National Instruments Switch NI 6238 User Manual

DAQ M Series  
NI 6238/6239 User Manual  
Isolated Current Input/Current Output Devices  
NI 6238/6239 User Manual  
July 2006  
371913A-01  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Important Information  
Warranty  
The NI 6238/6239 is warranted against defects in materials and workmanship for a period of three years from the date of shipment, as evidenced  
by receipts or other documentation. National Instruments will, at its option, repair or replace equipment that proves to be defective during the  
warranty period. This warranty includes parts and labor.  
The media on which you receive National Instruments software are warranted not to fail to execute programming instructions, due to defects in  
materials and workmanship, for a period of 90 days from date of shipment, as evidenced by receipts or other documentation. National Instruments  
will, at its option, repair or replace software media that do not execute programming instructions if National Instruments receives notice of such defects  
during the warranty period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.  
A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside of the package before any  
equipment will be accepted for warranty work. National Instruments will pay the shipping costs of returning to the owner parts which are covered by  
warranty.  
National Instruments believes that the information in this document is accurate. The document has been carefully reviewed for technical accuracy. In  
the event that technical or typographical errors exist, National Instruments reserves the right to make changes to subsequent editions of this document  
without prior notice to holders of this edition. The reader should consult National Instruments if errors are suspected. In no event shall National  
Instruments be liable for any damages arising out of or related to this document or the information contained in it.  
EXCEPT AS SPECIFIED HEREIN, NATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND SPECIFICALLY DISCLAIMS ANY WARRANTY OF  
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL  
INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER. NATIONAL INSTRUMENTS WILL NOT BE LIABLE FOR DAMAGES RESULTING  
FROM LOSS OF DATA, PROFITS, USE OF PRODUCTS, OR INCIDENTAL OR CONSEQUENTIAL DAMAGES, EVEN IF ADVISED OF THE POSSIBILITY THEREOF. This limitation of  
the liability of National Instruments will apply regardless of the form of action, whether in contract or tort, including negligence. Any action against  
National Instruments must be brought within one year after the cause of action accrues. National Instruments shall not be liable for any delay in  
performance due to causes beyond its reasonable control. The warranty provided herein does not cover damages, defects, malfunctions, or service  
failures caused by owner’s failure to follow the National Instruments installation, operation, or maintenance instructions; owner’s modification of the  
product; owner’s abuse, misuse, or negligent acts; and power failure or surges, fire, flood, accident, actions of third parties, or other events outside  
reasonable control.  
Copyright  
Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical, including photocopying,  
recording, storing in an information retrieval system, or translating, in whole or in part, without the prior written consent of National  
Instruments Corporation.  
National Instruments respects the intellectual property of others, and we ask our users to do the same. NI software is protected by copyright and other  
intellectual property laws. Where NI software may be used to reproduce software or other materials belonging to others, you may use NI software only  
to reproduce materials that you may reproduce in accordance with the terms of any applicable license or other legal restriction.  
Trademarks  
National Instruments, NI, ni.com, and LabVIEW are trademarks of National Instruments Corporation. Refer to the Terms of Use section  
on ni.com/legalfor more information about National Instruments trademarks.  
FireWire® is the registered trademark of Apple Computer, Inc. Other product and company names mentioned herein are trademarks or trade names  
of their respective companies.  
Members of the National Instruments Alliance Partner Program are business entities independent from National Instruments and have no agency,  
partnership, or joint-venture relationship with National Instruments.  
Patents  
For patents covering National Instruments products, refer to the appropriate location: Help»Patents in your software, the patents.txtfile  
on your CD, or ni.com/patents.  
WARNING REGARDING USE OF NATIONAL INSTRUMENTS PRODUCTS  
(1) NATIONAL INSTRUMENTS PRODUCTS ARE NOT DESIGNED WITH COMPONENTS AND TESTING FOR A LEVEL OF  
RELIABILITY SUITABLE FOR USE IN OR IN CONNECTION WITH SURGICAL IMPLANTS OR AS CRITICAL COMPONENTS IN  
ANY LIFE SUPPORT SYSTEMS WHOSE FAILURE TO PERFORM CAN REASONABLY BE EXPECTED TO CAUSE SIGNIFICANT  
INJURY TO A HUMAN.  
