Figure 10-1. I/O Port Register Summary (Continued)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
102  
Freescale Semiconductor  
Port A  
10.2 Port A  
Port A is an 8-bit, general-purpose, bidirectional I/O port.  
10.2.1 Port A Data Register  
The port A data register (PTA) contains a data latch for each of the eight port A pins.  
Address:  
$0000  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
PTA7  
PTA6  
PTA5  
PTA4  
PTA3  
PTA2  
PTA1  
PTA0  
Unaffected by reset  
Figure 10-2. Port A Data Register (PTA)  
PTA[7:0] — Port A Data Bits  
These read/write bits are software programmable. Data direction of each port A pin is under the control  
of the corresponding bit in data direction register A. Reset has no effect on port A data.  
10.2.2 Data Direction Register A  
Data direction register A (DDRA) determines whether each port A pin is an input or an output. Writing a  
logic 1 to a DDRA bit enables the output buffer for the corresponding port A pin; a logic 0 disables the  
output buffer.  
Address:  
$0004  
Bit 7  
6
DDRA6  
0
5
DDRA5  
0
4
DDRA4  
0
3
DDRA3  
0
2
DDRA2  
0
1
DDRA1  
0
Bit 0  
DDRA0  
0
Read:  
Write:  
Reset:  
DDRA7  
0
Figure 10-3. Data Direction Register A (DDRA)  
DDRA[7:0] — Data Direction Register A Bits  
These read/write bits control port A data direction. Reset clears DDRA[7:0], configuring all port A pins  
as inputs.  
1 = Corresponding port A pin configured as output  
0 = Corresponding port A pin configured as input  
NOTE  
Avoid glitches on port A pins by writing to the port A data register before  
changing data direction register A bits from 0 to 1.  
Figure 10-4 shows the port A I/O logic.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
103  
             
Input/Output (I/O) Ports (PORTS)  
READ DDRA ($0004)  
WRITE DDRA ($0004)  
WRITE PTA ($0000)  
DDRAx  
PTAx  
RESET  
PTAx  
READ PTA ($0000)  
Figure 10-4. Port A I/O Circuit  
When bit DDRAx is a logic 1, reading address $0000 reads the PTAx data latch. When bit DDRAx is a  
logic 0, reading address $0000 reads the voltage level on the pin. The data latch can always be written,  
regardless of the state of its data direction bit. Table 10-1 summarizes the operation of the port A pins.  
Table 10-1. Port A Pin Functions  
Accesses to DDRA  
Read/Write  
Accesses to PTA  
DDRA Bit  
PTA Bit  
I/O Pin Mode  
Read  
Write  
(1)  
(2)  
(3)  
0
DDRA[7:0]  
Pin  
X
Input, Hi-Z  
PTA[7:0]  
1
X
Output  
DDRA[7:0]  
PTA[7:0]  
PTA[7:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
10.3 Port B  
Port B is an 8-bit, general-purpose, bidirectional I/O port that shares its pins with the analog-to-digital  
convertor (ADC) module.  
10.3.1 Port B Data Register  
The port B data register (PTB) contains a data latch for each of the eight port B pins.  
Address:  
$0001  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
PTB7  
PTB6  
PTB5  
PTB4  
PTB3  
PTB2  
PTB1  
PTB0  
Unaffected by reset  
Figure 10-5. Port B Data Register (PTB)  
PTB[7:0] — Port B Data Bits  
These read/write bits are software-programmable. Data direction of each port B pin is under the control  
of the corresponding bit in data direction register B. Reset has no effect on port B data.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
104  
Freescale Semiconductor  
           
Port B  
10.3.2 Data Direction Register B  
Data direction register B (DDRB) determines whether each port B pin is an input or an output. Writing a  
logic 1 to a DDRB bit enables the output buffer for the corresponding port B pin; a logic 0 disables the  
output buffer.  
Address:  
$0005  
Bit 7  
6
DDRB6  
0
5
DDRB5  
0
4
DDRB4  
0
3
DDRB3  
0
2
DDRB2  
0
1
DDRB1  
0
Bit 0  
DDRB0  
0
Read:  
Write:  
Reset:  
DDRB7  
0
Figure 10-6. Data Direction Register B (DDRB)  
DDRB[7:0] — Data Direction Register B Bits  
These read/write bits control port B data direction. Reset clears DDRB[7:0], configuring all port B pins  
as inputs.  
1 = Corresponding port B pin configured as output  
0 = Corresponding port B pin configured as input  
NOTE  
Avoid glitches on port B pins by writing to the port B data register before  
changing data direction register B bits from 0 to 1.  
Figure 10-7 shows the port B I/O logic.  
READ DDRB ($0005)  
WRITE DDRB ($0005)  
DDRBx  
RESET  
WRITE PTB ($0001)  
PTBx  
PTBx  
READ PTB ($0001)  
Figure 10-7. Port B I/O Circuit  
When bit DDRBx is a logic 1, reading address $0001 reads the PTBx data latch. When bit DDRBx is a  
logic 0, reading address $0001 reads the voltage level on the pin. The data latch can always be written,  
regardless of the state of its data direction bit. Table 10-2 summarizes the operation of the port B pins.  
Table 10-2. Port B Pin Functions  
Accesses to DDRB  
Read/Write  
Accesses to PTB  
DDRB Bit  
PTB Bit  
I/O Pin Mode  
Read  
Write  
(1)  
(2)  
(3)  
0
1
DDRB[7:0]  
Pin  
X
Input, Hi-Z  
PTB[7:0]  
X
Output  
DDRB[7:0]  
PTB[7:0]  
PTB[7:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
105  
         
Input/Output (I/O) Ports (PORTS)  
10.4 Port C  
Port C is a 7-bit, general-purpose, bidirectional I/O port that shares two of its pins with the analog-to-digital  
convertor module (ADC).  
10.4.1 Port C Data Register  
The port C data register (PTC) contains a data latch for each of the seven port C pins.  
Address:  
$0002  
Bit 7  
0
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
PTC6  
PTC5  
PTC4  
PTC3  
PTC2  
PTC1  
PTC0  
R
Unaffected by reset  
R
= Reserved  
Figure 10-8. Port C Data Register (PTC)  
PTC[6:0] — Port C Data Bits  
These read/write bits are software-programmable. Data direction of each port C pin is under the control  
of the corresponding bit in data direction register C. Reset has no effect on port C data.  
10.4.2 Data Direction Register C  
Data direction register C (DDRC) determines whether each port C pin is an input or an output. Writing a  
logic 1 to a DDRC bit enables the output buffer for the corresponding port C pin; a logic 0 disables the  
output buffer.  
Address:  
$0006  
Bit 7  
0
6
5
DDRC5  
0
4
DDRC4  
0
3
DDRC3  
0
2
DDRC2  
0
1
DDRC1  
0
Bit 0  
DDRC0  
0
Read:  
Write:  
Reset:  
DDRC6  
R
0
0
R
= Reserved  
Figure 10-9. Data Direction Register C (DDRC)  
DDRC[6:0] — Data Direction Register C Bits  
These read/write bits control port C data direction. Reset clears DDRC[6:0], configuring all port C pins  
as inputs.  
1 = Corresponding port C pin configured as output  
0 = Corresponding port C pin configured as input  
NOTE  
Avoid glitches on port C pins by writing to the port C data register before  
changing data direction register C bits from 0 to 1.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
106  
Freescale Semiconductor  
             
Port D  
Figure 10-10 shows the port C I/O logic.  
READ DDRC ($0006)  
WRITE DDRC ($0006)  
RESET  
DDRCx  
PTCx  
WRITE PTC ($0002)  
PTCx  
READ PTC ($0002)  
Figure 10-10. Port C I/O Circuit  
When bit DDRCx is a logic 1, reading address $0002 reads the PTCx data latch. When bit DDRCx is a  
logic 0, reading address $0002 reads the voltage level on the pin. The data latch can always be written,  
regardless of the state of its data direction bit. Table 10-3 summarizes the operation of the port C pins.  
Table 10-3. Port C Pin Functions  
DDRC Bit  
PTC Bit  
I/O Pin Mode  
Accesses to DDRC  
Read/Write  
Accesses to PTC  
Read  
Pin  
Write  
(1)  
(2)  
(3)  
0
1
DDRC[6:0]  
X
Input, Hi-Z  
PTC[6:0]  
PTC[6:0]  
X
Output  
DDRC[6:0]  
PTC[6:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
10.5 Port D  
Port D is a 7-bit, input-only port that shares its pins with the pulse width modulator for motor control  
module (PMC).  
The port D data register (PTD) contains a data latch for each of the seven port pins.  
Address:  
$0003  
Bit 7  
0
6
PTD6  
R
5
PTD5  
R
4
PTD4  
R
3
PTD3  
R
2
PTD2  
R
1
PTD1  
R
Bit 0  
PTD0  
R
Read:  
Write:  
Reset:  
R
Unaffected by reset  
R
= Reserved  
Figure 10-11. Port D Data Register (PTD)  
PTD[6:0] — Port D Data Bits  
These read/write bits are software programmable. Reset has no effect on port D data.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
107  
         
Input/Output (I/O) Ports (PORTS)  
Figure 10-12 shows the port D input logic.  
READ PTD ($0003)  
PTDx  
Figure 10-12. Port D Input Circuit  
Reading address $0003 reads the voltage level on the pin. Table 10-4 summarizes the operation of the  
port D pins.  
Table 10-4. Port D Pin Functions  
Accesses to PTD  
PTD Bit  
Pin Mode  
Read  
Write  
(1)  
(2)  
(3)  
Pin  
X
Input, Hi-Z  
PTD[6:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
10.6 Port E  
Port E is an 8-bit, special function port that shares five of its pins with the timer interface module (TIM)  
and two of its pins with the serial communications interface module (SCI).  
10.6.1 Port E Data Register  
The port E data register (PTE) contains a data latch for each of the eight port E pins.  
Address:  
$0008  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
PTE7  
PTE6  
PTE5  
PTE4  
PTE3  
PTE2  
PTE1  
PTE0  
Unaffected by reset  
Figure 10-13. Port E Data Register (PTE)  
PTE[7:0] — Port E Data Bits  
PTE[7:0] are read/write, software-programmable bits. Data direction of each port E pin is under the  
control of the corresponding bit in data direction register E.  
NOTE  
Data direction register E (DDRE) does not affect the data direction of port  
E pins that are being used by the TIMA or TIMB. However, the DDRE bits  
always determine whether reading port E returns the states of the latches  
or the states of the pins.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
108  
Freescale Semiconductor  
         
Port E  
10.6.2 Data Direction Register E  
Data direction register E (DDRE) determines whether each port E pin is an input or an output. Writing a  
logic 1 to a DDRE bit enables the output buffer for the corresponding port E pin; a logic 0 disables the  
output buffer.  
Address:  
$000C  
Bit 7  
6
DDRE6  
0
5
DDRE5  
0
4
DDRE4  
0
3
DDRE3  
0
2
DDRE2  
0
1
DDRE1  
0
Bit 0  
DDRE0  
0
Read:  
Write:  
Reset:  
DDRE7  
0
Figure 10-14. Data Direction Register E (DDRE)  
DDRE[7:0] — Data Direction Register E Bits  
These read/write bits control port E data direction. Reset clears DDRE[7:0], configuring all port E pins  
as inputs.  
1 = Corresponding port E pin configured as output  
0 = Corresponding port E pin configured as input  
NOTE  
Avoid glitches on port E pins by writing to the port E data register before  
changing data direction register E bits from 0 to 1.  
Figure 10-15 shows the port E I/O logic.  
READ DDRE ($000C)  
WRITE DDRE ($000C)  
DDREx  
RESET  
WRITE PTE ($0008)  
PTEx  
PTEx  
READ PTE ($0008)  
Figure 10-15. Port E I/O Circuit  
When bit DDREx is a logic 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a  
logic 0, reading address $0008 reads the voltage level on the pin. The data latch can always be written,  
regardless of the state of its data direction bit. Table 10-5 summarizes the operation of the port E pins.  
Table 10-5. Port E Pin Functions  
Accesses to DDRE  
Read/Write  
Accesses to PTE  
DDRE Bit  
PTE Bit  
I/O Pin Mode  
Read  
Write  
(1)  
(2)  
(3)  
0
DDRE[7:0]  
Pin  
X
Input, Hi-Z  
PTE[7:0]  
1
X
Output  
DDRE[7:0]  
PTE[7:0]  
PTE[7:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
109  
       
Input/Output (I/O) Ports (PORTS)  
10.7 Port F  
Port F is a 6-bit, special function port that shares four of its pins with the serial peripheral interface module  
(SPI) and two pins with the serial communications interface (SCI).  
10.7.1 Port F Data Register  
The port F data register (PTF) contains a data latch for each of the six port F pins.  
Address:  
$0009  
Bit 7  
0
6
0
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
PTF5  
PTF4  
PTF3  
PTF2  
PTF1  
PTF0  
R
R
Unaffected by reset  
R
= Reserved  
Figure 10-16. Port F Data Register (PTF)  
PTF[5:0] — Port F Data Bits  
These read/write bits are software programmable. Data direction of each port F pin is under the control  
of the corresponding bit in data direction register F. Reset has no effect on PTF[5:0].  
NOTE  
Data direction register F (DDRF) does not affect the data direction of port F  
pins that are being used by the SPI or SCI module. However, the DDRF bits  
always determine whether reading port F returns the states of the latches  
or the states of the pins.  
10.7.2 Data Direction Register F  
Data direction register F (DDRF) determines whether each port F pin is an input or an output. Writing a  
logic 1 to a DDRF bit enables the output buffer for the corresponding port F pin; a logic 0 disables the  
output buffer.  
Address:  
$000D  
Bit 7  
0
6
0
5
DDRF5  
0
4
DDRF4  
0
3
DDRF3  
0
2
DDRF2  
0
1
DDRF1  
0
Bit 0  
DDRF0  
0
Read:  
Write:  
Read:  
R
R
R
= Reserved  
Figure 10-17. Data Direction Register F (DDRF)  
DDRF[5:0] — Data Direction Register F Bits  
These read/write bits control port F data direction. Reset clears DDRF[5:0], configuring all port F pins  
as inputs.  
1 = Corresponding port F pin configured as output  
0 = Corresponding port F pin configured as input  
NOTE  
Avoid glitches on port F pins by writing to the port F data register before  
changing data direction register F bits from 0 to 1.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
110  
Freescale Semiconductor  
             
Port F  
Figure 10-18 shows the port F I/O logic.  
READ DDRF ($000D)  
WRITE DDRF ($000D)  
RESET  
DDRFx  
PTFx  
WRITE PTF ($0009)  
PTFx  
READ PTF ($0009)  
Figure 10-18. Port F I/O Circuit  
When bit DDRFx is a logic 1, reading address $0009 reads the PTFx data latch. When bit DDRFx is a  
logic 0, reading address $0009 reads the voltage level on the pin. The data latch can always be written,  
regardless of the state of its data direction bit. Table 10-6 summarizes the operation of the port F pins.  
Table 10-6. Port F Pin Functions  
Accesses to DDRF  
Read/Write  
Accesses to PTF  
DDRF Bit  
PTF Bit  
I/O Pin Mode  
Read  
Write  
(1)  
(2)  
(3)  
0
DDRF[6:0]  
Pin  
X
Input, Hi-Z  
PTF[6:0]  
1
X
Output  
DDRF[6:0]  
PTF[6:0]  
PTF[6:0]  
1. X = don’t care  
2. Hi-Z = high impedance  
3. Writing affects data register, but does not affect input.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
111  
 
Input/Output (I/O) Ports (PORTS)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
112  
Freescale Semiconductor  
Chapter 11  
Power-On Reset (POR)  
11.1 Introduction  
This section describes the power-on reset (POR) module.  
11.2 Functional Description  
The POR module provides a known, stable signal to the microcontroller unit (MCU) at power-on. This  
signal tracks VDD until the MCU generates a feedback signal to indicate that it is properly initialized. At  
this time, the POR drives its output low.  
The POR is not a brown-out detector, low-voltage detector, or glitch detector. VDD at the POR must go  
completely to 0 to reset the microcontroller unit (MCU). To detect power-loss conditions, use a low-voltage  
inhibit module (LVI) or other suitable circuit.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
113  
     
Power-On Reset (POR)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
114  
Freescale Semiconductor  
Chapter 12  
Pulse-Width Modulator for Motor Control (PWMMC)  
12.1 Introduction  
This section describes the pulse-width modulator for motor control (PWMMC, version A). The PWM  
module can generate three complementary PWM pairs or six independent PWM signals. These  
PWM signals can be center-aligned or edge-aligned. A block diagram of the PWM module is shown in  
A12-bit timer PWM counter is common to all six channels. PWM resolution is one clock period for  
edge-aligned operation and two clock periods for center-aligned operation. The clock period is dependent  
on the internal operating frequency (fOP) and a programmable prescaler. The highest resolution for  
edge-aligned operation is 125 ns (fOP = 8 MHz). The highest resolution for center-aligned operation is  
250 ns (fOP = 8 MHz).  
When generating complementary PWM signals, the module features automatic dead-time insertion to the  
PWM output pairs and transparent toggling of PWM data based upon sensed motor phase current  
polarity.  
A summary of the PWM registers is shown in Figure 12-3.  
12.2 Features  
Features of the PWMMC include:  
Three complementary PWM pairs or six independent PWM signals  
Edge-aligned PWM signals or center-aligned PWM signals  
PWM signal polarity control  
20-mA current sink capability on PWM pins  
Manual PWM output control through software  
Programmable fault protection  
Complementary mode featuring:  
Dead-time insertion  
Separate top/bottom pulse width correction via current sensing or programmable software bits  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
115  
       
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
PTC1/ATD9(1)  
PTC0/ATD8  
USER FLASH VECTOR SPACE — 46 BYTES  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 12-1. Block Diagram Highlighting PWMMC Block and Pins  
Features  
8
CPU BUS  
PWM1 PIN  
PWM2 PIN  
PWM CHANNELS 1 AND 2  
PWM CHANNELS 3 AND 4  
PWM3 PIN  
PWM4 PIN  
PWM5 PIN  
PWM6 PIN  
PWM CHANNELS 5 AND 6  
FAULT  
INTERRUPT  
PINS  
4
12  
TIMEBASE  
3
COIL CURRENT  
POLARITY PINS  
Figure 12-2. PWM Module Block Diagram  
Addr.  
Register Name  
Bit 7  
DISX  
0
6
DISY  
0
5
4
PWMF  
0
3
ISENS1  
0
2
1
LDOK  
0
Bit 0  
PWMEN  
0
Read:  
PWM Control Register 1  
PWMINT  
ISENS0  
$0020  
(PCTL1) Write:  
Reset:  
Read:  
0
0
0
IPOL3  
0
PWM Control Register 2  
LDFQ1  
0
LDFQ0  
0
IPOL1  
0
IPOL2  
0
PRSC1  
0
PRSC0  
0
$0021  
$0022  
$0023  
$0024  
(PCTL2) Write:  
Reset:  
Read:  
0
Fault Control Register  
FINT4 FMODE4  
FINT3  
FMODE3  
FINT2  
FMODE2  
FINT1 FMODE1  
(FCR) Write:  
Reset:  
Read: FPIN4  
(FSR) Write:  
0
0
0
0
0
0
0
0
FFLAG4  
FPIN3  
FFLAG3  
FPIN2  
FFLAG2  
FPIN1  
FFLAG1  
Fault Status Register  
Reset:  
Read:  
U
0
0
U
0
DT5  
U
0
DT3  
U
0
DT1  
0
DT6  
DT4  
DT2  
Fault Acknowledge Register  
(FTACK) Write:  
Reset:  
FTACK4  
0
FTACK3  
0
FTACK2  
0
FTACK1  
0
0
0
0
0
R
= Reserved  
Bold  
= Buffered  
X = Indeterminate  
Figure 12-3. Register Summary (Sheet 1 of 3)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
117  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
PWM Output Control  
Register (PWMOUT) Write:  
0
OUTCTL  
OUT6  
OUT5  
OUT4  
OUT3  
OUT2  
OUT1  
$0025  
Reset:  
0
0
0
0
0
0
0
0
0
0
0
0
Read:  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
PWM Counter Register High  
$0026  
$0027  
$0028  
$0029  
$002A  
$002B  
$002C  
$002D  
$002E  
$002F  
(PCNTH) Write:  
Reset:  
0
0
0
0
0
0
0
0
Read: Bit 7  
(PCNTL) Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Bit 0  
PWM Counter Register Low  
Reset:  
Read:  
0
0
0
0
0
0
0
0
0
Bit 11  
X
0
Bit 10  
X
0
Bit 9  
X
0
Bit 8  
X
PWM Counter Modulo Register  
High (PMODH) Write:  
Reset:  
0
Bit 7  
X
0
Bit 6  
X
0
Bit 5  
X
0
Bit 4  
X
Read:  
PWM Counter Modulo Register  
Bit 3  
X
Bit 2  
X
Bit 1  
X
Bit 0  
X
Low (PMODL) Write:  
Reset:  
Read:  
PWM 1 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL1H) Write:  
Reset:  
Read:  
PWM 1 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL1L) Write:  
Reset:  
Read:  
PWM 2 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL2H) Write:  
Reset:  
Read:  
PWM 2 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL2L) Write:  
Reset:  
Read:  
PWM 3 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL3H) Write:  
Reset:  
Read:  
PWM 3 Value Register Low  
Bit 7  
Bit 6  
Bit 5  
0
Bit 4  
Bit 3  
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL3L) Write:  
Reset:  
0
0
0
0
R
= Reserved  
Bold  
= Buffered  
X = Indeterminate  
Figure 12-3. Register Summary (Sheet 2 of 3)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
118  
Freescale Semiconductor  
Features  
Addr.  
Register Name  
Bit 7  
Bit 15  
0
6
Bit 14  
0
5
Bit 13  
0
4
Bit 12  
0
3
Bit 11  
0
2
Bit 10  
0
1
Bit 9  
0
Bit 0  
Bit 8  
0
Read:  
PWM 4 Value Register High  
$0030  
(PVAL4H) Write:  
Reset:  
Read:  
PWM 4 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
$0031  
$0032  
$0033  
$0034  
$0035  
$0036  
$0037  
(PVAL4L) Write:  
Reset:  
Read:  
PWM 5 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL5H) Write:  
Reset:  
Read:  
PWM 5 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PVAL5L) Write:  
Reset:  
Read:  
PWM 6 Value Register High  
Bit 15  
0
Bit 14  
0
Bit 13  
0
Bit 12  
0
Bit 11  
0
Bit 10  
0
Bit 9  
0
Bit 8  
0
(PVAL6H) Write:  
Reset:  
Read:  
PWM 6 Value Register Low  
Bit 7  
0
Bit 6  
0
Bit 5  
0
Bit 4  
0
Bit 3  
0
Bit 2  
0
Bit 1  
0
Bit 0  
0
(PMVAL6L) Write:  
Reset:  
Read:  
Dead-Time Write-Once  
Register (DEADTM) Write:  
Bit 7  
1
Bit 6  
1
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Reset:  
Read:  
PWM Disable Mapping  
Write-Once Register Write:  
Bit 7  
Bit 6  
Bit 5  
1
Bit 4  
Bit 3  
Bit 2  
1
Bit 1  
1
Bit 0  
1
Reset:  
1
1
1
1
R
= Reserved  
Bold  
= Buffered  
X = Indeterminate  
Figure 12-3. Register Summary (Sheet 3 of 3)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
119  
Pulse-Width Modulator for Motor Control (PWMMC)  
12.3 Timebase  
This section provides a discussion of the timebase.  
12.3.1 Resolution  
In center-aligned mode, a 12-bit up/down counter is used to create the PWM period. Therefore, the PWM  
resolution in center-aligned mode is two clocks (highest resolution is 250 ns @ fOP = 8 MHz) as shown in  
Figure 12-4. The up/down counter uses the value in the timer modulus register to determine its maximum  
count. The PWM period will equal:  
[(timer modulus) x (PWM clock period) x 2].  
UP/DOWN COUNTER  
MODULUS = 4  
PERIOD = 8 X (PWM CLOCK PERIOD)  
PWM = 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM = 4  
Figure 12-4. Center-Aligned PWM (Positive Polarity)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
120  
Freescale Semiconductor  
     
Timebase  
For edge-aligned mode, a 12-bit up-only counter is used to create the PWM period. Therefore, the PWM  
resolution in edge-aligned mode is one clock (highest resolution is125 ns @ fOP = 8 MHz) as shown in  
Figure 12-5. Again, the timer modulus register is used to determine the maximum count. The PWM period  
will equal:  
(timer modulus) x (PWM clock period)  
Center-aligned operation versus edge-aligned operation is determined by the option EDGE. See 5.2  
UP-ONLY COUNTER  
MODULUS = 4  
PERIOD = 4 X (PWM  
CLOCK PERIOD)  
PWM = 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM = 4  
Figure 12-5. Edge-Aligned PWM (Positive Polarity)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
121  
 
Pulse-Width Modulator for Motor Control (PWMMC)  
12.3.2 Prescaler  
To permit lower PWM frequencies, a prescaler is provided which will divide the PWM clock frequency by  
1, 2, 4, or 8. Table 12-1 shows how setting the prescaler bits in PWM control register 2 affects the PWM  
clock frequency. This prescaler is buffered and will not be used by the PWM generator until the LDOK bit  
is set and a new PWM reload cycle begins.  
Table 12-1. PWM Prescaler  
Prescaler Bits  
PWM Clock Frequency  
PRSC1 and PRSC0  
f
00  
01  
10  
11  
OP  
f
f
f
/2  
/4  
/8  
OP  
OP  
OP  
12.4 PWM Generators  
Pulse-width modulator (PWM) generators are discussed in this subsection.  
12.4.1 Load Operation  
To help avoid erroneous pulse widths and PWM periods, the modulus, prescaler, and PWM value  
registers are buffered. New PWM values, counter modulus values, and prescalers can be loaded from  
their buffers into the PWM module every one, two, four, or eight PWM cycles. LDFQ1 and LDFQ0 in PWM  
control register 2 are used to control this reload frequency, as shown in Table 12-2. When a reload cycle  
arrives, regardless of whether an actual reload occurs (as determined by the LDOK bit), the PWM reload  
flag bit in PWM control register 1 will be set. If the PWMINT bit in PWM control register 1 is set, a CPU  
interrupt request will be generated when PWMF is set. Software can use this interrupt to calculate new  
PWM parameters in real time for the PWM module.  
Table 12-2. PWM Reload Frequency  
Reload Frequency Bits  
PWM Reload Frequency  
LDFQ1 and LDFQ0  
00  
01  
10  
11  
Every PWM cycle  
Every 2 PWM cycles  
Every 4 PWM cycles  
Every 8 PWM cycles  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
122  
Freescale Semiconductor  
         
PWM Generators  
For ease of software, the LDFQx bits are buffered. When the LDFQx bits are changed, the reload  
frequency will not change until the previous reload cycle is completed. See Figure 12-6.  
NOTE  
When reading the LDFQx bits, the value is the buffered value (for example,  
not necessarily the value being acted upon).  
RELOAD  
RELOAD  
RELOAD  
RELOAD RELOADRELOADRELOAD  
CHANGE RELOAD  
FREQUENCY TO  
EVERY 4 CYCLES  
CHANGE RELOAD  
FREQUENCY TO  
EVERY CYCLE  
Figure 12-6. Reload Frequency Change  
PWMINT enables CPU interrupt requests as shown in Figure 12-7. When this bit is set, CPU interrupt  
requests are generated when the PWMF bit is set. When the PWMINT bit is clear, PWM interrupt requests  
are inhibited. PWM reloads will still occur at the reload rate, but no interrupt requests will be generated.  
READ PWMF AS 1,  
WRITE PWMF AS 0  
OR  
VDD  
RESET  
RESET  
PWMF  
CPU INTERRUPT  
REQUEST  
D
LATCH  
PWM RELOAD  
PWMINT  
CK  
Figure 12-7. PWM Interrupt Requests  
To prevent a partial reload of PWM parameters from occurring while the software is still calculating them,  
an interlock bit controlled from software is provided. This bit informs the PWM module that all the PWM  
parameters have been calculated, and it is “okay” to use them. A new modulus, prescaler, and/or PWM  
value cannot be loaded into the PWM module until the LDOK bit in PWM control register 1 is set. When  
the LDOK bit is set, these new values are loaded into a second set of registers and used by the PWM  
generator at the beginning of the next PWM reload cycle as shown in Figure 12-8, Figure 12-9,  
Figure 12-10, and Figure 12-11. After these values are loaded, the LDOK bit is cleared.  
NOTE  
When the PWM module is enabled (via the PWMEN bit), a load will occur  
if the LDOK bit is set. Even if it is not set, an interrupt will occur if the  
PWMINT bit is set. To prevent this, the software should clear the PWMINT  
bit before enabling the PWM module.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
123  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
LDFQ1:LDFQ0 = 00 (RELOAD EVERY CYCLE)  
UP/DOWN  
COUNTER  
LDOK = 1  
MODULUS = 3  
PWM VALUE = 2  
PWMF SET  
LDOK = 1  
LDOK = 0  
MODULUS = 3  
PWM VALUE = 2  
PWMF SET  
LDOK = 0  
MODULUS = 3  
PWM VALUE = 1  
PWMF SET  
MODULUS = 3  
PWM VALUE = 1  
PWMF SET  
PWM  
Figure 12-8. Center-Aligned PWM Value Loading  
LDFQ1:LDFQ0 = 00 (RELOAD EVERY CYCLE)  
UP/DOWN  
COUNTER  
LDOK = 1  
LDOK = 1  
MODULUS = 3  
PWM VALUE = 1  
PWMF SET  
LDOK = 1  
MODULUS = 2 MODULUS = 1  
PWMVALUE = 1 PWM VALUE = 1  
LDOK = 1  
LDOK = 0  
MODULUS = 2  
PWM VALUE = 1  
PWMF SET  
MODULUS = 2  
PWM VALUE = 1  
PWMF SET  
PWMF SET  
PWMF SET  
PWM  
Figure 12-9. Center-Aligned Loading of Modulus  
LDFQ1:LDFQ0 = 00 (RELOAD EVERY CYCLE)  
UP-ONLY  
COUNTER  
LDOK = 1  
MODULUS = 3  
PWM VALUE = 2  
PWMF SET  
LDOK = 1  
MODULUS = 3  
PWM VALUE = 1 PWM VALUE = 2  
LDOK = 0  
MODULUS = 3  
PWM VALUE = 1  
PWMF SET  
LDOK = 0  
MODULUS = 3  
LDOK = 0  
MODULUS = 3  
PWM VALUE = 1  
PWMF SET  
PWMF SET  
PWMF SET  
PWM  
Figure 12-10. Edge-Aligned PWM Value Loading  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
124  
Freescale Semiconductor  
     
PWM Generators  
LDFQ1:LDFQ0 = 00 (RELOAD EVERY CYCLE)  
UP-ONLY  
COUNTER  
LDOK = 1  
LDOK = 1  
LDOK = 0  
LDOK = 1  
MODULUS = 3  
PWM VALUE = 2  
PWMF SET  
MODULUS = 4  
PWM VALUE = 2  
PWMF SET  
MODULUS = 1  
PWM VALUE = 2  
PWMF SET  
MODULUS = 2  
PWM VALUE = 2  
PWMF SET  
PWM  
Figure 12-11. Edge-Aligned Modulus Loading  
12.4.2 PWM Data Overflow and Underflow Conditions  
The PWM value registers are 16-bit registers. Although the counter is only 12 bits, the user may write a  
16-bit signed value to a PWM value register. As shown in Figure 12-4 and Figure 12-5, if the PWM value  
is less than or equal to zero, the PWM will be inactive for the entire period. Conversely, if the PWM value  
is greater than or equal to the timer modulus, the PWM will be active for the entire period. Refer to  
NOTE  
The terms “active” and “inactive” refer to the asserted and negated states  
of the PWM signals and should not be confused with the high-impedance  
state of the PWM pins.  
Table 12-3. PWM Data Overflow and Underflow Conditions  
PWMVALxH:PWMVALxL  
$0000–$0FFF  
Condition  
Normal  
PWM Value Used  
Per register contents  
$FFF  
$1000–$7FFF  
Overflow  
Underflow  
$8000–$FFFF  
$000  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
125  
     
Pulse-Width Modulator for Motor Control (PWMMC)  
12.5 Output Control  
This subsection discusses output control.  
12.5.1 Selecting Six Independent PWMs or Three Complementary PWM Pairs  
The PWM outputs can be configured as six independent PWM channels or three complementary channel  
pairs. The option INDEP determines which mode is used (see 5.2 Functional Description). If  
complementary operation is chosen, the PWM pins are paired as shown in Figure 12-12. Operation of  
one pair is then determined by one PWM value register. This type of operation is meant for use in motor  
drive circuits such as the one in Figure 12-13.  
PWM1 PIN  
PWM VALUE REGISTER  
PWM VALUE REGISTER  
PWM VALUE REGISTER  
PWMS 1 AND 2  
PWM2 PIN  
PWM3 PIN  
PWM4 PIN  
PWMS 3 AND 4  
PWM5 PIN  
PWM6 PIN  
PWMS 5 AND 6  
Figure 12-12. Complementary Pairing  
PWM  
3
PWM  
1
PWM  
5
TO  
AC  
MOTOR  
INPUTS  
PWM  
2
PWM  
4
PWM  
6
Figure 12-13. Typical AC Motor Drive  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
126  
Freescale Semiconductor  
       
Output Control  
When complementary operation is used, two additional features are provided:  
Dead-time insertion  
Separate top/bottom pulse width correction to correct for distortions caused by the motor drive  
characteristics  
If independent operation is chosen, each PWM has its own PWM value register.  
12.5.2 Dead-Time Insertion  
As shown in Figure 12-13, in complementary mode, each PWM pair can be used to drive  
top-side/bottom-side transistors.  
When controlling dc-to-ac inverters such as this, the top and bottom PWMs in one pair should never be  
active at the same time. In Figure 12-13, if PWM1 and PWM2 were on at the same time, large currents  
would flow through the two transistors as they discharge the bus capacitor. The IGBTs could be  
weakened or destroyed.  
Simply forcing the two PWMs to be inversions of each other is not always sufficient. Since a time delay is  
associated with turning off the transistors in the motor drive, there must be a dead-time between the  
deactivation of one PWM and the activation of the other.  
A dead-time can be specified in the dead-time write-once register. This 8-bit value specifies the number  
of CPU clock cycles to use for the dead-time. The dead-time is not affected by changes in the PWM period  
caused by the prescaler.  
Dead-time insertion is achieved by feeding the top PWM outputs of the PWM generator into dead-time  
generators, as shown in Figure 12-14. Current sensing determines which PWM value of a PWM generator  
pair to use for the top PWM in the next PWM cycle. See 12.5.3 Top/Bottom Correction with Motor Phase  
Current Polarity Sensing. When output control is enabled, the odd OUT bits, rather than the PWM  
generator outputs, are fed into the dead-time generators. See 12.5.5 PWM Output Port Control.  
Whenever an input to a dead-time generator transitions, a dead-time is inserted (for example, both PWMs  
in the pair are forced to their inactive state). The bottom PWM signal is generated from the top PWM and  
the dead-time. In the case of output control enabled, the odd OUTx bits control the top PWMs, the even  
OUTx bits control the bottom PWMs with respect to the odd OUTx bits (see Table 12-6). Figure 12-15  
shows the effects of the dead-time insertion.  
As seen in Figure 12-15, some pulse width distortion occurs when the dead-time is inserted. The active  
pulse widths are reduced. For example, in Figure 12-15, when the PWM value register is equal to two,  
the ideal waveform (with no dead-time) has pulse widths equal to four. However, the actual pulse widths  
shrink to two after a dead-time of two was inserted. In this example, with the prescaler set to divide by  
one and center-aligned operation selected, this distortion can be compensated for by adding or  
subtracting half the dead-time value to or from the PWM register value. This correction is further described  
Further examples of dead-time insertion are shown in Figure 12-16 and Figure 12-17. Figure 12-16 shows  
the effects of dead-time insertion at the duty cycle boundaries (near 0 percent and 100 percent duty  
cycles). Figure 12-17 shows the effects of dead-time insertion on pulse widths smaller than the dead-time.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
127  
 
Pulse-Width Modulator for Motor Control (PWMMC)  
OUTPUT CONTROL  
(OUTCTL)  
OUT2  
OUT4  
OUT6  
MUX  
PWMPAIR12  
TOP  
PWM1  
PWM2  
PWM (TOP)  
(TOP)  
(PWM1)  
DEAD-TIME  
POSTDT (TOP)  
PREDT (TOP)  
OUTX  
BOTTOM  
(PWM2)  
SELECT  
MUX  
PWMPAIR34  
(TOP)  
TOP  
(PWM3)  
PWM (TOP)  
PWM3  
PWM4  
DEAD-TIME  
POSTDT (TOP)  
PREDT (TOP)  
OUTX  
BOTTOM  
(PWM4)  
SELECT  
6
MUX  
PWMPAIR56  
(TOP)  
TOP  
(PWM5)  
PWM (TOP)  
PWM5  
PWM6  
DEAD-TIME  
POSTDT (TOP)  
PREDT (TOP)  
OUTX  
BOTTOM  
(PWM6)  
SELECT  
Figure 12-14. Dead-Time Generators  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
128  
Freescale Semiconductor  
 
Output Control  
UP/DOWN COUNTER  
MODULUS = 4  
PWM VALUE = 2  
PWM VALUE = 3  
PWM VALUE = 2  
PWM1 W/  
NO DEAD-TIME  
PWM2 W/  
NO DEAD-TIME  
PWM1 W/  
DEAD-TIME = 2  
2
2
2
2
PWM2 W/  
DEAD-TIME = 2  
2
2
Figure 12-15. Effects of Dead-Time Insertion  
UP/DOWN COUNTER  
MODULUS = 3  
PWM VALUE = 1  
PWM VALUE = 1  
PWM VALUE = 3  
PWM VALUE = 3  
PWM1 W/  
NO DEAD-TIME  
PWM2 W/  
NO DEAD-TIME  
PWM1 W/  
DEAD-TIME = 2  
2
2
PWM2 W/  
DEAD-TIME = 2  
2
2
Figure 12-16. Dead-Time at Duty Cycle Boundaries  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
129  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
UP/DOWN COUNTER  
MOUDULUS = 3  
PWM VALUE = 2  
PWM VALUE = 3  
PWM VALUE = 2  
PWM VALUE = 1  
PWM1 W/  
NO DEAD-TIME  
PWM2 W/  
NO DEAD-TIME  
PWM1 W/  
3
3
3
DEAD-TIME = 3  
PWM2 W/  
DEAD-TIME = 3  
3
3
3
Figure 12-17. Dead-Time and Small Pulse Widths  
12.5.3 Top/Bottom Correction with Motor Phase Current Polarity Sensing  
Ideally, when complementary pairs are used, the PWM pairs are inversions of each other, as shown in  
Figure 12-18. When PWM1 is active, PWM2 is inactive, and vice versa. In this case, the motor terminal  
voltage is never allowed to float and is strictly controlled by the PWM waveforms.  
UP/DOWN COUNTER  
MODULUS = 4  
PWM1  
PWM VALUE = 1  
PWM2  
PWM3  
PWM VALUE = 2  
PWM4  
PWM5  
PWM VALUE = 3  
PWM6  
Figure 12-18. Ideal Complementary Operation (Dead-Time = 0)  
However, when dead-time is inserted, the motor voltage is allowed to float momentarily during the  
dead-time interval, creating a distortion in the motor current waveform. This distortion is aggravated by  
dissimilar turn-on and turn-off delays of each of the transistors.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
130  
Freescale Semiconductor  
     
