USER
MANUAL
MODEL 285
and 285S
RS-232 to RS-485
Interface Converters
Revision C and above
SALES OFFICE
(301) 975-1000
TECHNICAL SUPPORT
(301) 975-1007
Part# 07M285-B
Doc# 047012UB
Revised 9/29/93
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3.0 CONFIGURATION
The Model 285 is configured using six PC board mounted switch-
es. Figure 1 (below) shows the switch locations, along with the loca-
tion of the terminal blocks and optional surge protectors:
3.2 SETTING CONFIGURATION SWITCHES SW1 AND SW2
The five switches shown in Figure 3 (below) configure the Model
285 for RTS/CTS delay, echo, method of carrier control, impedance,
and 2-wire/4-wire operation. These switches are located internally on
the Model 285's PC board. To access SW1 and SW2, use a small flat
blade screw driver to pop open the Model 285's case as shown in
Figure 4 (below):
DCE/DTE
Surge
Switch
Suppressors
(285S only)
"ON"
2-wire/4-wire
Switch
Terminal
Block
Control
Switches
"OFF"
SW1
SW2
Figure 1. Model 285 board, showing switch locations
Figure 3. Close up of switches SW1 and SW2 on the PC board
3.1 SETTING THE DTE/DCE SWITCH
For your convenience, the Model 285 has an externally accessi-
ble DTE/DCE switch (see Figure 2, below). If the device connected to
the Model 285 is a modem or multiplexer (or is wired like one), set the
switch to "DTE". This setting causes the Model 285 to behave like
Data Terminal Equipment and transmit data on pin 2.
If the device connected to the Model 285 is a PC, terminal or host
computer (or is wired like one), set the switch to "DCE". This setting
causes the Model 285 to behave like Data Communications Equipment
and transmit data on pin 3.
DCE
DTE
Figure 2. Close up of external DCE/DTE switch
Figure 4. Opening the Model 285's plastic case with a small screw driver
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3.2.1 CONFIGURATION SWITCH FUNCTIONS
3.2.2 CONFIGURATION SWITCH APPLICATIONS
The table and descriptions below detail the functions of the five
configuration switches. Read this information carefully before setting
the switches.
The table below shows you how to set the Model 285's configu-
ration switches to fit several common applications. If you have any
questions about the proper settings for your application, call Patton
Technical Support at (301) 975-1007.
SWITCH SUMMARY TABLE
Position
SW1-1
SW1-2
SW1-3
SW1-4
SW2
Function
RTS/CTS Delay
Echo Enable
Carrier Control
Impedance
Off Position
0 mSec
On Position
8 mSec
TYPICAL SWITCH APPLICATIONS
Point-to-Point
4W HDX
Multi-point
2W
Switch
Settings
Echo "Off"
Echo "On"
Constantly "On" Controlled by RTS
4W
2W
4W
High (120K Ohm)
2-wire
Low (120 Ohm)
4-wire
RTS/CTS (SW1-1)*
Echo (SW1-2)
ON
OFF
OFF
ON
ON
ON
ON
OFF
ON
ON
ON
ON
OFF
ON
2 wire/4 wire
Carrier (SW1-3)
Master-OFF
Slaves-ON
SW1-1: RTS/CTS Delay: Switch 1-1 determines how long cir-
cuit CB (CTS) takes to become active after RTS is asserted (DCE
Mode only). RTS delay of 8 mSec will give any signal from any other
device time to clear the transmit line. In DTE mode, CTS is open.
Impedance (SW1-4)
2wire/4wire (SW2)
ON
ON
ON
ON
ON
Master - ON
Slaves - HIGH
Last Slave - ON
OFF
ON
OFF
SW1-2: Echo Enable: With Switch 1-2 in the ON position, the
285 echoes transmitted data back to the transmitting device. This is
so the user can see what is being transmitting to the remote device.
(Typically used in half duplex modes only).
*NOTE: RTS/CTS Delay (SW1-1) setting should be based upon transmission timing.
SW1-3: Carrier: With Switch 1-3 in the ON position, the 285
transmitter operation follows circuit CA (Request to Send). When RTS
is low, the 285 transmitter operation is off (0V) (DCE mode only).
3.2.3 WHEN YOU'RE FINISHED CONFIGURING...
Once you've finished setting the Model 285's configuration
switches, pause before you snap the case halves back together. If you
are connecting the RS-485 interface using the internal terminal blocks,
go to Section 4.1.3 and continue the installation procedure. If you are
connecting the RS-485 interface using RS-11, RS-45 or DB-25, go
ahead and snap the case halves back together now (don't force a fit—
make sure all the pieces are properly set before snapping the case
halves shut).