(2) IN ANY APPLICATION, INCLUDING THE ABOVE, RELIABILITY OF OPERATION OF THE SOFTWARE PRODUCTS CAN BE  
IMPAIRED BY ADVERSE FACTORS, INCLUDING BUT NOT LIMITED TO FLUCTUATIONS IN ELECTRICAL POWER SUPPLY,  
COMPUTER HARDWARE MALFUNCTIONS, COMPUTER OPERATING SYSTEM SOFTWARE FITNESS, FITNESS OF COMPILERS  
AND DEVELOPMENT SOFTWARE USED TO DEVELOP AN APPLICATION, INSTALLATION ERRORS, SOFTWARE AND HARDWARE  
COMPATIBILITY PROBLEMS, MALFUNCTIONS OR FAILURES OF ELECTRONIC MONITORING OR CONTROL DEVICES,  
TRANSIENT FAILURES OF ELECTRONIC SYSTEMS (HARDWARE AND/OR SOFTWARE), UNANTICIPATED USES OR MISUSES, OR  
ERRORS ON THE PART OF THE USER OR APPLICATIONS DESIGNER (ADVERSE FACTORS SUCH AS THESE ARE HEREAFTER  
COLLECTIVELY TERMED “SYSTEM FAILURES”). ANY APPLICATION WHERE A SYSTEM FAILURE WOULD CREATE A RISK OF  
HARM TO PROPERTY OR PERSONS (INCLUDING THE RISK OF BODILY INJURY AND DEATH) SHOULD NOT BE RELIANT SOLELY  
UPON ONE FORM OF ELECTRONIC SYSTEM DUE TO THE RISK OF SYSTEM FAILURE. TO AVOID DAMAGE, INJURY, OR DEATH,  
THE USER OR APPLICATION DESIGNER MUST TAKE REASONABLY PRUDENT STEPS TO PROTECT AGAINST SYSTEM FAILURES,  
INCLUDING BUT NOT LIMITED TO BACK-UP OR SHUT DOWN MECHANISMS. BECAUSE EACH END-USER SYSTEM IS  
CUSTOMIZED AND DIFFERS FROM NATIONAL INSTRUMENTS' TESTING PLATFORMS AND BECAUSE A USER OR APPLICATION  
DESIGNER MAY USE NATIONAL INSTRUMENTS PRODUCTS IN COMBINATION WITH OTHER PRODUCTS IN A MANNER NOT  
EVALUATED OR CONTEMPLATED BY NATIONAL INSTRUMENTS, THE USER OR APPLICATION DESIGNER IS ULTIMATELY  
RESPONSIBLE FOR VERIFYING AND VALIDATING THE SUITABILITY OF NATIONAL INSTRUMENTS PRODUCTS WHENEVER  
Download from Www.Somanuals.com. All Manuals Search And Download.  
NATIONAL INSTRUMENTS PRODUCTS ARE INCORPORATED IN A SYSTEM OR APPLICATION, INCLUDING, WITHOUT  
LIMITATION, THE APPROPRIATE DESIGN, PROCESS AND SAFETY LEVEL OF SUCH SYSTEM OR APPLICATION.  
Download from Www.Somanuals.com. All Manuals Search And Download.  