Output Control  
For a typical motor drive inverter as shown in Figure 12-13, for a given top/bottom transistor pair, only one  
of the transistors will be effective in controlling the output voltage at any given time depending on the  
direction of the motor current for that pair. To achieve distortion correction, one of two different correction  
factors must be added to the desired PWM value, depending on whether the top or bottom transistor is  
controlling the output voltage. Therefore, the software is responsible for calculating both compensated  
PWM values and placing them in an odd/even PWM register pair. By supplying the PWM module with  
information regarding which transistor (top or bottom) is controlling the output voltage at any given time  
(for instance, the current polarity for that motor phase), the PWM module selects either the odd or even  
numbered PWM value register to be used by the PWM generator.  
Current sensing or programmable software bits are then used to determine which PWM value to use. If  
the current sensed at the motor for that PWM pair is positive (voltage on current pin ISx is low) or bit IPOLx  
in PWM control register 2 is low, the top PWM value is used for the PWM pair. Likewise, if the current  
sensed at the motor for that PWM pair is negative (voltage on current pin ISx is high) or bit IPOLx in PWM  
control register 2 is high, the bottom PWM value is used. See Table 12-4.  
NOTE  
This text assumes the user will provide current sense circuitry which causes  
the voltage at the corresponding input pin to be low for positive current and  
high for negative current. See Figure 12-19 for current convention. In  
addition, it assumes the top PWMs are PWMs 1, 3, and 5 while the bottom  
PWMs are PWMs 2, 4, and 6.  
Table 12-4. Current Sense Pins  
Voltage  
Current  
on Current  
Sense Pin  
PWM Value  
Register Used  
PWMs  
Affected  
Sense Pin  
or Bit  
or IPOLx Bit  
IS1 or IPOL1  
IS1 or IPOL1  
Logic 0  
Logic 1  
PWM value register 1  
PWM value register 2  
PWMs 1 and 2  
PWMs 1 and 2  
I+  
I-  
Figure 12-19. Current Convention  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
131  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
To allow for correction based on different current sensing methods or correction controlled by software,  
the ISENS1 and ISENS0 bits in PWM control register 1 are provided to choose the correction method.  
These bits provide correction according to Table 12-5.  
Table 12-5. Correction Methods  
Current Correction Bits  
Correction Method  
ISENS1 and ISENS0  
00  
Bits IPOL1, IPOL2, and IPOL3 used for correction  
01  
Current sensing on pins IS1, IS2, and IS3 occurs during the  
dead-time.  
10  
Current sensing on pins IS1, IS2, and IS3 occurs at the half  
11  
cycle in center-aligned mode and at the end of the cycle in  
edge-aligned mode.  
If correction is to be done in software or is not necessary, setting ISENS1:ISENS0 = 00 or = 01 causes  
the correction to be based on bits IPOL1, IPOL2, and IPOL3 in PWM control register 2. If correction is not  
required, the user can initialize the IPOLx bits and then only load one PWM value register per PWM pair.  
To allow the user to use a current sense scheme based upon sensed phase voltage during dead-time,  
setting ISENS1:ISENS0 = 10 causes the polarity of the Ix pin to be latched when both the top and bottom  
PWMs are off (for example, during the dead-time). At the 0 percent and 100 percent duty cycle  
boundaries, there is no dead-time so no new current value is sensed.  
To accommodate other current sensing schemes, setting ISENS1:ISENS0 = 11 causes the polarity of the  
current sense pin to be latched half-way into the PWM cycle in center-aligned mode and at the end of the  
cycle in edge-aligned mode. Therefore, even at 0 percent and 100 percent duty cycle, the current is  
sensed.  
Distortion correction is only available in complementary mode. At the beginning of the PWM period, the  
PWM uses this latched current value or polarity bit to decide whether the top PWM value or bottom PWM  
value is used. Figure 12-20 shows an example of top/bottom correction for PWMs 1 and 2.  
NOTE  
The IPOLx bits and the values latched on the ISx pins are buffered so that  
only one PWM register is used per PWM cycle. If the IPOLx bits or the  
current sense values change during a PWM period, this new value will not  
be used until the next PWM period. The ISENSx bits are NOT buffered;  
therefore, changing the current sensing method could affect the present  
PWM cycle.  
When the PWM is first enabled by setting PWMEN, PWM value registers 1, 3, and 5 will be used if the  
ISENSx bits are configured for current sensing correction. This is because no current will have previously  
been sensed.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
132  
Freescale Semiconductor  
 
Output Control  
PWM VALUE REG. 1 = 1  
PWM VALUE REG. 2 = 2  
IS1 NEGATIVE  
PWM = 2  
IS1 POSITIVE  
PWM = 1  
IS1 POSITIVE  
PWM = 1  
IS1 NEGATIVE  
PWM = 2  
PWM1  
PWM2  
Figure 12-20. Top/Bottom Correction for PWMs 1 and 2  
12.5.4 Output Polarity  
The output polarity of the PWMs is determined by two options: TOPNEG and BOTNEG. The top polarity  
option, TOPNEG, controls the polarity of PWMs 1, 3, and 5. The bottom polarity option, BOTNEG,  
controls the polarity of PWMs 2, 4, and 6. Positive polarity means that when the PWM is active, the PWM  
output is high. Conversely, negative polarity means that when the PWM is active, PWM output is low. See  
NOTE  
Both bits are found in the CONFIG register, which is a write-once register.  
This reduces the chances of the software inadvertently changing the  
polarity of the PWM signals and possibly damaging the motor drive  
hardware.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
133  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
CENTER-ALIGNED POSITIVE POLARITY  
EDGE-ALIGNED POSITIVE POLARITY  
UP-ONLY COUNTER  
MODULUS = 4  
UP/DOWN COUNTER  
MODULUS = 4  
PWM <= 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM >= 4  
PWM <= 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM >= 4  
CENTER-ALIGNED NEGATIVE POLARITY  
EDGE-ALIGNED NEGATIVE POLARITY  
UP-ONLY COUNTER  
MODULUS = 4  
UP/DOWN COUNTER  
MODULUS = 4  
PWM <= 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM >= 4  
PWM <= 0  
PWM = 1  
PWM = 2  
PWM = 3  
PWM >= 4  
Figure 12-21. PWM Polarity  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
134  
Freescale Semiconductor  
 
Output Control  
12.5.5 PWM Output Port Control  
Conditions may arise in which the PWM pins need to be individually controlled. This is made possible by  
the PWM output control register (PWMOUT) shown in Figure 12-22.  
Address:  
$0025  
Bit 7  
0
6
OUTCTL  
0
5
OUT6  
0
4
OUT5  
0
3
OUT4  
0
2
OUT3  
0
1
OUT2  
0
Bit 0  
OUT1  
0
Read:  
Write:  
Reset:  
0
= Unimplemented  
Figure 12-22. PWM Output Control Register (PWMOUT)  
If the OUTCTL bit is set, the PWM pins can be controlled by the OUTx bits. These bits behave according  
to Table 12-6.  
Table 12-6. OUTx Bits  
OUTx Bit  
Complementary Mode  
1 — PWM1 is active.  
Independent Mode  
1 — PWM1 is active.  
0 — PWM1 is inactive.  
OUT1  
0 — PWM1 is inactive.  
1 — PWM2 is complement of PWM 1.  
0 — PWM2 is inactive.  
1 — PWM2 is active.  
0 — PWM2 is inactive.  
OUT2  
OUT3  
OUT4  
OUT5  
OUT6  
1 — PWM3 is active.  
0 — PWM3 is inactive.  
1 — PWM3 is active.  
0 — PWM3 is inactive.  
1 — PWM4 is complement of PWM 3.  
0 — PWM4 is inactive.  
1 — PWM4 is active.  
0 — PWM4 is inactive.  
1 — PWM5 is active.  
0 — PWM5 is inactive.  
1 — PWM5 is active.  
0 — PWM5 is inactive.  
1 — PWM 6 is complement of PWM 5.  
0 — PWM6 is inactive.  
1 — PWM6 is active.  
0 — PWM6 is inactive.  
When OUTCTL is set, the polarity options TOPPOL and BOTPOL will still affect the outputs. In addition,  
if complementary operation is in use, the PWM pairs will not be allowed to be active simultaneously, and  
dead-time will still not be violated. When OUTCTL is set and complementary operation is in use, the odd  
OUTx bits are inputs to the dead-time generators as shown in Figure 12-15. Dead-time is inserted  
whenever the odd OUTx bit toggles as shown in Figure 12-23. Although dead-time is not inserted when  
the even OUTx bits change, there will be no dead-time violation as shown in Figure 12-24.  
Setting the OUTCTL bit does not disable the PWM generator and current sensing circuitry. They continue  
to run, but are no longer controlling the output pins. In addition, OUTCTL will control the PWM pins even  
when PWMEN = 0. When OUTCTL is cleared, the outputs of the PWM generator become the inputs to  
the dead-time and output circuitry at the beginning of the next PWM cycle.  
NOTE  
To avoid an unexpected dead-time occurrence, it is recommended that the  
OUTx bits be cleared prior to entering and prior to exiting individual PWM  
output control mode.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
135  
     
Pulse-Width Modulator for Motor Control (PWMMC)  
UP/DOWN COUNTER  
MODULUS = 4  
DEAD-TIME = 2  
PWM VALUE = 3  
OUTCTL  
OUT1  
OUT2  
PWM1  
PWM2  
PWM1/PWM2  
DEAD-TIME  
2
2
2
DEAD-TIME INSERTED AS PART OF DEAD-TIME INSERTED DUE  
DEAD-TIME INSERTED  
DUE TO CLEARING OF  
OUT1 BIT  
NORMAL PWM OPERATION AS  
CONTROLLED BY CURRENT  
SENSING AND PWM GENERATOR  
TO SETTING OF OUT1 BIT  
Figure 12-23. Dead-Time Insertion During OUTCTL = 1  
UP/DOWN COUNTER  
MODULUS = 4  
DEAD-TIME = 2  
PWM VALUE = 3  
OUTCTL  
OUT1  
OUT2  
PWM1  
PWM2  
2
2
2
2
PWM1/PWM2  
DEAD-TIME  
NO DEAD-TIME INSERTED  
BECAUSE OUT1 IS NOT  
TOGGLING  
DEAD-TIME INSERTED BECAUSE  
WHEN OUTCTL WAS SET, THE  
STATE OF OUT1 WAS SUCH THAT  
PWM1 WAS DIRECTED TO TOGGLE  
DEAD-TIME INSERTED  
BECAUSE OUT1 TOGGLES,  
DIRECTING PWM1 TO  
TOGGLE  
Figure 12-24. Dead-Time Insertion During OUTCTL = 1  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
136  
Freescale Semiconductor  
   
Fault Protection  
12.6 Fault Protection  
Conditions may arise in the external drive circuitry which require that the PWM signals become inactive  
immediately, such as an overcurrent fault condition. Furthermore, it may be desirable to selectively  
disable PWM(s) solely with software.  
One or more PWM pins can be disabled (forced to their inactive state) by applying a logic high to any of  
the four external fault pins or by writing a logic high to either of the disable bits (DISX and DISY in PWM  
control register 1). Figure 12-26 shows the structure of the PWM disabling scheme. While the PWM pins  
are disabled, they are forced to their inactive state. The PWM generator continues to run — only the  
output pins are disabled.  
To allow for different motor configurations and the controlling of more than one motor, the PWM disabling  
function is organized as two banks, bank X and bank Y. Bank information combines with information from  
the disable mapping register to allow selective PWM disabling. Fault pin 1, fault pin 2, and PWM disable  
bit X constitute the disabling function of bank X. Fault pin 3, fault pin 4, and PWM disable bit Y constitute  
the disabling function of bank Y. Figure 12-25 and Figure 12-27 show the disable mapping write-once  
register and the decoding scheme of the bank which selectively disables PWM(s). When all bits of the  
disable mapping register are set, any disable condition will disable all PWMs.  
A fault can also generate a CPU interrupt. Each fault pin has its own interrupt vector.  
Address: $0037  
Bit 7  
Bit 7  
1
6
Bit 6  
1
5
Bit 5  
1
4
Bit 4  
1
3
Bit 3  
1
2
Bit 2  
1
1
Bit 1  
1
Bit 0  
Bit 0  
1
Read:  
Write:  
Reset:  
Figure 12-25. PWM Disable Mapping Write-Once Register (DISMAP)  
12.6.1 Fault Condition Input Pins  
A logic high level on a fault pin disables the respective PWM(s) determined by the bank and the disable  
mapping register. Each fault pin incorporates a filter to assist in rejecting spurious faults. All of the external  
fault pins are software-configurable to re-enable the PWMs either with the fault pin (automatic mode) or  
with software (manual mode). Each fault pin has an associated FMODE bit to control the PWM  
re-enabling method. Automatic mode is selected by setting the FMODEx bit in the fault control register.  
Manual mode is selected when FMODEx is clear.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
137  
       
Pulse-Width Modulator for Motor Control (PWMMC)  
DISX  
SOFTWARE X DISABLE  
CYCLE START  
S
R
Q
BANK X  
DISABLE  
FMODE2  
FAULT PIN 2 DISABLE  
AUTO  
MODE  
FPIN2  
LOGIC HIGH FOR FAULT  
S
R
Q
TWO  
ONE  
SAMPLE  
FILTER  
S
R
Q
SHOT  
FFLAG2  
FAULT  
PIN2  
MANUAL  
MODE  
CLEAR BY WRITING 1 TO FTACK4  
INTERRUPT REQUEST  
FINT2  
The example is of fault pin 2 with DISX. Fault pin 4 with DISY is logically similar and affects BANK Y disable.  
Note: In manual mode (FMODE = 0), faults 2 and 4 may be cleared only if a logic level low at the input of the fault  
pin is present.  
CYCLE START  
FMODE1  
FAULT PIN 1 DISABLE  
AUTO  
MODE  
FPIN1  
LOGIC HIGH FOR FAULT  
TWO  
S
R
Q
BANK X DISABLE  
ONE  
SHOT  
FAULT  
PIN1  
SAMPLE  
FILTER  
S
R
Q
FFLAG1  
MANUAL  
MODE  
CLEAR BY WRITING 1 TO FTACK1  
INTERRUPT REQUEST  
FINT1  
The example is of fault pin 1. Fault pin 3 is logically similar and affects BANK Y disable.  
Note: In manual mode (FMODE = 0), faults 1 and 3 may be cleared regardless of the logic level at the input of the fault pin.  
Figure 12-26. PWM Disabling Scheme  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
138  
Freescale Semiconductor  
 
Fault Protection  
BIT 7  
DISABLE  
PWM PIN 1  
BIT 6  
BIT 5  
DISABLE  
PWM PIN 2  
DISABLE  
PWM PIN 3  
BIT 4  
BIT 3  
BANK X  
DISABLE  
BANK Y  
DISABLE  
DISABLE  
PWM PIN 4  
BIT 2  
DISABLE  
PWM PIN 5  
BIT 1  
BIT 0  
DISABLE  
PWM PIN 6  
Figure 12-27. PWM Disabling Decode Scheme  
12.6.1.1 Fault Pin Filter  
Each fault pin incorporates a filter to assist in determining a genuine fault condition. After a fault pin has  
been logic low for one CPU cycle, a rising edge (logic high) will be synchronously sampled once per CPU  
cycle for two cycles. If both samples are detected logic high, the corresponding FPIN bit and FFLAG bit  
will be set. The FPIN bit will remain set until the corresponding fault pin is logic low and synchronously  
sampled once in the following CPU cycle.  
12.6.1.2 Automatic Mode  
In automatic mode, the PWM(s) are disabled immediately once a filtered fault condition is detected (logic  
high). The PWM(s) remain disabled until the filtered fault condition is cleared (logic low) and a new PWM  
cycle begins as shown in Figure 12-28. Clearing the corresponding FFLAGx event bit will not enable the  
PWMs in automatic mode.  
The filtered fault pin’s logic state is reflected in the respective FPINx bit. Any write to this bit is overwritten  
by the pin state. The FFLAGx event bit is set with each rising edge of the respective fault pin after filtering  
has been applied. To clear the FFLAGx bit, the user must write a 1 to the corresponding FTACKx bit.  
f the FINTx bit is set, a fault condition resulting in setting the corresponding FFLAG bit will also latch a  
CPU interrupt request. The interrupt request latch is not cleared until one of these actions occurs:  
The FFLAGx bit is cleared by writing a 1 to the corresponding FTACKx bit.  
The FINTx bit is cleared. This will not clear the FFLAGx bit.  
A reset automatically clears all four interrupt latches.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
139  
     
Pulse-Width Modulator for Motor Control (PWMMC)  
FILTERED FAULT PIN  
PWM(S) ENABLED  
PWM(S) ENABLED  
PWM(S) DISABLED (INACTIVE)  
Figure 12-28. PWM Disabling in Automatic Mode  
IIf prior to a vector fetch, the interrupt request latch is cleared by one of the actions listed, a CPU interrupt  
will no longer be requested. A vector fetch does not alter the state of the PWMs, the FFLAGx event flag,  
or FINTx.  
NOTE  
If the FFLAGx or FINTx bits are not cleared during the interrupt service  
routine, the interrupt request latch will not be cleared.  
12.6.1.3 Manual Mode  
In manual mode, the PWM(s) are disabled immediately once a filtered fault condition is detected (logic  
high). The PWM(s) remain disabled until software clears the corresponding FFLAGx event bit and a new  
PWM cycle begins. In manual mode, the fault pins are grouped in pairs, each pair sharing common  
functionality. A fault condition on pins 1 and 3 may be cleared, allowing the PWM(s) to enable at the start  
of a PWM cycle regardless of the logic level at the fault pin. See Figure 12-29. A fault condition on pins 2  
and 4 can only be cleared, allowing the PWM(s) to enable, if a logic low level at the fault pin is present at  
the start of a PWM cycle. See Figure 12-30.  
The function of the fault control and event bits is the same as in automatic mode except that the PWMs  
are not re-enabled until the FFLAGx event bit is cleared by writing to the FTACKx bit and the filtered fault  
condition is cleared (logic low).  
FILTERED FAULT PIN 1 OR 3  
PWM(S) ENABLED  
PWM(S) ENABLED  
PWM(S) DISABLED  
FFLAGX CLEARED  
Figure 12-29. PWM Disabling in Manual Mode (Example 1)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
140  
Freescale Semiconductor  
     
Fault Protection  
FILTERED FAULT PIN 2 OR 4  
PWM(S) ENABLED  
PWM(S) ENABLED  
PWM(S) DISABLED  
FFLAGX CLEARED  
Figure 12-30. PWM Disabling in Manual Mode (Example 2)  
12.6.2 Software Output Disable  
Setting PWM disable bit DISX or DISY in PWM control register 1 immediately disables the corresponding  
PWM pins as determined by the bank and disable mapping register. The PWM pin(s) remain disabled  
until the PWM disable bit is cleared and a new PWM cycle begins as shown in Figure 12-31. Setting a  
PWM disable bit does not latch a CPU interrupt request, and there are no event flags associated with the  
PWM disable bits.  
12.6.3 Output Port Control  
When operating the PWMs using the OUTx bits (OUTCTL = 1), fault protection applies as described in  
this section. Due to the absence of periodic PWM cycles, fault conditions are cleared upon each CPU  
cycle and the PWM outputs are re-enabled, provided all fault clearing conditions are satisfied.  
DISABLE BIT  
PWM(S) ENABLED  
PWM(S) DISABLED  
PWM(S) ENABLED  
Figure 12-31. PWM Software Disable  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
141  
       
Pulse-Width Modulator for Motor Control (PWMMC)  
12.7 Initialization and the PWMEN Bit  
For proper operation, all registers should be initialized and the LDOK bit should be set before enabling  
the PWM via the PWMEN bit. When the PWMEN bit is first set, a reload will occur immediately, setting  
the PWMF flag and generating an interrupt if PWMINT is set. In addition, in complementary mode, PWM  
value registers 1, 3, and 5 will be used for the first PWM cycle if current sensing is selected.  
NOTE  
If the LDOK bit is not set when PWMEN is set after a RESET, the prescaler  
and PWM values will be 0, but the modulus will be unknown. If the LDOK  
bit is not set after the PWMEN bit has been cleared then set (without a  
RESET), the modulus value that was last loaded will be used.  
If the dead-time register (DEADTM) is changed after PWMEN or OUTCTL  
is set, an improper dead-time insertion could occur. However, the  
dead-time can never be shorter than the specified value.  
Because of the equals-comparator architecture of this PWM, the modulus  
= 0 case is considered illegal. Therefore, the modulus register is not reset,  
and a modulus value of 0 will result in waveforms inconsistent with the other  
modulus waveforms. See 12.9.2 PWM Counter Modulo Registers.  
When PWMEN is set, the PWM pins change from high impedance to outputs. At this time, assuming no  
fault condition is present, the PWM pins will drive according to the PWM values, polarity, and dead-time.  
See the timing diagram in Figure 12-32.  
CPU CLOCK  
PWMEN  
DRIVE ACCORDING TO PWM  
VALUE, POLARITY, AND DEAD-TIME  
HI-Z IF OUTCTL = 0  
PWM PINS  
HI-Z IF OUTCTL = 0  
Figure 12-32. PWMEN and PWM Pins  
When the PWMEN bit is cleared, this will occur:  
PWM pins will be three-stated unless OUTCTL = 1.  
PWM counter is cleared and will not be clocked.  
Internally, the PWM generator will force its outputs to 0 to avoid glitches when the PWMEN is set  
again.  
When PWMEN is cleared, these features remain active:  
All fault circuitry  
Manual PWM pin control via the PWMOUT register  
Dead-time insertion when PWM pins change via the PWMOUT register  
NOTE  
The PWMF flag and pending CPU interrupts are NOT cleared when  
PWMEN = 0.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
142  
Freescale Semiconductor  
   
PWM Operation in Wait Mode  
12.8 PWM Operation in Wait Mode  
When the microcontroller is put in low-power wait mode via the WAIT instruction, all clocks to the PWM  
module will continue to run. If an interrupt is issued from the PWM module (via a reload or a fault), the  
microcontroller will exit wait mode.  
Clearing the PWMEN bit before entering wait mode will reduce power consumption in wait mode because  
the counter, prescaler divider, and LDFQ divider will no longer be clocked. In addition, power will be  
reduced because the PWMs will no longer toggle.  
12.9 Control Logic Block  
This subsection provides a description of the control logic block.  
12.9.1 PWM Counter Registers  
The PWM counter registers (PCNTH and PCNTL) display the 12-bit up/down or up-only counter. When  
the high byte of the counter is read, the lower byte is latched. PCNTL will hold this latched value until it is  
read. See Figure 12-33 and Figure 12-34.  
Address:  
$0026  
Bit 7  
0
6
0
5
0
4
0
3
2
1
Bit 0  
Bit 8  
Read:  
Write:  
Reset:  
Bit 11  
Bit 10  
Bit 9  
0
0
0
0
0
0
0
0
= Unimplemented  
Figure 12-33. PWM Counter Register High (PCNTH)  
Address:  
$0027  
Bit 7  
Bit 7  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Write:  
Reset:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
0
0
0
0
0
0
0
0
= Unimplemented  
Figure 12-34. PWM Counter Register Low (PCNTL)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
143  
             
Pulse-Width Modulator for Motor Control (PWMMC)  
12.9.2 PWM Counter Modulo Registers  
The PWM counter modulus registers (PMODH and PMODL) hold a 12-bit unsigned number that  
determines the maximum count for the up/down or up-only counter. In center-aligned mode, the PWM  
period will be twice the modulus (assuming no prescaler). In edge-aligned mode, the PWM period will  
equal the modulus. See Figure 12-35 and Figure 12-36.  
Address:  
$0028  
Bit 7  
0
6
0
5
0
4
0
3
Bit 11  
X
2
Bit 10  
X
1
Bit 9  
X
Bit 0  
Bit 8  
X
Read:  
Write:  
Reset:  
0
0
0
0
= Unimplemented  
X = Indeterminate  
Figure 12-35. PWM Counter Modulo Register High (PMODH)  
Address:  
$0029  
Bit 7  
Bit 7  
X
6
Bit 6  
X
5
Bit 5  
X
4
Bit 4  
X
3
Bit 3  
X
2
Bit 2  
X
1
Bit 1  
X
Bit 0  
Bit 0  
X
Read:  
Write:  
Reset:  
X = Indeterminate  
Figure 12-36. PWM Counter Modulo Register Low (PMODL)  
To avoid erroneous PWM periods, this value is buffered and will not be used by the PWM generator until  
the LDOK bit has been set and the next PWM load cycle begins.  
NOTE  
When reading this register, the value read is the buffer (not necessarily the  
value the PWM generator is currently using).  
Because of the equals-comparator architecture of this PWM, the  
modulus = 0 case is considered illegal. Therefore, the modulus register is  
not reset, and a modulus value of 0 will result in waveforms inconsistent  
with the other modulus waveforms. If a modulus of 0 is loaded, the counter  
will continually count down from $FFF. This operation will not be tested or  
guaranteed (the user should consider it illegal). However, the dead-time  
constraints and fault conditions will still be guaranteed.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
144  
Freescale Semiconductor  
       
Control Logic Block  
12.9.3 PWMx Value Registers  
Each of the six PWMs has a 16-bit PWM value register.  
Bit 7  
6
5
Bit 13  
0
4
Bit 12  
0
3
Bit 11  
0
2
Bit 10  
0
1
Bit 9  
0
Bit 0  
Read:  
Write:  
Reset:  
Bit 15  
Bit 14  
Bit 8  
0
0
0
Bold  
= Buffered  
Figure 12-37. PWMx Value Registers High (PVALxH)  
Bit 7  
6
5
Bit 5  
0
4
Bit 4  
0
3
Bit 3  
0
2
Bit 2  
0
1
Bit 1  
0
Bit 0  
Bit 0  
0
Read:  
Write:  
Reset:  
Bit 7  
Bit 6  
0
0
Bold  
= Buffered  
Figure 12-38. PWMx Value Registers Low (PVALxL)  
The 16-bit signed value stored in this register determines the duty cycle of the PWM. The duty cycle is  
defined as: (PWM value/modulus) x 100.  
Writing a number less than or equal to 0 causes the PWM to be off for the entire PWM period. Writing a  
number greater than or equal to the 12-bit modulus causes the PWM to be on for the entire PWM period.  
If the complementary mode is selected, the PWM pairs share PWM value registers.  
To avoid erroneous PWM pulses, this value is buffered and will not be used by the PWM generator until  
the LDOK bit has been set and the next PWM load cycle begins.  
NOTE  
When reading these registers, the value read is the buffer (not necessarily  
the value the PWM generator is currently using).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
145  
       
Pulse-Width Modulator for Motor Control (PWMMC)  
12.9.4 PWM Control Register 1  
PWM control register 1 (PCTL1) controls PWM enabling/disabling, the loading of new modulus, prescaler,  
PWM values, and the PWM correction method. In addition, this register contains the software disable bits  
to force the PWM outputs to their inactive states (according to the disable mapping register).  
Address:  
$0020  
Bit 7  
6
DISY  
0
5
PWMINT  
0
4
PWMF  
0
3
ISENS1  
0
2
ISENS0  
0
1
LDOK  
0
Bit 0  
PWMEN  
0
Read:  
Write:  
Reset:  
DISX  
0
Figure 12-39. PWM Control Register 1 (PCTL1)  
DISX — Software Disable Bit for Bank X Bit  
This read/write bit allows the user to disable one or more PWM pins in bank X. The pins that are  
disabled are determined by the disable mapping write-once register.  
1 = Disable PWM pins in bank X.  
0 = Re-enable PWM pins at beginning of next PWM cycle.  
DISY — Software Disable Bit for Bank Y Bit  
This read/write bit allows the user to disable one or more PWM pins in bank Y. The pins that are  
disabled are determined by the disable mapping write-once register.  
1 = Disable PWM pins in bank Y.  
0 = Re-enable PWM pins at beginning of next PWM cycle.  
PWMINT — PWM Interrupt Enable Bit  
This read/write bit allows the user to enable and disable PWM CPU interrupts. If set, a CPU interrupt  
will be pending when the PWMF flag is set.  
1 = Enable PWM CPU interrupts.  
0 = Disable PWM CPU interrupts.  
NOTE  
When PWMINT is cleared, pending CPU interrupts are inhibited.  
PWMF — PWM Reload Flag  
This read/write bit is set at the beginning of every reload cycle regardless of the state of the LDOK bit.  
This bit is cleared by reading PWM control register 1 with the PWMF flag set, then writing a logic 0 to  
PWMF. If another reload occurs before the clearing sequence is complete, then writing logic 0 to  
PWMF has no effect.  
1 = New reload cycle began.  
0 = New reload cycle has not begun.  
NOTE  
When PWMF is cleared, pending PWM CPU interrupts are cleared (not  
including fault interrupts).  
ISENS1 and ISENS0 — Current Sense Correction Bits  
These read/write bits select the top/bottom correction scheme as shown in Table 12-7.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
146  
Freescale Semiconductor  
     
Control Logic Block  
Table 12-7. Correction Methods  
Current Correction Bits  
ISENS1 and ISENS0  
Correction Method  
00  
01  
Bits IPOL1, IPOL2, and IPOL3 are used for correction.  
Current sensing on pins IS1, IS2, and IS3 occurs during the  
dead-time.  
10  
11  
Current sensing on pins IS1, IS2, and IS3 occurs at the half  
cycle in center-aligned mode and at the end of the cycle in  
edge-aligned mode.  
1. The polarity of the ISx pin is latched when both the top and bottom PWMs are off. At  
the 0% and 100% duty cycle boundaries, there is no dead-time, so no new current  
value is sensed.  
2. Current is sensed even with 0% and 100% duty cycle.  
NOTE  
The ISENSx bits are not buffered. Changing the current sensing method  
can affect the present PWM cycle.  
LDOK— Load OK Bit  
This read/write bit loads the prescaler bits of the PMCTL2 register and the entire PMMODH/L and  
PWMVALH/L registers into a set of buffers. The buffered prescaler divisor, PWM counter modulus  
value, and PWM pulse will take effect at the next PWM load. Set LDOK by reading it when it is logic 0  
and then writing a logic 1 to it. LDOK is automatically cleared after the new values are loaded or can  
be manually cleared before a reload by writing a 0 to it. Reset clears LDOK.  
1 = Load prescaler, modulus, and PWM values.  
0 = Do not load new modulus, prescaler, and PWM values.  
NOTE  
The user should initialize the PWM registers and set the LDOK bit before  
enabling the PWM.  
A PWM CPU interrupt request can still be generated when LDOK is 0.  
PWMEN — PWM Module Enable Bit  
This read/write bit enables and disables the PWM generator and the PWM pins. When PWMEN is  
clear, the PWM generator is disabled and the PWM pins are in the high-impedance state (unless  
OUTCTL = 1).  
When the PWMEN bit is set, the PWM generator and PWM pins are activated.  
For more information, see 12.7 Initialization and the PWMEN Bit.  
1 = PWM generator and PWM pins enabled  
0 = PWM generator and PWM pins disabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
147  
 
Pulse-Width Modulator for Motor Control (PWMMC)  
12.9.5 PWM Control Register 2  
PWM control register 2 (PCTL2) controls the PWM load frequency, the PWM correction method, and the  
PWM counter prescaler. For ease of software and to avoid erroneous PWM periods, some of these  
register bits are buffered. The PWM generator will not use the prescaler value until the LDOK bit has been  
set, and a new PWM cycle is starting. The correction bits are used at the beginning of each PWM cycle  
(if the ISENSx bits are configured for software correction). The load frequency bits are not used until the  
current load cycle is complete.  
See Figure 12-40.  
NOTE  
The user should initialize this register before enabling the PWM.  
Address:  
$0021  
Bit 7  
6
LDFQ0  
0
5
0
4
3
2
IPOL3  
0
1
PRSC1  
0
Bit 0  
PRSC0  
0
Read:  
Write:  
Reset:  
LDFQ1  
IPOL1  
IPOL2  
0
0
0
0
= Unimplemented  
Bold  
= Buffered  
Figure 12-40. PWM Control Register 2 (PCTL2)  
LDFQ1 and LDFQ0 — PWM Load Frequency Bits  
These buffered read/write bits select the PWM CPU load frequency according to Table 12-8.  
NOTE  
When reading these bits, the value read is the buffer value (not necessarily  
the value the PWM generator is currently using).  
The LDFQx bits take effect when the current load cycle is complete  
regardless of the state of the load okay bit, LDOK.  
Table 12-8. PWM Reload Frequency  
Reload Frequency Bits  
PWM Reload Frequency  
LDFQ1 and LDFQ0  
00  
01  
10  
11  
Every PWM cycle  
Every 2 PWM cycles  
Every 4 PWM cycles  
Every 8 PWM cycles  
NOTE  
Reading the LPFQx bit reads the buffered values and not necessarily the  
values currently in effect.  
IPOL1 — Top/Bottom Correction Bit for PWM Pair 1 (PWMs 1 and 2)  
This buffered read/write bit selects which PWM value register is used if top/bottom correction is to be  
achieved without current sensing.  
1 = Use PWM value register 2.  
0 = Use PWM value register 1.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
148  
Freescale Semiconductor  
       
Control Logic Block  
NOTE  
When reading this bit, the value read is the buffer value (not necessarily the  
value the output control block is currently using).  
The IPOLx bits take effect at the beginning of the next load cycle,  
regardless of the state of the load okay bit, LDOK.  
IPOL2 — Top/Bottom Correction Bit for PWM Pair 2 (PWMs 3 and 4)  
This buffered read/write bit selects which PWM value register is used if top/bottom correction is to be  
achieved without current sensing.  
1 = Use PWM value register 4.  
0 = Use PWM value register 3.  
NOTE  
When reading this bit, the value read is the buffer value (not necessarily the  
value the output control block is currently using).  
IPOL3 — Top/Bottom Correction Bit for PWM Pair 3 (PWMs 5 and 6)  
This buffered read/write bit selects which PWM value register is used if top/bottom correction is to be  
achieved without current sensing.  
1 = Use PWM value register 6.  
0 = Use PWM value register 5.  
NOTE  
When reading this bit, the value read is the buffer value (not necessarily the  
value the output control block is currently using).  
PRSC1 and PRSC0 — PWM Prescaler Bits  
These buffered read/write bits allow the PWM clock frequency to be modified as shown in Table 12-9.  
NOTE  
When reading these bits, the value read is the buffer value (not necessarily  
the value the PWM generator is currently using).  
Table 12-9. PWM Prescaler  
Prescaler Bits  
PWM Clock Frequency  
PRSC1 and PRSC0  
f
00  
01  
10  
11  
OP  
f
f
f
/2  
/4  
/8  
OP  
OP  
OP  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
149  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
12.9.6 Dead-Time Write-Once Register  
The dead-time write-once register (DEADTM) holds an 8-bit value which specifies the number of CPU  
clock cycles to use for the dead-time when complementary PWM mode is selected. After this register is  
written for the first time, it cannot be rewritten unless a reset occurs. Dead-time is not affected by changes  
to the prescaler value.  
Address:  
$0036  
Bit 7  
6
Bit 6  
1
5
Bit 5  
1
4
Bit 4  
1
3
Bit 3  
1
2
Bit 2  
1
1
Bit 1  
1
Bit 0  
Bit 0  
1
Read:  
Write:  
Reset:  
Bit 7  
1
Figure 12-41. Dead-Time Write-Once Register (DEADTM)  
12.9.7 PWM Disable Mapping Write-Once Register  
The PWM disable mapping write-once register (DISMAP) holds an 8-bit value which determines which  
PWM pins will be disabled if an external fault or software disable occurs. For a further description of  
disable mapping, see 12.6 Fault Protection. After this register is written for the first time, it cannot be  
rewritten unless a reset occurs.  
Address:  
$0037  
Bit 7  
6
Bit 6  
1
5
Bit 5  
1
4
Bit 4  
1
3
Bit 3  
1
2
Bit 2  
1
1
Bit 1  
1
Bit 0  
Bit 0  
1
Read:  
Write:  
Reset:  
Bit 7  
1
Figure 12-42. PWM Disable Mapping Write-Once Register (DISMAP)  
12.9.8 Fault Control Register  
The fault control register (FCR) controls the fault-protection circuitry.  
Address: $0022  
Bit 7  
FINT4  
0
6
FMODE4  
0
5
FINT3  
0
4
FMODE3  
0
3
FINT2  
0
2
FMODE2  
0
1
FINT1  
0
Bit 0  
FMODE1  
0
Read:  
Write:  
Reset:  
Figure 12-43. Fault Control Register (FCR)  
FINT4 — Fault 4 Interrupt Enable Bit  
This read/write bit allows the CPU interrupt caused by faults on fault pin 4 to be enabled. The fault  
protection circuitry is independent of this bit and will always be active. If a fault is detected, the PWM  
pins will still be disabled according to the disable mapping register.  
1 = Fault pin 4 will cause CPU interrupts.  
0 = Fault pin 4 will not cause CPU interrupts.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
150  
Freescale Semiconductor  
               
Control Logic Block  
FMODE4 —Fault Mode Selection for Fault Pin 4 Bit (automatic versus manual mode)  
This read/write bit allows the user to select between automatic and manual mode faults. For further  
descriptions of each mode, see 12.6 Fault Protection.  
1 = Automatic mode  
0 = Manual mode  
FINT3 — Fault 3 Interrupt Enable Bit  
This read/write bit allows the CPU interrupt caused by faults on fault pin 3 to be enabled. The fault  
protection circuitry is independent of this bit and will always be active. If a fault is detected, the PWM  
pins will still be disabled according to the disable mapping register.  
1 = Fault pin 3 will cause CPU interrupts.  
0 = Fault pin 3 will not cause CPU interrupts.  
FMODE3 —Fault Mode Selection for Fault Pin 3 Bit (automatic versus manual mode)  
This read/write bit allows the user to select between automatic and manual mode faults. For further  
descriptions of each mode, see 12.6 Fault Protection.  
1 = Automatic mode  
0 = Manual mode  
FINT2 — Fault 2 Interrupt Enable Bit  
This read/write bit allows the CPU interrupt caused by faults on fault pin 2 to be enabled. The fault  
protection circuitry is independent of this bit and will always be active. If a fault is detected, the PWM  
pins will still be disabled according to the disable mapping register.  
1 = Fault pin 2 will cause CPU interrupts.  
0 = Fault pin 2 will not cause CPU interrupts.  
FMODE2 —Fault Mode Selection for Fault Pin 2 Bit  
(automatic versus manual mode)  
This read/write bit allows the user to select between automatic and manual mode faults. For further  
descriptions of each mode, see 12.6 Fault Protection.  
1 = Automatic mode  
0 = Manual mode  
FINT1 — Fault 1 Interrupt Enable Bit  
This read/write bit allows the CPU interrupt caused by faults on fault pin 1 to be enabled. The fault  
protection circuitry is independent of this bit and will always be active. If a fault is detected, the PWM  
pins will still be disabled according to the disable mapping register.  
1 = Fault pin 1 will cause CPU interrupts.  
0 = Fault pin 1 will not cause CPU interrupts.  
FMODE1 —Fault Mode Selection for Fault Pin 1 Bit (automatic versus manual mode)  
This read/write bit allows the user to select between automatic and manual mode faults. For further  
descriptions of each mode, see 12.6 Fault Protection.  
1 = Automatic mode  
0 = Manual mode  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
151  
Pulse-Width Modulator for Motor Control (PWMMC)  
12.9.9 Fault Status Register  
The fault status register (FSR) is a read-only register that indicates the current fault status.  
Address:  
$0023  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
Write:  
Reset:  
FPIN4  
FFLAG4  
FPIN3  
FFLAG3  
FPIN2  
FFLAG2  
FPIN1  
FFLAG1  
U
0
U
0
U
0
U
0
= Unimplemented  
U = Unaffected  
Figure 12-44. Fault Status Register (FSR)  
FPIN4 — State of Fault Pin 4 Bit  
This read-only bit allows the user to read the current state of fault  
pin 4.  
1 = Fault pin 4 is at logic 1.  
0 = Fault pin 4 is at logic 0.  
FFLAG4 — Fault Event Flag 4  
The FFLAG4 event bit is set within two CPU cycles after a rising edge on fault pin 4. To clear the  
FFLAG4 bit, the user must write a 1 to the FTACK4 bit in the fault acknowledge register.  
1 = A fault has occurred on fault pin 4.  
0 = No new fault on fault pin 4  
FPIN3 — State of Fault Pin 3 Bit  
This read-only bit allows the user to read the current state of fault  
pin 3.  
1 = Fault pin 3 is at logic 1.  
0 = Fault pin 3 is at logic 0.  
FFLAG3 — Fault Event Flag 3  
The FFLAG3 event bit is set within two CPU cycles after a rising edge on fault pin 3. To clear the  
FFLAG3 bit, the user must write a 1 to the FTACK3 bit in the fault acknowledge register.  
1 = A fault has occurred on fault pin 3.  
0 = No new fault on fault pin 3.  
FPIN2 — State of Fault Pin 2 Bit  
This read-only bit allows the user to read the current state of fault pin 2.  
1 = Fault pin 2 is at logic 1.  
0 = Fault pin 2 is at logic 0.  
FFLAG2 — Fault Event Flag 2  
The FFLAG2 event bit is set within two CPU cycles after a rising edge on fault pin 2. To clear the  
FFLAG2 bit, the user must write a 1 to the FTACK2 bit in the fault acknowledge register.  
1 = A fault has occurred on fault pin 2.  
0 = No new fault on fault pin 2  
FPIN1 — State of Fault Pin 1 Bit  
This read-only bit allows the user to read the current state of fault pin 1.  
1 = Fault pin 1 is at logic 1.  
0 = Fault pin 1 is at logic 0.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
152  
Freescale Semiconductor  
     