SW1-4: Impedance: Switch 1-4 defines a termination resist-
ance.The 285 transmitter can drive 50 unit loads including two termina-
tionresistances of 120 Ohms each.
SW2: 2 Wire/ 4 Wire: Switch 2 determines 2 wire (half duplex)
or 4 wire operation.
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4.0 INSTALLATION
4.1.2 4-WIRE CONNECTION USING RJ-11 OR RJ-45
Once you have properly set the configuration switches, you are
ready to connect the Model 285 to your system. This section tells you
how to properly connect the Model 285 to the RS-485 and RS-232
interfaces, and how to operate the Model 285.
The RJ-11 and RJ-45 connectors on the Model 285's RS-485 side
are pre-wired for a standard TELCO wiring environment. The
signal/pin relationships are shown below:
RJ-11
SIGNAL
RJ-45
SIGNAL
4.1 CONNECTION TO THE RS-485 INTERFACE
1...................GND*
2...................RCV-
3...................XMT+
4...................XMT-
5...................RCV+
6...................GND
1 .................N/C
2 .................GND*
3 .................RCV-
4 .................XMT+
5 .................XMT-
6 .................RCV+
7 .................GND
8 .................N/C
To function properly, the Model 285 must have one or two twisted
pairs of metallic wire. These pairs must be "dry" (unconditioned)
metallic wire, between 19 and 26 AWG (the higher number gauges
may limit distance somewhat).
For your convenience, the Model 285 is available with several dif-
ferent physical interfaces on the RS-485 side: DB-25 (following the
RS-520 standard), RJ-11 jack, RJ-45 jack, and terminal blocks with
strain relief.
In most modular RS-485 applications it is necessary to use a
"cross over" cable. The diagram below shows how a cross over cable
should be constructed for an environment where both the Model 285
and the RS-485 device use a 6-wire RJ-11 connector. Similar logic
should be followed when using RJ-45 connectors or a combination of
the two.
4.1.1 4-WIRE CONNECTION USING THE DB-25
The DB-25 connector on the Model 285's RS-485 side conforms to
the RS-530 interface standard. When connecting to an RS-485
device that also conforms to the RS-530 standard, your cable should
be "crossed over" in the manner shown below:
MODEL 285
SIGNAL PIN#
RS-485 DEVICE
422 SIGNAL
PIN#
GND*
RCV-
XMT+
XMT-
RCV+
GND
1
2
3
4
5
6
MODEL 285
RS-485 (530) DEVICE
.........................4
XMT-
RCV+
RCV-
XMT+
SIGNAL
DB-25 PIN
DB-25 PIN
SIGNAL
RCV+
.........................5
.........................2
.........................3
XMT+
XMT-
2...........................3
14...........................16
RCV-
RCV+
RCV-
3...........................2
16...........................14
XMT+
XMT-
*Connection to ground is optional
NOTE: It is not necessary that the RS-485 device adhere to the RS-530 stan-
dard. However, you must make sure that the signals, polarities, and pairing of
your connection conform to the above diagram.
1
2
3
4
5
6
7
8
1
2
3
4
5
6
**Standard AT&T pin assignements - yours may be different.
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4.1.3 4-WIRE CONNECTION USING TERMINAL BLOCKS
6. If there is a shield around the telephone cable, it may be con-
nected to "G" on the terminal block. We recommend connecting the
shield at the computer end only to avoid ground loops. A ground wire
is not necessary for proper operation of the Model 285.
If your RS-485 application requires you to connect two pairs of
bare wires to the Model 285, you will need to open the case to access
the terminal blocks. The following instructions will tell you how to open
the case, connect the bare wires to the terminal blocks, and fasten the
strain relief collar in place so that the wires won't pull loose.
7. When you finish connecting the wires to the terminal block, the
assembly should resemble the diagram below:
1. You should already have the case open for the configuration
procedure. If not, open the case according to the diagram in Section
3.2.
2. Strip the outer insulation from the twisted pairs about one inch
from the end.
3. Strip back the insulation on each of the 2 twisted pair wires
about .25".