About This Manual  
Measurement Studio........................................................................................xvi  
ANSI C without NI Application Software ......................................................xvi  
Device Documentation and Specifications......................................................xvii  
Chapter 1  
Installing NI-DAQmx....................................................................................................1-1  
Installing Other Software...............................................................................................1-1  
Device Pinouts ...............................................................................................................1-1  
Chapter 2  
DAQ-STC2......................................................................................................2-2  
Calibration Circuitry........................................................................................2-3  
Cables and Accessories..................................................................................................2-4  
Chapter 3  
Connector Information  
I/O Connector Signal Descriptions................................................................................3-1  
RTSI Connector Pinout..................................................................................................3-3  
© National Instruments Corporation  
v
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Contents  
Chapter 4  
Analog Input  
AI Start Trigger Signal.................................................................................... 4-22  
Using a Digital Source...................................................................... 4-22  
Routing AI Start Trigger to an Output Terminal.............................. 4-22  
AI Reference Trigger Signal........................................................................... 4-23  
Using a Digital Source...................................................................... 4-24  
Routing AI Reference Trigger Signal to an Output Terminal.......... 4-24  
NI 6238/6239 User Manual  
vi  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Using a Digital Source ......................................................................4-24  
Chapter 5  
Analog Output  
Using an Internal Source...................................................................5-8  
Using an External Source..................................................................5-8  
Other Timing Requirements..............................................................5-9  
Chapter 6  
I/O Protection.................................................................................................................6-1  
Programmable Power-Up States....................................................................................6-1  
Connecting Digital I/O Signals......................................................................................6-2  
Logic Conventions.........................................................................................................6-3  
Getting Started with DIO Applications in Software......................................................6-4  
© National Instruments Corporation  
vii  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Contents  
Chapter 7  
Counters  
Single Semi-Period Measurement .................................................... 7-9  
Buffered Semi-Period Measurement ................................................ 7-10  
Retriggerable Single Pulse Generation............................................. 7-22  
Pulse Train Generation.................................................................................... 7-23  
Continuous Pulse Train Generation.................................................. 7-23  
Frequency Generation..................................................................................... 7-24  
Using the Frequency Generator........................................................ 7-24  
Frequency Division......................................................................................... 7-25  
Pulse Generation for ETS ............................................................................... 7-25  
NI 6238/6239 User Manual  
viii  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
When To Use Duplicate Count Prevention.......................................7-38  
Enabling Duplicate Count Prevention in NI-DAQmx ......................7-38  
Synchronization Modes...................................................................................7-38  
80 MHz Source Mode.......................................................................7-39  
Other Internal Source Mode..............................................................7-39  
External Source Mode.......................................................................7-40  
© National Instruments Corporation  
ix  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Contents  
Chapter 8  
PFI  
Using PFI Terminals as Static Digital Inputs and Outputs............................................ 8-3  
Connecting PFI Input Signals........................................................................................ 8-3  
I/O Protection ................................................................................................................ 8-5  
Chapter 9  
Digital Isolation............................................................................................................. 9-2  
Chapter 10  
RTSI Filters..................................................................................................... 10-6  
PXI Clock and Trigger Signals...................................................................................... 10-7  
PXI_CLK10 .................................................................................................... 10-8  
PXI Triggers.................................................................................................... 10-8  
PXI_STAR Trigger......................................................................................... 10-8  
PXI_STAR Filters........................................................................................... 10-8  
NI 6238/6239 User Manual  
x
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Chapter 11  
Bus Interface  
Using PXI with CompactPCI ..........................................................................11-3  
Data Transfer Methods ..................................................................................................11-3  
Interrupt Request (IRQ)...................................................................................11-4  
Changing Data Transfer Methods between DMA and IRQ............................11-4  
Chapter 12  
Triggering  
Appendix A  
Device-Specific Information  
Appendix B  
Troubleshooting  
Analog Input ..................................................................................................................B-1  
Analog Output................................................................................................................B-2  
Appendix C  
Technical Support and Professional Services  
Glossary  
Index  
Figures  
Figure A-1. NI 6238 Pinout ......................................................................................A-2  
Figure A-2. NI 6239 Pinout ......................................................................................A-5  
© National Instruments Corporation  
xi  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
About This Manual  
The NI 6238/6239 User Manual contains information about using the  
NI 6238 and NI 6239 M Series data acquisition (DAQ) devices with  
NI-DAQmx 8.1 and later. National Instruments 6238/6239 devices feature  
up to eight differential analog input (AI) channels, two analog output (AO)  
channels, two counters, six lines of digital input (DI), and four lines of  
digital output (DO).  
Conventions  
The following conventions are used in this manual:  
<>  
Angle brackets that contain numbers separated by an ellipsis represent  
a range of values associated with a bit or signal name—for example,  
AO <3..0>.  
»
The » symbol leads you through nested menu items and dialog box options  
to a final action. The sequence File»Page Setup»Options directs you to  
pull down the File menu, select the Page Setup item, and select Options  
from the last dialog box.  
This icon denotes a tip, which alerts you to advisory information.  
This icon denotes a note, which alerts you to important information.  
This icon denotes a caution, which advises you of precautions to take to  
avoid injury, data loss, or a system crash. When this symbol is marked on a  
product, refer to the NI 6238/6239 Specifcations for information about  
precautions to take.  
When symbol is marked on a product, it denotes a warning advising you to  
take precautions to avoid electrical shock.  
When symbol is marked on a product, it denotes a component that may be  
hot. Touching this component may result in bodily injury.  
bold  
Bold text denotes items that you must select or click in the software, such  
as menu items and dialog box options. Bold text also denotes parameter  
names.  