Control Logic Block  
FFLAG1 — Fault Event Flag 1  
The FFLAG1 event bit is set within two CPU cycles after a rising edge on fault pin 1. To clear the  
FFLAG1 bit, the user must write a 1 to the FTACK1 bit in the fault acknowledge register.  
1 = A fault has occurred on fault pin 1.  
0 = No new fault on fault pin 1.  
12.9.10 Fault Acknowledge Register  
The fault acknowledge register (FTACK) is used to acknowledge and clear the FFLAGs. In addition, it is  
used to monitor the current sensing bits to test proper operation.  
Address: $0024  
Bit 7  
0
6
5
4
DT5  
3
2
DT3  
1
Bit 0  
DT1  
Read:  
Write:  
Reset:  
0
FTACK4  
0
DT6  
DT4  
DT2  
FTACK3  
0
FTACK2  
0
FTACK1  
0
0
0
0
0
= Unimplemented  
Figure 12-45. Fault Acknowledge Register (FTACK)  
FTACK4 — Fault Acknowledge 4 Bit  
The FTACK4 bit is used to acknowledge and clear FFLAG4. This bit will always read 0. Writing a 1 to  
this bit will clear FFLAG4. Writing a 0 will have no effect.  
FTACK3 — Fault Acknowledge 3 Bit  
The FTACK3 bit is used to acknowledge and clear FFLAG3. This bit will always read 0. Writing a 1 to  
this bit will clear FFLAG3. Writing a 0 will have no effect.  
FTACK2 — Fault Acknowledge 2 Bit  
The FTACK2 bit is used to acknowledge and clear FFLAG2. This bit will always read 0. Writing a 1 to  
this bit will clear FFLAG2. Writing a 0 will have no effect.  
FTACK1 — Fault Acknowledge 1 Bit  
The FTACK1 bit is used to acknowledge and clear FFLAG1. This bit will always read 0. Writing a 1 to  
this bit will clear FFLAG1. Writing a 0 will have no effect.  
DT6 — Dead-Time 6 Bit  
Current sensing pin IS3 is monitored immediately before dead-time ends due to the assertion of  
PWM6.  
DT5 — Dead-Time 5 Bit  
Current sensing pin IS3 is monitored immediately before dead-time ends due to the assertion of  
PWM5.  
DT4 — Dead-Time 4 Bit  
Current sensing pin IS2 is monitored immediately before dead-time ends due to the assertion of  
PWM4.  
DT3 — Dead-Time 3 Bit  
Current sensing pin IS2 is monitored immediately before dead-time ends due to the assertion of  
PWM3.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
153  
     
Pulse-Width Modulator for Motor Control (PWMMC)  
DT2 — Dead-Time 2 Bit  
Current sensing pin IS1 is monitored immediately before dead-time ends due to the assertion of  
PWM2.  
DT1 — Dead-Time 1 Bit  
Current sensing pin IS1 is monitored immediately before dead-time ends due to the assertion of  
PWM1.  
12.9.11 PWM Output Control Register  
The PWM output control register (PWMOUT) is used to manually control the PWM pins.  
Address: $0025  
Bit 7  
0
6
OUTCTL  
0
5
OUT6  
0
4
OUT5  
0
3
OUT4  
0
2
OUT3  
0
1
OUT2  
0
Bit 0  
OUT1  
0
Read:  
Write:  
Reset:  
0
= Unimplemented  
Figure 12-46. PWM Output Control Register (PWMOUT)  
OUTCTL— Output Control Enable Bit  
This read/write bit allows the user to manually control the PWM pins. When set, the PWM generator is  
no longer the input to the dead-time and output circuitry. The OUTx bits determine the state of the  
PWM pins. Setting the OUTCTL bit does not disable the PWM generator. The generator continues to  
run, but is no longer the input to the PWM dead-time and output circuitry. When OUTCTL is cleared,  
the outputs of the PWM generator immediately become the inputs to the dead-time and output circuitry.  
1 = PWM outputs controlled manually  
0 = PWM outputs determined by PWM generator  
OUT6–OUT1— PWM Pin Output Control Bits  
These read/write bits control the PWM pins according to Table 12-10.  
Table 12-10. OUTx Bits  
OUTx Bit  
Complementary Mode  
1 — PWM1 is active.  
0 — PWM1 is inactive.  
Independent Mode  
1 — PWM1 is active.  
0 — PWM1 is inactive.  
OUT1  
1 — PWM2 is complement of PWM 1.  
0 — PWM2 is inactive.  
1 — PWM2 is active.  
0 — PWM2 is inactive.  
OUT2  
OUT3  
OUT4  
OUT5  
OUT6  
1 — PWM3 is active.  
0 — PWM3 is inactive.  
1 — PWM3 is active.  
0 — PWM3 is inactive.  
1 — PWM4 is complement of PWM 3.  
0 — PWM4 is inactive.  
1 — PWM4 is active.  
0 — PWM4 is inactive.  
1 — PWM5 is active.  
0 — PWM5 is inactive.  
1 — PWM5 is active.  
0 — PWM5 is inactive.  
1 — PWM 6 is complement of PWM 5.  
0 — PWM6 is inactive.  
1 — PWM6 is active.  
0 — PWM6 is inactive.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
154  
Freescale Semiconductor  
       
PWM Glossary  
12.10 PWM Glossary  
CPU cycle — One internal bus cycle (1/fOP  
)
PWM clock cycle (or period) — One tick of the PWM counter (1/fOP with no prescaler). See  
PWM cycle (or period)  
Center-aligned mode: The time it takes the PWM counter to count up and count down (modulus *  
2/fOP assuming no prescaler). See Figure 12-47.  
Edge-aligned mode: The time it takes the PWM counter to count up (modulus/fOP). See Figure  
12-47.  
Center-Aligned Mode  
PWM CLOCK CYCLE  
PWM CYCLE (OR PERIOD)  
Edge-Aligned Mode  
PWM  
CLOCK  
CYCLE  
PWM CYCLE (OR PERIOD)  
Figure 12-47. PWM Clock Cycle and PWM Cycle Definitions  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
155  
   
Pulse-Width Modulator for Motor Control (PWMMC)  
PWM Load Frequency — Frequency at which new PWM parameters get loaded into the PWM. See  
LDFQ1:LDFQ0 = 01 — Reload Every Two Cycles  
PWM LOAD CYCLE  
(1/PWM LOAD FREQUENCY)  
RELOAD NEW  
MODULUS,  
RELOAD NEW  
MODULUS,  
PRESCALER, &  
PWM VALUES IF  
LDOK = 1  
PRESCALER, &  
PWM VALUES IF  
LDOK = 1  
Figure 12-48. PWM Load Cycle/Frequency Definition  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
156  
Freescale Semiconductor  
 
Chapter 13  
Serial Communications Interface Module (SCI)  
This section describes the serial communications interface module (SCI, version D), which allows  
high-speed asynchronous communications with peripheral devices and other microcontroller units  
(MCUs).  
13.2 Features  
Features of the SCI module include:  
Full-duplex operation  
Standard mark/space non-return-to-zero (NRZ) format  
32 programmable baud rates  
Programmable 8-bit or 9-bit character length  
Separately enabled transmitter and receiver  
Separate receiver and transmitter CPU interrupt requests  
Separate receiver and transmitter  
Programmable transmitter output polarity  
Two receiver wakeup methods:  
Idle line wakeup  
Address mark wakeup  
Interrupt-driven operation with eight interrupt flags:  
Transmitter empty  
Transmission complete  
Receiver full  
Idle receiver input  
Receiver overrun  
Noise error  
Framing error  
Parity error  
Receiver framing error detection  
Hardware parity checking  
1/16 bit-time noise detection  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
157  
       
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
PTC1/ATD9(1)  
PTC0/ATD8  
USER FLASH VECTOR SPACE — 46 BYTES  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 13-1. Block Diagram Highlighting SCI Block and Pins  
Functional Description  
13.3 Functional Description  
Figure 13-2 shows the structure of the SCI module. The SCI allows full-duplex, asynchronous, NRZ serial  
communication among the MCU and remote devices, including other MCUs. The transmitter and receiver  
of the SCI operate independently, although they use the same baud rate generator. During normal  
operation, the CPU monitors the status of the SCI, writes the data to be transmitted, and processes  
received data.  
INTERNAL BUS  
SCI DATA  
REGISTER  
SCI DATA  
REGISTER  
RECEIVE  
SHIFT REGISTER  
TRANSMIT  
SHIFT REGISTER  
PTF4/RxD  
PTF5/TxD  
TXINV  
SCTIE  
R8  
T8  
TCIE  
SCRIE  
ILIE  
TE  
SCTE  
TC  
RE  
RWU  
SBK  
SCRF  
IDLE  
OR  
NF  
FE  
PE  
ORIE  
NEIE  
FEIE  
PEIE  
LOOPS  
ENSCI  
LOOPS  
RECEIVE  
CONTROL  
FLAG  
CONTROL  
TRANSMIT  
CONTROL  
WAKEUP  
CONTROL  
M
BKF  
RPF  
ENSCI  
WAKE  
ILTY  
PEN  
PTY  
PRE- BAUD RATE  
SCALER GENERATOR  
fOP  
÷ 4  
DATA SELECTION  
CONTROL  
÷ 16  
Figure 13-2. SCI Module Block Diagram  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
159  
   
Serial Communications Interface Module (SCI)  
Addr.  
Register Name  
Bit 7  
LOOPS  
0
6
ENSCI  
0
5
4
M
3
WAKE  
0
2
ILTY  
0
1
PEN  
0
Bit 0  
PTY  
0
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
SCI Control Register 1  
(SCC1)  
TXINV  
0
$0038  
0
SCI Control Register 2  
(SCC2)  
SCTIE  
TCIE  
0
SCRIE  
ILIE  
TE  
RE  
0
RWU  
0
SBK  
0
$0039  
$003A  
$003B  
$003C  
$003D  
$003E  
0
R8  
R
0
0
0
0
0
SCI Control Register 3  
(SCC3)  
T8  
ORIE  
NEIE  
FEIE  
PEIE  
R
R
U
U
TC  
R
0
0
0
OR  
R
0
NF  
R
0
FE  
R
0
PE  
R
Read: SCTE  
SCRF  
R
IDLE  
R
SCI Status Register 1  
(SCS1)  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
Read:  
Write:  
Reset:  
R
1
1
0
0
0
0
0
0
0
0
0
0
0
0
BKF  
R
RPF  
R
SCI Status Register 2  
(SCS2)  
R
R
R
R
R
R
0
0
0
0
0
0
0
0
R7  
T7  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
R0  
T0  
SCI Data Register  
(SCDR)  
Unaffected by reset  
0
R
0
0
0
SCI Baud Rate Register  
(SCBR)  
SCP1  
0
SCP0  
R
SCR2  
0
SCR1  
0
SCR0  
0
R
0
0
0
= Reserved  
U = Unaffected  
R
Figure 13-3. SCI I/O Register Summary  
13.3.1 Data Format  
The SCI uses the standard non-return-to-zero mark/space data format illustrated in Figure 13-4.  
8-BIT DATA FORMAT  
BIT M IN SCC1 CLEAR  
POSSIBLE  
PARITY  
BIT  
NEXT  
START  
BIT  
START  
BIT  
STOP  
BIT  
BIT 0  
BIT 1  
BIT 2  
BIT 3  
BIT 4  
BIT 5  
BIT 6  
BIT 7  
9-BIT DATA FORMAT  
BIT M IN SCC1 SET  
POSSIBLE  
PARITY  
BIT  
NEXT  
START  
BIT  
START  
BIT  
BIT 0  
BIT 1  
BIT 2  
BIT 3  
BIT 4  
BIT 5  
BIT 6  
BIT 7  
BIT 8  
STOP  
BIT  
Figure 13-4. SCI Data Formats  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
160  
Freescale Semiconductor  
   
Functional Description  
13.3.2 Transmitter  
Figure 13-5 shows the structure of the SCI transmitter.  
INTERNAL BUS  
PRE- BAUD  
SCALER DIVIDER  
÷ 16  
÷ 4  
SCI DATA REGISTER  
SCP1  
SCP0  
SCR2  
SCR1  
SCR0  
11-BIT  
TRANSMIT  
SHIFT REGISTER  
H
8
7
6
5
4
3
2
1
0
L
PTF5/TxD  
TXINV  
M
PEN  
PTY  
PARITY  
GENERATION  
T8  
TRANSMITTER CPU  
INTERRUPT REQUEST  
TRANSMITTER  
CONTROL LOGIC  
SCTE  
SBK  
SCTE  
LOOPS  
ENSCI  
TE  
SCTIE  
SCTIE  
TC  
TC  
TCIE  
TCIE  
Figure 13-5. SCI Transmitter  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
161  
   
Serial Communications Interface Module (SCI)  
13.3.2.1 Character Length  
The transmitter can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1  
(SCC1) determines character length. When transmitting 9-bit data, bit T8 in SCI control register 3 (SCC3)  
is the ninth bit (bit 8).  
13.3.2.2 Character Transmission  
During an SCI transmission, the transmit shift register shifts a character out to the PTF5/TxD pin. The SCI  
data register (SCDR) is the write-only buffer between the internal data bus and the transmit shift register.  
To initiate an SCI transmission:  
1. Enable the SCI by writing a 1 to the enable SCI bit (ENSCI) in SCI control register 1 (SCC1).  
2. Enable the transmitter by writing a 1 to the transmitter enable bit (TE) in SCI control register 2  
(SCC2).  
3. Clear the SCI transmitter empty bit by first reading SCI status register 1 (SCS1) and then writing  
to the SCDR.  
4. Repeat step 3 for each subsequent transmission.  
At the start of a transmission, transmitter control logic automatically loads the transmit shift register with  
a preamble of 1s. After the preamble shifts out, control logic transfers the SCDR data into the transmit  
shift register. A 0 start bit automatically goes into the least significant bit (LSB) position of the transmit shift  
register. A 1 stop bit goes into the most significant bit (MSB) position.  
The SCI transmitter empty bit, SCTE, in SCS1 becomes set when the SCDR transfers a byte to the  
transmit shift register. The SCTE bit indicates that the SCDR can accept new data from the internal data  
bus. If the SCI transmit interrupt enable bit, SCTIE, in SCC2 is also set, the SCTE bit generates a  
transmitter CPU interrupt request.  
When the transmit shift register is not transmitting a character, the PTF5/TxD pin goes to the idle  
condition, logic 1. If at any time software clears the ENSCI bit in SCI control register 1 (SCC1), the  
transmitter and receiver relinquish control of the port E pins.  
13.3.2.3 Break Characters  
Writing a 1 to the send break bit, SBK, in SCC2 loads the transmit shift register with a break character. A  
break character contains all 0s and has no start, stop, or parity bit. Break character length depends on  
the M bit in SCC1. As long as SBK is at 1, transmitter logic continuously loads break characters into the  
transmit shift register. After software clears the SBK bit, the shift register finishes transmitting the last  
break character and then transmits at least one logic 1. The automatic logic 1 at the end of a break  
character guarantees the recognition of the start bit of the next character.  
The SCI recognizes a break character when a start bit is followed by eight or nine logic 0 data bits and a  
logic 0 where the stop bit should be.  
Receiving a break character has these effects on SCI registers:  
Sets the framing error bit (FE) in SCS1  
Sets the SCI receiver full bit (SCRF) in SCS1  
Clears the SCI data register (SCDR)  
Clears the R8 bit in SCC3  
Sets the break flag bit (BKF) in SCS2  
May set the overrun (OR), noise flag (NF), parity error (PE), or reception-in-progress flag (RPF) bits  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
162  
Freescale Semiconductor  
     
Functional Description  
13.3.2.4 Idle Characters  
An idle character contains all 1s and has no start, stop, or parity bit. Idle character length depends on the  
M bit in SCC1. The preamble is a synchronizing idle character that begins every transmission.  
If the TE bit is cleared during a transmission, the PTF5/TxD pin becomes idle after completion of the  
transmission in progress. Clearing and then setting the TE bit during a transmission queues an idle  
character to be sent after the character currently being transmitted.  
NOTE  
When a break sequence is followed immediately by an idle character, this  
SCI design exhibits a condition in which the break character length is  
reduced by one half bit time. In this instance, the break sequence will  
consist of a valid start bit, eight or nine data bits (as defined by the M bit in  
SCC1) of logic 0 and one half data bit length of logic 0 in the stop bit position  
followed immediately by the idle character. To ensure a break character of  
the proper length is transmitted, always queue up a byte of data to be  
transmitted while the final break sequence is in progress.  
When queueing an idle character, return the TE bit to 1 before the stop bit  
of the current character shifts out to the PTF5/TxD pin. Setting TE after the  
stop bit appears on PTF5/TxD causes data previously written to the SCDR  
to be lost.  
A good time to toggle the TE bit is when the SCTE bit becomes set and just  
before writing the next byte to the SCDR.  
13.3.2.5 Inversion of Transmitted Output  
The transmit inversion bit (TXINV) in SCI control register 1 (SCC1) reverses the polarity of transmitted  
data. All transmitted values, including idle, break, start, and stop bits, are inverted when TXINV is at 1.  
13.3.2.6 Transmitter Interrupts  
These conditions can generate CPU interrupt requests from the SCI transmitter:  
SCI transmitter empty (SCTE) — The SCTE bit in SCS1 indicates that the SCDR has transferred  
a character to the transmit shift register. SCTE can generate a transmitter CPU interrupt request.  
Setting the SCI transmit interrupt enable bit, SCTIE, in SCC2 enables the SCTE bit to generate  
transmitter CPU interrupt requests.  
Transmission complete (TC) — The TC bit in SCS1 indicates that the transmit shift register and the  
SCDR are empty and that no break or idle character has been generated. The transmission  
complete interrupt enable bit, TCIE, in SCC2 enables the TC bit to generate transmitter CPU  
interrupt requests.  
13.3.3 Receiver  
Figure 13-6 shows the structure of the SCI receiver.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
163  
       
Serial Communications Interface Module (SCI)  
INTERNAL BUS  
SCR2  
SCR1  
SCR0  
SCP1  
SCP0  
SCI DATA REGISTER  
PRE- BAUD  
SCALER DIVIDER  
÷ 4  
÷ 16  
11-BIT  
RECEIVE SHIFT REGISTER  
fOP  
DATA  
RECOVERY  
H
8
7
6
5
4
3
2
1
0
L
PTF4/RxD  
ALL 0s  
BKF  
RPF  
M
RWU  
SCRF  
IDLE  
WAKE  
ILTY  
WAKEUP  
LOGIC  
PEN  
PTY  
R8  
PARITY  
CHECKING  
IDLE  
ILIE  
ILIE  
SCRF  
SCRIE  
SCRIE  
OR  
OR  
ORIE  
ORIE  
NF  
NF  
NEIE  
NEIE  
FE  
FE  
FEIE  
FEIE  
PE  
PE  
PEIE  
PEIE  
Figure 13-6. SCI Receiver Block Diagram  
13.3.3.1 Character Length  
The receiver can accommodate either 8-bit or 9-bit data. The state of the M bit in SCI control register 1  
(SCC1) determines character length. When receiving 9-bit data, bit R8 in SCI control register 2 (SCC2)  
is the ninth bit (bit 8). When receiving 8-bit data, bit R8 is a copy of the eighth bit (bit 7).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
164  
Freescale Semiconductor  
   
Functional Description  
13.3.3.2 Character Reception  
During an SCI reception, the receive shift register shifts characters in from the PTF4/RxD pin. The SCI  
data register (SCDR) is the read-only buffer between the internal data bus and the receive shift register.  
After a complete character shifts into the receive shift register, the data portion of the character transfers  
to the SCDR. The SCI receiver full bit, SCRF, in SCI status register 1 (SCS1) becomes set, indicating that  
the received byte can be read. If the SCI receive interrupt enable bit, SCRIE, in SCC2 is also set, the  
SCRF bit generates a receiver CPU interrupt request.  
13.3.3.3 Data Sampling  
The receiver samples the PTF4/RxD pin at the RT clock rate. The RT clock is an internal signal with a  
frequency 16 times the baud rate. To adjust for baud rate mismatch, the RT clock is resynchronized at  
these times (see Figure 13-7):  
After every start bit  
After the receiver detects a data bit change from 1 to 0 (after the majority of data bit samples at  
RT8, RT9, and RT10 return a valid 1 and the majority of the next RT8, RT9, and RT10 samples  
return a valid 0)  
START BIT  
LSB  
PTF4/RxD  
SAMPLES  
START BIT  
QUALIFICATION  
START BIT  
VERIFICATION  
DATA  
SAMPLING  
RT  
CLOCK  
RT CLOCK  
STATE  
RT CLOCK  
RESET  
Figure 13-7. Receiver Data Sampling  
To locate the start bit, data recovery logic does an asynchronous search for a 0 preceded by three 1s.  
When the falling edge of a possible start bit occurs, the RT clock begins to count to 16.  
To verify the start bit and to detect noise, data recovery logic takes samples at RT3, RT5, and RT7.  
Table 13-1 summarizes the results of the start bit verification samples.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
165  
     
Serial Communications Interface Module (SCI)  
Table 13-1. Start Bit Verification  
RT3, RT5, and RT7  
Samples  
Start Bit  
Verification  
Noise Flag  
000  
001  
010  
011  
100  
101  
110  
111  
Yes  
Yes  
Yes  
No  
0
1
1
0
1
0
0
0
Yes  
No  
No  
No  
If start bit verification is not successful, the RT clock is reset and a new search for a start bit begins.  
To determine the value of a data bit and to detect noise, recovery logic takes samples at RT8, RT9, and  
RT10. Table 13-2 summarizes the results of the data bit samples.  
Table 13-2. Data Bit Recovery  
RT8, RT9, and RT10  
Samples  
Data Bit  
Determination  
Noise Flag  
000  
001  
010  
011  
100  
101  
110  
111  
0
0
0
1
0
1
1
1
0
1
1
1
1
1
1
0
NOTE  
The RT8, RT9, and RT10 samples do not affect start bit verification. If any  
or all of the RT8, RT9, and RT10 start bit samples are 1s following a  
successful start bit verification, the noise flag (NF) is set and the receiver  
assumes that the bit is a start bit.  
To verify a stop bit and to detect noise, recovery logic takes samples at RT8, RT9, and RT10. Table 13-3  
summarizes the results of the stop bit samples.  
Table 13-3. Stop Bit Recovery  
RT8, RT9, and RT10  
Samples  
Framing  
Error Flag  
Noise Flag  
000  
001  
010  
011  
100  
101  
110  
111  
1
1
1
0
1
0
0
0
0
1
1
1
1
1
1
0
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
166  
Freescale Semiconductor  
     
Functional Description  
13.3.3.4 Framing Errors  
If the data recovery logic does not detect a 1 where the stop bit should be in an incoming character, it sets  
the framing error bit, FE, in SCS1. The FE flag is set at the same time that the SCRF bit is set. A break  
character that has no stop bit also sets the FE bit.  
13.3.3.5 Receiver Wakeup  
So that the MCU can ignore transmissions intended only for other receivers in multiple-receiver systems,  
the receiver can be put into a standby state. Setting the receiver wakeup bit, RWU, in SCC2 puts the  
receiver into a standby state during which receiver interrupts are disabled.  
Depending on the state of the WAKE bit in SCC1, either of two conditions on the PTF4/RxD pin can bring  
the receiver out of the standby state:  
Address mark — An address mark is a 1 in the most significant bit position of a received character.  
When the WAKE bit is set, an address mark wakes the receiver from the standby state by clearing  
the RWU bit. The address mark also sets the SCI receiver full bit, SCRF. Software can then  
compare the character containing the address mark to the user-defined address of the receiver. If  
they are the same, the receiver remains awake and processes the characters that follow. If they  
are not the same, software can set the RWU bit and put the receiver back into the standby state.  
Idle input line condition — When the WAKE bit is clear, an idle character on the PTF4/RxD pin  
wakes the receiver from the standby state by clearing the RWU bit. The idle character that wakes  
the receiver does not set the receiver idle bit, IDLE, or the SCI receiver full bit, SCRF. The idle line  
type bit, ILTY, determines whether the receiver begins counting 1s as idle character bits after the  
start bit or after the stop bit.  
NOTE  
Clearing the WAKE bit after the PTF4/RxD pin has been idle can cause the  
receiver to wake up immediately.  
13.3.3.6 Receiver Interrupts  
These sources can generate CPU interrupt requests from the SCI receiver:  
SCI receiver full (SCRF) — The SCRF bit in SCS1 indicates that the receive shift register has  
transferred a character to the SCDR. SCRF can generate a receiver CPU interrupt request. Setting  
the SCI receive interrupt enable bit, SCRIE, in SCC2 enables the SCRF bit to generate receiver  
CPU interrupts.  
Idle input (IDLE) — The IDLE bit in SCS1 indicates that 10 or 11 consecutive 1s shifted in from the  
PTF4/RxD pin. The idle line interrupt enable bit, ILIE, in SCC2 enables the IDLE bit to generate  
CPU interrupt requests.  
13.3.3.7 Error Interrupts  
These receiver error flags in SCS1 can generate CPU interrupt requests:  
Receiver overrun (OR) — The OR bit indicates that the receive shift register shifted in a new  
character before the previous character was read from the SCDR. The previous character remains  
in the SCDR, and the new character is lost. The overrun interrupt enable bit, ORIE, in SCC3  
enables OR to generate SCI error CPU interrupt requests.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
167  
       
Serial Communications Interface Module (SCI)  
Noise flag (NF) — The NF bit is set when the SCI detects noise on incoming data or break  
characters, including start, data, and stop bits. The noise error interrupt enable bit, NEIE, in SCC3  
enables NF to generate SCI error CPU interrupt requests.  
Framing error (FE) — The FE bit in SCS1 is set when a 0 occurs where the receiver expects a stop  
bit. The framing error interrupt enable bit, FEIE, in SCC3 enables FE to generate SCI error CPU  
interrupt requests.  
Parity error (PE) — The PE bit in SCS1 is set when the SCI detects a parity error in incoming data.  
The parity error interrupt enable bit, PEIE, in SCC3 enables PE to generate SCI error CPU interrupt  
requests.  
13.4 Wait Mode  
The WAIT and STOP instructions put the MCU in low power-consumption standby modes.  
The SCI module remains active after the execution of a WAIT instruction. In wait mode the SCI module  
registers are not accessible by the CPU. Any enabled CPU interrupt request from the SCI module can  
bring the MCU out of wait mode.  
If SCI module functions are not required during wait mode, reduce power consumption by disabling the  
module before executing the WAIT instruction.  
13.5 SCI During Break Module Interrupts  
The system integration module (SIM) controls whether status bits in other modules can be cleared during  
interrupts generated by the break module. The BCFE bit in the SIM break flag control register (SBFCR)  
enables software to clear status bits during the break state.  
To allow software to clear status bits during a break interrupt, write a 1 to the BCFE bit. If a status bit is  
cleared during the break state, it remains cleared when the MCU exits the break state.  
To protect status bits during the break state, write a 0 to the BCFE bit. With BCFE at 0 (its default state),  
software can read and write I/O registers during the break state without affecting status bits. Some status  
bits have a 2-step read/write clearing procedure. If software does the first step on such a bit before the  
break, the bit cannot change during the break state as long as BCFE is at 0. After the break, doing the  
second step clears the status bit.  
13.6 I/O Signals  
Port F shares two of its pins with the SCI module. The two SCI input/output (I/O) pins are:  
PTF5/TxD — Transmit data  
PTF4/RxD — Receive data  
13.6.1 PTF5/TxD (Transmit Data)  
The PTF5/TxD pin is the serial data output from the SCI transmitter. The SCI shares the PTF5/TxD pin  
with port F. When the SCI is enabled, the PTF5/TxD pin is an output regardless of the state of the DDRF5  
bit in data direction register F (DDRF).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
168  
Freescale Semiconductor  
       
I/O Registers  
13.6.2 PTF4/RxD (Receive Data)  
The PTF4/RxD pin is the serial data input to the SCI receiver. The SCI shares the PTF4/RxD pin with  
port F. When the SCI is enabled, the PTF4/RxD pin is an input regardless of the state of the DDRF4 bit  
in data direction register F (DDRF).  
13.7 I/O Registers  
These I/O registers control and monitor SCI operation:  
SCI control register 1 (SCC1)  
SCI control register 2 (SCC2)  
SCI control register 3 (SCC3)  
SCI status register 1 (SCS1)  
SCI status register 2 (SCS2)  
SCI data register (SCDR)  
SCI baud rate register (SCBR)  
13.7.1 SCI Control Register 1  
SCI control register 1 (SCC1):  
Enables loop-mode operation  
Enables the SCI  
Controls output polarity  
Controls character length  
Controls SCI wakeup method  
Controls idle character detection  
Enables parity function  
Controls parity type  
Address: $0038  
Bit 7  
LOOPS  
0
6
ENSCI  
0
5
TXINV  
0
4
M
0
3
WAKE  
0
2
ILTY  
0
1
PEN  
0
Bit 0  
PTY  
0
Read:  
Write:  
Reset:  
Figure 13-8. SCI Control Register 1 (SCC1)  
LOOPS — Loop Mode Select Bit  
This read/write bit enables loop mode operation. In loop mode the PTF4/RxD pin is disconnected from  
the SCI, and the transmitter output goes into the receiver input. Both the transmitter and the receiver  
must be enabled to use loop mode. Reset clears the  
LOOPS bit.  
1 = Loop mode enabled  
0 = Normal operation enabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
169  
         
Serial Communications Interface Module (SCI)  
ENSCI — Enable SCI Bit  
This read/write bit enables the SCI and the SCI baud rate generator. Clearing ENSCI sets the SCTE  
and TC bits in SCI status register 1 and disables transmitter interrupts. Reset clears the ENSCI bit.  
1 = SCI enabled  
0 = SCI disabled  
TXINV — Transmit Inversion Bit  
This read/write bit reverses the polarity of transmitted data. Reset clears the TXINV bit.  
1 = Transmitter output inverted  
0 = Transmitter output not inverted  
NOTE  
Setting the TXINV bit inverts all transmitted values, including idle, break,  
start, and stop bits.  
M — Mode (Character Length) Bit  
This read/write bit determines whether SCI characters are eight or nine bits long. See Table 13-4. The  
ninth bit can serve as an extra stop bit, as a receiver wakeup signal, or as a parity bit. Reset clears the  
M bit.  
1 = 9-bit SCI characters  
0 = 8-bit SCI characters  
WAKE — Wakeup Condition Bit  
This read/write bit determines which condition wakes up the SCI: a 1 (address mark) in the most  
significant bit (MSB) position of a received character or an idle condition on the PTF4/RxD pin. Reset  
clears the WAKE bit.  
1 = Address mark wakeup  
0 = Idle line wakeup  
ILTY — Idle Line Type Bit  
This read/write bit determines when the SCI starts counting 1s as idle character bits. The counting  
begins either after the start bit or after the stop bit. If the count begins after the start bit, then a string  
of 1s preceding the stop bit may cause false recognition of an idle character. Beginning the count after  
the stop bit avoids false idle character recognition, but requires properly synchronized transmissions.  
Reset clears the ILTY bit.  
1 = Idle character bit count begins after stop bit.  
0 = Idle character bit count begins after start bit.  
PEN — Parity Enable Bit  
This read/write bit enables the SCI parity function. See Table 13-4. When enabled, the parity function  
inserts a parity bit in the most significant bit position. See Figure 13-4. Reset clears the PEN bit.  
1 = Parity function enabled  
0 = Parity function disabled  
PTY — Parity Bit  
This read/write bit determines whether the SCI generates and checks for odd parity or even parity. See  
1 = Odd parity  
0 = Even parity  
NOTE  
Changing the PTY bit in the middle of a transmission or reception can  
generate a parity error.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
170  
Freescale Semiconductor  
I/O Registers  
Table 13-4. Character Format Selection  
Control Bits  
PEN:PTY  
Character Format  
Start  
Bits  
Data  
Bits  
Stop  
Bits  
Character  
Length  
M
Parity  
0
1
0
0
1
1
0X  
0X  
10  
11  
10  
11  
1
1
1
1
1
1
8
9
7
7
8
8
None  
None  
Even  
Odd  
1
1
1
1
1
1
10 bits  
11 bits  
10 bits  
10 bits  
11 bits  
11 bits  
Even  
Odd  
13.7.2 SCI Control Register 2  
SCI control register 2 (SCC2):  
Enables these CPU interrupt requests:  
Enables the SCTE bit to generate transmitter CPU interrupt requests  
Enables the TC bit to generate transmitter CPU interrupt requests  
Enables the SCRF bit to generate receiver CPU interrupt requests  
Enables the IDLE bit to generate receiver CPU interrupt requests  
Enables the transmitter  
Enables the receiver  
Enables SCI wakeup  
Transmits SCI break characters  
Address: $0039  
Bit 7  
SCTIE  
0
6
TCIE  
0
5
SCRIE  
0
4
ILIE  
0
3
TE  
0
2
RE  
0
1
RWU  
0
Bit 0  
SBK  
0
Read:  
Write:  
Reset:  
Figure 13-9. SCI Control Register 2 (SCC2)  
SCTIE — SCI Transmit Interrupt Enable Bit  
This read/write bit enables the SCTE bit to generate SCI transmitter CPU interrupt requests. Setting  
the SCTIE bit in SCC3 enables SCTE CPU interrupt requests. Reset clears the SCTIE bit.  
1 = SCTE enabled to generate CPU interrupt  
0 = SCTE not enabled to generate CPU interrupt  
TCIE — Transmission Complete Interrupt Enable Bit  
This read/write bit enables the TC bit to generate SCI transmitter CPU interrupt requests. Reset clears  
the TCIE bit.  
1 = TC enabled to generate CPU interrupt requests  
0 = TC not enabled to generate CPU interrupt requests  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
171  
       
Serial Communications Interface Module (SCI)  
SCRIE — SCI Receive Interrupt Enable Bit  
This read/write bit enables the SCRF bit to generate SCI receiver CPU interrupt requests. Setting the  
SCRIE bit in SCC3 enables the SCRF bit to generate CPU interrupt requests. Reset clears the SCRIE  
bit.  
1 = SCRF enabled to generate CPU interrupt  
0 = SCRF not enabled to generate CPU interrupt  
ILIE — Idle Line Interrupt Enable Bit  
This read/write bit enables the IDLE bit to generate SCI receiver CPU interrupt requests. Reset clears  
the ILIE bit.  
1 = IDLE enabled to generate CPU interrupt requests  
0 = IDLE not enabled to generate CPU interrupt requests  
TE — Transmitter Enable Bit  
Setting this read/write bit begins the transmission by sending a preamble of 10 or 11 1s from the  
transmit shift register to the PTF5/TxD pin. If software clears the TE bit, the transmitter completes any  
transmission in progress before the PTF5/TxD returns to the idle condition (logic 1). Clearing and then  
setting TE during a transmission queues an idle character to be sent after the character currently being  
transmitted. Reset clears the TE bit.  
1 = Transmitter enabled  
0 = Transmitter disabled  
NOTE  
Writing to the TE bit is not allowed when the enable SCI bit (ENSCI) is clear.  
ENSCI is in SCI control register 1.  
RE — Receiver Enable Bit  
Setting this read/write bit enables the receiver. Clearing the RE bit disables the receiver but does not  
affect receiver interrupt flag bits. Reset clears the RE bit.  
1 = Receiver enabled  
0 = Receiver disabled  
NOTE  
Writing to the RE bit is not allowed when the enable SCI bit (ENSCI) is  
clear. ENSCI is in SCI control register 1.  
RWU — Receiver Wakeup Bit  
This read/write bit puts the receiver in a standby state during which receiver interrupts are disabled.  
The WAKE bit in SCC1 determines whether an idle input or an address mark brings the receiver out  
of the standby state and clears the RWU bit. Reset clears the RWU bit.  
1 = Standby state  
0 = Normal operation  
SBK — Send Break Bit  
Setting and then clearing this read/write bit transmits a break character followed by a 1. The 1 after the  
break character guarantees recognition of a valid start bit. If SBK remains set, the transmitter  
continuously transmits break characters with no 1s between them. Reset clears the SBK bit.  
1 = Transmit break characters  
0 = No break characters being transmitted  
NOTE  
Do not toggle the SBK bit immediately after setting the SCTE bit. Toggling  
SBK too early causes the SCI to send a break character instead of a  
preamble.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
172  
Freescale Semiconductor  
I/O Registers  
13.7.3 SCI Control Register 3  
SCI control register 3 (SCC3):  
Stores the ninth SCI data bit received and the ninth SCI data bit to be transmitted  
Enables SCI receiver full (SCRF)  
Enables SCI transmitter empty (SCTE)  
Enables the following interrupts:  
Receiver overrun interrupts  
Noise error interrupts  
Framing error interrupts  
Parity error interrupts  
Address:  
$003A  
Bit 7  
R8  
R
6
5
0
4
0
3
2
NEIE  
0
1
FEIE  
0
Bit 0  
PEIE  
0
Read:  
Write:  
Reset:  
T8  
ORIE  
R
0
R
0
U
U
0
R
= Reserved  
U = Unaffected  
Figure 13-10. SCI Control Register 3 (SCC3)  
R8 — Received Bit 8  
When the SCI is receiving 9-bit characters, R8 is the read-only ninth bit (bit 8) of the received character.  
R8 is received at the same time that the SCDR receives the other eight bits.  
When the SCI is receiving 8-bit characters, R8 is a copy of the eighth bit (bit 7). Reset has no effect on  
the R8 bit.  
T8 — Transmitted Bit 8  
When the SCI is transmitting 9-bit characters, T8 is the read/write ninth bit (bit 8) of the transmitted  
character. T8 is loaded into the transmit shift register at the same time that the SCDR is loaded into  
the transmit shift register. Reset has no effect on the T8 bit.  
ORIE — Receiver Overrun Interrupt Enable Bit  
This read/write bit enables SCI error CPU interrupt requests generated by the receiver overrun bit, OR.  
1 = SCI error CPU interrupt requests from OR bit enabled  
0 = SCI error CPU interrupt requests from OR bit disabled  
NEIE — Receiver Noise Error Interrupt Enable Bit  
This read/write bit enables SCI error CPU interrupt requests generated by the noise error bit, NE.  
Reset clears NEIE.  
1 = SCI error CPU interrupt requests from NE bit enabled  
0 = SCI error CPU interrupt requests from NE bit disabled  
FEIE — Receiver Framing Error Interrupt Enable Bit  
This read/write bit enables SCI error CPU interrupt requests generated by the framing error bit, FE.  
Reset clears FEIE.  
1 = SCI error CPU interrupt requests from FE bit enabled  
0 = SCI error CPU interrupt requests from FE bit disabled  
PEIE — Receiver Parity Error Interrupt Enable Bit  
This read/write bit enables SCI receiver CPU interrupt requests generated by the parity error bit, PE.  
1 = SCI error CPU interrupt requests from PE bit enabled  
0 = SCI error CPU interrupt requests from PE bit disabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
173  
     