8. Place the 2 halves of the strain relief assembly on either side
of the telephone wire and press together very lightly. Slide the assem-
bly so that it is about 2 inches from the terminal posts and press
together firmly. If your cable diameter is too small or too large for our
strain relief, please contact our technical support. We have strain relief
assemblies to accommodate most cable diameters.
4. Connect one pair of wires to XMT+ and XMT- (transmit positive
and negative) on the terminal block, making careful note of which color
is positive, and which color is negative.
5. Connect the other pair of wires to RCV+ and RCV- (receive
positive and negative) on the terminal block, again making careful note
of which color is positive, and which color is negative.
Ultimately, you will want to construct a two pair cross over cable
that makes a connection with the RS-485 device as shown below:
Model 285
RS-485 Device
XMT+.............................RCV+
XMT-..............................RCV-
RCV+.............................XMT+
RCV-..............................XMT-
(continued)
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9. Insert the strain relief assembly with the wire going through it
into the slot in the bottom half of the modem case and set it into the
recess in the case.
4.1.4 2-WIRE CONNECTION
Most RS-485 devices employ a two-wire, half duplex configuration.
When using this configuration, be sure to first set the Model 285 to
"two wire" mode—then use only the transmit (XMT) pair as shown
below:
285 SIGNAL
RS-485 SIGNAL
XMT+....................................+
XMT-.....................................-
The above wiring pattern applies regardless of whether you are
making the RS-485 connection via DB-25, RJ-11, RJ-45 or terminal
blocks. For specific wiring instructions, please refer to the previous
pages of Section 4.
10. BEND the top half of the case as necessary to place it over
the strain relief assembly. Do not snap the case together yet.
4.2 CONNECTION TO THE RS-232 INTERFACE
Once you have properly configured the Model 285 and connected
the twisted pair wires correctly, all that remains is to plug the 285
directly into the DB-25 port of the RS-232 device. After doing so,
remember to insert and tighten the two captive connector screws.
(Note: If you must use a cable to connect the Model 285 to the RS-232
device, make sure it is a straight through cable of the shortest possible
length—we recommend 6 feet or less).
4.3 OPERATING THE MODEL 285
Once the Model 285 is properly installed, it should operate trans-
parently—as if it were a standard cable connection. Operating power
is derived from the RS-232 data and control signals; there is no
"ON/OFF" switch. All data signals from the RS-232 and RS-485 inter-
faces are passed straight through. Additionally, one hardware flow
control signal is passed in each direction.
11. Insert one captive screw through a saddle washer and then
insert the captive screw with the washer on it, through the hole in the
DB-25 end of the case. Snap that side of the case closed. Repeat the
process for the other side. This completes the cable installation
process.
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APPENDIX A
APPENDIX B
SPECIFICATIONS
RS-232C PIN CONFIGURATIONS
Transmission Format: Asynchronous
Data Rate: Up to 115,200 bps
DIRECTION
STANDARD "DCE" SETTING
DIRECTION
1- (FG) Frame Ground
2- (TD) Transmit Data
3- (RD) Receive Data
4- (RTS) Request to Send
5- (CTS) Clear to Send
6- (DSR) Data Set Ready
7- (SG) Signal Ground
To Model 285
From Model 285
To Model 285
Transmit Line: 2, 4 wire unconditioned twisted pair
Transmit Mode: Full or half duplex
Transmit Level: 0 dBm
From Model 285
From Model 285
To Model 285
Data Term. Ready (DTR) - 20
8- (DCD) Data Carrier Detect From Model 285
Range: Up to 9 miles
Control Signals: DSR turns "ON" immediately after the terminal
raises DTR; DCD turns "ON" after recognizing the
receive signal from the line; CTS turns on after
the terminal raises RTS
DIRECTION
STANDARD "DTE" SETTING
DIRECTION
Carrier: The carrier is strap selected either continuous operation or
switched operation, controlled by RTS
1- (FG) Frame Ground
2- (TD) Transmit Data
3- (RD) Receive Data
From Model 285
To Model 285
From Model 285
To Model 285
To Model 285
Surge Protection: 600W power dissipation at 1 mS and response
time less than 1.0 pS
4- (RTS) Request to Send
5- (CTS) Clear to Send
6- (DSR) Data Set Ready
7- (SG) Signal Ground
8- (DCD) Data Carrier Detect
Power: None required, uses ultra low power from EIA data and con
trol signals
From Model 285 Data Term. Ready (DTR) - 20
To Model 285
Size: 2.66" x 2.10" x 0.73"
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APPENDIX C
BLOCK DIAGRAM
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