© National Instruments Corporation  
xiii  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
About This Manual  
italic  
Italic text denotes variables, emphasis, a cross-reference, or an introduction  
to a key concept. Italic text also denotes text that is a placeholder for a word  
or value that you must supply.  
monospace  
Text in this font denotes text or characters that you should enter from the  
keyboard, sections of code, programming examples, and syntax examples.  
This font is also used for the proper names of disk drives, paths, directories,  
programs, subprograms, subroutines, device names, functions, operations,  
variables, filenames, and extensions.  
Related Documentation  
Each application software package and driver includes information about  
writing applications for taking measurements and controlling measurement  
devices. The following references to documents assume you have  
NI-DAQmx 8.1 or later, and where applicable, version 7.0 or later of the NI  
application software.  
NI-DAQ  
The DAQ Getting Started Guide describes how to install your NI-DAQmx  
for Windows software, your NI-DAQmx-supported DAQ device, and how  
to confirm that your device is operating properly. Select Start»All  
Programs»National Instruments»NI-DAQ»DAQ Getting Started  
Guide.  
The NI-DAQ Readme lists which devices are supported by this version of  
NI-DAQ. Select Start»All Programs»National Instruments»NI-DAQ»  
NI-DAQ Readme.  
The NI-DAQmx Help contains general information about measurement  
concepts, key NI-DAQmx concepts, and common applications that are  
applicable to all programming environments. Select Start»All Programs»  
National Instruments»NI-DAQ»NI-DAQmx Help.  
NI-DAQmx for Linux  
The DAQ Getting Started Guide describes how to install your  
NI-DAQmx-supported DAQ device and confirm that your device is  
operating properly.  
The NI-DAQ Readme for Linux lists supported devices and includes  
software installation instructions, frequently asked questions, and known  
issues.  
NI 6238/6239 User Manual  
xiv  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
About This Manual  
The C Function Reference Help describes functions and attributes.  
The NI-DAQmx for Linux Configuration Guide provides configuration  
instructions, templates, and instructions for using test panels.  
Note All NI-DAQmx documentation for Linux is installed at  
/usr/local/natinst/nidaqmx/docs.  
NI-DAQmx Base  
The NI-DAQmx Base Getting Started Guide describes how to install your  
NI-DAQmx Base software, your NI-DAQmx Base-supported DAQ device,  
and how to confirm that your device is operating properly. Select Start»All  
Programs»National Instruments»NI-DAQmx Base»Documentation»  
Getting Started Guide.  
The NI-DAQmx Base Readme lists which devices are supported by this  
version of NI-DAQmx Base. Select Start»All Programs»National  
Instruments»NI-DAQmx Base»Documentation»Readme.  
The NI-DAQmx Base VI Reference Help contains VI reference and general  
information about measurement concepts. In LabVIEW, select Help»  
NI-DAQmx Base VI Reference Help.  
The NI-DAQmx Base C Reference Help contains C reference and general  
information about measurement concepts. Select Start»All Programs»  
National Instruments»NI-DAQmx Base»Documentation»C Function  
Reference Manual.  
LabVIEW  
If you are a new user, use the Getting Started with LabVIEW manual to  
familiarize yourself with the LabVIEW graphical programming  
environment and the basic LabVIEW features you use to build data  
acquisition and instrument control applications. Open the Getting Started  
with LabVIEW manual by selecting Start»All Programs»National  
Instruments»LabVIEW»LabVIEW Manuals or by navigating to the  
labview\manuals directoryand opening  
LV_Getting_Started.pdf.  
Use the LabVIEW Help, available by selecting Help»Search the  
LabVIEW Help in LabVIEW, to access information about LabVIEW  
programming concepts, step-by-step instructions for using LabVIEW, and  
reference information about LabVIEW VIs, functions, palettes, menus, and  
© National Instruments Corporation  
xv  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
About This Manual  
tools. Refer to the following locations on the Contents tab of the LabVIEW  
Help for information about NI-DAQmx:  
Getting Started»Getting Started with DAQ—Includes overview  
information and a tutorial to learn how to take an NI-DAQmx  
measurement in LabVIEW using the DAQ Assistant.  
VI and Function Reference»Measurement I/O VIs and  
Functions—Describes the LabVIEW NI-DAQmx VIs and properties.  