Serial Communications Interface Module (SCI)  
13.7.4 SCI Status Register 1  
SCI status register 1 (SCS1) contains flags to signal these conditions:  
Transfer of SCDR data to transmit shift register complete  
Transmission complete  
Transfer of receive shift register data to SCDR complete  
Receiver input idle  
Receiver overrun  
Noisy data  
Framing error  
Parity error  
Address: $003B  
Bit 7  
SCTE  
R
6
5
SCRF  
R
4
IDLE  
R
3
OR  
R
2
NF  
R
1
FE  
R
Bit 0  
PE  
R
Read:  
Write:  
Reset:  
TC  
R
1
1
0
0
0
0
0
0
R
= Reserved  
Figure 13-11. SCI Status Register 1 (SCS1)  
SCTE — SCI Transmitter Empty Bit  
This clearable, read-only bit is set when the SCDR transfers a character to the transmit shift register.  
SCTE can generate an SCI transmitter CPU interrupt request. When the SCTIE bit in SCC2 is set,  
SCTE generates an SCI transmitter CPU interrupt request. In normal operation, clear the SCTE bit by  
reading SCS1 with SCTE set and then writing to SCDR. Reset sets the SCTE bit.  
1 = SCDR data transferred to transmit shift register  
0 = SCDR data not transferred to transmit shift register  
TC — Transmission Complete Bit  
This read-only bit is set when the SCTE bit is set and no data, preamble, or break character is being  
transmitted. TC generates an SCI transmitter CPU interrupt request if the TCIE bit in SCC2 is also set.  
TC is cleared automatically when data, preamble, or break is queued and ready to be sent. There may  
be up to 1.5 transmitter clocks of latency between queueing data, preamble, and break and the  
transmission actually starting. Reset sets the TC bit.  
1 = No transmission in progress  
0 = Transmission in progress  
SCRF — SCI Receiver Full Bit  
This clearable, read-only bit is set when the data in the receive shift register transfers to the SCI data  
register. SCRF can generate an SCI receiver CPU interrupt request. When the SCRIE bit in SCC2 is  
set, SCRF generates a CPU interrupt request. In normal operation, clear the SCRF bit by reading  
SCS1 with SCRF set and then reading the SCDR. Reset clears SCRF.  
1 = Received data available in SCDR  
0 = Data not available in SCDR  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
174  
Freescale Semiconductor  
     
I/O Registers  
IDLE — Receiver Idle Bit  
This clearable, read-only bit is set when 10 or 11 consecutive 1s appear on the receiver input. IDLE  
generates an SCI error CPU interrupt request if the ILIE bit in SCC2 is also set. Clear the IDLE bit by  
reading SCS1 with IDLE set and then reading the SCDR. After the receiver is enabled, it must receive  
a valid character that sets the SCRF bit before an idle condition can set the IDLE bit. Also, after the  
IDLE bit has been cleared, a valid character must again set the SCRF bit before an idle condition can  
set the IDLE bit. Reset clears the  
IDLE bit.  
1 = Receiver input idle  
0 = Receiver input active or idle since the IDLE bit was cleared  
OR — Receiver Overrun Bit  
This clearable, read-only bit is set when software fails to read the SCDR before the receive shift  
register receives the next character. The OR bit generates an SCI error CPU interrupt request if the  
ORIE bit in SCC3 is also set. The data in the shift register is lost, but the data already in the SCDR is  
not affected. Clear the OR bit by reading SCS1 with OR set and then reading the SCDR. Reset clears  
the OR bit.  
1 = Receive shift register full and SCRF = 1  
0 = No receiver overrun  
Software latency may allow an overrun to occur between reads of SCS1 and SCDR in the flag-clearing  
sequence. Figure 13-12 shows the normal flag-clearing sequence and an example of an overrun  
caused by a delayed flag-clearing sequence. The delayed read of SCDR does not clear the OR bit  
because OR was not set when SCS1 was read. Byte 2 caused the overrun and is lost. The next  
flag-clearing sequence reads byte 3 in the SCDR instead of byte 2.  
NORMAL FLAG CLEARING SEQUENCE  
BYTE 1  
BYTE 2  
BYTE 3  
BYTE 4  
READ SCS1  
SCRF = 1  
OR = 0  
READ SCS1  
SCRF = 1  
OR = 0  
READ SCS1  
SCRF = 1  
OR = 0  
READ SCDR  
BYTE 1  
READ SCDR  
BYTE 2  
READ SCDR  
BYTE 3  
DELAYED FLAG CLEARING SEQUENCE  
BYTE 1  
BYTE 2  
BYTE 3  
BYTE 4  
READ SCS1  
SCRF = 1  
OR = 0  
READ SCS1  
SCRF = 1  
OR = 1  
READ SCDR  
BYTE 1  
READ SCDR  
BYTE 3  
Figure 13-12. Flag Clearing Sequence  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
175  
 
Serial Communications Interface Module (SCI)  
In applications that are subject to software latency or in which it is important to know which byte is lost  
due to an overrun, the flag-clearing routine can check the OR bit in a second read of SCS1 after  
reading the data register.  
NF — Receiver Noise Flag Bit  
This clearable, read-only bit is set when the SCI detects noise on the PTF4/RxD pin. NF generates an  
NF CPU interrupt request if the NEIE bit in SCC3 is also set. Clear the NF bit by reading SCS1 and  
then reading the SCDR. Reset clears the NF bit.  
1 = Noise detected  
0 = No noise detected  
FE — Receiver Framing Error Bit  
This clearable, read-only bit is set when a 0 is accepted as the stop bit. FE generates an SCI error CPU  
interrupt request if the FEIE bit in SCC3 also is set. Clear the FE bit by reading SCS1 with FE set and  
then reading the SCDR. Reset clears the FE bit.  
1 = Framing error detected  
0 = No framing error detected  
PE — Receiver Parity Error Bit  
This clearable, read-only bit is set when the SCI detects a parity error in incoming data. PE generates  
a PE CPU interrupt request if the PEIE bit in SCC3 is also set. Clear the PE bit by reading SCS1 with  
PE set and then reading the SCDR. Reset clears the PE bit.  
1 = Parity error detected  
0 = No parity error detected  
13.7.5 SCI Status Register 2  
SCI status register 2 (SCS2) contains flags to signal these conditions:  
Break character detected  
Incoming data  
Address:  
$003C  
Bit 7  
0
6
5
0
4
0
3
0
2
0
1
BKF  
R
Bit 0  
RPF  
R
Read:  
Write:  
Reset:  
0
R
R
R
0
R
0
R
0
R
0
0
0
0
0
R
= Reserved  
Figure 13-13. SCI Status Register 2 (SCS2)  
BKF — Break Flag  
This clearable, read-only bit is set when the SCI detects a break character on the PTF4/RxD pin. In  
SCS1, the FE and SCRF bits are also set. In 9-bit character transmissions, the R8 bit in SCC3 is  
cleared. BKF does not generate a CPU interrupt request. Clear BKF by reading SCS2 with BKF set  
and then reading the SCDR. Once cleared, BKF can become set again only after logic 1s again appear  
on the PTF4/RxD pin followed by another break character. Reset clears the BKF bit.  
1 = Break character detected  
0 = No break character detected  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
176  
Freescale Semiconductor  
     
I/O Registers  
RPF —Reception-in-Progress Flag  
This read-only bit is set when the receiver detects a logic 0 during the RT1 time period of the start bit  
search. RPF does not generate an interrupt request. RPF is reset after the receiver detects false start  
bits (usually from noise or a baud rate mismatch, or when the receiver detects an idle character. Polling  
RPF before disabling the SCI module or entering stop mode can show whether a reception is in  
progress.  
1 = Reception in progress  
0 = No reception in progress  
13.7.6 SCI Data Register  
The SCI data register (SCDR) is the buffer between the internal data bus and the receive and transmit  
shift registers. Reset has no effect on data in the SCI data register.  
Address:  
$003D  
Bit 7  
R7  
6
5
4
3
2
1
Bit 0  
R0  
Read:  
Write:  
Reset:  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
T7  
T0  
Unaffected by reset  
Figure 13-14. SCI Data Register (SCDR)  
R7/T7:R0/T0 — Receive/Transmit Data Bits  
Reading address $003D accesses the read-only received data bits, R7:R0. Writing to address $003D  
writes the data to be transmitted, T7:T0. Reset has no effect on the SCI data register.  
13.7.7 SCI Baud Rate Register  
The baud rate register (SCBR) selects the baud rate for both the receiver and the transmitter.  
Address:  
$003E  
Bit 7  
0
6
5
SCP1  
0
4
SCP0  
0
3
0
2
SCR2  
0
1
SCR1  
0
Bit 0  
SCR0  
0
Read:  
Write:  
Reset:  
0
R
R
R
0
0
0
R
= Reserved  
Figure 13-15. SCI Baud Rate Register (SCBR)  
SCP1 and SCP0 — SCI Baud Rate Prescaler Bits  
These read/write bits select the baud rate prescaler divisor as shown in Table 13-5. Reset clears SCP1  
and SCP0.  
Table 13-5. SCI Baud Rate Prescaling  
SCP1:SCP0  
Prescaler Divisor (PD)  
00  
01  
10  
11  
1
3
4
13  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
177  
             
Serial Communications Interface Module (SCI)  
SCR2–SCR0 — SCI Baud Rate Select Bits  
These read/write bits select the SCI baud rate divisor as shown in Table 13-6. Reset clears  
SCR2–SCR0.  
Table 13-6. SCI Baud Rate Selection  
SCR2:SCR1:SCR0  
Baud Rate Divisor (BD)  
000  
001  
010  
011  
100  
101  
110  
111  
1
2
4
8
16  
32  
64  
128  
Use this formula to calculate the SCI baud rate:  
f
OP  
Baud rate = ------------------------------------  
64 × PD × BD  
where:  
f
OP = internal operating frequency  
PD = prescaler divisor  
BD = baud rate divisor  
Table 13-7 shows the SCI baud rates that can be generated with a 4.9152-MHz crystal with the CGM set  
for an fOP of 7.3728 MHz and the CGM set for an fOP of 4.9152 MHz.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
178  
Freescale Semiconductor  
 
I/O Registers  
Table 13-7. SCI Baud Rate Selection Examples  
Baud Rate  
(f = 7.3728 MHz)  
Baud Rate  
(f = 4.9152 MHz)  
Prescaler  
Divisor (PD)  
Baud Rate  
Divisor (BD)  
SCP1:SCP0  
SCR2:SCR1:SCR0  
OP  
OP  
00  
00  
00  
00  
00  
00  
00  
00  
01  
01  
01  
01  
01  
01  
01  
01  
10  
10  
10  
10  
10  
10  
10  
10  
11  
11  
11  
11  
11  
11  
11  
11  
1
1
000  
001  
010  
011  
100  
101  
110  
111  
000  
001  
010  
011  
100  
101  
110  
111  
000  
001  
010  
011  
100  
101  
110  
111  
000  
001  
010  
011  
100  
101  
110  
111  
1
2
115,200  
57,600  
28,800  
14,400  
7200  
76,800  
38,400  
19,200  
9600  
4800  
2400  
1200  
600  
1
4
1
8
1
16  
32  
64  
128  
1
1
3600  
1
1800  
1
900  
3
38,400  
19,200  
9600  
25,600  
12,800  
6400  
3200  
1600  
800  
3
2
3
4
3
8
4800  
3
16  
32  
64  
128  
1
2400  
3
1200  
3
600  
400  
3
300  
200  
4
28,800  
14,400  
7200  
19,200  
9600  
4800  
2400  
1200  
600  
4
2
4
4
4
8
3600  
4
16  
32  
64  
128  
1
1800  
4
900  
4
450  
300  
4
225  
150  
13  
13  
13  
13  
13  
13  
13  
13  
8861.5  
4430.7  
2215.4  
1107.7  
553.8  
276.9  
138.5  
69.2  
5907.7  
2953.8  
1476.9  
738.5  
369.2  
184.6  
92.3  
2
4
8
16  
32  
64  
128  
46.2  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
179  
 
Serial Communications Interface Module (SCI)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
180  
Freescale Semiconductor  
Chapter 14  
System Integration Module (SIM)  
14.1 Introduction  
This section describes the system integration module (SIM). Together with the central processor unit  
(CPU), the SIM controls all microcontroller unit (MCU) activities.  
A block diagram of the SIM is shown in Figure 14-1.  
The SIM is a system state controller that coordinates CPU and exception timing. The SIM is responsible  
for:  
Bus clock generation and control for CPU and peripherals:  
Wait/reset/break entry and recovery  
Internal clock control  
Master reset control, including power-on reset (POR) and computer operating properly (COP)  
timeout  
Interrupt control:  
Acknowledge timing  
Arbitration control timing  
Vector address generation  
CPU enable/disable timing  
Modular architecture expandable to 128 interrupt sources  
Table 14-1 shows the internal signal names used in this section.  
Table 14-1. Signal Name Conventions  
Signal Name  
CGMXCLK  
CGMVCLK  
CGMOUT  
IAB  
Description  
Buffered version of OSC1 from clock generator module (CGM)  
Phase-locked loop (PLL) circuit output  
PLL-based or OSC1-based clock output from CGM module (bus clock = CGMOUT divided by two)  
Internal address bus  
IDB  
Internal data bus  
PORRST  
IRST  
Signal from the power-on reset module to the SIM  
Internal reset signal  
R/W  
Read/write signal  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
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181  
       
System Integration Module (SIM)  
MODULE WAIT  
WAIT  
CONTROL  
CPU WAIT (FROM CPU)  
SIMOSCEN (TO CGM)  
SIM  
COUNTER  
COP CLOCK  
CGMXCLK (FROM CGM)  
CGMOUT (FROM CGM)  
÷ 2  
CLOCK  
CONTROL  
CLOCK GENERATORS  
INTERNAL CLOCKS  
LVI (FROM LVI MODULE)  
RESET  
PIN LOGIC  
POR CONTROL  
RESET PIN CONTROL  
MASTER  
RESET  
CONTROL  
ILLEGAL OPCODE (FROM CPU)  
ILLEGAL ADDRESS (FROM ADDRESS  
MAP DECODERS)  
SIM RESET STATUS REGISTER  
COP (FROM COP MODULE)  
RESET  
INTERRUPT SOURCES  
CPU INTERFACE  
INTERRUPT CONTROL  
AND PRIORITY DECODE  
Figure 14-1. SIM Block Diagram  
14.2 SIM Bus Clock Control and Generation  
The bus clock generator provides system clock signals for the CPU and peripherals on the MCU. The  
system clocks are generated from an incoming clock, CGMOUT, as shown in Figure 14-2. This clock  
can come from either an external oscillator or from the on-chip phase-locked loop (PLL) circuit. See  
14.2.1 Bus Timing  
In user mode, the internal bus frequency is either the crystal oscillator output (CGMXCLK) divided by four  
or the PLL output (CGMVCLK) divided by four. See Chapter 4 Clock Generator Module (CGM).  
14.2.2 Clock Startup from POR or LVI Reset  
When the power-on reset (POR) module or the low-voltage inhibit (LVI) module generates a reset, the  
clocks to the CPU and peripherals are inactive and held in an inactive phase until after the 4096  
CGMXCLK cycle POR timeout has completed. The RST pin is driven low by the SIM during this entire  
period. The internal bus (IBUS) clocks start upon completion of the timeout.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
182  
Freescale Semiconductor  
       
Reset and System Initialization  
CGMXCLK  
CGMOUT  
OSC1  
SIM COUNTER  
CLOCK  
SELECT  
CIRCUIT  
A
B
BUS CLOCK  
÷ 2  
÷ 2  
GENERATORS  
CGMVCLK  
S*  
*When S = 1,  
CGMOUT = B  
BCS  
SIM  
PLL  
PTC2  
MONITOR MODE  
USER MODE  
CGM  
Figure 14-2. CGM Clock Signals  
14.2.3 Clocks in Wait Mode  
In wait mode, the CPU clocks are inactive. The SIM also produces two sets of clocks for other modules.  
Refer to the wait mode subsection of each module to see if the module is active or inactive in wait mode.  
Some modules can be programmed to be active in wait mode.  
14.3 Reset and System Initialization  
The MCU has these reset sources:  
Power-on reset module (POR)  
External reset pin (RST)  
Computer operating properly (COP) module  
Low-voltage inhibit (LVI) module  
Illegal opcode  
Illegal address  
All of these resets produce the vector $FFFE–FFFF ($FEFE–FEFF in monitor mode) and assert the  
internal reset signal (IRST). IRST causes all registers to be returned to their default values and all  
modules to be returned to their reset states.  
An internal reset clears the SIM counter (see 14.4 SIM Counter), but an external reset does not. Each of  
the resets sets a corresponding bit in the SIM reset status register (SRSR). See 14.7.2 SIM Reset Status  
14.3.1 External Pin Reset  
Pulling the asynchronous RST pin low halts all processing. The PIN bit of the SIM reset status register  
(SRSR) is set as long as RST is held low for a minimum of 67 CGMXCLK cycles, assuming that neither  
the POR nor the LVI was the source of the reset. See Table 14-2 for details. Figure 14-3 shows the relative  
timing.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
183  
       
System Integration Module (SIM)  
Table 14-2. PIN Bit Set Timing  
Reset Type  
POR/LVI  
Number of Cycles Required to Set PIN  
4163 (4096 + 64 + 3)  
67 (64 + 3)  
All others  
CGMOUT  
RST  
IAB  
VECT H  
VECT L  
PC  
Figure 14-3. External Reset Timing  
14.3.2 Active Resets from Internal Sources  
All internal reset sources actively pull the RST pin low for 32 CGMXCLK cycles to allow resetting of  
external peripherals. The internal reset signal (IRST) continues to be asserted for an additional 32 cycles  
(see Figure 14-5). An internal reset can be caused by an illegal address, illegal opcode, COP timeout,  
ILLEGAL ADDRESS RST  
ILLEGAL OPCODE RST  
COPRST  
LVI  
INTERNAL RESET  
POR  
Figure 14-4. Sources of Internal Reset  
NOTE  
For LVI or POR resets, the SIM cycles through 4096 CGMXCLK cycles  
during which the SIM forces the RST pin low. The internal reset signal then  
follows the sequence from the falling edge of RST, as shown in Figure 14-5.  
IRST  
RST PULLED LOW BY MCU  
32 CYCLES  
RST  
32 CYCLES  
CGMXCLK  
IAB  
VECTOR HIGH  
Figure 14-5. Internal Reset Timing  
The COP reset is asynchronous to the bus clock.  
The active reset feature allows the part to issue a reset to peripherals and other chips within a system  
built around the MCU.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
184  
Freescale Semiconductor  
           
Reset and System Initialization  
14.3.2.1 Power-On Reset (POR)  
When power is first applied to the MCU, the power-on reset (POR) module generates a pulse to indicate  
that power-on has occurred. The external reset pin (RST) is held low while the SIM counter counts out  
4096 CGMXCLK cycles. Sixty-four CGMXCLK cycles later, the CPU and memories are released from  
reset to allow the reset vector sequence to occur.  
OSC1  
PORRST  
4096  
CYCLES  
32  
CYCLES  
32  
CYCLES  
CGMXCLK  
CGMOUT  
RST  
IAB  
$FFFE  
$FFFF  
Figure 14-6. POR Recovery  
At power-on, these events occur:  
A POR pulse is generated.  
The internal reset signal is asserted.  
The SIM enables CGMOUT.  
Internal clocks to the CPU and modules are held inactive for 4096 CGMXCLK cycles to allow  
stabilization of the oscillator.  
The RST pin is driven low during the oscillator stabilization time.  
The POR bit of the SIM reset status register (SRSR) is set and all other bits in the register are  
cleared.  
14.3.2.2 Computer Operating Properly (COP) Reset  
An input to the SIM is reserved for the COP reset signal. The overflow of the COP counter causes an  
internal reset and sets the COP bit in the SIM reset status register (SRSR). The SIM actively pulls down  
the RST pin for all internal reset sources.  
To prevent a COP module timeout, write any value to location $FFFF. Writing to location $FFFF clears  
the COP counter and bits 12–4 of the SIM counter. The SIM counter output, which occurs at least every  
213–24 CGMXCLK cycles, drives the COP counter. The COP should be serviced as soon as possible out  
of reset to guarantee the maximum amount of time before the first timeout.  
The COP module is disabled if the RST pin or the IRQ pin is held at VHI while the MCU is in monitor mode.  
The COP module can be disabled only through combinational logic conditioned with the high voltage  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
185  
   
System Integration Module (SIM)  
signal on the RST or the IRQ pin. This prevents the COP from becoming disabled as a result of external  
noise. During a break state, VHI on the RST pin disables the COP module.  
14.3.2.3 Illegal Opcode Reset  
The SIM decodes signals from the CPU to detect illegal instructions. An illegal instruction sets the ILOP  
bit in the SIM reset status register (SRSR) and causes a reset.  
Because the MC68HC908MR32 has stop mode disabled, execution of the STOP instruction will cause  
an illegal opcode reset.  
14.3.2.4 Illegal Address Reset  
An opcode fetch from addresses other than FLASH or RAM addresses generates an illegal address reset  
(unimplemented locations within memory map). The SIM verifies that the CPU is fetching an opcode prior  
to asserting the ILAD bit in the SIM reset status register (SRSR) and resetting the MCU. A data fetch from  
an unmapped address does not generate a reset.  
14.3.2.5 Forced Monitor Mode Entry Reset (MENRST)  
The MENRST module monitors the reset vector fetches and will assert an internal reset if it detects that  
the reset vectors are erased ($FF). When the MCU comes out of reset, it is forced into monitor mode.  
14.3.2.6 Low-Voltage Inhibit (LVI) Reset  
The low-voltage inhibit (LVI) module asserts its output to the SIM when the VDD voltage falls to the VLVRX  
voltage and remains at or below that level for at least nine consecutive CPU cycles (see 19.5 DC Electrical  
Characteristics). The LVI bit in the SIM reset status register (SRSR) is set, and the external reset pin  
(RST) is held low while the SIM counter counts out 4096 CGMXCLK cycles. Sixty-four CGMXCLK cycles  
later, the CPU is released from reset to allow the reset vector sequence to occur. The SIM actively pulls  
down the RST pin for all internal reset sources.  
14.4 SIM Counter  
The SIM counter is used by the power-on reset (POR) module to allow the oscillator time to stabilize  
before enabling the internal bus (IBUS) clocks. The SIM counter also serves as a prescaler for the  
computer operating properly (COP) module. The SIM counter overflow supplies the clock for the COP  
module. The SIM counter is 13 bits long and is clocked by the falling edge of CGMXCLK.  
14.4.1 SIM Counter During Power-On Reset  
The power-on reset (POR) module detects power applied to the MCU. At power-on, the POR circuit  
asserts the signal PORRST. Once the SIM is initialized, it enables the clock generation (CGM) module to  
drive the bus clock state machine.  
14.4.2 SIM Counter and Reset States  
External reset has no effect on the SIM counter. The SIM counter is free-running after all reset states. For  
counter control and internal reset recovery sequences, see 14.3.2 Active Resets from Internal Sources.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
186  
Freescale Semiconductor  
               
Exception Control  
14.5 Exception Control  
Normal, sequential program execution can be changed in three different ways:  
1. Interrupts:  
a. Maskable hardware CPU interrupts  
b. Non-maskable software interrupt instruction (SWI)  
2. Reset  
3. Break interrupts  
14.5.1 Interrupts  
At the beginning of an interrupt, the CPU saves the CPU register contents on the stack and sets the  
interrupt mask (I bit) to prevent additional interrupts. At the end of an interrupt, the return-from-interrupt  
(RTI) instruction recovers the CPU register contents from the stack so that normal processing can  
resume. Figure 14-7 shows interrupt entry timing. Figure 14-9 shows interrupt recovery timing.  
MODULE  
INTERRUPT  
I BIT  
START  
ADDR  
IAB  
IDB  
DUMMY  
SP  
SP – 1  
SP – 2  
SP – 3  
SP – 4  
VECT H  
VECT L  
DUMMY PC – 1[7:0] PC – 1[15:8]  
X
A
CCR  
V DATA H V DATA L OPCODE  
R/W  
Figure 14-7. Interrupt Entry  
Interrupts are latched, and arbitration is performed in the SIM at the start of interrupt processing. The  
arbitration result is a constant that the CPU uses to determine which vector to fetch. Once an interrupt is  
latched by the SIM, no other interrupt can take precedence, regardless of priority, until the latched  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
187  
     
System Integration Module (SIM)  
FROM RESET  
YES  
BREAK OR SWI  
INTERRUPT?  
NO  
YES  
I BIT SET?  
NO  
YES  
INTERRUPT?  
STACK CPU REGISTERS  
SET I BIT  
LOAD PC WITH INTERRUPT VECTOR  
AS MANY INTERRUPTS AS EXIST ON CHIP  
FETCH NEXT  
INSTRUCTION  
SWI  
INSTRUCTION?  
YES  
YES  
NO  
RTI  
INSTRUCTION?  
UNSTACK CPU REGISTERS  
EXECUTE INSTRUCTION  
NO  
Figure 14-8. Interrupt Processing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
188  
Freescale Semiconductor  
 
Exception Control  
MODULE  
INTERRUPT  
I BIT  
IAB  
SP – 4  
SP – 3  
SP – 2  
SP – 1  
SP  
PC  
PC + 1  
IDB  
R/W  
CCR  
A
X
PC – 1[7:0] PC – 1[15:8] OPCODE OPERAND  
Figure 14-9. Interrupt Recovery  
14.5.1.1 Hardware Interrupts  
A hardware interrupt does not stop the current instruction. Processing of a hardware interrupt begins after  
completion of the current instruction. When the current instruction is complete, the SIM checks all pending  
hardware interrupts. If interrupts are not masked (I bit clear in the condition code register), and if the  
corresponding interrupt enable bit is set, the SIM proceeds with interrupt processing; otherwise, the next  
instruction is fetched and executed.  
If more than one interrupt is pending at the end of an instruction execution, the highest priority interrupt is  
serviced first. Figure 14-10 demonstrates what happens when two interrupts are pending. If an interrupt  
is pending upon exit from the original interrupt service routine, the pending interrupt is serviced before the  
load-accumulator-from- memory (LDA) instruction is executed.  
CLI  
LDA#$FF  
BACKGROUND ROUTINE  
INT1  
INT2  
PSHH  
INT1 INTERRUPT SERVICE ROUTINE  
PULH  
RTI  
PSHH  
INT2 INTERRUPT SERVICE ROUTINE  
PULH  
RTI  
Figure 14-10. Interrupt Recognition Example  
The LDA opcode is prefetched by both the INT1 and INT2 RTI instructions. However, in the case of the  
INT1 RTI prefetch, this is a redundant operation.  
NOTE  
To maintain compatibility with the M6805 Family, the H register is not  
pushed on the stack during interrupt entry. If the interrupt service routine  
modifies the H register or uses the indexed addressing mode, software  
should save the H register and then restore it prior to exiting the routine.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
189  
     
System Integration Module (SIM)  
14.5.1.2 Software Interrupt (SWI) Instruction  
The software interrupt (SWI) instruction is a non-maskable instruction that causes an interrupt regardless  
of the state of the interrupt mask  
(I bit) in the condition code register.  
14.5.2 Reset  
All reset sources always have equal and highest priority and cannot be arbitrated.  
14.6 Low-Power Mode  
Executing the WAIT instruction puts the MCU in a low power-consumption mode for standby situations.  
The SIM holds the CPU in a non-clocked state. WAIT clears the interrupt mask (I) in the condition code  
register, allowing interrupts to occur.  
14.6.1 Wait Mode  
In wait mode, the CPU clocks are inactive while the peripheral clocks continue to run. Figure 14-11 shows  
the timing for wait mode entry.  
A module that is active during wait mode can wake up the CPU with an interrupt if the interrupt is enabled.  
Stacking for the interrupt begins one cycle after the WAIT instruction during which the interrupt occurred.  
Refer to the wait mode subsection of each module to see if the module is active or inactive in wait mode.  
Some modules can be programmed to be active in wait mode.  
Wait mode can also be exited by a reset. If the COP disable bit, COPD, in the configuration register is  
logic 0, then the computer operating properly module (COP) is enabled and remains active in wait mode.  
IAB  
IDB  
WAIT ADDR  
WAIT ADDR + 1  
SAME  
SAME  
PREVIOUS DATA  
NEXT OPCODE  
SAME  
SAME  
R/W  
Note: Previous data can be operand data or the WAIT opcode, depending on the  
last instruction.  
Figure 14-11. Wait Mode Entry Timing  
Figure 14-12 and Figure 14-13 show the timing for wait recovery.  
IAB  
IDB  
$6E0B  
$A6  
$6E0C  
$00FF  
$00FE  
$00FD  
$00FC  
$A6  
$A6  
$01  
$0B  
$6E  
EXITSTOPWAIT  
Note: EXITSTOPWAIT = RST pin OR CPU interrupt  
Figure 14-12. Wait Recovery from Interrupt  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
190  
Freescale Semiconductor  
           
SIM Registers  
32  
CYCLES  
32  
CYCLES  
IAB  
$6E0B  
$A6  
RST VCT H RST VCT L  
IDB $A6  
RST  
$A6  
CGMXCLK  
Figure 14-13. Wait Recovery from Internal Reset  
14.6.2 Stop Mode  
In stop mode, the SIM counter is reset and the system clocks are disabled. An interrupt request from a  
module can cause an exit from stop mode. Stacking for interrupts begins after the selected stop recovery  
time has elapsed. Reset or break also causes an exit from stop mode.  
The SIM disables the clock generator module outputs (CGMOUT and CGMXCLK) in stop mode, stopping  
the CPU and peripherals. Stop recovery time is hard wired at the normal delay of 4096 CGMXCLK cycles.  
It is important to note that when using the PWM generator, its outputs will stop toggling when stop mode  
is entered. The PWM module must be disabled before entering stop mode to prevent external inverter  
failure.  
14.7 SIM Registers  
This subsection describes the SIM registers.  
14.7.1 SIM Break Status Register  
The SIM break status register (SBSR) contains a flag to indicate that a break caused an exit from wait  
mode.  
Address:  
$FE00  
BIt 7  
6
5
4
3
2
1
Bit 0  
R
Read:  
Write:  
Reset:  
SBSW  
R
R
R
R
R
R
(1)  
Note  
0
R
= Reserved  
Note 1. Writing a logic 0 clears SBSW.  
Figure 14-14. SIM Break Status Register (SBSR)  
SBSW — SIM Break Stop/Wait  
This status bit is useful in applications requiring a return to wait mode after exiting from a break  
interrupt. Clear SBSW by writing a logic 0 to it. Reset clears SBSW.  
1 = Wait mode was exited by break interrupt.  
0 = Wait mode was not exited by break interrupt.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
191  
         
System Integration Module (SIM)  
SBSW can be read within the break state SWI routine. The user can modify the return address on the  
stack by subtracting one from it.  
14.7.2 SIM Reset Status Register  
The SIM reset status register (SRSR) contains six flags that show the source of the last reset. Clear the  
SIM reset status register by reading it. A power-on reset sets the POR bit and clears all other bits in the  
register.  
Address: $FE01  
BIt 7  
POR  
R
6
5
COP  
R
4
ILOP  
R
3
ILAD  
R
2
1
LVI  
R
Bit 0  
0
Read:  
Write:  
Reset:  
PIN  
MENRST  
R
R
0
R
1
0
0
0
0
0
0
R
= Reserved  
Figure 14-15. SIM Reset Status Register (SRSR)  
POR — Power-On Reset Bit  
1 = Last reset caused by POR circuit  
0 = Read of SRSR  
PIN — External Reset Bit  
1 = Last reset caused by external reset pin (RST)  
0 = POR or read of SRSR  
COP — Computer Operating Properly Reset Bit  
1 = Last reset caused by COP counter  
0 = POR or read of SRSR  
ILOP — Illegal Opcode Reset Bit  
1 = Last reset caused by an illegal opcode  
0 = POR or read of SRSR  
ILAD — Illegal Address Reset Bit (opcode fetches only)  
1 = Last reset caused by an opcode fetch from an illegal address  
0 = POR or read of SRSR  
MENRST — Forced Monitor Mode Entry Reset Bit  
1 = Last reset caused by the MENRST circuit  
0 = POR or read of SRSR  
LVI — Low-Voltage Inhibit Reset Bit  
1 = Last reset caused by the LVI circuit  
0 = POR or read of SRSR  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
192  
Freescale Semiconductor  
     
SIM Registers  
14.7.3 SIM Break Flag Control Register  
The SIM break control register (SBFCR) contains a bit that enables software to clear status bits while the  
MCU is in a break state.  
Address:  
$FE03  
BIt 7  
6
5
4
3
2
1
Bit 0  
R
Read:  
Write:  
Reset:  
BCFE  
R
R
R
R
R
R
0
R
= Reserved  
Figure 14-16. SIM Break Flag Control Register (SBFCR)  
BCFE — Break Clear Flag Enable Bit  
This read/write bit enables software to clear status bits by accessing status registers while the MCU is  
in a break state. To clear status bits during the break state, the BCFE bit must be set.  
1 = Status bits clearable during break  
0 = Status bits not clearable during break  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
193  
   
System Integration Module (SIM)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
194  
Freescale Semiconductor  
Chapter 15  
Serial Peripheral Interface Module (SPI)  
15.1 Introduction  
The serial peripheral interface (SPI) module allows full-duplex, synchronous, serial communications with  
peripheral devices.  
15.2 Features  
Features of the SPI module include:  
Full-duplex operation  
Master and slave modes  
Double-buffered operation with separate transmit and receive registers  
Four master mode frequencies (maximum = bus frequency ÷ 2)  
Maximum slave mode frequency = bus frequency  
Serial clock with programmable polarity and phase  
Two separately enabled interrupts with central processor unit (CPU) service:  
SPRF (SPI receiver full)  
SPTE (SPI transmitter empty)  
Mode fault error flag with CPU interrupt capability  
Overflow error flag with CPU interrupt capability  
Programmable wired-OR mode  
I2C (inter-integrated circuit) compatibility  
15.3 Pin Name Conventions  
The generic names of the SPI input/output (I/O) pins are:  
SS, slave select  
SPSCK, SPI serial clock  
MOSI, master out/slave in  
MISO, master in/slave out  
SPI pins are shared by parallel I/O ports or have alternate functions. The full name of an SPI pin reflects  
the name of the shared port pin or the name of an alternate pin function. The generic pin names appear  
in the text that follows. Table 15-1 shows the full names of the SPI I/O pins.  
Table 15-1. Pin Name Conventions  
Generic Pin Names:  
MISO  
MOSI  
SPSCK  
SS  
Full Pin Names: PTF3/MISO  
PTF2/MOSI PTF0/SPSCK  
PTF1/SS  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
195  
           
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
PTC1/ATD9(1)  
PTC0/ATD8  
USER FLASH VECTOR SPACE — 46 BYTES  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 15-1. Block Diagram Highlighting SPI Block and Pins  
Functional Description  
15.4 Functional Description  
Figure 15-2 shows the structure of the SPI module and Figure 15-3 shows the locations and contents of  
the SPI I/O registers.  
The SPI module allows full-duplex, synchronous, serial communication between the microcontroller unit  
(MCU) and peripheral devices, including other MCUs. Software can poll the SPI status flags or SPI  
operation can be interrupt-driven. All SPI interrupts can be serviced by the CPU.  
INTERNAL BUS  
TRANSMIT DATA REGISTER  
CGMOUT ÷ 2  
(FROM SIM)  
SHIFT REGISTER  
MISO  
MOSI  
7
6
5
4
3
2
1
0
÷ 2  
÷ 8  
CLOCK  
DIVIDER  
RECEIVE DATA REGISTER  
÷ 32  
÷ 128  
PIN  
CONTROL  
LOGIC  
CLOCK  
SELECT  
SPSCK  
SS  
SPMSTR  
SPE  
M
S
CLOCK  
LOGIC  
SPR1  
SPR0  
SPMSTR  
CPHA  
CPOL  
SPWOM  
TRANSMITTER CPU INTERRUPT REQUEST  
RECEIVER/ERROR CPU INTERRUPT REQUEST  
MODFEN  
ERRIE  
SPTIE  
SPRIE  
SPE  
SPI  
CONTROL  
SPRF  
SPTE  
OVRF  
MODF  
Figure 15-2. SPI Module Block Diagram  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
197  
   
Serial Peripheral Interface Module (SPI)  
Addr.  
Register Name  
Bit 7  
SPRIE  
0
6
5
4
3
2
1
SPE  
0
Bit 0  
SPTIE  
0
Read:  
SPI Control Register  
(SPCR) Write:  
R
0
SPMSTR  
CPOL  
CPHA  
SPWOM  
0
$0044  
Reset:  
1
OVRF  
R
0
MODF  
R
1
SPTE  
R
Read: SPRF  
SPI Status and Control  
ERRIE  
MODFEN  
SPR1  
SPR0  
$0045  
$0046  
Register (SPSCR) Write:  
R
0
Reset:  
Read:  
0
0
0
1
0
0
0
R7  
T7  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
R0  
T0  
SPI Data Register  
(SPDR) Write:  
Reset:  
Unaffected by reset  
R
= Reserved  
Figure 15-3. SPI I/O Register Summary  
15.4.1 Master Mode  
The SPI operates in master mode when the SPI master bit, SPMSTR, is set.  
NOTE  
Configure the SPI modules as master or slave before enabling them.  
Enable the master SPI before enabling the slave SPI. Disable the slave SPI  
before disabling the master SPI. See 15.12.1 SPI Control Register.  
Only a master SPI module can initiate transmissions. Software begins the transmission from a master SPI  
module by writing to the SPI data register. If the shift register is empty, the byte immediately transfers to  
the shift register, setting the SPI transmitter empty bit, SPTE. The byte begins shifting out on the MOSI  
pin under the control of the serial clock. See Figure 15-4.  
MASTER MCU  
SLAVE MCU  
MISO  
MOSI  
MISO  
MOSI  
SHIFT REGISTER  
SHIFT REGISTER  
SPSCK  
SS  
SPSCK  
SS  
BAUD RATE  
GENERATOR  
VDD  
Figure 15-4. Full-Duplex Master-Slave Connections  
The SPR1 and SPR0 bits control the baud rate generator and determine the speed of the shift register.  
See 15.12.2 SPI Status and Control Register. Through the SPSCK pin, the baud-rate generator of the  
master also controls the shift register of the slave peripheral.  
As the byte shifts out on the MOSI pin of the master, another byte shifts in from the slave on the master’s  
MISO pin. The transmission ends when the receiver full bit, SPRF, becomes set. At the same time that  
SPRF becomes set, the byte from the slave transfers to the receive data register. In normal operation,  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
198  
Freescale Semiconductor  
     