Taking Measurements—Contains the conceptual and how-to  
information you need to acquire and analyze measurement data in  
LabVIEW, including common measurements, measurement  
fundamentals, NI-DAQmx key concepts, and device considerations.  
LabWindows/CVI™  
The Data Acquisition book of the LabWindows/CVI Help contains  
measurement concepts for NI-DAQmx. This book also contains Taking an  
NI-DAQmx Measurement in LabWindows/CVI, which includes  
step-by-step instructions about creating a measurement task using the DAQ  
Assistant. In LabWindows/CVI, select Help»Contents, then select Using  
LabWindows/CVI»Data Acquisition.  
The NI-DAQmx Library book of the LabWindows/CVI Help contains API  
overviews and function reference for NI-DAQmx. Select Library  
Reference»NI-DAQmx Library in the LabWindows/CVI Help.  
Measurement Studio  
The NI Measurement Studio Help contains function reference,  
measurement concepts, and a walkthrough for using the Measurement  
Studio NI-DAQmx .NET and Visual C++ class libraries. This help  
collection is integrated into the Microsoft Visual Studio .NET  
documentation. In Visual Studio .NET, select Help»Contents.  
Note You must have Visual Studio .NET installed to view the NI Measurement Studio  
Help.  
ANSI C without NI Application Software  
The NI-DAQmx Help contains API overviews and general information  
about measurement concepts. Select Start»All Programs»National  
Instruments»NI-DAQmx Help.  
NI 6238/6239 User Manual  
xvi  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
About This Manual  
.NET Languages without NI Application Software  
The NI Measurement Studio Help contains function reference and  
measurement concepts for using the Measurement Studio NI-DAQmx  
.NET and Visual C++ class libraries. This help collection is integrated into  
the Visual Studio .NET documentation. In Visual Studio .NET, select  
Help»Contents.  
Note You must have Visual Studio .NET installed to view the NI Measurement Studio  
Help.  
Device Documentation and Specifications  
The NI 6238/6239 Specifications contains all specifications for NI 6238  
and NI 6239 M Series devices.  
NI-DAQ 7.0 and later includes the Device Document Browser, which  
contains online documentation for supported DAQ, SCXI, and switch  
devices, such as help files describing device pinouts, features, and  
operation, and PDF files of the printed device documents. You can find,  
view, and/or print the documents for each device using the Device  
Document Browser at any time by inserting the CD. After installing the  
Device Document Browser, device documents are accessible from Start»  
All Programs»National Instruments»NI-DAQ»Browse Device  
Documentation.  
Training Courses  
If you need more help getting started developing an application with NI  
products, NI offers training courses. To enroll in a course or obtain a  
detailed course outline, refer to ni.com/training.  
Technical Support on the Web  
For additional support, refer to ni.com/supportor zone.ni.com.  
Note You can download these documents at ni.com/manuals.  
DAQ specifications and some DAQ manuals are available as PDFs. You  
must have Adobe Acrobat Reader with Search and Accessibility 5.0.5 or  
later installed to view the PDFs. Refer to the Adobe Systems Incorporated  
Web site at www.adobe.comto download Acrobat Reader. Refer to the  
National Instruments Product Manuals Library at ni.com/manualsfor  
updated documentation resources.  
© National Instruments Corporation  
xvii  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                 
1
Getting Started  
M Series NI 6238/6239 devices feature eight differential analog input (AI)  
channels, two analog output (AO) channels, two counters, six lines of  
digital input (DI), and four lines of digital output (DO). If you have not  
already installed your device, refer to the DAQ Getting Started Guide. For  
NI 6238 and NI 6239 device specifications, refer to the NI 6238/6239  
Specifications on ni.com/manuals.  
Before installing your DAQ device, you must install the software you plan  
to use with the device.  
Installing NI-DAQmx  
The DAQ Getting Started Guide, which you can download at  
ni.com/manuals, offers NI-DAQmx users step-by-step instructions for  
installing software and hardware, configuring channels and tasks, and  
getting started developing an application.  
Installing Other Software  
If you are using other software, refer to the installation instructions that  
accompany your software.  
Installing the Hardware  
The DAQ Getting Started Guide contains non-software-specific  
information on how to install PCI and PXI devices, as well as accessories  
and cables.  
Device Pinouts  
Refer to Appendix A, Device-Specific Information, for NI 6238/6239  
device pinouts.  
© National Instruments Corporation  
1-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                   
Chapter 1  
Getting Started  
Device Specifications  
Refer to the NI 6238/6239 Specifications, available on the NI-DAQ Device  
Document Browser or ni.com/manuals, for more detailed information  
on NI 6238/6239 devices.  
Device Accessories and Cables  
NI offers a variety of accessories and cables to use with your DAQ device.  
Refer to Appendix A, Device-Specific Information, or ni.comfor more  
information.  
NI 6238/6239 User Manual  
1-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
2
DAQ System Overview  
Figure 2-1 shows a typical DAQ system, which includes sensors,  
transducers, cables that connect the various devices to the accessories, the  
M Series device, programming software, and PC. The following sections  
cover the components of a typical DAQ system.  
Sensors and  
Transducers  
Cables and  
Accessories  
DAQ  
Hardware  
DAQ  
Software  
Personal  
Computer  
Figure 2-1. Components of a Typical DAQ System  
DAQ Hardware  
DAQ hardware digitizes input signals, performs D/A conversions to  
generate analog output signals, and measures and controls digital I/O  
signals. Figure 2-2 features the components of the NI 6238/6239 devices.  
© National Instruments Corporation  
2-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 2  
DAQ System Overview  
A
Isolation  
Barrier  
Analog Input  
AI GND  
A
Digital  
Routing  
and Clock  
Generation  
Analog Output  
Bus  
Interface  
A
Bus  
AO GND  
Digital  
Isolators  
Counters  
RTSI  
PFI/Static DI  
P0  
P1  
P0.GND  
P1.GND  
PFI/Static DO  
Figure 2-2. General NI 6238/6239 Block Diagram  
DAQ-STC2  
The DAQ-STC2 implements a high-performance digital engine for  
NI 6238/6239 data acquisition hardware. Some key features of this engine  
include the following:  
Flexible AI and AO sample and convert timing  
Many triggering modes  
Independent AI and AO FIFOs  
Generation and routing of RTSI signals for multi-device  
synchronization  
Generation and routing of internal and external timing signals  
Two flexible 32-bit counter/timer modules with hardware gating  
Static DIO signals  
PLL for clock synchronization  
PCI/PXI interface  
Independent scatter-gather DMA controllers for all acquisition and  
generation functions  
NI 6238/6239 User Manual  
2-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 2  
DAQ System Overview  
Calibration Circuitry  
The M Series analog inputs and outputs can self calibrate to correct gain  
and offset errors. You can calibrate the device to minimize AI and AO  
errors caused by time and temperature drift at run time. No external  
circuitry is necessary; an internal reference ensures high accuracy and  
stability over time and temperature changes.  
Factory-calibration constants are permanently stored in an onboard  
EEPROM and cannot be modified. When you self-calibrate the device,  
software stores new constants in a user-modifiable section of the EEPROM.  
To return a device to its initial factory calibration settings, software can  
copy the factory-calibration constants to the user-modifiable section of the  
EEPROM. Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more  
information on using calibration constants.  
Sensors and Transducers  
Sensors can generate electrical signals to measure physical phenomena,  
such as temperature, force, sound, or light. Some commonly used sensors  
are strain gauges, thermocouples, thermistors, angular encoders, linear  
encoders, and resistance temperature detectors (RTDs).  
Note Current input measurement devices can only interface with sensors that output a  
current.  
To measure signals from these various transducers, you must convert them  
into a form that a DAQ device can accept. For example, the output voltage  
of most thermocouples is very small and susceptible to noise. Therefore,  
you may need to amplify or filter the thermocouple output before digitizing  
it, or use the smallest measurement range available within the DAQ device.  
For more information about sensors, refer to the following:  
For general information about sensors, visit ni.com/sensors.  
If you are using LabVIEW, refer to the LabVIEW Help by selecting  
Help»Search the LabVIEW Help in LabVIEW, and then navigate to  
the Taking Measurements book on the Contents tab.  
If you are using other application software, refer to Common Sensors  
in the NI-DAQmx Help, which can be accessed from Start»All  
Programs»National Instruments»NI-DAQ»NI-DAQmx Help.  
© National Instruments Corporation  
2-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 2  
DAQ System Overview  
Cables and Accessories  
NI offers a variety of products to use with NI 6238/6239 devices, including  
cables, connector blocks, and other accessories, as follows:  
Cables and cable assemblies  
Shielded  
Unshielded ribbon  
For more specific information about these products, refer to ni.com.  