Transmission Formats  
SPRF signals the end of a transmission. Software clears SPRF by reading the SPI status and control  
register with SPRF set and then reading the SPI data register. Writing to the SPI data register clears the  
SPTE bit.  
15.4.2 Slave Mode  
The SPI operates in slave mode when the SPMSTR bit is clear. In slave mode the SPSCK pin is the input  
for the serial clock from the master MCU. Before a data transmission occurs, the SS pin of the slave SPI  
must be at logic 0. SS must remain low until the transmission is complete. See 15.6.2 Mode Fault Error.  
In a slave SPI module, data enters the shift register under the control of the serial clock from the master  
SPI module. After a byte enters the shift register of a slave SPI, it transfers to the receive data register,  
and the SPRF bit is set. To prevent an overflow condition, slave software then must read the receive data  
register before another full byte enters the shift register.  
The maximum frequency of the SPSCK for an SPI configured as a slave is the bus clock speed (which is  
twice as fast as the fastest master SPSCK clock that can be generated). The frequency of the SPSCK for  
an SPI configured as a slave does not have to correspond to any SPI baud rate. The baud rate only  
controls the speed of the SPSCK generated by an SPI configured as a master. Therefore, the frequency  
of the SPSCK for an SPI configured as a slave can be any frequency less than or equal to the bus speed.  
When the master SPI starts a transmission, the data in the slave shift register begins shifting out on the  
MISO pin. The slave can load its shift register with a new byte for the next transmission by writing to its  
transmit data register. The slave must write to its transmit data register at least one bus cycle before the  
master starts the next transmission. Otherwise, the byte already in the slave shift register shifts out on the  
MISO pin. Data written to the slave shift register during a transmission remains in a buffer until the end of  
the transmission.  
When the clock phase bit (CPHA) is set, the first edge of SPSCK starts a transmission. When CPHA is  
clear, the falling edge of SS starts a transmission. See 15.5 Transmission Formats.  
NOTE  
If the write to the data register is late, the SPI transmits the data already in  
the shift register from the previous transmission.  
SPSCK must be in the proper idle state before the slave is enabled to  
prevent SPSCK from appearing as a clock edge.  
15.5 Transmission Formats  
During an SPI transmission, data is simultaneously transmitted (shifted out serially) and received (shifted  
in serially). A serial clock synchronizes shifting and sampling on the two serial data lines. A slave select  
line allows selection of an individual slave SPI device; slave devices that are not selected do not interfere  
with SPI bus activities. On a master SPI device, the slave select line can optionally be used to indicate  
multiple-master bus contention.  
15.5.1 Clock Phase and Polarity Controls  
Software can select any of four combinations of serial clock (SPSCK) phase and polarity using two bits  
in the SPI control register (SPCR). The clock polarity is specified by the CPOL control bit, which selects  
an active high or low clock and has no significant effect on the transmission format.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
199  
     
Serial Peripheral Interface Module (SPI)  
The clock phase (CPHA) control bit selects one of two fundamentally different transmission formats. The  
clock phase and polarity should be identical for the master SPI device and the communicating slave  
device. In some cases, the phase and polarity are changed between transmissions to allow a master  
device to communicate with peripheral slaves having different requirements.  
NOTE  
Before writing to the CPOL bit or the CPHA bit, disable the SPI by clearing  
the SPI enable bit (SPE).  
15.5.2 Transmission Format When CPHA = 0  
Figure 15-5 shows an SPI transmission in which CPHA is logic 0. The figure should not be used as a  
replacement for data sheet parametric information.Two waveforms are shown for SPSCK: one for  
CPOL = 0 and another for CPOL = 1. The diagram may be interpreted as a master or slave timing  
diagram since the serial clock (SPSCK), master in/slave out (MISO), and master out/slave in (MOSI) pins  
are directly connected between the master and the slave. The MISO signal is the output from the slave,  
and the MOSI signal is the output from the master. The SS line is the slave select input to the slave. The  
slave SPI drives its MISO output only when its slave select input (SS) is at logic 0, so that only the selected  
slave drives to the master. The SS pin of the master is not shown but is assumed to be inactive. The SS  
pin of the master must be high or must be reconfigured as general-purpose I/O not affecting the SPI. (See  
15.6.2 Mode Fault Error.) When CPHA = 0, the first SPSCK edge is the MSB capture strobe. Therefore,  
the slave must begin driving its data before the first SPSCK edge, and a falling edge on the SS pin is used  
to start the slave data transmission. The slave’s SS pin must be toggled back to high and then low again  
between each byte transmitted as shown in Figure 15-6.  
SPSCK CYCLE #  
FOR REFERENCE  
1
2
3
4
5
6
7
8
SPSCK, CPOL = 0  
SPSCK, CPOL = 1  
MOSI  
FROM MASTER  
MSB  
BIT 6  
BIT 6  
BIT 5  
BIT 5  
BIT 4  
BIT 4  
BIT 3  
BIT 3  
BIT 2  
BIT 2  
BIT 1  
BIT 1  
LSB  
LSB  
MISO  
FROM SLAVE  
MSB  
SS, TO SLAVE  
CAPTURE STROBE  
Figure 15-5. Transmission Format (CPHA = 0)  
MISO/MOSI  
MASTER SS  
BYTE 1  
BYTE 2  
BYTE 3  
SLAVE SS  
CPHA = 0  
SLAVE SS  
CPHA = 1  
Figure 15-6. CPHA/SS Timing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
200  
Freescale Semiconductor  
     
Transmission Formats  
When CPHA = 0 for a slave, the falling edge of SS indicates the beginning of the transmission. This  
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data. Once the  
transmission begins, no new data is allowed into the shift register from the transmit data register.  
Therefore, the SPI data register of the slave must be loaded with transmit data before the falling edge of  
SS. Any data written after the falling edge is stored in the transmit data register and transferred to the shift  
register after the current transmission.  
15.5.3 Transmission Format When CPHA = 1  
Figure 15-7 shows an SPI transmission in which CPHA is logic 1. The figure should not be used as a  
replacement for data sheet parametric information. Two waveforms are shown for SPSCK: one for  
CPOL = 0 and another for CPOL = 1. The diagram may be interpreted as a master or slave timing  
diagram since the serial clock (SPSCK), master in/slave out (MISO), and master out/slave in (MOSI) pins  
are directly connected between the master and the slave. The MISO signal is the output from the slave,  
and the MOSI signal is the output from the master. The SS line is the slave select input to the slave. The  
slave SPI drives its MISO output only when its slave select input (SS) is at logic 0, so that only the selected  
slave drives to the master. The SS pin of the master is not shown but is assumed to be inactive. The SS  
pin of the master must be high or must be reconfigured as general-purpose I/O not affecting the SPI. See  
15.6.2 Mode Fault Error. When CPHA = 1, the master begins driving its MOSI pin on the first SPSCK  
edge. Therefore, the slave uses the first SPSCK edge as a start transmission signal. The SS pin can  
remain low between transmissions. This format may be preferable in systems having only one master and  
only one slave driving the MISO data line.  
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the beginning of the transmission. This  
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data. Once the  
transmission begins, no new data is allowed into the shift register from the transmit data register.  
Therefore, the SPI data register of the slave must be loaded with transmit data before the first edge of  
SPSCK. Any data written after the first edge is stored in the transmit data register and transferred to the  
shift register after the current transmission.  
SPSCK CYCLE #  
FOR REFERENCE  
1
2
3
4
5
6
7
8
SPSCK, CPOL = 0  
SPSCK, CPOL = 1  
MOSI  
FROM MASTER  
MSB  
MSB  
BIT 6  
BIT 6  
BIT 5  
BIT 5  
BIT 4  
BIT 4  
BIT 3  
BIT 3  
BIT 2  
BIT 2  
BIT 1  
BIT 1  
LSB  
MISO  
FROM SLAVE  
LSB  
SS, TO SLAVE  
CAPTURE STROBE  
Figure 15-7. Transmission Format (CPHA = 1)  
15.5.4 Transmission Initiation Latency  
When the SPI is configured as a master (SPMSTR = 1), writing to the SPDR starts a transmission. CPHA  
has no effect on the delay to the start of the transmission, but it does affect the initial state of the SPSCK  
signal. When CPHA = 0, the SPSCK signal remains inactive for the first half of the first SPSCK cycle.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
201  
     
Serial Peripheral Interface Module (SPI)  
When CPHA = 1, the first SPSCK cycle begins with an edge on the SPSCK line from its inactive to its  
active level. The SPI clock rate (selected by SPR1:SPR0) affects the delay from the write to SPDR and  
the start of the SPI transmission. See Figure 15-8 The internal SPI clock in the master is a free-running  
derivative of the internal MCU clock. To conserve power, it is enabled only when both the SPE and  
SPMSTR bits are set. SPSCK edges occur halfway through the low time of the internal MCU clock. Since  
the SPI clock is free-running, it is uncertain where the write to the SPDR occurs relative to the slower  
SPSCK. This uncertainty causes the variation in the initiation delay shown in Figure 15-8. This delay is  
no longer than a single SPI bit time. That is, the maximum delay is two MCU bus cycles for DIV2, eight  
MCU bus cycles for DIV8, 32 MCU bus cycles for DIV32, and 128 MCU bus cycles for DIV128.  
WRITE  
TO SPDR  
INITIATION DELAY  
BUS  
CLOCK  
MOSI  
MSB  
BIT 6  
BIT 5  
SPSCK  
CPHA = 1  
SPSCK  
CPHA = 0  
SPSCK CYCLE  
NUMBER  
1
2
3
INITIATION DELAY FROM WRITE SPDR TO TRANSFER BEGIN  
WRITE  
TO SPDR  
BUS  
CLOCK  
SPSCK = INTERNAL CLOCK ÷ 2;  
2 POSSIBLE START POINTS  
EARLIEST LATEST  
WRITE  
TO SPDR  
BUS  
CLOCK  
EARLIEST  
WRITE  
TO SPDR  
SPSCK = INTERNAL CLOCK ÷ 8;  
8 POSSIBLE START POINTS  
LATEST  
LATEST  
LATEST  
BUS  
CLOCK  
EARLIEST  
WRITE  
TO SPDR  
SPSCK = INTERNAL CLOCK ÷ 32;  
32 POSSIBLE START POINTS  
BUS  
CLOCK  
EARLIEST  
SPSCK = INTERNAL CLOCK ÷ 128;  
128 POSSIBLE START POINTS  
Figure 15-8. Transmission Start Delay (Master)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
202  
Freescale Semiconductor  
 
Error Conditions  
15.6 Error Conditions  
These flags signal SPI error conditions:  
Overflow (OVRF) — Failing to read the SPI data register before the next full byte enters the shift  
register sets the OVRF bit. The new byte does not transfer to the receive data register, and the  
unread byte still can be read. OVRF is in the SPI status and control register.  
Mode fault error (MODF) — The MODF bit indicates that the voltage on the slave select pin (SS)  
is inconsistent with the mode of the SPI. MODF is in the SPI status and control register.  
15.6.1 Overflow Error  
The overflow flag (OVRF) becomes set if the receive data register still has unread data from a previous  
transmission when the capture strobe of bit 1 of the next transmission occurs. If an overflow occurs, all  
data received after the overflow and before the OVRF bit is cleared does not transfer to the receive data  
register and does not set the SPI receiver full bit (SPRF). The unread data that transferred to the receive  
data register before the overflow occurred can still be read. Therefore, an overflow error always indicates  
the loss of data. Clear the overflow flag by reading the SPI status and control register and then reading  
the SPI data register.  
OVRF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE) is also  
set. MODF and OVRF can generate a receiver/error CPU interrupt request. See Figure 15-11. It is not  
possible to enable MODF or OVRF individually to generate a receiver/error CPU interrupt request.  
However, leaving MODFEN low prevents MODF from being set.  
If the CPU SPRF interrupt is enabled and the OVRF interrupt is not, watch for an overflow condition.  
Figure 15-9 shows how it is possible to miss an overflow. The first part of Figure 15-9 shows how it is  
possible to read the SPSCR and SPDR to clear the SPRF without problems. However, as illustrated by  
the second transmission example, the OVRF bit can be set in between the time that SPSCR and SPDR  
are read.  
BYTE 1  
1
BYTE 2  
4
BYTE 3  
6
BYTE 4  
8
SPRF  
OVRF  
READ  
SPSCR  
2
5
5
READ  
SPDR  
3
7
1
2
BYTE 1 SETS SPRF BIT.  
CPU READS SPSCR WITH SPRF BIT SET  
AND OVRF BIT CLEAR.  
CPU READS SPSCR WITH SPRF BIT SET  
AND OVRF BIT CLEAR.  
CPU READS BYTE 1 IN SPDR,  
CLEARING SPRF BIT.  
6
7
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.  
3
4
CPU READS BYTE 2 IN SPDR, CLEARING SPRF BIT,  
BUT NOT OVRF BIT.  
BYTE 2 SETS SPRF BIT.  
8
BYTE 4 FAILS TO SET SPRF BIT BECAUSE  
OVRF BIT IS NOT CLEARED. BYTE 4 IS LOST.  
Figure 15-9. Missed Read of Overflow Condition  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
203  
     
Serial Peripheral Interface Module (SPI)  
In this case, an overflow can easily be missed. Since no more SPRF interrupts can be generated until this  
OVRF is serviced, it is not obvious that bytes are being lost as more transmissions are completed. To  
prevent this, either enable the OVRF interrupt or do another read of the SPSCR following the read of the  
SPDR. This ensures that the OVRF was not set before the SPRF was cleared and that future  
transmissions can set the SPRF bit. Figure 15-10 illustrates this process. Generally, to avoid this second  
SPSCR read, enable the OVRF interrupt to the CPU by setting the ERRIE bit.  
BYTE 1  
1
BYTE 2  
5
BYTE 3  
7
BYTE 4  
11  
SPI RECEIVE  
COMPLETE  
SPRF  
OVRF  
READ  
SPSCR  
2
4
6
9
12  
14  
READ  
SPDR  
3
8
10  
13  
1
2
8
9
BYTE 1 SETS SPRF BIT.  
CPU READS BYTE 2 IN SPDR,  
CLEARING SPRF BIT.  
CPU READS SPSCR WITH SPRF BIT SET  
AND OVRF BIT CLEAR.  
CPU READS SPSCR AGAIN  
TO CHECK OVRF BIT.  
3
4
CPU READS BYTE 1 IN SPDR,  
CLEARING SPRF BIT.  
10  
CPU READS BYTE 2 SPDR,  
CLEARING OVRF BIT.  
CPU READS SPSCR AGAIN  
TO CHECK OVRF BIT.  
11  
12  
13  
BYTE 4 SETS SPRF BIT.  
CPU READS SPSCR.  
5
6
BYTE 2 SETS SPRF BIT.  
CPU READS SPSCR WITH SPRF BIT SET  
AND OVRF BIT CLEAR.  
CPU READS BYTE 4 IN SPDR,  
CLEARING SPRF BIT.  
7
BYTE 3 SETS OVRF BIT. BYTE 3 IS LOST.  
14  
CPU READS SPSCR AGAIN  
TO CHECK OVRF BIT.  
Figure 15-10. Clearing SPRF When OVRF Interrupt Is Not Enabled  
15.6.2 Mode Fault Error  
Setting the SPMSTR bit selects master mode and configures the SPSCK and MOSI pins as outputs and  
the MISO pin as an input. Clearing SPMSTR selects slave mode and configures the SPSCK and MOSI  
pins as inputs and the MISO pin as an output. The mode fault bit, MODF, becomes set any time the state  
of the slave select pin, SS, is inconsistent with the mode selected by SPMSTR.  
To prevent SPI pin contention and damage to the MCU, a mode fault error occurs if:  
The SS pin of a slave SPI goes high during a transmission.  
The SS pin of a master SPI goes low at any time.  
For the MODF flag to be set, the mode fault error enable bit (MODFEN) must be set. Clearing the  
MODFEN bit does not clear the MODF flag but does prevent MODF from being set again after MODF is  
cleared.  
MODF generates a receiver/error CPU interrupt request if the error interrupt enable bit (ERRIE) is also  
set. The SPRF, MODF, and OVRF interrupts share the same CPU interrupt vector. MODF and OVRF can  
generate a receiver/error CPU interrupt request. See Figure 15-11. It is not possible to enable MODF or  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
204  
Freescale Semiconductor  
   
Error Conditions  
OVRF individually to generate a receiver/error CPU interrupt request. However, leaving MODFEN low  
prevents MODF from being set.  
In a master SPI with the mode fault enable bit (MODFEN) set, the mode fault flag (MODF) is set if SS  
goes to logic 0. A mode fault in a master SPI causes these events to occur:  
If ERRIE = 1, the SPI generates an SPI receiver/error CPU interrupt request.  
The SPE bit is cleared.  
The SPTE bit is set.  
The SPI state counter is cleared.  
The data direction register of the shared I/O port regains control of port drivers.  
NOTE  
To prevent bus contention with another master SPI after a mode fault error,  
clear all SPI bits of the data direction register of the shared I/O port before  
enabling the SPI.  
When configured as a slave (SPMSTR = 0), the MODF flag is set if SS goes high during a transmission.  
When CPHA = 0, a transmission begins when SS goes low and ends once the incoming SPSCK goes  
back to its idle level following the shift of the eighth data bit. When CPHA = 1, the transmission begins  
when the SPSCK leaves its idle level and SS is already low. The transmission continues until the SPSCK  
returns to its idle level following the shift of the last data bit. See 15.5 Transmission Formats.  
NOTE  
Setting the MODF flag does not clear the SPMSTR bit. Reading SPMSTR  
when MODF = 1 will indicate a mode fault error occurred in either master  
mode or slave mode.  
When CPHA = 0, a MODF occurs if a slave is selected (SS is at logic 0) and  
later unselected (SS is at logic 1) even if no SPSCK is sent to that slave.  
This happens because SS at logic 0 indicates the start of the transmission  
(MISO driven out with the value of MSB) for CPHA = 0. When CPHA = 1, a  
slave can be selected and then later unselected with no transmission  
occurring. Therefore, MODF does not occur since a transmission was  
never begun.  
In a slave SPI (MSTR = 0), the MODF bit generates an SPI receiver/error CPU interrupt request if the  
ERRIE bit is set. The MODF bit does not clear the SPE bit or reset the SPI in any way. Software can abort  
the SPI transmission by clearing the SPE bit of the slave.  
NOTE  
A logic 1 voltage on the SS pin of a slave SPI puts the MISO pin in a high  
impedance state. Also, the slave SPI ignores all incoming SPSCK clocks,  
even if it was already in the middle of a transmission.  
To clear the MODF flag, read the SPSCR with the MODF bit set and then write to the SPCR register. This  
entire clearing procedure must occur with no MODF condition existing or else the flag is not cleared.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
205  
Serial Peripheral Interface Module (SPI)  
15.7 Interrupts  
Four SPI status flags can be enabled to generate CPU interrupt requests as shown in Table 15-2.  
Table 15-2. SPI Interrupts  
Flag  
Request  
SPTE transmitter empty  
SPRF receiver full  
OVRF overflow  
SPI transmitter CPU interrupt request (SPTIE = 1, SPE = 1)  
SPI receiver CPU interrupt request (SPRIE = 1)  
SPI receiver/error interrupt request (ERRIE = 1)  
SPI receiver/error interrupt request (ERRIE = 1)  
MODF mode fault  
The SPI transmitter interrupt enable bit (SPTIE) enables the SPTE flag to generate transmitter CPU  
interrupt requests, provided that the SPI is enabled (SPE = 1).  
The SPI receiver interrupt enable bit (SPRIE) enables the SPRF bit to generate receiver CPU interrupt  
requests, provided that the SPI is enabled (SPE = 1). (See Figure 15-11.)  
SPTE  
SPTIE  
SPRF  
SPE  
SPI TRANSMITTER  
CPU INTERRUPT REQUEST  
SPRIE  
SPI RECEIVER/ERROR  
CPU INTERRUPT REQUEST  
ERRIE  
MODF  
OVRF  
Figure 15-11. SPI Interrupt Request Generation  
The error interrupt enable bit (ERRIE) enables both the MODF and OVRF bits to generate a receiver/error  
CPU interrupt request.  
The mode fault enable bit (MODFEN) can prevent the MODF flag from being set so that only the OVRF  
bit is enabled by the ERRIE bit to generate receiver/error CPU interrupt requests.  
These sources in the SPI status and control register can generate CPU interrupt requests:  
SPI receiver full bit (SPRF) — The SPRF bit becomes set every time a byte transfers from the shift  
register to the receive data register. If the SPI receiver interrupt enable bit, SPRIE, is also set,  
SPRF can generate either an SPI receiver/error or CPU interrupt.  
SPI transmitter empty (SPTE) — The SPTE bit becomes set every time a byte transfers from the  
transmit data register to the shift register. If the SPI transmit interrupt enable bit, SPTIE, is also set,  
SPTE can generate either an SPTE or CPU interrupt request.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
206  
Freescale Semiconductor  
     
Resetting the SPI  
15.8 Resetting the SPI  
Any system reset completely resets the SPI. Partial resets occur whenever the SPI enable bit (SPE) is  
low. Whenever SPE is low:  
The SPTE flag is set.  
Any transmission currently in progress is aborted.  
The shift register is cleared.  
The SPI state counter is cleared, making it ready for a new complete transmission.  
All the SPI port logic is defaulted back to being general-purpose I/O.  
These items are reset only by a system reset:  
All control bits in the SPCR  
All control bits in the SPSCR (MODFEN, ERRIE, SPR1, and SPR0)  
The status flags SPRF, OVRF, and MODF  
By not resetting the control bits when SPE is low, the user can clear SPE between transmissions without  
having to set all control bits again when SPE is set back high for the next transmission.  
By not resetting the SPRF, OVRF, and MODF flags, the user can still service these interrupts after the  
SPI has been disabled. The user can disable the SPI by writing 0 to the SPE bit. The SPI can also be  
disabled by a mode fault occurring in an SPI that was configured as a master with the MODFEN bit set.  
15.9 Queuing Transmission Data  
The double-buffered transmit data register allows a data byte to be queued and transmitted. For an SPI  
configured as a master, a queued data byte is transmitted immediately after the previous transmission  
has completed. The SPI transmitter empty flag (SPTE) indicates when the transmit data buffer is ready  
to accept new data. Write to the transmit data register only when the SPTE bit is high. Figure 15-12  
shows the timing associated with doing back-to-back transmissions with the SPI (SPSCK has  
CPHA:CPOL = 1:0).  
For a slave, the transmit data buffer allows back-to-back transmissions without the slave precisely timing  
its writes between transmissions as in a system with a single data buffer. Also, if no new data is written  
to the data buffer, the last value contained in the shift register is the next data word to be transmitted.  
For an idle master or idle slave that has no data loaded into its transmit buffer, the SPTE is set again no  
more than two bus cycles after the transmit buffer empties into the shift register. This allows the user to  
queue up a 16-bit value to send. For an already active slave, the load of the shift register cannot occur  
until the transmission is completed. This implies that a back-to-back write to the transmit data register is  
not possible. The SPTE indicates when the next write can occur.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
207  
   
Serial Peripheral Interface Module (SPI)  
1
3
8
WRITE TO SPDR  
SPTE  
5
10  
2
SPSCK  
CPHA:CPOL = 1:0  
MOSI  
MSBBIT BIT BIT BIT BIT BIT LSBMSBBIT BIT BIT BIT BIT BIT LSBMSBBIT BIT BIT  
4
6
BYTE 1  
5
4
3
2
1
6
BYTE 2  
5
4
3
2
1
6
BYTE 3  
5
4
9
SPRF  
READ SPSCR  
READ SPDR  
6
11  
7
12  
1
2
CPU WRITES BYTE 1 TO SPDR, CLEARING SPTE BIT.  
7
8
CPU READS SPDR, CLEARING SPRF BIT.  
CPU WRITES BYTE 3 TO SPDR, QUEUEING BYTE  
3 AND CLEARING SPTE BIT.  
BYTE 1 TRANSFERS FROM TRANSMIT DATA  
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.  
9
SECOND INCOMING BYTE TRANSFERS FROM SHIFT  
REGISTER TO RECEIVE DATA REGISTER, SETTING  
SPRF BIT.  
CPU WRITES BYTE 2 TO SPDR, QUEUEING BYTE 2  
AND CLEARING SPTE BIT.  
3
4
10  
FIRST INCOMING BYTE TRANSFERS FROM SHIFT  
REGISTER TO RECEIVE DATA REGISTER, SETTING  
SPRF BIT.  
BYTE 3 TRANSFERS FROM TRANSMIT DATA  
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.  
11  
12  
CPU READS SPSCR WITH SPRF BIT SET.  
CPU READS SPDR, CLEARING SPRF BIT.  
5
6
BYTE 2 TRANSFERS FROM TRANSMIT DATA  
REGISTER TO SHIFT REGISTER, SETTING SPTE BIT.  
CPU READS SPSCR WITH SPRF BIT SET.  
Figure 15-12. SPRF/SPTE CPU Interrupt Timing  
15.10 Low-Power Mode  
The WAIT instruction puts the MCU in a low power-consumption standby mode.  
The SPI module remains active after the execution of a WAIT instruction. In wait mode the SPI module  
registers are not accessible by the CPU. Any enabled CPU interrupt request from the SPI module can  
bring the MCU out of wait mode.  
If SPI module functions are not required during wait mode, reduce power consumption by disabling the  
SPI module before executing the WAIT instruction.  
To exit wait mode when an overflow condition occurs, enable the OVRF bit to generate CPU interrupt  
requests by setting the error interrupt enable bit (ERRIE). See 15.7 Interrupts.  
Since the SPTE bit cannot be cleared during a break with the BCFE bit cleared, a write to the transmit  
data register in break mode does not initiate a transmission nor is this data transferred into the shift  
register. Therefore, a write to the SPDR in break mode with the BCFE bit cleared has no effect.  
15.11 I/O Signals  
The SPI module has five I/O pins and shares four of them with a parallel I/O port. The pins are:  
MISO — Data received  
MOSI — Data transmitted  
SPSCK — Serial clock  
SS — Slave select  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
208  
Freescale Semiconductor  
     
I/O Signals  
The SPI has limited inter-integrated circuit (I2C) capability (requiring software support) as a master in a  
single-master environment. To communicate with I2C peripherals, MOSI becomes an open-drain output  
when the SPWOM bit in the SPI control register is set. In I2C communication, the MOSI and MISO pins  
are connected to a bidirectional pin from the I2C peripheral and through a pullup resistor to VDD  
.
15.11.1 MISO (Master In/Slave Out)  
MISO is one of the two SPI module pins that transmits serial data. In full duplex operation, the MISO pin  
of the master SPI module is connected to the MISO pin of the slave SPI module. The master SPI  
simultaneously receives data on its MISO pin and transmits data from its MOSI pin.  
Slave output data on the MISO pin is enabled only when the SPI is configured as a slave. The SPI is  
configured as a slave when its SPMSTR bit is logic 0 and its SS pin is at logic 0. To support a  
multiple-slave system, a logic 1 on the SS pin puts the MISO pin in a high-impedance state.  
When enabled, the SPI controls data direction of the MISO pin regardless of the state of the data direction  
register of the shared  
I/O port.  
15.11.2 MOSI (Master Out/Slave In)  
MOSI is one of the two SPI module pins that transmits serial data. In full-duplex operation, the MOSI pin  
of the master SPI module is connected to the MOSI pin of the slave SPI module. The master SPI  
simultaneously transmits data from its MOSI pin and receives data on its MISO pin.  
When enabled, the SPI controls data direction of the MOSI pin regardless of the state of the data direction  
register of the shared I/O port.  
15.11.3 SPSCK (Serial Clock)  
The serial clock synchronizes data transmission between master and slave devices. In a master MCU,  
the SPSCK pin is the clock output. In a slave MCU, the SPSCK pin is the clock input. In full-duplex  
operation, the master and slave MCUs exchange a byte of data in eight serial clock cycles.  
When enabled, the SPI controls data direction of the SPSCK pin regardless of the state of the data  
direction register of the shared I/O port.  
15.11.4 SS (Slave Select)  
The SS pin has various functions depending on the current state of the SPI. For an SPI configured as a  
slave, the SS is used to select a slave. For CPHA = 0, the SS is used to define the start of a transmission.  
See 15.5 Transmission Formats. Since it is used to indicate the start of a transmission, the SS must be  
toggled high and low between each byte transmitted for the CPHA = 0 format. However, it can remain low  
between transmissions for the CPHA = 1 format. See Figure 15-13.  
MISO/MOSI  
BYTE 1  
BYTE 2  
BYTE 3  
MASTER SS  
SLAVE SS  
CPHA = 0  
SLAVE SS  
CPHA = 1  
Figure 15-13. CPHA/SS Timing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
209  
         
Serial Peripheral Interface Module (SPI)  
When an SPI is configured as a slave, the SS pin is always configured as an input. It cannot be used as  
a general-purpose I/O regardless of the state of the MODFEN control bit. However, the MODFEN bit can  
still prevent the state of the SS from creating a MODF error. See 15.12.2 SPI Status and Control Register.  
NOTE  
A logic 1 voltage on the SS pin of a slave SPI puts the MISO pin in a  
high-impedance state. The slave SPI ignores all incoming SPSCK clocks,  
even if it was already in the middle of a transmission.  
When an SPI is configured as a master, the SS input can be used in conjunction with the MODF flag to  
prevent multiple masters from driving MOSI and SPSCK. (See 15.6.2 Mode Fault Error.) For the state of  
the SS pin to set the MODF flag, the MODFEN bit in the SPSCK register must be set. If the MODFEN bit  
is low for an SPI master, the SS pin can be used as a general-purpose I/O under the control of the data  
direction register of the shared I/O port. With MODFEN high, it is an input-only pin to the SPI regardless  
of the state of the data direction register of the shared I/O port.  
The CPU can always read the state of the SS pin by configuring the appropriate pin as an input and  
reading the port data register. See Table 15-3.  
Table 15-3. SPI Configuration  
SPE  
SPMSTR  
MODFEN  
SPI Configuration  
Not enabled  
State of SS Logic  
General-purpose I/O; SS ignored by SPI  
Input-only to SPI  
(1)  
0
1
1
1
X
X
0
X
0
1
1
Slave  
Master without MODF  
Master with MODF  
General-purpose I/O; SS ignored by SPI  
Input-only to SPI  
1
1. X = don’t care  
15.11.5 V (Clock Ground)  
SS  
VSS is the ground return for the serial clock pin, SPSCK, and the ground for the port output buffers. To  
reduce the ground return path loop and minimize radio frequency (RF) emissions, connect the ground pin  
of the slave to the VSS pin of the master.  
15.12 I/O Registers  
Three registers control and monitor SPI operation:  
SPI control register, SPCR  
SPI status and control register, SPSCR  
SPI data register, SPDR  
15.12.1 SPI Control Register  
The SPI control register (SPCR):  
Enables SPI module interrupt requests  
Selects CPU interrupt requests or DMA service requests  
Configures the SPI module as master or slave  
Selects serial clock polarity and phase  
Configures the SPSCK, MOSI, and MISO pins as open-drain outputs  
Enables the SPI module  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
210  
Freescale Semiconductor  
       
I/O Registers  
Address: $0044  
Bit 7  
6
5
SPMSTR  
1
4
CPOL  
0
3
CPHA  
1
2
SPWOM  
0
1
SPE  
0
Bit 0  
SPTIE  
0
Read:  
Write:  
Reset:  
SPRIE  
R
0
0
R
= Reserved  
Figure 15-14. SPI Control Register (SPCR)  
SPRIE — SPI Receiver Interrupt Enable Bit  
This read/write bit enables CPU interrupt requests generated by the SPRF bit. The SPRF bit is set  
when a byte transfers from the shift register to the receive data register. Reset clears the SPRIE bit.  
1 = SPRF CPU interrupt requests enabled  
0 = SPRF CPU interrupt requests disabled  
SPMSTR — SPI Master Bit  
This read/write bit selects master mode operation or slave mode operation. Reset sets the SPMSTR  
bit.  
1 = Master mode  
0 = Slave mode  
CPOL — Clock Polarity Bit  
This read/write bit determines the logic state of the SPSCK pin between transmissions. See Figure  
15-5 and Figure 15-7. To transmit data between SPI modules, the SPI modules must have identical  
CPOL values. Reset clears the CPOL bit.  
CPHA — Clock Phase Bit  
This read/write bit controls the timing relationship between the serial clock and SPI data. See Figure  
15-5 and Figure 15-7. To transmit data between SPI modules, the SPI modules must have identical  
CPHA bits. When CPHA = 0, the SS pin of the slave SPI module must be set to logic 1 between bytes.  
See Figure 15-13. Reset sets the CPHA bit.  
When CPHA = 0 for a slave, the falling edge of SS indicates the beginning of the transmission. This  
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data, once the  
transmission begins, no new data is allowed into the shift register from the data register. Therefore,  
the slave data register must be loaded with the desired transmit data before the falling edge of SS. Any  
data written after the falling edge is stored in the data register and transferred to the shift register at  
the current transmission.  
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the beginning of the transmission.  
The same applies when SS is high for a slave. The MISO pin is held in a high-impedance state, and  
the incoming SPSCK is ignored. In certain cases, it may also cause the MODF flag to be set. See  
15.6.2 Mode Fault Error. A logic 1 on the SS pin does not in any way affect the state of the SPI state  
machine.  
SPWOM — SPI Wired-OR Mode Bit  
This read/write bit disables the pullup devices on pins SPSCK, MOSI, and MISO so that those pins  
become open-drain outputs.  
1 = Wired-OR SPSCK, MOSI, and MISO pins  
0 = Normal push-pull SPSCK, MOSI, and MISO pins  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
211  
   
Serial Peripheral Interface Module (SPI)  
SPE — SPI Enable Bit  
This read/write bit enables the SPI module. Clearing SPE causes a partial reset of the SPI. See 15.8  
1 = SPI module enabled  
0 = SPI module disabled  
SPTIE— SPI Transmit Interrupt Enable Bit  
This read/write bit enables CPU interrupt requests generated by the SPTE bit. SPTE is set when a byte  
transfers from the transmit data register to the shift register. Reset clears the SPTIE bit.  
1 = SPTE CPU interrupt requests enabled  
0 = SPTE CPU interrupt requests disabled  
15.12.2 SPI Status and Control Register  
The SPI status and control register (SPSCR) contains flags to signal these conditions:  
Receive data register full  
Failure to clear SPRF bit before next byte is received (overflow error)  
Inconsistent logic level on SS pin (mode fault error)  
Transmit data register empty  
The SPI status and control register also contains bits that perform these functions:  
Enable error interrupts  
Enable mode fault error detection  
Select master SPI baud rate  
Address: $0045  
Bit 7  
SPRF  
R
6
5
OVRF  
R
4
MODF  
R
3
SPTE  
R
2
MODFEN  
0
1
SPR1  
0
Bit 0  
SPR0  
0
Read:  
Write:  
Reset:  
ERRIE  
0
0
0
0
1
R
= Reserved  
Figure 15-15. SPI Status and Control Register (SPSCR)  
SPRF — SPI Receiver Full Bit  
This clearable, read-only flag is set each time a byte transfers from the shift register to the receive data  
register. SPRF generates a CPU interrupt request if the SPRIE bit in the SPI control register is set also.  
During an SPRF CPU interrupt (DMAS = 0), the CPU clears SPRF by reading the SPI status and  
control register with SPRF set and then reading the SPI data register.  
Reset clears the SPRF bit.  
1 = Receive data register full  
0 = Receive data register not full  
ERRIE — Error Interrupt Enable Bit  
This read/write bit enables the MODF and OVRF bits to generate CPU interrupt requests. Reset clears  
the ERRIE bit.  
1 = MODF and OVRF can generate CPU interrupt requests.  
0 = MODF and OVRF cannot generate CPU interrupt requests.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
212  
Freescale Semiconductor  
     
I/O Registers  
OVRF — Overflow Bit  
This clearable, read-only flag is set if software does not read the byte in the receive data register before  
the next full byte enters the shift register. In an overflow condition, the byte already in the receive data  
register is unaffected, and the byte that shifted in last is lost. Clear the OVRF bit by reading the SPI  
status and control register with OVRF set and then reading the receive data register. Reset clears the  
OVRF bit.  
1 = Overflow  
0 = No overflow  
MODF — Mode Fault Bit  
This clearable, read-only flag is set in a slave SPI if the SS pin goes high during a transmission with  
the MODFEN bit set. In a master SPI, the MODF flag is set if the SS pin goes low at any time with the  
MODFEN bit set. Clear the MODF bit by reading the SPI status and control register (SPSCR) with  
MODF set and then writing to the SPI control register (SPCR). Reset clears the MODF bit.  
1 = SS pin at inappropriate logic level  
0 = SS pin at appropriate logic level  
SPTE — SPI Transmitter Empty Bit  
This clearable, read-only flag is set each time the transmit data register transfers a byte into the shift  
register. SPTE generates an SPTE CPU interrupt request or an SPTE DMA service request if the  
SPTIE bit in the SPI control register is set also.  
NOTE  
Do not write to the SPI data register unless the SPTE bit is high.  
For an idle master of idle slave that has no data loaded into its transmit buffer, the SPTE will be set  
again within two bus cycles since the transmit buffer empties into the shift register. This allows the user  
to queue up a 16-bit value to send. For an already active slave, the load of the shift register cannot  
occur until the transmission is completed. This implies that a back-to-back write to the transmit data  
register is not possible. The SPTE indicates when the next write can occur.  
Reset sets the SPTE bit.  
1 = Transmit data register empty  
0 = Transmit data register not empty  
MODFEN — Mode Fault Enable Bit  
This read/write bit, when set to 1, allows the MODF flag to be set. If the MODF flag is set, clearing the  
MODFEN does not clear the MODF flag. If the SPI is enabled as a master and the MODFEN bit is low,  
then the SS pin is available as a general-purpose I/O.  
If the MODFEN bit is set, then this pin is not available as a general-purpose I/O. When the SPI is  
enabled as a slave, the SS pin is not available as a general-purpose I/O regardless of the value of  
If the MODFEN bit is low, the level of the SS pin does not affect the operation of an enabled SPI  
configured as a master. For an enabled SPI configured as a slave, having MODFEN low only prevents  
the MODF flag from being set. It does not affect any other part of SPI operation. See 15.6.2 Mode Fault  
SPR1 and SPR0 — SPI Baud Rate Select Bits  
In master mode, these read/write bits select one of four baud rates as shown in Table 15-4. SPR1 and  
SPR0 have no effect in slave mode. Reset clears SPR1 and SPR0.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
213  
Serial Peripheral Interface Module (SPI)  
Table 15-4. SPI Master Baud Rate Selection  
SPR1:SPR0  
Baud Rate Divisor (BD)  
00  
01  
10  
11  
2
8
32  
128  
Use this formula to calculate the SPI baud rate:  
CGMOUT  
Baud rate = --------------------------  
2 × BD  
where:  
CGMOUT = base clock output of the clock generator module (CGM)  
BD = baud rate divisor  
15.12.3 SPI Data Register  
The SPI data register consists of the read-only receive data register and the write-only transmit data  
register. Writing to the SPI data register writes data into the transmit data register. Reading the SPI data  
register reads data from the receive data register. The transmit data and receive data registers are  
separate registers that can contain different values. See Figure 15-2.  
Address: $0046  
Bit 7  
R7  
6
5
4
3
2
1
Bit 0  
R0  
Read:  
Write:  
Reset:  
R6  
T6  
R5  
T5  
R4  
T4  
R3  
T3  
R2  
T2  
R1  
T1  
T7  
T0  
Indeterminate after reset  
Figure 15-16. SPI Data Register (SPDR)  
R7:R0/T7:T0 — Receive/Transmit Data Bits  
NOTE  
Do not use read-modify-write instructions on the SPI data register since the  
register read is not the same as the register written.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
214  
Freescale Semiconductor  
       
Chapter 16  
Timer Interface A (TIMA)  
16.1 Introduction  
This section describes the timer interface module A (TIMA). The TIMA is a 4-channel timer that provides:  
Timing reference with input capture  
Output compare  
Pulse-width modulator functions  
Figure 16-2 is a block diagram of the TIMA.  
16.2 Features  
Features of the TIMA include:  
Four input capture/output compare channels:  
Rising-edge, falling-edge, or any-edge input capture trigger  
Set, clear, or toggle output compare action  
Buffered and unbuffered pulse-width modulator (PWM) signal generation  
Programmable TIMA clock input:  
7-frequency internal bus clock prescaler selection  
External TIMA clock input (4-MHz maximum frequency)  
Free-running or modulo up-count operation  
Toggle any channel pin on overflow  
TIMA counter stop and reset bits  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
215  
       
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
PTC1/ATD9(1)  
PTC0/ATD8  
USER FLASH VECTOR SPACE — 46 BYTES  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 16-1. Block Diagram Highlighting TIMA Block and Pins  
Features  
TCLK  
PTE3/TCLKA  
PRESCALER SELECT  
INTERNAL  
BUS CLOCK  
PRESCALER  
TSTOP  
PS2  
PS1  
PS0  
TRST  
16-BIT COUNTER  
INTER-  
RUPT  
LOGIC  
TOF  
TOIE  
16-BIT COMPARATOR  
TMODH:TMODL  
ELS0B  
ELS0A  
CHANNEL 0  
16-BIT COMPARATOR  
TCH0H:TCH0L  
TOV0  
CH0MAX  
PTE4  
LOGIC  
PTE4/TCH0A  
CH0F  
MS0B  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH0IE  
MS0A  
ELS1B ELS1A  
CHANNEL 1  
16-BIT COMPARATOR  
TCH1H:TCH1L  
TOV1  
CH1MAX  
PTE5  
LOGIC  
PTE5/TCH1A  
CH1F  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH1IE  
MS1A  
ELS2B ELS2A  
CHANNEL 2  
16-BIT COMPARATOR  
TCH2H:TCH2L  
TOV2  
CH2MAX  
PTE6  
LOGIC  
PTE6/TCH2A  
CH2F  
MS2B  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH2IE  
MS2A  
ELS3B ELS3A  
CHANNEL 3  
16-BIT COMPARATOR  
TCH3H:TCH3L  
TOV3  
CH3MAX  
PTE7  
LOGIC  
PTE7/TCH3A  
CH3F  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH3IE  
MS3A  
Figure 16-2. TIMA Block Diagram  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
217  
 
Timer Interface A (TIMA)  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read: TOF  
0
TRST  
0
0
R
TIMA Status/Control Register  
TOIE  
TSTOP  
PS2  
PS1  
PS0  
$000E  
(TASC) Write:  
0
0
TIMA Counter Register High  
Reset:  
0
Bit 14  
R
1
Bit 13  
R
0
0
Bit 10  
R
0
Bit 9  
R
0
Bit 8  
R
Read: Bit 15  
Bit 12  
R
Bit 11  
R
$000F  
$0010  
$0011  
$0012  
$0013  
$0014  
$0015  
$0016  
$0017  
$0018  
$0019  
(TACNTH) Write:  
R
0
Reset:  
0
0
0
0
0
0
0
Read: Bit 7  
Bit 6  
R
Bit 5  
R
Bit 4  
R
Bit 3  
R
Bit 2  
R
Bit 1  
R
Bit 0  
R
TIMA Counter Register Low  
(TACNTL) Write:  
R
0
Reset:  
Read:  
0
0
0
0
0
0
0
TIMA Counter Modulo  
Bit 15  
1
14  
13  
12  
11  
10  
9
1
1
1
Bit 8  
1
Register High (TAMODH) Write:  
Reset:  
1
1
1
1
1
Read:  
TIMA Counter Modulo  
Register Low (TAMODL) Write:  
Bit 7  
6
1
5
1
4
1
3
2
Bit 0  
1
Reset:  
1
1
ELS0B  
0
1
ELS0A  
0
Read: CH0F  
TIMA Channel 0 Status/Control  
CH0IE  
0
MS0B  
0
MS0A  
0
TOV0 CH0MAX  
Register (TASC0) Write:  
0
0
Reset:  
Read:  
0
9
0
TIMA Channel 0 Register High  
Bit 15  
14  
13  
12  
11  
10  
Bit 8  
(TACH0H) Write:  
Reset:  
Read:  
Indeterminate after reset  
TIMA Channel 0 Register Low  
Bit 7  
6
5
4
3
2
1
Bit 0  
(TACH0L) Write:  
Reset:  
Read: CH1F  
Indeterminate after reset  
0
R
0
TIMA Channel 1 Status/Control  
CH1IE  
MS1A  
0
ELS1B  
ELS1A  
TOV1 CH1MAX  
Register (TASC1) Write:  
0
0
Reset:  
Read:  
0
0
0
0
9
0
TIMA Channel 1 Register High  
Bit 15  
14  
13  
12  
11  
10  
Bit 8  
(TACH1H) Write:  
Reset:  
Read:  
Indeterminate after reset  
TIMA Channel 1 Register Low  
Bit 7  
6
5
4
3
2
1
Bit 0  
(TACH1L) Write:  
Reset:  
Read: CH2F  
Indeterminate after reset  
TIMA Channel 2 Status/Control  
CH2IE  
MS2B  
0
MS2A  
0
ELS2B  
0
ELS2A  
0
TOV2 CH2MAX  
Register (TASC2) Write:  
0
0
Reset:  
0
0
0
= Reserved  
R
Figure 16-3. TIM I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
218  
Freescale Semiconductor  
Functional Description  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read:  
TIMA Channel 2 Register High  
Bit 15  
14  
13  
12  
11  
10  
9
Bit 8  
$001A  
(TACH2H) Write:  
Reset:  
Read:  
Indeterminate after reset  
TIMA Channel 2 Register Low  
Bit 7  
6
5
4
3
2
1
Bit 0  
$001B  
$001C  
$001D  
$001E  
(TACH2L) Write:  
Reset:  
Read: CH3F  
Indeterminate after reset  
0
R
0
TIMA Channel 3 Status/Control  
CH3IE  
MS3A  
0
ELS3B  
ELS3A  
TOV3 CH3MAX  
Register (TASC3) Write:  
0
0
Reset:  
Read:  
0
0
0
0
9
0
TIMA Channel 3 Register High  
Bit 15  
14  
13  
12  
11  
10  
Bit 8  
(TACH3H) Write:  
Reset:  
Read:  
Indeterminate after reset  
TIMA Channel 3 Register Low  
Bit 7  
R
6
5
4
3
2
1
Bit 0  
(TACH3L) Write:  
Reset:  
Indeterminate after reset  
= Reserved  
Figure 16-3. TIM I/O Register Summary (Continued)  
16.3 Functional Description  
Figure 16-2 shows the TIMA structure. The central component of the TIMA is the 16-bit TIMA counter that  
can operate as a free-running counter or a modulo up-counter. The TIMA counter provides the timing  
reference for the input capture and output compare functions. The TIMA counter modulo registers,  
TAMODH–TAMODL, control the modulo value of the TIMA counter. Software can read the TIMA counter  
value at any time without affecting the counting sequence.  
The four TIMA channels are programmable independently as input capture or output compare channels.  
16.3.1 TIMA Counter Prescaler  
The TIMA clock source can be one of the seven prescaler outputs or the TIMA clock pin, PTE3/TCLKA.  
The prescaler generates seven clock rates from the internal bus clock. The prescaler select bits, PS[2:0],  
in the TIMA status and control register select the TIMA clock source.  
16.3.2 Input Capture  
An input capture function has three basic parts:  
1. Edge select logic  
2. Input capture latch  
3. 16-bit counter  
Two 8-bit registers, which make up the 16-bit input capture register, are used to latch the value of the  
free-running counter after the corresponding input capture edge detector senses a defined transition. The  
polarity of the active edge is programmable. The level transition which triggers the counter transfer is  
defined by the corresponding input edge bits (ELSxB and ELSxA in TASC0–TASC3 control registers with  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
219  
     
Timer Interface A (TIMA)  
x referring to the active channel number). When an active edge occurs on the pin of an input capture  
channel, the TIMA latches the contents of the TIMA counter into the TIMA channel registers,  
TACHxH–TACHxL. Input captures can generate TIMA CPU interrupt requests. Software can determine  
that an input capture event has occurred by enabling input capture interrupts or by polling the status flag  
bit.  
The free-running counter contents are transferred to the TIMA channel status and control register  
(TACHxH–TACHxL, see 16.7.5 TIMA Channel Registers) on each proper signal transition regardless of  
whether the TIMA channel flag (CH0F–CH3F in TASC0–TASC3 registers) is set or clear. When the status  
flag is set, a CPU interrupt is generated if enabled. The value of the count latched or “captured” is the time  
of the event. Because this value is stored in the input capture register two bus cycles after the actual event  
occurs, user software can respond to this event at a later time and determine the actual time of the event.  
However, this must be done prior to another input capture on the same pin; otherwise, the previous time  
value will be lost.  
By recording the times for successive edges on an incoming signal, software can determine the period  
and/or pulse width of the signal. To measure a period, two successive edges of the same polarity are  
captured. To measure a pulse width, two alternate polarity edges are captured. Software should track the  
overflows at the 16-bit module counter to extend its range.  
Another use for the input capture function is to establish a time reference. In this case, an input capture  
function is used in conjunction with an output compare function. For example, to activate an output signal  
a specified number of clock cycles after detecting an input event (edge), use the input capture function to  
record the time at which the edge occurred. A number corresponding to the desired delay is added to this  
captured value and stored to an output compare register (see  
16.7.5 TIMA Channel Registers). Because both input captures and output compares are referenced to  
the same 16-bit modulo counter, the delay can be controlled to the resolution of the counter independent  
of software latencies.  
Reset does not affect the contents of the input capture channel registers.  
16.3.3 Output Compare  
With the output compare function, the TIMA can generate a periodic pulse with a programmable polarity,  
duration, and frequency. When the counter reaches the value in the registers of an output compare  
channel, the TIMA can set, clear, or toggle the channel pin. Output compares can generate TIMA CPU  
interrupt requests.  
16.3.3.1 Unbuffered Output Compare  
Any output compare channel can generate unbuffered output compare pulses as described in 16.3.3  
Output Compare. The pulses are unbuffered because changing the output compare value requires writing  
the new value over the old value currently in the TIMA channel registers.  
An unsynchronized write to the TIMA channel registers to change an output compare value could cause  
incorrect operation for up to two counter overflow periods. For example, writing a new value before the  
counter reaches the old value but after the counter reaches the new value prevents any compare during  
that counter overflow period. Also, using a TIMA overflow interrupt routine to write a new, smaller output  
compare value may cause the compare to be missed. The TIMA may pass the new value before it is  
written.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
220  
Freescale Semiconductor  
   
Functional Description  
Use this method to synchronize unbuffered changes in the output compare value on channel x:  
When changing to a smaller value, enable channel x output compare interrupts and write the new  
value in the output compare interrupt routine. The output compare interrupt occurs at the end of  
the current output compare pulse. The interrupt routine has until the end of the counter overflow  
period to write the new value.  
When changing to a larger output compare value, enable TIMA overflow interrupts and write the  
new value in the TIMA overflow interrupt routine. The TIMA overflow interrupt occurs at the end of  
the current counter overflow period. Writing a larger value in an output compare interrupt routine  
(at the end of the current pulse) could cause two output compares to occur in the same counter  
overflow period.  
16.3.3.2 Buffered Output Compare  
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the  
PTE4/TCH0A pin. The TIMA channel registers of the linked pair alternately control the output.  
Setting the MS0B bit in TIMA channel 0 status and control register (TASC0) links channel 0 and  
channel 1. The output compare value in the TIMA channel 0 registers initially controls the output on the  
PTE4/TCH0A pin. Writing to the TIMA channel 1 registers enables the TIMA channel 1 registers to  
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA  
channel registers (0 or 1) that control the output are the ones written to last. TASC0 controls and monitors  
the buffered output compare function, and TIMA channel 1 status and control register (TASC1) is unused.  
While the MS0B bit is set, the channel 1 pin, PTE5/TCH1A, is available as a general-purpose I/O pin.  
Channels 2 and 3 can be linked to form a buffered output compare channel whose output appears on the  
PTE6/TCH2A pin. The TIMA channel registers of the linked pair alternately control the output.  
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and  
channel 3. The output compare value in the TIMA channel 2 registers initially controls the output on the  
PTE6/TCH2A pin. Writing to the TIMA channel 3 registers enables the TIMA channel 3 registers to  
synchronously control the output after the TIMA overflows. At each subsequent overflow, the TIMA  
channel registers (2 or 3) that control the output are the ones written to last. TASC2 controls and monitors  
the buffered output compare function, and TIMA channel 3 status and control register (TASC3) is unused.  
While the MS2B bit is set, the channel 3 pin, PTE7/TCH3A, is available as a general-purpose I/O pin.  
NOTE  
In buffered output compare operation, do not write new output compare  
values to the currently active channel registers. User software should track  
the currently active channel to prevent writing a new value to the active  
channel. Writing to the active channel registers is the same as generating  
unbuffered output compares.  
16.3.4 Pulse-Width Modulation (PWM)  
By using the toggle-on-overflow feature with an output compare channel, the TIMA can generate a PWM  
signal. The value in the TIMA counter modulo registers determines the period of the PWM signal. The  
channel pin toggles when the counter reaches the value in the TIMA counter modulo registers. The time  
between overflows is the period of the PWM signal.  
As Figure 16-4 shows, the output compare value in the TIMA channel registers determines the pulse width  
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIMA  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
221  
   
Timer Interface A (TIMA)  
to clear the channel pin on output compare if the polarity of the PWM pulse is 1 (ELSxA = 0). Program the  
TIMA to set the pin if the polarity of the PWM pulse is 0 (ELSxA = 1).  
The value in the TIMA counter modulo registers and the selected prescaler output determines the  
frequency of the PWM output. The frequency of an 8-bit PWM signal is variable in 256 increments. Writing  
$00FF (255) to the TIMA counter modulo registers produces a PWM period of 256 times the internal bus  
clock period if the prescaler select value is $000 (see 16.7.1 TIMA Status and Control Register).  
The value in the TIMA channel registers determines the pulse width of the PWM output. The pulse width  
of an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIMA channel registers  
produces a duty cycle of 128/256 or 50 percent.  
OVERFLOW  
OVERFLOW  
OVERFLOW  
PERIOD  
POLARITY = 1  
(ELSxA = 0)  
TCHx  
TCHx  
PULSE  
WIDTH  
POLARITY = 0  
(ELSxA = 1)  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
Figure 16-4. PWM Period and Pulse Width  
16.3.4.1 Unbuffered PWM Signal Generation  
Any output compare channel can generate unbuffered PWM pulses as described in 16.3.4 Pulse-Width  
Modulation (PWM). The pulses are unbuffered because changing the pulse width requires writing the new  
pulse width value over the value currently in the TIMA channel registers.  
An unsynchronized write to the TIMA channel registers to change a pulse width value could cause  
incorrect operation for up to two PWM periods. For example, writing a new value before the counter  
reaches the old value but after the counter reaches the new value prevents any compare during that PWM  
period. Also, using a TIMA overflow interrupt routine to write a new, smaller pulse width value may cause  
the compare to be missed. The TIMA may pass the new value before it is written to the TIMA channel  
registers.  
Use this method to synchronize unbuffered changes in the PWM pulse width on channel x:  
When changing to a shorter pulse width, enable channel x output compare interrupts and write the  
new value in the output compare interrupt routine. The output compare interrupt occurs at the end  
of the current pulse. The interrupt routine has until the end of the PWM period to write the new  
value.  
When changing to a longer pulse width, enable TIMA overflow interrupts and write the new value  
in the TIMA overflow interrupt routine. The TIMA overflow interrupt occurs at the end of the current  
PWM period. Writing a larger value in an output compare interrupt routine (at the end of the current  
pulse) could cause two output compares to occur in the same PWM period.  
NOTE  
In PWM signal generation, do not program the PWM channel to toggle on  
output compare. Toggling on output compare prevents reliable 0 percent  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
222  
Freescale Semiconductor  
   
Functional Description  
duty cycle generation and removes the ability of the channel to self-correct  
in the event of software error or noise. Toggling on output compare also can  
cause incorrect PWM signal generation when changing the PWM pulse  
width to a new, much larger value.  
16.3.4.2 Buffered PWM Signal Generation  
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the  
PTE4/TCH0A pin. The TIMA channel registers of the linked pair alternately control the pulse width of the  
output.  
Setting the MS0B bit in TIMA channel 0 status and control register (TASC0) links channel 0 and  
channel 1. The TIMA channel 0 registers initially control the pulse width on the PTE4/TCH0A pin. Writing  
to the TIMA channel 1 registers enables the TIMA channel 1 registers to synchronously control the pulse  
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers  
(0 or 1) that control the pulse width are the ones written to last. TASC0 controls and monitors the buffered  
PWM function, and TIMA channel 1 status and control register (TASC1) is unused. While the MS0B bit is  
set, the channel 1 pin, PTE5/TCH1A, is available as a general-purpose  
I/O pin.  
Channels 2 and 3 can be linked to form a buffered PWM channel whose output appears on the  
PTE6/TCH2A pin. The TIMA channel registers of the linked pair alternately control the pulse width of the  
output.  
Setting the MS2B bit in TIMA channel 2 status and control register (TASC2) links channel 2 and  
channel 3. The TIMA channel 2 registers initially control the pulse width on the PTE6/TCH2A pin. Writing  
to the TIMA channel 3 registers enables the TIMA channel 3 registers to synchronously control the pulse  
width at the beginning of the next PWM period. At each subsequent overflow, the TIMA channel registers  
(2 or 3) that control the pulse width are written to last. TASC2 controls and monitors the buffered PWM  
function, and TIMA channel 3 status and control register (TASC3) is unused. While the MS2B bit is set,  
the channel 3 pin, PTE7/TCH3A, is available as a general-purpose  
I/O pin.  
NOTE  
In buffered PWM signal generation, do not write new pulse width values to  
the currently active channel registers. User software should track the  
currently active channel to prevent writing a new value to the active  
channel. Writing to the active channel registers is the same as generating  
unbuffered PWM signals.  
16.3.4.3 PWM Initialization  
To ensure correct operation when generating unbuffered or buffered PWM signals, use this initialization  
procedure:  
1. In the TIMA status and control register (TASC):  
a. Stop the TIMA counter by setting the TIMA stop bit, TSTOP.  
b. Reset the TIMA counter and prescaler by setting the TIMA reset bit, TRST.  
2. In the TIMA counter modulo registers (TAMODH–TAMODL), write the value for the required PWM  
period.  
3. In the TIMA channel x registers (TACHxH–TACHxL), write the value for the required pulse width.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
223  
   
Timer Interface A (TIMA)  
4. In TIMA channel x status and control register (TSCx):  
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare  
or PWM signals) to the mode select bits, MSxB–MSxA. (See Table 16-2.)  
b. Write 1 to the toggle-on-overflow bit, TOVx.  
c. Write 1:0 (polarity 1 — to clear output on compare) or 1:1 (polarity 0 — to set output on  
compare) to the edge/level select bits, ELSxB–ELSxA. The output action on compare must  
force the output to the complement of the pulse width level. (See Table 16-2.)  
NOTE  
In PWM signal generation, do not program the PWM channel to toggle on  
output compare. Toggling on output compare prevents reliable 0 percent  
duty cycle generation and removes the ability of the channel to self-correct  
in the event of software error or noise. Toggling on output compare can also  
cause incorrect PWM signal generation when changing the PWM pulse  
width to a new, much larger value.  
5. In the TIMA status control register (TASC), clear the TIMA stop bit, TSTOP.  
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIMA  
channel 0 registers (TACH0H–TACH0L) initially control the buffered PWM output. TIMA status control  
register 0 (TASC0) controls and monitors the PWM signal from the linked channels. MS0B takes priority  
over MS0A.  
Setting MS2B links channels 2 and 3 and configures them for buffered PWM operation. The TIMA  
channel 2 registers (TACH2H–TACH2L) initially control the buffered PWM output. TIMA status control  
register 2 (TASC2) controls and monitors the PWM signal from the linked channels. MS2B takes priority  
over MS2A.  
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIMA overflows. Subsequent output  
compares try to force the output to a state it is already in and have no effect. The result is a 0 percent duty  
cycle output.  
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a 100  
percent duty cycle output. (See 16.7.4 TIMA Channel Status and Control Registers.)  
16.4 Interrupts  
These TIMA sources can generate interrupt requests:  
TIMA overflow flag (TOF) — The timer overflow flag (TOF) bit is set when the TIMA counter  
reaches the modulo value programmed in the TIMA counter modulo registers. The TIMA overflow  
interrupt enable bit, TOIE, enables TIMA overflow interrupt requests. TOF and TOIE are in the  
TIMA status and control registers.  
TIMA channel flags (CH3F–CH0F) — The CHxF bit is set when an input capture or output compare  
occurs on channel x. Channel x TIMA CPU interrupt requests are controlled by the channel x  
interrupt enable bit, CHxIE.  
16.5 Wait Mode  
The WAIT instruction puts the MCU in low power-consumption standby mode.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
224  
Freescale Semiconductor  
   
I/O Signals  
The TIMA remains active after the execution of a WAIT instruction. In wait mode, the TIMA registers are  
not accessible by the CPU. Any enabled CPU interrupt request from the TIMA can bring the MCU out of  
wait mode.  
If TIMA functions are not required during wait mode, reduce power consumption by stopping the TIMA  
before executing the WAIT instruction.  
16.6 I/O Signals  
Port E shares five of its pins with the TIMA:  
PTE3/TCLKA is an external clock input to the TIMA prescaler.  
The four TIMA channel I/O pins are PTE4/TCH0A, PTE5/TCH1A, PTE6/TCH2A, and  
PTE7/TCH3A.  
16.6.1 TIMA Clock Pin (PTE3/TCLKA)  
PTE3/TCLKA is an external clock input that can be the clock source for the TIMA counter instead of the  
prescaled internal bus clock. Select the PTE3/TCLKA input by writing logic 1s to the three prescaler select  
The maximum TCLK frequency is the least: 4 MHz or bus frequency ÷ 2.  
PTE3/TCLKA is available as a general-purpose I/O pin when not used as the TIMA clock input. When the  
PTE3/TCLKA pin is the TIMA clock input, it is an input regardless of the state of the DDRE3 bit in data  
direction register E.  
16.6.2 TIMA Channel I/O Pins (PTE4/TCH0A–PTE7/TCH3A)  
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.  
PTE2/TCH0 and PTE4/TCH2 can be configured as buffered output compare or buffered PWM pins.  
16.7 I/O Registers  
These input/output (I/O) registers control and monitor TIMA operation:  
TIMA status and control register (TASC)  
TIMA control registers (TACNTH–TACNTL)  
TIMA counter modulo registers (TAMODH–TAMODL)  
TIMA channel status and control registers (TASC0, TASC1, TASC2, and TASC3)  
TIMA channel registers (TACH0H–TACH0L, TACH1H–TACH1L, TACH2H–TACH2L, and  
TACH3H–TACH3L)  
16.7.1 TIMA Status and Control Register  
The TIMA status and control register:  
Enables TIMA overflow interrupts  
Flags TIMA overflows  
Stops the TIMA counter  
Resets the TIMA counter  
Prescales the TIMA counter clock  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
225  
         
Timer Interface A (TIMA)  
Address: $000E  
Bit 7  
TOF  
0
6
5
TSTOP  
1
4
0
3
0
2
PS2  
0
1
PS1  
0
Bit 0  
PS0  
0
Read:  
Write:  
Reset:  
TOIE  
TRST  
0
R
0
0
0
R
= Reserved  
Figure 16-5. TIMA Status and Control Register (TASC)  
TOF — TIMA Overflow Flag  
This read/write flag is set when the TIMA counter reaches the modulo value programmed in the TIMA  
counter modulo registers. Clear TOF by reading the TIMA status and control register when TOF is set  
and then writing a logic 0 to TOF. If another TIMA overflow occurs before the clearing sequence is  
complete, then writing logic 0 to TOF has no effect. Therefore, a TOF interrupt request  
cannot be lost due to inadvertent clearing of TOF. Reset clears the TOF bit. Writing a logic 1 to TOF  
has no effect.  
1 = TIMA counter has reached modulo value.  
0 = TIMA counter has not reached modulo value.  
TOIE — TIMA Overflow Interrupt Enable Bit  
This read/write bit enables TIMA overflow interrupts when the TOF bit becomes set. Reset clears the  
TOIE bit.  
1 = TIMA overflow interrupts enabled  
0 = TIMA overflow interrupts disabled  
TSTOP — TIMA Stop Bit  
This read/write bit stops the TIMA counter. Counting resumes when TSTOP is cleared. Reset sets the  
TSTOP bit, stopping the TIMA counter until software clears the TSTOP bit.  
1 = TIMA counter stopped  
0 = TIMA counter active  
NOTE  
Do not set the TSTOP bit before entering wait mode if the TIMA is required  
to exit wait mode. Also when the TSTOP bit is set and the timer is  
configured for input capture operation, input captures are inhibited until the  
TSTOP bit is cleared.  
TRST — TIMA Reset Bit  
Setting this write-only bit resets the TIMA counter and the TIMA prescaler. Setting TRST has no effect  
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMA  
counter is reset and always reads as logic 0. Reset clears the TRST bit.  
1 = Prescaler and TIMA counter cleared  
0 = No effect  
NOTE  
Setting the TSTOP and TRST bits simultaneously stops the TIMA counter  
at a value of $0000.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
226  
Freescale Semiconductor  
   
I/O Registers  
PS[2:0] — Prescaler Select Bits  
These read/write bits select either the PTE3/TCLKA pin or one of the seven prescaler outputs as the  
input to the TIMA counter as Table 16-1 shows. Reset clears the PS[2:0] bits.  
Table 16-1. Prescaler Selection  
PS[2:0]  
000  
TIMA Clock Source  
Internal bus clock ÷1  
Internal bus clock ÷ 2  
Internal bus clock ÷ 4  
Internal bus clock ÷ 8  
Internal bus clock ÷ 16  
Internal bus clock ÷ 32  
Internal bus clock ÷ 64  
PTE3/TCLKA  
001  
010  
011  
100  
101  
110  
111  
16.7.2 TIMA Counter Registers  
The two read-only TIMA counter registers contain the high and low bytes of the value in the TIMA counter.  
Reading the high byte (TACNTH) latches the contents of the low byte (TACNTL) into a buffer. Subsequent  
reads of TACNTH do not affect the latched TACNTL value until TACNTL is read. Reset clears the TIMA  
counter registers. Setting the TIMA reset bit (TRST) also clears the TIMA counter registers.  
NOTE  
If TACNTH is read during a break interrupt, be sure to unlatch TACNTL by  
reading TACNTL before exiting the break interrupt. Otherwise, TACNTL  
retains the value latched during the break.  
Register Name and Address:  
Bit 7  
TACNTH — $000F  
6
Bit 14  
R
5
Bit 13  
R
4
3
Bit 11  
R
2
Bit 10  
R
1
Bit 9  
R
Bit 0  
Bit 8  
R
Read:  
Write:  
Reset:  
Bit 15  
Bit 12  
R
0
R
0
0
0
0
0
0
0
Register Name and Address:  
Bit 7  
TACNTL — $0010  
6
5
Bit 5  
R
4
3
Bit 3  
R
2
Bit 2  
R
1
Bit 1  
R
Bit 0  
Bit 0  
R
Read:  
Write:  
Reset:  
Bit 7  
R
Bit 6  
Bit 4  
R
R
0
0
0
0
0
0
0
0
R
= Reserved  
Figure 16-6. TIMA Counter Registers (TACNTH and TACNTL)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
227  
       
Timer Interface A (TIMA)  
16.7.3 TIMA Counter Modulo Registers  
The read/write TIMA modulo registers contain the modulo value for the TIMA counter. When the TIMA  
counter reaches the modulo value, the overflow flag (TOF) becomes set, and the TIMA counter resumes  
counting from $0000 at the next timer clock. Writing to the high byte (TAMODH) inhibits the TOF bit and  
overflow interrupts until the low byte (TAMODL) is written. Reset sets the TIMA counter modulo registers.  
Register Name and Address:  
Bit 7  
TAMODH — $0011  
6
Bit 14  
1
5
Bit 13  
1
4
Bit 12  
1
3
Bit 11  
1
2
Bit 10  
1
1
Bit 9  
1
Bit 0  
Bit 8  
1
Read:  
Bit 15  
Write:  
Reset:  
1
Register Name and Address:  
Bit 7  
TAMODL — $0012  
6
Bit 6  
1
5
Bit 5  
1
4
3
Bit 3  
1
2
Bit 2  
1
1
Bit 1  
1
Bit 0  
Bit 0  
1
Read:  
Bit 7  
Write:  
Bit 4  
1
Reset:  
1
Figure 16-7. TIMA Counter Modulo Registers  
(TAMODH and TAMODL)  
NOTE  
Reset the TIMA counter before writing to the TIMA counter modulo registers.  
16.7.4 TIMA Channel Status and Control Registers  
Each of the TIMA channel status and control registers:  
Flags input captures and output compares  
Enables input capture and output compare interrupts  
Selects input capture, output compare, or PWM operation  
Selects high, low, or toggling output on output compare  
Selects rising edge, falling edge, or any edge as the active input capture trigger  
Selects output toggling on TIMA overflow  
Selects 0 percent and 100 percent PWM duty cycle  
Selects buffered or unbuffered output compare/PWM operation  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
228  
Freescale Semiconductor  
       
I/O Registers  
Register Name and Address:  
Bit 7  
TASC0 — $0013  
5
6
CH0IE  
0
4
3
ELS0B  
0
2
ELS0A  
0
1
TOV0  
0
Bit 0  
CH0MAX  
0
Read:  
Write:  
Reset:  
CH0F  
MS0B  
0
MS0A  
0
0
0
Register Name and Address:  
Bit 7  
TASC1 — $0016  
6
CH1IE  
0
5
0
4
3
ELS1B  
0
2
ELS1A  
0
1
TOV1  
0
Bit 0  
CH1MAX  
0
Read:  
Write:  
Reset:  
CH1F  
MS1A  
0
0
0
R
0
Register Name and Address:  
Bit 7  
TASC2 — $0019  
5
6
CH2IE  
0
4
3
ELS2B  
0
2
ELS2A  
0
1
TOV2  
0
Bit 0  
CH2MAX  
0
Read:  
Write:  
Reset:  
CH2F  
MS2B  
0
MS2A  
0
0
0
Register Name and Address:  
Bit 7  
TASC3 — $001C  
6
5
0
4
3
ELS3B  
0
2
ELS3A  
0
1
TOV3  
0
Bit 0  
CH3MAX  
0
Read:  
Write:  
Reset:  
CH3F  
CH3IE  
MS3A  
0
0
0
R
0
0
R
= Reserved  
Figure 16-8. TIMA Channel Status  
and Control Registers (TASC0–TASC3)  
CHxF — Channel x Flag Bit  
When channel x is an input capture channel, this read/write bit is set when an active edge occurs on  
the channel x pin. When channel x is an output compare channel, CHxF is set when the value in the  
TIMA counter registers matches the value in the TIMA channel x registers.  
When CHxIE = 1, clear CHxF by reading TIMA channel x status and control register with CHxF set,  
and then writing a 0 to CHxF. If another interrupt request occurs before the clearing sequence is  
complete, then writing 0 to CHxF has no effect. Therefore, an interrupt request cannot be lost due to  
inadvertent clearing of CHxF.  
Reset clears the CHxF bit. Writing a 1 to CHxF has no effect.  
1 = Input capture or output compare on channel x  
0 = No input capture or output compare on channel x  
CHxIE — Channel x Interrupt Enable Bit  
This read/write bit enables TIMA CPU interrupts on channel x.  
Reset clears the CHxIE bit.  
1 = Channel x CPU interrupt requests enabled  
0 = Channel x CPU interrupt requests disabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
229  
   
Timer Interface A (TIMA)  
MSxB — Mode Select Bit B  
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMA  
channel 0 and TIMA channel 2 status and control registers.  
Setting MS0B disables the channel 1 status and control register and reverts TCH1A pin to  
general-purpose I/O.  
Setting MS2B disables the channel 3 status and control register and reverts TCH3A pin to  
general-purpose I/O.  
Reset clears the MSxB bit.  
1 = Buffered output compare/PWM operation enabled  
0 = Buffered output compare/PWM operation disabled  
MSxA — Mode Select Bit A  
When ELSxB:A 00, this read/write bit selects either input capture operation or unbuffered output  
compare/PWM operation. See Table 16-2.  
1 = Unbuffered output compare/PWM operation  
0 = Input capture operation  
When ELSxB:A = 00, this read/write bit selects the initial output level of the TCHxA pin once PWM,  
input capture, or output compare operation is enabled. See Table 16-2. Reset clears the MSxA bit.  
1 = Initial output level low  
0 = Initial output level high  
NOTE  
Before changing a channel function by writing to the MSxB or MSxA bit, set  
the TSTOP and TRST bits in the TIMA status and control register (TASC).  
ELSxB and ELSxA — Edge/Level Select Bits  
When channel x is an input capture channel, these read/write bits control the active edge-sensing logic  
on channel x.  
When channel x is an output compare channel, ELSxB and ELSxA control the channel x output  
behavior when an output compare occurs.  
When ELSxB and ELSxA are both clear, channel x is not connected to port E, and pin PTEx/TCHxA  
is available as a general-purpose I/O pin. However, channel x is at a state determined by these bits  
and becomes transparent to the respective pin when PWM, input capture, or output compare mode is  
enabled. Table 16-2 shows how ELSxB and ELSxA work. Reset clears the ELSxB and ELSxA bits.  
NOTE  
Before enabling a TIMA channel register for input capture operation, make  
sure that the PTEx/TACHx pin is stable for at least two bus clocks.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
230  
Freescale Semiconductor  
I/O Registers  
Table 16-2. Mode, Edge, and Level Selection  
MSxB:MSxA  
ELSxB:ELSxA  
Mode  
Configuration  
Pin under port control; initialize timer output level high  
X0  
X1  
00  
00  
00  
01  
01  
01  
01  
1X  
1X  
1X  
00  
00  
01  
10  
11  
00  
01  
10  
11  
01  
10  
11  
Output preset  
Pin under port control; initialize timer output level low  
Capture on rising edge only  
Capture on falling edge only  
Capture on rising or falling edge  
Software compare only  
Input capture  
Output  
compare  
or PWM  
Toggle output on compare  
Clear output on compare  
Set output on compare  
Toggle output on compare  
Clear output on compare  
Buffered  
output compare  
or buffered PWM  
Set output on compare  
TOVx — Toggle-On-Overflow Bit  
When channel x is an output compare channel, this read/write bit controls the behavior of the channel  
x output when the TIMA counter overflows. When channel x is an input capture channel, TOVx has no  
effect. Reset clears the TOVx bit.  
1 = Channel x pin toggles on TIMA counter overflow.  
0 = Channel x pin does not toggle on TIMA counter overflow.  
NOTE  
When TOVx is set, a TIMA counter overflow takes precedence over a  
channel x output compare if both occur at the same time.  
CHxMAX — Channel x Maximum Duty Cycle Bit  
When the TOVx is 1 and clear output on compare is selected, setting the CHxMAX bit forces the duty  
cycle of buffered and unbuffered PWM signals to 100 percent. As Figure 16-9 shows, CHxMAX bit  
takes effect in the cycle after it is set or cleared. The output stays at 100 percent duty cycle level until  
the cycle after CHxMAX is cleared.  
OVERFLOW  
OVERFLOW  
OVERFLOW  
OVERFLOW  
OVERFLOW  
PERIOD  
PTEx/TCHx  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
CHxMAX  
TOVx  
Figure 16-9. CHxMAX Latency  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
231  
   
Timer Interface A (TIMA)  
16.7.5 TIMA Channel Registers  
These read/write registers contain the captured TIMA counter value of the input capture function or the  
output compare value of the output compare function. The state of the TIMA channel registers after reset  
is unknown.  
In input capture mode (MSxB:MSxA = 0:0), reading the high byte of the TIMA channel x registers  
(TACHxH) inhibits input captures until the low byte (TACHxL) is read.  
In output compare mode (MSxB:MSxA 0:0), writing to the high byte of the TIMA channel x registers  
(TACHxH) inhibits output compares until the low byte (TACHxL) is written.  
Register Name and Address:  
Bit 7  
TACH0H — $0014  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Bit 15  
Write:  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Reset:  
Indeterminate after reset  
Register Name and Address:  
Bit 7  
TACH0L — $0015  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
Register Name and Address: TACH1H — $0017  
Bit 7  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Write:  
Reset:  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Indeterminate after reset  
Register Name and Address:  
Bit 7  
TACH1L — $0018  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
Register Name and Address:  
Bit 7  
TACH2H — $001A  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Bit 15  
Write:  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Reset:  
Indeterminate after reset  
Figure 16-10. TIMA Channel Registers  
(TACH0H/L–TACH3H/L)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
232  
Freescale Semiconductor  
     
I/O Registers  
Register Name and Address:  
Bit 7  
TACH2L — $001B  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
Register Name and Address:  
Bit 7  
TACH3H — $001D  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Bit 15  
Write:  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Reset:  
Indeterminate after reset  
Register Name and Address:  
Bit 7  
TACH3L — $001E  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
Figure 16-10. TIMA Channel Registers  
(TACH0H/L–TACH3H/L) (Continued)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
233  
Timer Interface A (TIMA)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
234  
Freescale Semiconductor  
Chapter 17  
Timer Interface B (TIMB)  
17.1 Introduction  
This section describes the timer interface module B (TIMB). The TIMB is a 2-channel timer that provides:  
Timing reference with input capture  
Output compare  
Pulse-width modulation functions  
Figure 17-2 is a block diagram of the TIMB.  
NOTE  
The TIMB module is not available in the 56-pin shrink dual in-line package  
(SDIP).  
17.2 Features  
Features of the TIMB include:  
Two input capture/output compare channels:  
Rising-edge, falling-edge, or any-edge input capture trigger  
Set, clear, or toggle output compare action  
Buffered and unbuffered pulse-width modulation (PWM) signal generation  
Programmable TIMB clock input:  
7-frequency internal bus clock prescaler selection  
External TIMB clock input (4-MHz maximum frequency)  
Free-running or modulo up-count operation  
Toggle any channel pin on overflow  
TIMB counter stop and reset bits  
17.3 Functional Description  
Figure 17-2 shows the TIMB structure. The central component of the TIMB is the 16-bit TIMB counter that  
can operate as a free-running counter or a modulo up-counter. The TIMB counter provides the timing  
reference for the input capture and output compare functions. The TIMB counter modulo registers,  
TBMODH–TBMODL, control the modulo value of the TIMB counter. Software can read the TIMB counter  
value at any time without affecting the counting sequence.  
The two TIMB channels are programmable independently as input capture or output compare channels.  
NOTE  
The TIMB module is not available in the 56-pin SDIP.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
235  
         
INTERNAL BUS  
M68HC08 CPU  
PTA7–PTA0  
CPU  
REGISTERS  
ARITHMETIC/LOGIC  
UNIT  
LOW-VOLTAGE INHIBIT  
MODULE  
PTB7/ATD7  
PTB6/ATD6  
PTB5/ATD5  
PTB4/ATD4  
PTB3/ATD3  
PTB2/ATD2  
PTB1/ATD1  
PTB0/ATD0  
COMPUTER OPERATING PROPERLY  
MODULE  
CONTROL AND STATUS REGISTERS — 112 BYTES  
USER FLASH — 32,256 BYTES  
TIMER INTERFACE  
MODULE A  
USER RAM — 768 BYTES  
PTC6  
PTC5  
TIMER INTERFACE  
MODULE B  
PTC4  
MONITOR ROM — 240 BYTES  
PTC3  
PTC2  
SERIAL COMMUNICATIONS INTERFACE  
MODULE  
PTC1/ATD9(1)  
PTC0/ATD8  
USER FLASH VECTOR SPACE — 46 BYTES  
OSC1  
PTD6/IS3  
CLOCK GENERATOR  
MODULE  
OSC2  
SERIAL PERIPHERAL INTERFACE  
MODULE(2)  
PTD5/IS2  
CGMXFC  
PTD4/IS1  
PTD3/FAULT4  
PTD2/FAULT3  
PTD1/FAULT2  
PTD0/FAULT1  
POWER-ON RESET  
MODULE  
SYSTEM INTEGRATION  
MODULE  
RST  
PTE7/TCH3A  
PTE6/TCH2A  
PTE5/TCH1A  
PTE4/TCH0A  
PTE3/TCLKA  
PTE2/TCH1B(1)  
PTE1/TCH0B(1)  
PTE0/TCLKB(1)  
IRQ  
MODULE  
IRQ  
SINGLE BREAK  
MODULE  
VDDA  
(3)  
VSSA  
ANALOG-TO-DIGITAL CONVERTER  
MODULE  
(3)  
VREFL  
VREFH  
PTF5/TxD  
PTF4/RxD  
PTF3/MISO(1)  
PTF2/MOSI(1)  
PWMGND  
PULSE-WIDTH MODULATOR  
MODULE  
PWM6–PWM1  
PTF1/SS(1)  
PTF0/SPSCK(1)  
VSS  
VDD  
POWER  
VDDAD  
VSSAD  
Notes:  
1. These pins are not available in the 56-pin SDIP package.  
2. This module is not available in the 56-pin SDIP package.  
3. In the 56-pin SDIP package, these pins are bonded together.  
Figure 17-1. Block Diagram Highlighting TIMB Block and Pins  
Functional Description  
TCLK  
PTE0/TCLKB  
INTERNAL  
BUS CLOCK  
PRESCALER SELECT  
PRESCALER  
TSTOP  
TRST  
PS2  
PS1  
PS0  
16-BIT COUNTER  
INTER-  
RUPT  
LOGIC  
TOF  
TOIE  
16-BIT COMPARATOR  
TMODH:TMODL  
ELS0B  
ELS0A  
CHANNEL 0  
16-BIT COMPARATOR  
TCH0H:TCH0L  
TOV0  
CH0MAX  
PTE1  
LOGIC  
PTE1/TCH0B  
CH0F  
MS0B  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH0IE  
MS0A  
ELS1B ELS1A  
CHANNEL 1  
16-BIT COMPARATOR  
TCH1H:TCH1L  
TOV1  
CH1MAX  
PTE2  
LOGIC  
PTE2/TCH1B  
CH1F  
INTER-  
RUPT  
LOGIC  
16-BIT LATCH  
CH1IE  
MS1A  
Figure 17-2. TIMB Block Diagram  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
Bit 0  
Read: TOF  
0
TRST  
0
0
R
TIMB Status/Control Register  
TOIE  
TSTOP  
PS2  
PS1  
PS0  
$0051  
(TBSC) Write:  
0
0
TIMB Counter Register High  
Reset:  
0
Bit 14  
R
1
Bit 13  
R
0
0
Bit 10  
R
0
Bit 9  
R
0
Bit 8  
R
Read: Bit 15  
Bit 12  
R
Bit 11  
R
$0052  
$0053  
$0054  
$0055  
(TBCNTH) Write:  
R
0
Reset:  
0
0
0
0
0
0
0
Read: Bit 7  
Bit 6  
R
Bit 5  
R
Bit 4  
R
Bit 3  
R
Bit 2  
R
Bit 1  
R
Bit 0  
R
TIMB Counter Register Low  
(TBCNTL) Write:  
R
0
Reset:  
Read:  
0
0
0
0
0
0
0
TIMB Counter Modulo Register  
Bit 15  
1
Bit 14  
1
Bit 13  
1
Bit 12  
1
Bit 11  
1
Bit 10  
1
Bit 9  
1
Bit 8  
1
High (TBMODH) Write:  
Reset:  
Read:  
TIMB Counter Modulo Register  
Bit 7  
Bit 6  
Bit 5  
1
Bit 4  
1
Bit 3  
1
Bit 2  
1
Bit 1  
1
Bit 0  
1
Low (TBMODL) Write:  
Reset:  
1
1
R
= Reserved  
Figure 17-3. TIMB I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
237  
 
Timer Interface B (TIMB)  
Addr.  
Register Name  
Bit 7  
6
5
4
3
ELS0B  
0
2
ELS0A  
0
1
Bit 0  
Read: CH0F  
TIMB Channel 0 Status/Control  
CH0IE  
0
MS0B  
0
MS0A  
0
TOV0 CH0MAX  
$0056  
Register Write:  
0
0
Reset:  
Read:  
0
0
TIMB Channel 0 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
$0057  
$0058  
$0059  
$005A  
$005B  
(TBCH0H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMB Channel 0 Register Low  
Bit 7  
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TBCH0L) Write:  
Reset:  
Read: CH1F  
0
R
0
TIMB Channel 1 Status/Control  
CH1IE  
0
MS1A  
0
ELS1B  
0
ELS1A  
0
TOV1 CH1MAX  
Register Write:  
0
0
Reset:  
Read:  
0
0
TIMB Channel 1 Register High  
Bit 15  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Bit 8  
(TBCH1H) Write:  
Reset:  
Read:  
Indeterminate after reset  
Bit 4 Bit 3  
Indeterminate after reset  
TIMB Channel 1 Register Low  
Bit 7  
R
Bit 6  
Bit 5  
Bit 2  
Bit 1  
Bit 0  
(TBCH1L) Write:  
Reset:  
= Reserved  
Figure 17-3. TIMB I/O Register Summary (Continued)  
17.3.1 TIMB Counter Prescaler  
The TIMB clock source can be one of the seven prescaler outputs or the TIMB clock pin, PTE0/TCLKB.  
The prescaler generates seven clock rates from the internal bus clock. The prescaler select bits, PS[2:0],  
in the TIMB status and control register select the TIMB clock source.  
17.3.2 Input Capture  
An input capture function has three basic parts:  
1. Edge select logic  
2. Input capture latch  
3. 16-bit counter  
Two 8-bit registers, which make up the 16-bit input capture register, are used to latch the value of the  
free-running counter after the corresponding input capture edge detector senses a defined transition. The  
polarity of the active edge is programmable. The level transition which triggers the counter transfer is  
defined by the corresponding input edge bits (ELSxB and ELSxA in TBSC0–TBSC1 control registers with  
x referring to the active channel number). When an active edge occurs on the pin of an input capture  
channel, the TIMB latches the contents of the TIMB counter into the TIMB channel registers,  
TCHxH–TCHxL. Input captures can generate TIMB CPU interrupt requests. Software can determine that  
an input capture event has occurred by enabling input capture interrupts or by polling the status flag bit.  
The free-running counter contents are transferred to the TIMB channel status and control register  
(TBCHxH–TBCHxL, see 17.7.5 TIMB Channel Registers) on each proper signal transition regardless of  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
238  
Freescale Semiconductor  
   
Functional Description  
whether the TIMB channel flag (CH0F–CH1F in TBSC0–TBSC1 registers) is set or clear. When the status  
flag is set, a CPU interrupt is generated if enabled. The value of the count latched or “captured” is the time  
of the event. Because this value is stored in the input capture register two bus cycles after the actual event  
occurs, user software can respond to this event at a later time and determine the actual time of the event.  
However, this must be done prior to another input capture on the same pin; otherwise, the previous time  
value will be lost.  
By recording the times for successive edges on an incoming signal, software can determine the period  
and/or pulse width of the signal. To measure a period, two successive edges of the same polarity are  
captured. To measure a pulse width, two alternate polarity edges are captured. Software should track the  
overflows at the 16-bit module counter to extend its range.  
Another use for the input capture function is to establish a time reference. In this case, an input capture  
function is used in conjunction with an output compare function. For example, to activate an output signal  
a specified number of clock cycles after detecting an input event (edge), use the input capture function to  
record the time at which the edge occurred. A number corresponding to the desired delay is added to this  
captured value and stored to an output compare register (see 17.7.5 TIMB Channel Registers). Because  
both input captures and output compares are referenced to the same 16-bit modulo counter, the delay  
can be controlled to the resolution of the counter independent of software latencies.  
Reset does not affect the contents of the input capture channel register (TBCHxH–TBCHxL).  
17.3.3 Output Compare  
With the output compare function, the TIMB can generate a periodic pulse with a programmable polarity,  
duration, and frequency. When the counter reaches the value in the registers of an output compare  
channel, the TIMB can set, clear, or toggle the channel pin. Output compares can generate TIMB CPU  
interrupt requests.  
17.3.3.1 Unbuffered Output Compare  
Any output compare channel can generate unbuffered output compare pulses as described in 17.3.3  
Output Compare. The pulses are unbuffered because changing the output compare value requires writing  
the new value over the old value currently in the TIMB channel registers.  
An unsynchronized write to the TIMB channel registers to change an output compare value could cause  
incorrect operation for up to two counter overflow periods. For example, writing a new value before the  
counter reaches the old value but after the counter reaches the new value prevents any compare during  
that counter overflow period. Also, using a TIMB overflow interrupt routine to write a new, smaller output  
compare value may cause the compare to be missed. The TIMB may pass the new value before it is  
written.  
Use this method to synchronize unbuffered changes in the output compare value on channel x:  
When changing to a smaller value, enable channel x output compare interrupts and write the new  
value in the output compare interrupt routine. The output compare interrupt occurs at the end of  
the current output compare pulse. The interrupt routine has until the end of the counter overflow  
period to write the new value.  
When changing to a larger output compare value, enable TIMB overflow interrupts and write the  
new value in the TIMB overflow interrupt routine. The TIMB overflow interrupt occurs at the end of  
the current counter overflow period. Writing a larger value in an output compare interrupt routine  
(at the end of the current pulse) could cause two output compares to occur in the same counter  
overflow period.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
239  
   
Timer Interface B (TIMB)  
17.3.3.2 Buffered Output Compare  
Channels 0 and 1 can be linked to form a buffered output compare channel whose output appears on the  
PTE1/TCH0B pin. The TIMB channel registers of the linked pair alternately control the output.  
Setting the MS0B bit in TIMB channel 0 status and control register (TBSC0) links channel 0 and channel  
1. The output compare value in the TIMB channel 0 registers initially controls the output on the  
PTE1/TCH0B pin. Writing to the TIMB channel 1 registers enables the TIMB channel 1 registers to  
synchronously control the output after the TIMB overflows. At each subsequent overflow, the TIMB  
channel registers (0 or 1) that control the output are the ones written to last. TSC0 controls and monitors  
the buffered output compare function, and TIMB channel 1 status and control register (TBSC1) is unused.  
While the MS0B bit is set, the channel 1 pin, PTE2/TCH1B, is available as a general-purpose I/O pin.  
NOTE  
In buffered output compare operation, do not write new output compare  
values to the currently active channel registers. User software should track  
the currently active channel to prevent writing a new value to the active  
channel. Writing to the active channel registers is the same as generating  
unbuffered output compares.  
17.3.4 Pulse-Width Modulation (PWM)  
By using the toggle-on-overflow feature with an output compare channel, the TIMB can generate a PWM  
signal. The value in the TIMB counter modulo registers determines the period of the PWM signal. The  
channel pin toggles when the counter reaches the value in the TIMB counter modulo registers. The time  
between overflows is the period of the PWM signal.  
As Figure 17-4 shows, the output compare value in the TIMB channel registers determines the pulse width  
of the PWM signal. The time between overflow and output compare is the pulse width. Program the TIMB  
to clear the channel pin on output compare if the polarity of the PWM pulse is 1 (ELSxA = 0). Program the  
TIMB to set the pin if the polarity of the PWM pulse is 0 (ELSxA = 1).  
OVERFLOW  
OVERFLOW  
OVERFLOW  
PERIOD  
POLARITY = 1  
(ELSxA = 0)  
TCHx  
TCHx  
PULSE  
WIDTH  
POLARITY = 0  
(ELSxA = 1)  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
Figure 17-4. PWM Period and Pulse Width  
The value in the TIMB counter modulo registers and the selected prescaler output determines the  
frequency of the PWM output. The frequency of an 8-bit PWM signal is variable in 256 increments. Writing  
$00FF (255) to the TIMB counter modulo registers produces a PWM period of 256 times the internal bus  
clock period if the prescaler select value is $000 (see 17.7.1 TIMB Status and Control Register).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
240  
Freescale Semiconductor  
     
Functional Description  
The value in the TIMB channel registers determines the pulse width of the PWM output. The pulse width  
of an 8-bit PWM signal is variable in 256 increments. Writing $0080 (128) to the TIMB channel registers  
produces a duty cycle of 128/256 or 50 percent.  
17.3.4.1 Unbuffered PWM Signal Generation  
Any output compare channel can generate unbuffered PWM pulses as described in 17.3.4 Pulse-Width  
Modulation (PWM). The pulses are unbuffered because changing the pulse width requires writing the new  
pulse width value over the value currently in the TIMB channel registers.  
An unsynchronized write to the TIMB channel registers to change a pulse width value could cause  
incorrect operation for up to two PWM periods. For example, writing a new value before the counter  
reaches the old value but after the counter reaches the new value prevents any compare during that PWM  
period. Also, using a TIMB overflow interrupt routine to write a new, smaller pulse width value may cause  
the compare to be missed. The TIMB may pass the new value before it is written to the TIMB channel  
registers.  
Use this method to synchronize unbuffered changes in the PWM pulse width on channel x:  
When changing to a shorter pulse width, enable channel x output compare interrupts and write the  
new value in the output compare interrupt routine. The output compare interrupt occurs at the end  
of the current pulse. The interrupt routine has until the end of the PWM period to write the new  
value.  
When changing to a longer pulse width, enable TIMB overflow interrupts and write the new value  
in the TIMB overflow interrupt routine. The TIMB overflow interrupt occurs at the end of the current  
PWM period. Writing a larger value in an output compare interrupt routine (at the end of the current  
pulse) could cause two output compares to occur in the same PWM period.  
NOTE  
In PWM signal generation, do not program the PWM channel to toggle on  
output compare. Toggling on output compare prevents reliable 0 percent  
duty cycle generation and removes the ability of the channel to self-correct  
in the event of software error or noise. Toggling on output compare also can  
cause incorrect PWM signal generation when changing the PWM pulse  
width to a new, much larger value.  
17.3.4.2 Buffered PWM Signal Generation  
Channels 0 and 1 can be linked to form a buffered PWM channel whose output appears on the  
PTE1/TCH0B pin. The TIMB channel registers of the linked pair alternately control the pulse width of the  
output.  
Setting the MS0B bit in TIMB channel 0 status and control register (TBSC0) links channel 0 and channel  
1. The TIMB channel 0 registers initially control the pulse width on the PTE1/TCH0B pin. Writing to the  
TIMB channel 1 registers enables the TIMB channel 1 registers to synchronously control the pulse width  
at the beginning of the next PWM period. At each subsequent overflow, the TIMB channel registers  
(0 or 1) that control the pulse width are the ones written to last. TBSC0 controls and monitors the buffered  
PWM function, and TIMB channel 1 status and control register (TBSC1) is unused. While the MS0B bit is  
set, the channel 1 pin, PTE2/TCH1B, is available as a general-purpose I/O pin.  
NOTE  
In buffered PWM signal generation, do not write new pulse width values to  
the currently active channel registers. User software should track the  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
241  
   
Timer Interface B (TIMB)  
currently active channel to prevent writing a new value to the active  
channel. Writing to the active channel registers is the same as generating  
unbuffered PWM signals.  
17.3.4.3 PWM Initialization  
To ensure correct operation when generating unbuffered or buffered PWM signals, use this initialization  
procedure:  
1. In the TIMB status and control register (TBSC):  
a. Stop the TIMB counter by setting the TIMB stop bit, TSTOP.  
b. Reset the TIMB counter and prescaler by setting the TIMB reset bit, TRST.  
2. In the TIMB counter modulo registers (TBMODH–TBMODL), write the value for the required PWM  
period.  
3. In the TIMB channel x registers (TBCHxH–TBCHxL), write the value for the required pulse width.  
4. In TIMB channel x status and control register (TBSCx):  
a. Write 0:1 (for unbuffered output compare or PWM signals) or 1:0 (for buffered output compare  
or PWM signals) to the mode select bits, MSxB–MSxA. (See Table 17-2.)  
b. Write 1 to the toggle-on-overflow bit, TOVx.  
c. Write 1:0 (polarity 1 — to clear output on compare) or 1:1 (polarity 0 — to set output on  
compare) to the edge/level select bits, ELSxB–ELSxA. The output action on compare must  
force the output to the complement of the pulse width level. (See Table 17-2.)  
NOTE  
In PWM signal generation, do not program the PWM channel to toggle on  
output compare. Toggling on output compare prevents reliable 0 percent  
duty cycle generation and removes the ability of the channel to self-correct  
in the event of software error or noise. Toggling on output compare can also  
cause incorrect PWM signal generation when changing the PWM pulse  
width to a new, much larger value.  
5. In the TIMB status control register (TBSC), clear the TIMB stop bit, TSTOP.  
Setting MS0B links channels 0 and 1 and configures them for buffered PWM operation. The TIMB channel  
0 registers (TBCH0H–TBCH0L) initially control the buffered PWM output. TIMB status control register 0  
(TBSC0) controls and monitors the PWM signal from the linked channels. MS0B takes priority over MS0A.  
Clearing the toggle-on-overflow bit, TOVx, inhibits output toggles on TIMB overflows. Subsequent output  
compares try to force the output to a state it is already in and have no effect. The result is a 0 percent duty  
cycle output.  
Setting the channel x maximum duty cycle bit (CHxMAX) and setting the TOVx bit generates a  
100 percent duty cycle output. (See 17.7.4 TIMB Channel Status and Control Registers.)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
242  
Freescale Semiconductor  
 
Interrupts  
17.4 Interrupts  
These TIMB sources can generate interrupt requests:  
TIMB overflow flag (TOF) — The timer overflow flag (TOF) bit is set when the TIMB counter  
reaches the modulo value programmed in the TIMB counter modulo registers. The TIMB overflow  
interrupt enable bit, TOIE, enables TIMB overflow interrupt requests. TOF and TOIE are in the  
TIMB status and control registers.  
TIMB channel flags (CH1F–CH0F) — The CHxF bit is set when an input capture or output compare  
occurs on channel x. Channel x TIMB CPU interrupt requests are controlled by the channel x  
interrupt enable bit, CHxIE.  
17.5 Wait Mode  
The WAIT instruction puts the MCU in low-power standby mode.  
The TIMB remains active after the execution of a WAIT instruction. In wait mode, the TIMB registers are  
not accessible by the CPU. Any enabled CPU interrupt request from the TIMB can bring the MCU out of  
wait mode.  
If TIMB functions are not required during wait mode, reduce power consumption by stopping the TIMB  
before executing the WAIT instruction.  
17.6 I/O Signals  
Port E shares three of its pins with the TIMB:  
PTE0/TCLKB is an external clock input to the TIMB prescaler.  
The two TIMB channel I/O pins are PTE1/TCH0B and PTE2/TCH1B.  
17.6.1 TIMB Clock Pin (PTE0/TCLKB)  
PTE0/TCLKB is an external clock input that can be the clock source for the TIMB counter instead of the  
prescaled internal bus clock. Select the PTE0/TCLKB input by writing 1s to the three prescaler select bits,  
The maximum TCLK frequency is the least: 4 MHz or bus frequency ÷ 2.  
PTE0/TCLKB is available as a general-purpose I/O pin or ADC channel when not used as the TIMB clock  
input. When the PTE0/TCLKB pin is the TIMB clock input, it is an input regardless of the state of the  
DDRE0 bit in data direction register E.  
17.6.2 TIMB Channel I/O Pins (PTE1/TCH0B–PTE2/TCH1B)  
Each channel I/O pin is programmable independently as an input capture pin or an output compare pin.  
PTE1/TCH0B and PTE2/TCH1B can be configured as buffered output compare or buffered PWM pins.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
243  
         
Timer Interface B (TIMB)  
17.7 I/O Registers  
These input/output (I/O) registers control and monitor TIMB operation:  
TIMB status and control register (TBSC)  
TIMB control registers (TBCNTH–TBCNTL)  
TIMB counter modulo registers (TBMODH–TBMODL)  
TIMB channel status and control registers (TBSC0 and TBSC1)  
TIMB channel registers (TBCH0H–TBCH0L and TBCH1H–TBCH1L)  
17.7.1 TIMB Status and Control Register  
The TIMB status and control register:  
Enables TIMB overflow interrupts  
Flags TIMB overflows  
Stops the TIMB counter  
Resets the TIMB counter  
Prescales the TIMB counter clock  
Address:  
$0051  
Bit 7  
TOF  
0
6
5
TSTOP  
1
4
0
3
0
2
PS2  
0
1
PS1  
0
Bit 0  
PS0  
0
Read:  
Write:  
Reset:  
TOIE  
TRST  
0
R
0
0
0
R
= Reserved  
Figure 17-5. TIMB Status and Control Register (TBSC)  
TOF — TIMB Overflow Flag  
This read/write flag is set when the TIMB counter reaches the modulo value programmed in the TIMB  
counter modulo registers. Clear TOF by reading the TIMB status and control register when TOF is set  
and then writing a logic 0 to TOF. If another TIMB overflow occurs before the clearing sequence is  
complete, then writing logic 0 to TOF has no effect. Therefore, a TOF interrupt request cannot be lost  
due to inadvertent clearing of TOF. Reset clears the TOF bit. Writing a logic 1 to TOF has no effect.  
1 = TIMB counter has reached modulo value.  
0 = TIMB counter has not reached modulo value.  
TOIE — TIMB Overflow Interrupt Enable Bit  
This read/write bit enables TIMB overflow interrupts when the TOF bit becomes set. Reset clears the  
TOIE bit.  
1 = TIMB overflow interrupts enabled  
0 = TIMB overflow interrupts disabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
244  
Freescale Semiconductor  
       
I/O Registers  
TSTOP — TIMB Stop Bit  
This read/write bit stops the TIMB counter. Counting resumes when TSTOP is cleared. Reset sets the  
TSTOP bit, stopping the TIMB counter until software clears the TSTOP bit.  
1 = TIMB counter stopped  
0 = TIMB counter active  
NOTE  
Do not set the TSTOP bit before entering wait mode if the TIMB is required  
to exit wait mode. Also, when the TSTOP bit is set and the timer is  
configured for input capture operation, input captures are inhibited until  
TSTOP is cleared.  
TRST — TIMB Reset Bit  
Setting this write-only bit resets the TIMB counter and the TIMB prescaler. Setting TRST has no effect  
on any other registers. Counting resumes from $0000. TRST is cleared automatically after the TIMB  
counter is reset and always reads as logic 0. Reset clears the TRST bit.  
1 = Prescaler and TIMB counter cleared  
0 = No effect  
NOTE  
Setting the TSTOP and TRST bits simultaneously stops the TIMB counter  
at a value of $0000.  
PS[2:0] — Prescaler Select Bits  
These read/write bits select either the PTE0/TCLKB pin or one of the seven prescaler outputs as the  
input to the TIMB counter as Table 17-1 shows. Reset clears the PS[2:0] bits.  
Table 17-1. Prescaler Selection  
PS[2:0]  
000  
TIMB Clock Source  
Internal bus clock ÷1  
Internal bus clock ÷ 2  
Internal bus clock ÷ 4  
Internal bus clock ÷ 8  
Internal bus clock ÷ 16  
Internal bus clock ÷ 32  
Internal bus clock ÷ 64  
PTE0/TCLKB  
001  
010  
011  
100  
101  
110  
111  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
245  
 
Timer Interface B (TIMB)  
17.7.2 TIMB Counter Registers  
The two read-only TIMB counter registers contain the high and low bytes of the value in the TIMB counter.  
Reading the high byte (TBCNTH) latches the contents of the low byte (TBCNTL) into a buffer. Subsequent  
reads of TBCNTH do not affect the latched TBCNTL value until TBCNTL is read. Reset clears the TIMB  
counter registers. Setting the TIMB reset bit (TRST) also clears the TIMB counter registers.  
NOTE  
If TBCNTH is read during a break interrupt, be sure to unlatch TBCNTL by  
reading TBCNTL before exiting the break interrupt. Otherwise, TBCNTL  
retains the value latched during the break.  
Register Name and Address:  
Bit 7  
TBCNTH — $0052  
6
Bit 14  
R
5
Bit 13  
R
4
3
Bit 11  
R
2
Bit 10  
R
1
Bit 9  
R
Bit 0  
Bit 8  
R
Read:  
Write:  
Reset:  
Bit 15  
Bit 12  
R
0
R
0
0
0
0
0
0
0
Register Name and Address:  
Bit 7  
TBCNTL — $0053  
6
5
Bit 5  
R
4
3
Bit 3  
R
2
Bit 2  
R
1
Bit 1  
R
Bit 0  
Bit 0  
R
Read:  
Write:  
Reset:  
Bit 7  
R
Bit 6  
Bit 4  
R
R
0
0
0
0
0
0
0
0
R
= Reserved  
Figure 17-6. TIMB Counter Registers (TBCNTH and TBCNTL)  
17.7.3 TIMB Counter Modulo Registers  
The read/write TIMB modulo registers contain the modulo value for the TIMB counter. When the TIMB  
counter reaches the modulo value, the overflow flag (TOF) becomes set, and the TIMB counter resumes  
counting from $0000 at the next timer clock. Writing to the high byte (TBMODH) inhibits the TOF bit and  
overflow interrupts until the low byte (TBMODL) is written. Reset sets the TIMB counter modulo registers.  
Register Name and Address:  
Bit 7  
TBMODH — $0054  
6
Bit 14  
1
5
Bit 13  
1
4
Bit 12  
1
3
Bit 11  
1
2
Bit 10  
1
1
Bit 9  
1
Bit 0  
Bit 8  
1
Read:  
Bit 15  
Write:  
Reset:  
1
Register Name and Address:  
Bit 7  
TBMODL — $0055  
6
Bit 6  
1
5
Bit 5  
1
4
3
Bit 3  
1
2
Bit 2  
1
1
Bit 1  
1
Bit 0  
Bit 0  
1
Read:  
Bit 7  
Write:  
Bit 4  
1
Reset:  
1
Figure 17-7. TIMB Counter Modulo Registers (TBMODH and TBMODL)  
NOTE  
Reset the TIMB counter before writing to the TIMB counter modulo registers.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
246  
Freescale Semiconductor  
           
I/O Registers  
17.7.4 TIMB Channel Status and Control Registers  
Each of the TIMB channel status and control registers:  
Flags input captures and output compares  
Enables input capture and output compare interrupts  
Selects input capture, output compare, or PWM operation  
Selects high, low, or toggling output on output compare  
Selects rising edge, falling edge, or any edge as the active input capture trigger  
Selects output toggling on TIMB overflow  
Selects 0 percent and 100 percent PWM duty cycle  
Selects buffered or unbuffered output compare/PWM operation  
Register Name and Address:  
Bit 7  
TBSC0 — $0056  
5
6
CH0IE  
0
4
3
ELS0B  
0
2
ELS0A  
0
1
TOV0  
0
Bit 0  
CH0MAX  
0
Read:  
Write:  
Reset:  
CH0F  
MS0B  
0
MS0A  
0
0
0
Register Name and Address:  
Bit 7  
TBSC1 — $0059  
6
5
0
4
3
ELS1B  
0
2
ELS1A  
0
1
TOV1  
0
Bit 0  
CH1MAX  
0
Read:  
Write:  
Reset:  
CH1F  
CH1IE  
MS1A  
0
0
0
R
0
0
R
= Reserved  
Figure 17-8. TIMB Channel Status and Control Registers (TBSC0–TBSC1)  
CHxF — Channel x Flag  
When channel x is an input capture channel, this read/write bit is set when an active edge occurs on  
the channel x pin. When channel x is an output compare channel, CHxF is set when the value in the  
TIMB counter registers matches the value in the TIMB channel x registers.  
When CHxIE = 1, clear CHxF by reading TIMB channel x status and control register with CHxF set,  
and then writing a 0 to CHxF. If another interrupt request occurs before the clearing sequence is  
complete, then writing 0 to CHxF has no effect. Therefore, an interrupt request cannot be lost due to  
inadvertent clearing of CHxF.  
Reset clears the CHxF bit. Writing a 1 to CHxF has no effect.  
1 = Input capture or output compare on channel x  
0 = No input capture or output compare on channel x  
CHxIE — Channel x Interrupt Enable Bit  
This read/write bit enables TIMB CPU interrupts on channel x.  
Reset clears the CHxIE bit.  
1 = Channel x CPU interrupt requests enabled  
0 = Channel x CPU interrupt requests disabled  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
247  
     
Timer Interface B (TIMB)  
MSxB — Mode Select Bit B  
This read/write bit selects buffered output compare/PWM operation. MSxB exists only in the TIMB  
channel 0.  
Setting MS0B disables the channel 1 status and control register and reverts TCH1B to  
general-purpose I/O.  
Reset clears the MSxB bit.  
1 = Buffered output compare/PWM operation enabled  
0 = Buffered output compare/PWM operation disabled  
MSxA — Mode Select Bit A  
When ELSxB:A 00, this read/write bit selects either input capture operation or unbuffered output  
compare/PWM operation. See Table 17-2.  
1 = Unbuffered output compare/PWM operation  
0 = Input capture operation  
When ELSxB:A = 00, this read/write bit selects the initial output level of the TCHx pin once PWM, input  
capture, or output compare operation is enabled. See Table 17-2. Reset clears the MSxA bit.  
1 = Initial output level low  
0 = Initial output level high  
NOTE  
Before changing a channel function by writing to the MSxB or MSxA bit, set  
the TSTOP and TRST bits in the TIMB status and control register (TBSC).  
ELSxB and ELSxA — Edge/Level Select Bits  
When channel x is an input capture channel, these read/write bits control the active edge-sensing logic  
on channel x.  
When channel x is an output compare channel, ELSxB and ELSxA control the channel x output  
behavior when an output compare occurs.  
When ELSxB and ELSxA are both clear, channel x is not connected to port E, and pin PTEx/TCHxB  
is available as a general-purpose I/O pin. However, channel x is at a state determined by these bits  
and becomes transparent to the respective pin when PWM, input capture, or output compare mode is  
enabled. Table 17-2 shows how ELSxB and ELSxA work. Reset clears the ELSxB and ELSxA bits.  
NOTE  
Before enabling a TIMB channel register for input capture operation, make  
sure that the PTEx/TBCHx pin is stable for at least two bus clocks.  
TOVx — Toggle-On-Overflow Bit  
When channel x is an output compare channel, this read/write bit controls the behavior of the channel  
x output when the TIMB counter overflows. When channel x is an input capture channel, TOVx has no  
effect. Reset clears the TOVx bit.  
1 = Channel x pin toggles on TIMB counter overflow.  
0 = Channel x pin does not toggle on TIMB counter overflow.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
248  
Freescale Semiconductor  
I/O Registers  
Table 17-2. Mode, Edge, and Level Selection  
MSxB:MSxA  
ELSxB:ELSxA  
Mode  
Configuration  
Pin under port control; initialize timer output level high  
X0  
X1  
00  
00  
00  
01  
01  
01  
01  
1X  
1X  
00  
00  
01  
10  
11  
00  
01  
10  
11  
01  
10  
Output preset  
Pin under port control; initialize timer output level low  
Capture on rising edge only  
Capture on falling edge only  
Capture on rising or falling edge  
Softare compare only  
Input capture  
Toggle output on compare  
Clear output on compare  
Output compare  
or PWM  
Set output on compare  
Buffered output  
compare  
or buffered  
PWM  
Toggle output on compare  
Clear output on compare  
1X  
11  
Set output on compare  
NOTE  
When TOVx is set, a TIMB counter overflow takes precedence over a  
channel x output compare if both occur at the same time.  
CHxMAX — Channel x Maximum Duty Cycle Bit  
When the TOVx is 1 and clear output on compare is selected, setting the CHxMAX bit forces the duty  
cycle of buffered and unbuffered PWM signals to 100 percent. As Figure 17-9 shows, CHxMAX bit  
takes effect in the cycle after it is set or cleared. The output stays at 100 percent duty cycle level until  
the cycle after CHxMAX is cleared.  
OVERFLOW  
OVERFLOW  
OVERFLOW  
OVERFLOW  
OVERFLOW  
PERIOD  
PTEx/TCHx  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
OUTPUT  
COMPARE  
CHxMAX  
TOVx  
Figure 17-9. CHxMAX Latency  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
249  
   
Timer Interface B (TIMB)  
17.7.5 TIMB Channel Registers  
These read/write registers contain the captured TIMB counter value of the input capture function or the  
output compare value of the output compare function. The state of the TIMB channel registers after reset  
is unknown.  
In input capture mode (MSxB–MSxA = 0:0), reading the high byte of the TIMB channel x registers  
(TBCHxH) inhibits input captures until the low byte (TBCHxL) is read.  
In output compare mode (MSxB–MSxA 0:0), writing to the high byte of the TIMB channel x registers  
(TBCHxH) inhibits output compares until the low byte (TBCHxL) is written.  
Register Name and Address:  
Bit 7  
TBCH0H — $0057  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Bit 15  
Write:  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Reset:  
Indeterminate after reset  
TBCH0L — $0058  
Register Name and Address:  
Bit 7  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
TBCH1H — $005A  
Register Name and Address:  
Bit 7  
6
5
4
3
2
1
Bit 0  
Bit 8  
Read:  
Bit 15  
Write:  
Bit 14  
Bit 13  
Bit 12  
Bit 11  
Bit 10  
Bit 9  
Reset:  
Indeterminate after reset  
TBCH1L — $005B  
Register Name and Address:  
Bit 7  
6
5
4
3
2
1
Bit 0  
Bit 0  
Read:  
Bit 7  
Write:  
Bit 6  
Bit 5  
Bit 4  
Bit 3  
Bit 2  
Bit 1  
Reset:  
Indeterminate after reset  
Figure 17-10. TIMB Channel Registers (TBCH0H/L–TBCH1H/L)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
250  
Freescale Semiconductor  
     
Chapter 18  
Development Support  
18.1 Introduction  
This section describes the break module, the monitor read-only memory (MON), and the monitor mode  
entry methods.  
18.2 Break Module (BRK)  
The break module (BRK) can generate a break interrupt that stops normal program flow at a defined  
address to enter a background program. Features include:  
Accessible input/output (I/O) registers during the break interrupt  
Central processor unit (CPU) generated break interrupts  
Software-generated break interrupts  
Computer operating properly (COP) disabling during break interrupts  
18.2.1 Functional Description  
When the internal address bus matches the value written in the break address registers, the break module  
issues a breakpoint signal to the CPU. The CPU then loads the instruction register with a software  
interrupt instruction (SWI) after completion of the current CPU instruction. The program counter vectors  
to $FFFC and $FFFD ($FEFC and $FEFD in monitor mode).  
These events can cause a break interrupt to occur:  
A CPU-generated address (the address in the program counter) matches the contents of the break  
address registers.  
Software writes a logic 1 to the BRKA bit in the break status and control register.  
When a CPU-generated address matches the contents of the break address registers, the break interrupt  
begins after the CPU completes its current instruction. A return-from-interrupt instruction (RTI) in the  
break routine ends the break interrupt and returns the microcontroller unit (MCU) to normal operation.  
Figure 18-1 shows the structure of the break module.  
18.2.1.1 Flag Protection During Break Interrupts  
The BCFE bit in the SIM break flag control register (SBFCR) enables software to clear status bits during  
the break state.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
251  
         
Development Support  
IAB15–IAB8  
BREAK ADDRESS REGISTER HIGH  
8-BIT COMPARATOR  
IAB15–IAB0  
CONTROL  
BREAK  
8-BIT COMPARATOR  
BREAK ADDRESS REGISTER LOW  
IAB7–IAB0  
Figure 18-1. Break Module Block Diagram  
Addr.  
Register Name  
Bit 7  
6
5
4
3
2
1
BW  
0
Bit 0  
Read:  
SIM Break Status Register  
R
R
R
R
R
R
R
$FE00  
(SBSR) Write:  
Reset:  
Read:  
SIM Break Flag Control  
BCFE  
0
R
R
R
R
R
R
R
$FE03  
$FE0C  
$FE0D  
$FE0E  
Register (SBFCR) Write:  
Reset:  
Read:  
Break Address Register High  
Bit 15  
0
14  
13  
0
12  
0
11  
0
10  
0
9
0
1
Bit 8  
0
(BRKH) Write:  
Reset:  
Read:  
0
Break Address Register Low  
Bit 7  
0
6
0
5
4
3
2
Bit 0  
(BRKL) Write:  
Reset:  
Read:  
0
0
0
0
0
0
0
0
0
0
0
0
Break Status and Control  
BRKE  
0
BRKA  
Register (BRKSCR) Write:  
Reset:  
0
0
0
0
0
0
0
Note: Writing a 0 clears BW.  
= Unimplemented  
R
= Reserved  
Figure 18-2. I/O Register Summary  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
252  
Freescale Semiconductor  
 
Break Module (BRK)  
18.2.1.2 CPU During Break Interrupts  
The CPU starts a break interrupt by:  
Loading the instruction register with the SWI instruction  
Loading the program counter with $FFFC and $FFFD ($FEFC and $FEFD in monitor mode)  
The break interrupt begins after completion of the CPU instruction in progress. If the break address  
register match occurs on the last cycle of a CPU instruction, the break interrupt begins immediately.  
18.2.1.3 TIM1 and TIM2 During Break Interrupts  
A break interrupt stops the timer counters.  
18.2.1.4 COP During Break Interrupts  
The COP is disabled during a break interrupt when VTST is present on the RST pin.  
18.2.2 Low-Power Modes  
The WAIT and STOP instructions put the MCU in low power- consumption standby modes.  
18.2.2.1 Wait Mode  
If enabled, the break module is active in wait mode. In the break routine, the user can subtract one from  
the return address on the stack if SBSW is set. Clear the BW bit by writing logic 0 to it.  
18.2.2.2 Stop Mode  
The break module is inactive in stop mode. The STOP instruction does not affect break module register  
states.  
18.2.3 Break Module Registers  
These registers control and monitor operation of the break module:  
Break status and control register (BRKSCR)  
Break address register high (BRKH)  
Break address register low (BRKL)  
SIM break status register (SBSR)  
SIM break flag control register (SBFCR)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
253  
             
Development Support  
18.2.3.1 Break Status and Control Register  
The break status and control register (BRKSCR) contains break module enable and status bits.  
Address: $FE0E  
Bit 7  
BRKE  
0
6
BRKA  
0
5
0
4
0
3
0
2
0
1
0
Bit 0  
0
Read:  
Write:  
Reset:  
0
0
0
0
0
0
= Unimplemented  
Figure 18-3. Break Status and Control Register (BRKSCR)  
BRKE — Break Enable Bit  
This read/write bit enables breaks on break address register matches. Clear BRKE by writing a logic  
0 to bit 7. Reset clears the BRKE bit.  
1 = Breaks enabled on 16-bit address match  
0 = Breaks disabled on 16-bit address match  
BRKA — Break Active Bit  
This read/write status and control bit is set when a break address match occurs. Writing a logic 1 to  
BRKA generates a break interrupt. Clear BRKA by writing a logic 0 to it before exiting the break routine.  
Reset clears the BRKA bit.  
1 = When read, break address match  
0 = When read, no break address match  
18.2.3.2 Break Address Registers  
The break address registers (BRKH and BRKL) contain the high and low bytes of the desired breakpoint  
address. Reset clears the break address registers.  
Address: $FE0C  
Bit 7  
Bit 15  
0
6
14  
0
5
13  
0
4
12  
0
3
11  
0
2
10  
0
1
9
0
Bit 0  
Bit 8  
0
Read:  
Write:  
Reset:  
Figure 18-4. Break Address Register High (BRKH)  
Address: $FE0D  
Bit 7  
6
6
0
5
5
0
4
4
0
3
3
0
2
2
0
1
1
0
Bit 0  
Bit 0  
0
Read:  
Bit 7  
Write:  
Reset:  
0
Figure 18-5. Break Address Register Low (BRKL)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
254  
Freescale Semiconductor  
               
Monitor ROM (MON)  
18.2.3.3 Break Status Register  
The break status register (SBSR) contains a flag to indicate that a break caused an exit from wait mode.  
The flag is useful in applications requiring a return to wait mode after exiting from a break interrupt.  
Address:  
$FE00  
Bit 7  
6
5
4
3
2
1
BW  
0
Bit 0  
R
Read:  
Write:  
Reset:  
R
R
R
R
R
R
Figure 18-6. SIM Break Status Register (SBSR)  
BW — Break Wait Bit  
This read/write bit is set when a break interrupt causes an exit from wait mode. Clear BW by writing a  
logic 0 to it. Reset clears BW.  
1 = Break interrupt during wait mode  
0 = No break interrupt during wait mode  
BW can be read within the break interrupt routine. The user can modify the return address on the stack  
by subtracting 1 from it.  
18.2.3.4 Break Flag Control Register  
The break flag control register (SBFCR) contains a bit that enables software to clear status bits while the  
MCU is in a break state.  
Address:  
$FE03  
Bit 7  
6
5
4
3
2
1
Bit 0  
R
Read:  
Write:  
Reset:  
BCFE  
R
R
R
R
R
R
0
R
= Reserved  
Figure 18-7. SIM Break Flag Control Register (SBFCR)  
BCFE — Break Clear Flag Enable Bit  
This read/write bit enables software to clear status bits by accessing status registers while the MCU is  
in a break state. To clear status bits during the break state, the BCFE bit must be set.  
1 = Status bits clearable during break  
0 = Status bits not clearable during break  
18.3 Monitor ROM (MON)  
The monitor ROM (MON) allows complete testing of the microcontroller unit (MCU) through a single-wire  
interface with a host computer. Monitor mode entry can be achieved without the use of VTST as long as  
vector addresses $FFFE and $FFFF are blank, thus reducing the hardware requirements for in-circuit  
programming.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
255  
           
Development Support  
Features include:  
Normal user-mode pin functionality  
One pin dedicated to serial communication between monitor ROM and host computer  
Standard mark/space non-return-to-zero (NRZ) communication with host computer  
4800 baud–28.8 Kbaud communication with host computer  
Execution of code in random-access memory (RAM) or ROM  
FLASH programming  
18.3.1 Functional Description  
The monitor ROM receives and executes commands from a host computer. Figure 18-8 shows a sample  
circuit used to enter monitor mode and communicate with a host computer via a standard RS-232  
interface.  
Simple monitor commands can access any memory address. In monitor mode, the MCU can execute  
host-computer code in RAM while all MCU pins retain normal operating mode functions. All  
communication between the host computer and the MCU is through the PTA0 pin. A level-shifting and  
multiplexing interface is required between PTA0 and the host computer. PTA0 is used in a wired-OR  
configuration and requires a pullup resistor.  
18.3.1.1 Entering Monitor Mode  
There are two methods for entering monitor:  
The first is the traditional M68HC08 method where VDD + VHI is applied to IRQ1 and the mode pins  
are configured appropriately.  
A second method, intended for in-circuit programming applications, will force entry into monitor  
mode without requiring high voltage on the IRQ1 pin when the reset vector locations of the FLASH  
are erased ($FF).  
NOTE  
For both methods, holding the PTC2 pin low when entering monitor mode  
causes a bypass of a divide-by-two stage at the oscillator. The CGMOUT  
frequency is equal to the CGMXCLK frequency, and the OSC1 input  
directly generates internal bus clocks. In this case, the OSC1 signal must  
have a 50 percent duty cycle at maximum bus frequency.  
Table 18-1 is a summary of the differences between user mode and monitor mode.  
Table 18-1. Mode Differences  
Functions  
Modes  
Rest  
Vector High  
Reset  
Vector Low  
Break  
Vector High  
Break  
Vector Low  
SWI  
Vector High  
SWI  
Vector Low  
COP  
User  
Enabled  
$FFFE  
$FEFE  
$FFFF  
$FEFF  
$FFFC  
$FEFC  
$FFFD  
$FEFD  
$FFFC  
$FEFC  
$FFFD  
$FEFD  
(1)  
Monitor  
Disabled  
1. If the high voltage (V + V ) is removed from the IRQ1 pin or the RST pin, the SIM asserts its COP enable output. The  
DD  
HI  
COP is a mask option enabled or disabled by the COPD bit in the configuration register.  
18.3.1.2 Normal Monitor Mode  
Table 18-2 shows the pin conditions for entering monitor mode.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
256  
Freescale Semiconductor  
       
Monitor ROM (MON)  
VDD  
10 kΩ  
MC68HC908MR16/  
MC68HC908MR32  
S1  
RST  
0.1 µF  
VHI  
10 kΩ  
IRQ  
VDDA  
VDDA  
1
20  
MC145407  
0.1 µF  
+
+
+
+
VDDAD  
10 µF  
10 µF  
VDDAD  
3
4
18  
17  
0.1 µF  
VREFH  
VDD  
10 µF  
10 µF  
VREFH  
2
19  
0.1 µF  
CGMXFC  
0.02 µF  
DB-25  
2
5
6
16  
15  
3
7
OSC1  
OSC2  
X1  
4.9152 MHz  
20 pF  
VDD  
10 MΩ  
VREFL  
VSSAD  
VSSA  
20 pF  
1
2
6
4
14  
3
MC74HC125  
PWMGND  
VSS  
5
VDD  
VDD  
0.1 µF  
VDD  
7
VDD  
10 kΩ  
10 kΩ  
PTA0  
PTA7  
PTC2  
A
B
S3  
VDD  
VDD  
10 kΩ  
10 kΩ  
S2 Position A — Bus clock = CGMXCLK ÷ 4 or CGMVCLK ÷ 4  
A
PTC3  
PTC4  
S2 Position B — Bus clock = CGMXCLK ÷ 2  
S3 Position A — Parallel communication  
S3 Position B — Serial communication  
S2  
B
Figure 18-8. Monitor Mode Circuit  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
257  
 
Table 18-2. Monitor Mode Signal Requirements and Options  
For Serial  
Communication(2)  
External  
Clock(1)  
RESET  
(S1)  
$FFFE  
/$FFFF  
PTC2  
(S2)  
Bus  
Frequency  
IRQ  
PLL PTC3 PTC4  
CGMOUT  
COP  
Comment  
Baud  
PTA7  
(S3)  
PTA0  
Rate(3) (4)  
X
GND  
VDD  
X
X
X
X
1
X
0
X
0
X
0
0
Disabled  
Disabled  
X
1
X
0
0
No operation until reset goes high  
9600  
PTC3 and PTC2 voltages only required if  
IRQ = VTST; PTC2 determines frequency  
4.9152  
MHz  
4.9152  
MHz  
2.4576  
MHz  
VTST  
or  
VTST  
OFF  
X
1
1
0
1
DNA  
9600  
DNA  
divider  
VDD  
PTC3 and PTC2 voltages only required if  
IRQ = VTST; PTC2 determines frequency  
9.8304  
MHz  
4.9152  
MHz  
2.4576  
MHz  
VTST  
or  
VTST  
X
OFF  
OFF  
OFF  
1
X
X
0
X
X
1
X
X
Disabled  
Disabled  
Enabled  
X
divider  
1
0
1
9600  
DNA  
$FFFF  
Blank  
9.8304  
MHz  
4.9152  
MHz  
2.4576  
MHz  
VDD  
VDD  
VDD  
External frequency always divided by 4  
X
$FFFF  
Blank  
Enters user mode — will encounter an  
illegal address reset  
VTST  
X
X
X
X
X
X
or  
GND  
VDD  
VDD  
Non-$FF  
Programmed  
or  
VTST  
OFF  
X
X
X
Enabled  
Enters user mode  
or  
GND  
1. External clock is derived by a 32.768 kHz crystal or a 4.9152/9.8304 MHz off-chip oscillator.  
2. DNA = does not apply, X = don’t care  
3. PAT0 = 1 if serial communication; PTA0 = X if parallel communication  
4. PTA7 = 0 serial, PTA7 = 1 parallel communication for security code entry  
 
Monitor ROM (MON)  
Enter monitor mode by either:  
Executing a software interrupt instruction (SWI) or  
Applying a logic 0 and then a logic 1 to the RST pin  
Once out of reset, the MCU waits for the host to send eight security bytes. After receiving the security  
bytes, the MCU sends a break signal (10 consecutive logic 0s) to the host computer, indicating that it is  
ready to receive a command. The break signal also provides a timing reference to allow the host to  
determine the necessary baud rate.  
Monitor mode uses alternate vectors for reset and SWI. The alternate vectors are in the $FE page instead  
of the $FF page and allow code execution from the internal monitor firmware instead of user code. The  
computer operating properly (COP) module is disabled in monitor mode as long as VHI is applied to either  
the IRQ pin or the RST pin. (See Chapter 14 System Integration Module (SIM) for more information on  
modes of operation.)  
18.3.1.3 Forced Monitor Mode  
If the voltage applied to the IRQ1 is less than VDD + VHI the MCU will come out of reset in user mode. The  
MENRST module is monitoring the reset vector fetches and will assert an internal reset if it detects that  
the reset vectors are erased ($FF). When the MCU comes out of reset, it is forced into monitor mode  
without requiring high voltage on the IRQ1 pin.  
The COP module is disabled in forced monitor mode. Any reset other than a POR reset will automatically  
force the MCU to come back to the forced monitor mode.  
18.3.1.4 Data Format  
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.  
NEXT  
START  
BIT  
START  
BIT  
STOP  
BIT  
BIT 0  
BIT 1  
BIT 2  
BIT 3  
BIT 4  
BIT 5  
BIT 6  
BIT 7  
Figure 18-9. Monitor Data Format  
NEXT  
START  
BIT  
START  
BIT  
STOP  
BIT  
$A5  
BIT 0  
BIT 1  
BIT 1  
BIT 2  
BIT 2  
BIT 3  
BIT 3  
BIT 4  
BIT 4  
BIT 5  
BIT 5  
BIT 6  
BIT 6  
BIT 7  
BIT 7  
STOP  
BIT  
START  
BIT  
NEXT  
START  
BIT  
BREAK  
BIT 0  
Figure 18-10. Sample Monitor Waveforms  
The data transmit and receive rate can be anywhere from 4800 baud to 28.8 Kbaud. Transmit and receive  
baud rates must be identical.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
259  
       
Development Support  
18.3.1.5 Echoing  
As shown in Figure 18-11, the monitor ROM immediately echoes each received byte back to the PTA0  
pin for error checking.  
SENT TO  
MONITOR  
READ  
READ  
ADDR. HIGH ADDR. HIGH ADDR. LOW ADDR. LOW  
DATA  
ECHO  
RESULT  
Figure 18-11. Read Transaction  
Any result of a command appears after the echo of the last byte of the command.  
18.3.1.6 Break Signal  
A start bit followed by nine low bits is a break signal. See Figure 18-12. When the monitor receives a break  
signal, it drives the PTA0 pin high for the duration of two bits before echoing the break signal.  
MISSING STOP BIT  
2--STOP-BIT DELAY BEFORE ZERO ECHO  
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
Figure 18-12. Break Transaction  
18.3.1.7 Commands  
The monitor ROM uses these commands (see Table 18-3Table 18-8):  
READ, read memory  
WRITE, write memory  
IREAD, indexed read  
IWRITE, indexed write  
READSP, read stack pointer  
RUN, run user program  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
260  
Freescale Semiconductor  
         
Monitor ROM (MON)  
Table 18-3. READ (Read Memory) Command  
Description  
Operand  
Read byte from memory  
2-byte address in high-byte:low-byte order  
Returns contents of specified address  
$4A  
Data Returned  
Opcode  
Command Sequence  
SENT TO MONITOR  
ADDRESS ADDRESS ADDRESS  
HIGH HIGH LOW  
ADDRESS  
LOW  
READ  
READ  
DATA  
ECHO  
RETURN  
Table 18-4. WRITE (Write Memory) Command  
Description  
Operand  
Write byte to memory  
2-byte address in high-byte:low-byte order; low byte followed by data byte  
Data Returned  
Opcode  
None  
$49  
Command Sequence  
FROM HOST  
ADDRESS ADDRESS ADDRESS ADDRESS  
HIGH  
DATA  
DATA  
WRITE  
ECHO  
WRITE  
HIGH  
LOW  
LOW  
Table 18-5. IREAD (Indexed Read) Command  
Description  
Operand  
Read next 2 bytes in memory from last address accessed  
2-byte address in high byte:low byte order  
Data Returned  
Opcode  
Returns contents of next two addresses  
$1A  
Command Sequence  
FROM HOST  
IREAD  
IREAD  
DATA  
DATA  
ECHO  
RETURN  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
261  
 
Development Support  
Table 18-6. IWRITE (Indexed Write) Command  
Description  
Write to last address accessed + 1  
Operand  
Data Returned  
Opcode  
Single data byte  
None  
$19  
Command Sequence  
FROM HOST  
DATA  
DATA  
IWRITE  
IWRITE  
ECHO  
A sequence of IREAD or IWRITE commands can access a block of memory sequentially over the full  
64-Kbyte memory map.  
Table 18-7. READSP (Read Stack Pointer) Command  
Description  
Operand  
Reads stack pointer  
None  
Data Returned  
Opcode  
Returns incremented stack pointer value (SP + 1) in high-byte:low-byte order  
$0C  
Command Sequence  
FROM HOST  
SP  
HIGH  
SP  
LOW  
READSP  
READSP  
ECHO  
RETURN  
Table 18-8. RUN (Run User Program) Command  
Description  
Operand  
Executes PULH and RTI instructions  
None  
Data Returned  
Opcode  
None  
$28  
Command Sequence  
FROM HOST  
RUN  
RUN  
ECHO  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
262  
Freescale Semiconductor  
 
Monitor ROM (MON)  
18.3.1.8 Baud Rate  
With a 4.9152-MHz crystal and the PTC2 pin at logic 1 during reset, data is transferred between the  
monitor and host at 4800 baud. If the PTC2 pin is at logic 0 during reset, the monitor baud rate is 9600.  
See Table 18-9.  
Table 18-9. Monitor Baud Rate Selection  
VCO Frequency Multiplier (N)  
1
2
3
4
5
6
Monitor baud rate  
4800  
9600  
14,400  
19,200  
24,000  
28,800  
18.3.2 Security  
A security feature discourages unauthorized reading of FLASH locations while in monitor mode. The host  
can bypass the security feature at monitor mode entry by sending eight security bytes that match the  
bytes at locations $FFF6–$FFFD. Locations $FFF6–$FFFD contain user-defined data.  
NOTE  
Do not leave locations $FFF6–$FFFD blank. For security reasons, program  
locations $FFF6–$FFFD even if they are not used for vectors.  
During monitor mode entry, the MCU waits after the power-on reset for the host to send the eight security  
bytes on pin PTA0. If the received bytes match those at locations $FFF6–$FFFD, the host bypasses the  
security feature and can read all FLASH locations and execute code from FLASH. Security remains  
bypassed until a power-on reset occurs. If the reset was not a power-on reset, security remains bypassed  
and security code entry is not required. (See Figure 18-13.)  
Upon power-on reset, if the received bytes of the security code do not match the data at locations  
$FFF6–$FFFD, the host fails to bypass the security feature. The MCU remains in monitor mode, but  
reading a FLASH location returns an invalid value and trying to execute code from FLASH causes an  
illegal address reset. After receiving the eight security bytes from the host, the MCU transmits a break  
character, signifying that it is ready to receive a command.  
NOTE  
The MCU does not transmit a break character until after the host sends the  
eight security bytes.  
To determine whether the security code entered is correct, check to see if bit 6 of RAM address $60 is  
set. If it is, then the correct security code has been entered and FLASH can be accessed.  
If the security sequence fails, the device can be reset (via power-pin reset only) and brought up in monitor  
mode to attempt another entry. After failing the security sequence, the FLASH mode can also be bulk  
erased by executing an erase routine that was downloaded into internal RAM. The bulk erase operation  
clears the security code locations so that all eight security bytes become $FF.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
263  
       
Development Support  
VDD  
RST  
PA7  
4096 + 32 CGMXCLK CYCLES  
24 BUS CYCLES  
256 BUS CYCLES (MINIMUM)  
FROM HOST  
PA0  
1
1
3
1
3
2
1
FROM MCU  
NOTES:  
1 = Echo delay, 2 bit times  
2 = Data return delay, 2 bit times  
3 = Wait 1 bit time before sending next byte.  
Figure 18-13. Monitor Mode Entry Timing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
264  
Freescale Semiconductor  
 
Chapter 19  
Electrical Specifications  
19.1 Introduction  
This section contains electrical and timing specifications.  
19.2 Absolute Maximum Ratings  
Maximum ratings are the extreme limits to which the microcontroller unit (MCU) can be exposed without  
permanently damaging it.  
NOTE  
This device is not guaranteed to operate properly at the maximum ratings. For guaranteed operating  
conditions, refer to 19.5 DC Electrical Characteristics.  
(1)  
Symbol  
Value  
Unit  
Characteristic  
V
Supply voltage  
Input voltage  
–0.3 to +6.0  
V
DD  
V
–0.3 to  
SS  
V
V
In  
V
+0.3  
DD  
V
V
+ 4 maximum  
25  
Input high voltage  
V
HI  
DD  
Maximum current per pin excluding V and V  
I
mA  
°C  
DD  
SS  
T
Storage temperature  
–55 to +150  
100  
STG  
Maximum current out of V  
I
mA  
mA  
SS  
MVSS  
Maximum current into V  
I
100  
DD  
MVDD  
1. Voltages referenced to V  
.
SS  
NOTE  
This device contains circuitry to protect the inputs against damage due to  
high static voltages or electric fields; however, it is advised that normal  
precautions be taken to avoid application of any voltage higher than  
maximum-rated voltages to this high-impedance circuit. For proper  
operation, it is recommended that VIn and VOut be constrained to the range  
VSS (VIn or VOut) VDD. Reliability of operation is enhanced if unused  
inputs are connected to an appropriate logic voltage level (for example,  
either VSS or VDD).  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
265  
       
Electrical Specifications  
19.3 Functional Operating Range  
Characteristic  
Symbol  
Value  
Unit  
°C  
(1)  
Operating temperature range  
T
–40 to 85  
–40 to 105  
MC68HC908MR24CFU  
MC68HC908MR24VFU  
A
V
Operating voltage range  
5.0 10%  
V
DD  
1. See Freescale representative for temperature availability.  
C = Extended temperature range (–40°C to +85°C)  
V = Automotive temperature range (–40°C to +105°C)  
19.4 Thermal Characteristics  
Characteristic  
Symbol  
Value  
76  
Unit  
°C/W  
W
Thermal resistance,  
64-pin QFP  
θ
JA  
P
I/O pin power dissipation  
User determined  
I/O  
P = (I x V ) + P  
I/O  
=
D
DD  
DD  
(1)  
P
W
Power dissipation  
D
K/(T + 273°C)  
J
P x (T + 273°C)  
D
A
(2)  
K
W/°C  
Constant  
2
+ P x θ  
D
JA  
T
T + (P x θ  
)
Average junction temperature  
°C  
J
A
D
JA  
T
Maximum junction temperature  
125  
°C  
JM  
1. Power dissipation is a function of temperature.  
2. K is a constant unique to the device. K can be determined for a known T and measured P With this value of K, P and  
A
D.  
D
T can be determined for any value of T .  
J
A
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
266  
Freescale Semiconductor  
   
DC Electrical Characteristics  
19.5 DC Electrical Characteristics  
(1)  
(2)  
Symbol  
Min  
–0.8  
Max  
Unit  
Characteristic  
Typ  
Output high voltage  
V
V
V
OH  
DD  
(I  
= –2.0 mA) all I/O pins  
Load  
Output low voltage  
(I = 1.6 mA) all I/O pins  
V
0.4  
V
OL  
Load  
PWM pin output source current  
(V = V –0.8 V)  
I
–7  
20  
mA  
OH  
OH  
DD  
PWM pin output sink current (V = 0.8 V)  
I
mA  
V
OL  
OL  
V
0.7 x V  
V
Input high voltage, all ports, IRQs, RESET, OSC1  
Input low voltage, all ports, IRQs, RESET, OSC1  
IH  
DD  
DD  
V
V
0.3 x V  
DD  
V
IL  
SS  
V
supply current  
DD  
(3)  
Run  
Wait  
30  
12  
700  
mA  
mA  
µA  
I
DD  
(4)  
(5)  
Stop  
I
I
I/O ports high-impedance leakage current  
Input current (input only pins)  
10  
1
µA  
IL  
In  
µA  
C
Capacitance  
Ports (as input or output)  
12  
8
Out  
pF  
C
In  
(6)  
V
V
4.0  
40  
4.35  
90  
4.65  
150  
V
Low-voltage inhibit reset  
LVR1  
LVH1  
Low-voltage reset/recover hysteresis  
mV  
Low-voltage inhibit reset recovery  
V
4.04  
4.5  
4.75  
V
REC1  
(V  
= V  
+ V  
)
REC1  
LVR1  
LVH1  
V
Low-voltage inhibit reset  
3.85  
150  
4.15  
210  
4.45  
250  
V
LVR2  
V
Low-voltage reset/recover hysteresis  
Low-voltage inhibit reset recovery  
mV  
LVH2  
V
4.0  
4.4  
4.6  
V
REC2  
(V  
= V  
+ V  
)
REC2  
LVR2  
LVH2  
(7)  
V
0
100  
mV  
V/ms  
V
POR re-arm voltage  
POR  
(8)  
R
0.035  
0
POR rise time ramp rate  
POR  
(9)  
V
700  
800  
8.0  
POR reset voltage  
PORRST  
V
V
+ 2.5  
Monitor mode entry voltage (on IRQ)  
V
Hi  
DD  
1. V = 5.0 Vdc 10%, V = 0 Vdc, T = T to T , unless otherwise noted.  
DD  
SS  
A
L
H
2. Typical values reflect average measurements at midpoint of voltage range, 25°C only.  
3. Run (operating) I measured using external square wave clock source (f = 8.2 MHz). All inputs 0.2 V from rail; no dc  
DD  
OSC  
loads; less than 100 pF on all outputs. C = 20 pF on OSC2; all ports configured as inputs; OSC2 capacitance linearly  
L
affects run I ; measured with all modules enabled  
DD  
4. Wait I measured using external square wave clock source (f  
= 8.2 MHz); all inputs 0.2 V from rail; no dc loads; less  
OSC  
DD  
than 100 pF on all outputs. C = 20 pF on OSC2; all ports configured as inputs; OSC2 capacitance linearly affects wait I  
;
L
DD  
measured with PLL and LVI enabled.  
5. Stop I measured with PLL and LVI disengaged, OCS1 grounded, no port pins sourcing current. It is measured through  
DD  
combination of V , V  
, and V  
.
DD  
DDAD  
DDA  
6. The low-voltage inhibit reset is software selectable. Refer to Chapter 9 Low-Voltage Inhibit (LVI).  
7. Maximum is highest voltage that POR is guaranteed.  
8. If minimum V is not reached before the internal POR is released, RST must be driven low externally until minimum V  
DD  
DD  
is reached.  
9. Maximum is highest voltage that POR is possible.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
267  
   
Electrical Specifications  
19.6 FLASH Memory Characteristics  
Characteristic  
RAM data retention voltage  
Symbol  
Min  
1.3  
1
Typ  
Max  
Unit  
V
V
RDR  
FLASH program bus clock frequency  
FLASH read bus clock frequency  
MHz  
Hz  
(1)  
0
8 M  
f
Read  
FLASH page erase time  
<1 K cycles  
>1 K cycles  
t
0.9  
3.6  
1
4
1.1  
5.5  
ms  
Erase  
t
FLASH mass erase time  
4
10  
5
40  
ms  
µs  
µs  
µs  
µs  
µs  
µs  
MErase  
t
FLASH PGM/ERASE to HVEN setup time  
FLASH high-voltage hold time  
FLASH high-voltage hold time (mass erase)  
FLASH program hold time  
NVS  
t
NVH  
t
100  
5
NVHL  
t
PGS  
t
FLASH program time  
30  
1
PROG  
(2)  
FLASH return to read time  
t
RCV  
(3)  
FLASH cumulative program HV period  
10 k  
15  
4
ms  
t
HV  
(4)  
100 k  
100  
Cycles  
Years  
FLASH endurance  
(5)  
FLASH data retention time  
1. f  
2. t  
is defined as the frequency range for which the FLASH memory can be read.  
is defined as the time it needs before the FLASH can be read after turning off the high voltage charge pump, by  
Read  
RCV  
clearing HVEN to 0.  
3. t is defined as the cumulative high voltage programming time to the same row before next erase.  
HV  
HV  
t
must satisfy this condition: t  
+ t  
+ t  
+ (t  
x 32) t maximum.  
NVS  
NVH  
PGS  
PROG HV  
4. Typical endurance was evaluated for this product family. For additional information on how Freescale defines Typical  
Endurance, please refer to Engineering Bulletin EB619.  
5. Typical data retention values are based on intrinsic capability of the technology measured at high temperature and de-rated  
to 25°C using the Arrhenius equation. For additional information on how Freescale defines Typical Data Retention, please  
refer to Engineering Bulletin EB618.  
19.7 Control Timing  
(1)  
Symbol  
Min  
Max  
Unit  
Characteristic  
(2)  
Frequency of operation  
Crystal option  
1
f
8
32.8  
MHz  
OSC  
(4)  
(3)  
dc  
External clock option  
f
Internal operating frequency  
RESET input pulse width low  
8.2  
MHz  
ns  
OP  
(5)  
t
50  
IRL  
1. V = 5.0 Vdc 10%, V = 0 Vdc; timing shown with respect to 20% V and 70% V , unless otherwise noted  
DD  
SS  
DD  
DD  
3. No more than 10% duty cycle deviation from 50%.  
4. Some modules may require a minimum frequency greater than dc for proper operation; see appropriate table for this  
information.  
5. Minimum pulse width reset is guaranteed to be recognized. It is possible for a smaller pulse width to cause a reset.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
268  
Freescale Semiconductor  
     
Serial Peripheral Interface Characteristics  
19.8 Serial Peripheral Interface Characteristics  
Diagram  
(2)  
Symbol  
Min  
Max  
Unit  
Characteristic  
Operating frequency  
Master  
Slave  
(1)  
Number  
f
fOP/2  
fOP/128  
dc  
MHz  
OP(M)  
f
f
OP(S)  
OP  
Cycle time  
Master  
Slave  
t
t
1
2
1
128  
CYC(M)  
CYC  
t
CYC(S)  
t
2
3
Enable lead time  
Enable lag time  
15  
15  
ns  
ns  
Lead(S)  
t
Lag(S)  
Clock (SPCK) high time  
Master  
Slave  
t
t
4
5
100  
50  
ns  
ns  
SCKH(M)  
SCKH(S)  
Clock (SPCK) low time  
Master  
Slave  
t
100  
50  
SCKL(M)  
t
SCKL(S)  
Data setup time (inputs)  
Master  
Slave  
t
45  
5
SU(M)  
6
7
ns  
ns  
t
SU(S)  
Data hold time (inputs)  
Master  
Slave  
t
0
15  
H(M)  
t
H(S)  
(3)  
Access time, slave  
CPHA = 0  
CHPA = 1  
t
0
0
40  
20  
A(CP0)  
8
9
ns  
ns  
ns  
t
A(CP1)  
(4)  
t
25  
Disable time, slave  
DIS(S)  
Data valid time after enable edge  
Master  
t
10  
10  
40  
V(M)  
(5)  
t
Slave  
V(S)  
1. V = 5.0 Vdc 10%, all timing is shown with respect to 20% V and 70% V , unless otherwise noted; assumes 100 pF  
DD  
DD  
DD  
load on all SPI pins  
2. Numbers refer to dimensions in Figure 19-1 and Figure 19-2.  
3. Time to data active from high-impedance state  
4. Hold time to high-impedance state  
5. With 100 pF on all SPI pins  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
269  
 
Electrical Specifications  
SS  
INPUT  
SS PIN OF MASTER HELD HIGH  
1
5
4
SPCK, CPOL = 0  
OUTPUT  
NOTE  
4
5
SPCK, CPOL = 1  
OUTPUT  
NOTE  
6
7
MISO  
INPUT  
MSB IN  
BITS 6–1  
BITS 6–1  
LSB IN  
10  
11  
MASTER MSB OUT  
10  
11  
MOSI  
OUTPUT  
MASTER LSB OUT  
Note: This first clock edge is generated internally, but is not seen at the SCK pin.  
a) SPI Master Timing (CPHA = 0)  
SS  
INPUT  
SS PIN OF MASTER HELD HIGH  
1
SPCK, CPOL = 0  
OUTPUT  
5
NOTE  
NOTE  
4
SPCK, CPOL = 1  
OUTPUT  
5
4
6
7
LSB IN  
11  
MISO  
INPUT  
MSB IN  
BITS 6–1  
BITS 6–1  
10  
MOSI  
OUTPUT  
11  
10  
MASTER MSB OUT  
MASTER LSB OUT  
Note: This last clock edge is generated internally, but is not seen at the SCK pin.  
b) SPI Master Timing (CPHA = 1)  
Figure 19-1. SPI Master Timing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
270  
Freescale Semiconductor  
 
Serial Peripheral Interface Characteristics  
SS  
INPUT  
3
1
SPCK, CPOL = 0  
INPUT  
11  
4
4
5
2
SPCK, CPOL = 1  
INPUT  
9
8
MISO  
INPUT  
SLAVE MSB OUT  
BITS 6–1  
BITS 6–1  
SLAVE LSB OUT  
11  
NOTE  
11  
6
7
10  
MOSI  
OUTPUT  
MSB IN  
LSB IN  
Note: Not defined, but normally MSB of character just received  
a) SPI Slave Timing (CPHA = 0)  
SS  
INPUT  
1
SPCK, CPOL = 0  
INPUT  
5
4
5
2
3
SPCK, CPOL = 1  
INPUT  
4
10  
9
8
MISO  
INPUT  
NOTE  
SLAVE MSB OUT  
BITS 6–1  
BITS 6–1  
SLAVE LSB OUT  
11  
6
7
10  
MOSI  
OUTPUT  
MSB IN  
LSB IN  
Note: Not defined, but normally LSB of character previously transmitted  
b) SPI Slave Timing (CPHA = 1)  
Figure 19-2. SPI Slave Timing  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
271  
 
Electrical Specifications  
19.9 TImer Interface Module Characteristics  
Characteristic  
Symbol  
Min  
Max  
Unit  
ns  
t
t
Input capture pulse width  
Input clock pulse width  
125  
TIH, TIL  
t
t
(1/f ) + 5  
ns  
TCH, TCL  
OP  
19.10 Clock Generation Module Component Specifications  
Characteristic  
Symbol  
Min  
Typ  
Max  
Notes  
Consult crystal  
manufacturing data  
C
Crystal load capacitance  
L
Consult crystal  
manufacturing data  
C
2 * C  
Crystal fixed capacitance  
Crystal tuning capacitance  
1
L
L
Consult crystal  
manufacturing data  
C
2 * C  
2
R
Feedback bias resistor  
Series resistor  
0
22 MΩ  
B
R
330 kΩ  
1 MΩ  
Not required  
S
C
*
FACT  
C
Filter capacitor  
F
(V  
/f  
)
DDA XCLK  
C
must provide low ac  
BYP  
impedance from  
/100 to 100*f  
C
Bypass capacitor  
0.1 µF  
f = f  
, so  
VCLK  
BYP  
XCLK  
series resistance must be  
considered  
19.11 CGM Operating Conditions  
Characteristic  
Crystal reference frequency  
Range nominal multiplier  
Symbol  
Min  
1
Typ  
Max  
8
Unit  
MHz  
MHz  
f
XCLK  
f
4.9152  
NOM  
f
VCO center-of-range frequency  
VCO frequency multiplier  
4.9152  
32.8  
15  
MHz  
VRS  
N
L
1
VCO center of range multiplier  
VCO operating frequency  
1
15  
f
f
f
VRSMAX  
VCLK  
VRSMIN  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
272  
Freescale Semiconductor  
     
CGM Acquisition/Lock Time Specifications  
19.12 CGM Acquisition/Lock Time Specifications  
Description  
Filter capacitor multiply factor  
Acquisition mode time factor  
Tracking mode time factor  
Symbol  
Min  
Typ  
Max  
Notes  
F/sV  
V
C
0.0154  
0.1135  
0.0174  
FACT  
K
ACQ  
K
V
TRK  
(8*V  
)/  
If C chosen  
DDA  
F
t
Manual mode time to stable  
ACQ  
(f  
(f  
*K  
correctly  
XCLK ACQ)  
(4*V  
)/  
If C chosen  
DDA  
F
t
Manual stable to lock time  
Manual acquisition time  
AL  
*K  
)
correctly  
XCLK TRK  
t
t
+t  
0
Lock  
ACQ AL  
Tracking mode entry frequency  
tolerance  
3.6%  
TRK  
Acquisition mode entry frequency  
tolerance  
7.2%  
6.3%  
ACQ  
Lock entry frequency tolerance  
Lock exit frequency tolerance  
0
0.9%  
1.8%  
Lock  
0.9%  
UNL  
Reference cycles per acquisition mode  
measurement  
n
32  
ACQ  
Reference cycles per tracking mode  
measurement  
n
128  
TRK  
(8*V  
)/  
If C chosen  
correctly  
DDA  
F
t
n
/f  
Automatic mode time to stable  
ACQ  
ACQ XCLK  
(f  
(f  
*K  
XCLK ACQ)  
(4*V  
)/  
If C chosen  
DDA  
F
t
n
/f  
Automatic stable to lock time  
Automatic lock time  
AL  
TRK XCLK  
*K  
)
correctly  
XCLK TRK  
t
t
+t  
0
Lock  
ACQ AL  
(f  
)
XCLK  
PLL jitter (deviation of average bus  
frequency over 2 ms)  
N = VCO  
freq. mult.  
f
J
*(0.025%)  
*(N/4)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
273  
 
Electrical Specifications  
19.13 Analog-to-Digital Converter (ADC) Characteristics  
Characteristic  
Symbol  
Min  
Typ  
Max  
Unit  
Notes  
V
should be tied to  
DDAD  
V
Supply voltage  
4.5  
5.5  
V
the same potential as  
via separate traces  
DDAD  
V
DD  
V
V
V
<= V  
Input voltages  
0
10  
V
Bits  
LSB  
Hz  
V
ADIN  
DDAD  
ADIN DDAD  
B
Resolution  
10  
AD  
A
Absolute accuracy  
ADC internal clock  
Conversion range  
Power-up time  
Conversion time  
Sample time  
4
Includes quantization  
AD  
f
t
= 1/f  
AIC ADIC  
500 k  
1.048 M  
ADIC  
R
V
V
AD  
SSAD  
DDAD  
t
t
t
t
cycles  
16  
17  
ADPU  
AIC  
AIC  
AIC  
t
cycles  
cycles  
16  
5
ADC  
t
ADS  
M
Monotonicity  
Guaranteed  
AD  
Z
V
= V  
= V  
Zero input reading  
Full-scale reading  
Input capacitance  
000  
3FC  
003  
3FF  
30  
Hex  
Hex  
pF  
ADI  
ADIN  
SSAD  
F
V
ADIN  
ADI  
DDAD  
C
Not tested  
ADI  
V
/V  
current  
I
1.6  
mA  
REFH REFL  
VREF  
Absolute accuracy  
(8-bit truncation mode)  
A
1
LSB  
LSB  
Includes quantization  
AD  
Quantization error  
(8-bit truncation mode)  
+ 7/8  
– 1/8  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
274  
Freescale Semiconductor  
   
Chapter 20  
Ordering Information and Mechanical Specifications  
20.1 Introduction  
This section provides ordering information for the MC68HC908MR16 and MC68HC908MR32 along with  
the dimensions for:  
64-lead plastic quad flat pack (QFP)  
56-pin shrink dual in-line package (SDIP)  
The following figures show the latest package drawings at the time of this publication. To make sure that  
you have the latest package specifications, contact your local Freescale Sales Office.  
20.2 Order Numbers  
Table 20-1. Order Numbers  
Operating  
Temperature Range  
(1)  
MC Order Number  
68HC908MR16CFU  
68HC908MR16VFU  
–40°C to +85°C  
–40°C to +105°C  
68HC908MR16CB  
68HC908MR16VB  
–40°C to +85°C  
–40°C to +105°C  
68HC908MR32CFU  
68HC908MR32VFU  
–40°C to +85°C  
–40°C to +105°C  
68HC908MR32CB  
68HC908MR32VB  
–40°C to +85°C  
–40°C to +105°C  
1. FU = quad flat pack  
B = shrink dual in-line package  
M C 6 8 H C 9 0 8 M R 3 2 X X X  
PACKAGE DESIGNATOR  
FAMILY  
TEMPERATURE RANGE  
Figure 20-1. Device Numbering System  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
275  
     
Ordering Information and Mechanical Specifications  
20.3 64-Pin Plastic Quad Flat Pack (QFP)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
276  
Freescale Semiconductor  
 
56-Pin Shrink Dual In-Line Package (SDIP)  
20.4 56-Pin Shrink Dual In-Line Package (SDIP)  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
277  
 
Ordering Information and Mechanical Specifications  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
278  
Freescale Semiconductor  
Appendix A  
MC68HC908MR16  
The information contained in this document pertains to the MC68HC908MR16 with the exception of that  
shown in Figure A-1.  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
Freescale Semiconductor  
279  
   
MC68HC908MR16  
$0000  
I/O REGISTERS — 96 BYTES  
RAM — 768 BYTES  
$005F  
$0060  
$035F  
$0360  
UNIMPLEMENTED — 31,904 BYTES  
FLASH — 16,128 BYTES  
$7FFF  
$8000  
$BEFF  
$BF00  
$FDFF  
UNIMPLEMENTED — 16,128 BYTES  
$FE00  
$FE01  
$FE02  
$FE03  
$FE04  
$FE05  
$FE06  
$FE07  
$FE08  
$FE09  
$FE0A  
$FE0B  
$FE0C  
$FE0D  
$FE0E  
$FE0F  
SIM BREAK STATUS REGISTER (SBSR)  
SIM RESET STATUS REGISTER (SRSR)  
RESERVED  
SIM BREAK FLAG CONTROL REGISTER (SBFCR)  
RESERVED  
RESERVED  
RESERVED  
RESERVED  
FLASH CONTROL REGISTER (FLCR)  
UNIMPLEMENTED  
UNIMPLEMENTED  
UNIMPLEMENTED  
SIM BREAK ADDRESS REGISTER HIGH (BRKH)  
SIM BREAK ADDRESS REGISTER LOW (BRKL)  
SIM BREAK FLAG CONTROL REGISTER (SBFCR)  
LVI STATUS AND CONTROL REGISTER (LVISCR)  
$FE10  
$FEFF  
MONITOR ROM — 240 BYTES  
$FF00  
$FF7D  
UNIMPLEMENTED — 126 BYTES  
FLASH BLOCK PROTECT REGISTER (FLBPR)  
UNIMPLEMENTED — 83 BYTES  
$FF7E  
$FF7F  
$FFD1  
$FFD2  
$FFFF  
VECTORS — 46 BYTES  
Figure A-1. MC68HC908MR16 Memory Map  
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1  
280  
Freescale Semiconductor  
 
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Semiconductor was negligent regarding the design or manufacture of the part.  
Freescale™ and the Freescale logo are trademarks of Freescale Semiconductor, Inc.  
All other product or service names are the property of their respective owners.  
© Freescale Semiconductor, Inc. 2005. All rights reserved.  
MC68HC908MR32  
Rev. 6.1, 07/2005  

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