Refer to the Custom Cabling section of this chapter, the Field Wiring  
Considerations section of Chapter 4, Analog Input, and Appendix A,  
Device-Specific Information, for information on how to select accessories  
for your M Series device.  
Custom Cabling  
NI offers cables and accessories for many applications. However, if you  
want to develop your own cable, the following kits can assist you:  
TB-37F-37SC—37-pin solder cup terminals, shell with strain relief  
TB-37F-37CP—37-pin crimp & poke terminals, shell with strain  
relief  
Also, adhere to the following guidelines for best results:  
For AI signals, use shielded, twisted-pair wires for each AI pair of  
differential inputs. Connect the shield for each signal pair to the ground  
reference at the source.  
Route the analog lines separately from the digital lines.  
When using a cable shield, use separate shields for the analog and  
digital sections of the cable. Failure to do so results in noise coupling  
into the analog signals from transient digital signals.  
For more information on the connectors used for DAQ devices, refer to the  
KnowledgeBase document, Specifications and Manufacturers for Board  
Mating Connectors, by going to ni.com/infoand entering the info code  
rdspmb.  
NI 6238/6239 User Manual  
2-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 2  
DAQ System Overview  
Programming Devices in Software  
National Instruments measurement devices are packaged with NI-DAQ  
driver software, an extensive library of functions and VIs you can call from  
your application software, such as LabVIEW or LabWindows/CVI, to  
program all the features of your NI measurement devices. Driver software  
has an application programming interface (API), which is a library of VIs,  
functions, classes, attributes, and properties for creating applications for  
your device.  
NI-DAQ includes two NI-DAQ drivers, Traditional NI-DAQ (Legacy) and  
NI-DAQmx. M Series devices use the NI-DAQmx driver. Each driver has  
its own API, hardware configuration, and software configuration. Refer to  
the DAQ Getting Started Guide for more information about the two drivers.  
NI-DAQmx includes a collection of programming examples to help you get  
started developing an application. You can modify example code and save  
it in an application. You can use examples to develop a new application or  
add example code to an existing application.  
To locate LabVIEW and LabWindows/CVI examples, open the National  
Instruments Example Finder.  
In LabVIEW, select Help»Find Examples.  
In LabWindows/CVI, select Help»NI Example Finder.  
Measurement Studio, Visual Basic, and ANSI C examples are located in the  
following directories:  
NI-DAQmx examples for Measurement Studio-supported languages  
are in the following directories:  
MeasurementStudio\VCNET\Examples\NIDaq  
MeasurementStudio\DotNET\Examples\NIDaq  
NI-DAQmx examples for ANSI C are in the  
NI-DAQ\Examples\DAQmx ANSI C Devdirectory  
For additional examples, refer to zone.ni.com.  
© National Instruments Corporation  
2-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
The I/O Connector Signal Descriptions and RTSI Connector Pinout  
sections contain information on M Series connectors. Refer to  
Appendix A, Device-Specific Information, for device I/O connector  
pinouts.  
I/O Connector Signal Descriptions  
Table 3-1 describes the signals found on the I/O connectors. Not all signals  
are available on all devices.  
Table 3-1. I/O Connector Signals  
Signal Name  
AI GND  
Reference  
Direction  
Description  
Analog Input Ground—These terminals are the input bias  
current return point. AI GND and AO GND are connected on  
the device.  
Note: AI GND and AO GND are isolated from earth ground,  
chassis ground, P0.GND, and P1.GND.  
AI <0..7>  
AI GND  
Input  
Analog Input Channels 0 to 7 —AI 0+ and AI 0– are the  
positive and negative inputs of differential analog input  
channel 0. Similarly, the following signal pairs also form  
differential input channels:  
<AI 1+, AI 1–>, <AI 2+, AI 2–>, <AI 3+, AI 3–>,  
<AI 4+, AI 4–>, <AI 5+, AI 5–>, <AI 6+, AI 6–>,  
<AI 7+, AI 7–>  
Also refer to the Analog Input Ground-Reference Settings  
section of Chapter 4, Analog Input.  
Note: AI <0..7> are isolated from earth ground and chassis  
ground.  
AO <0..1>  
AO GND  
Output  
Analog Output Channels 0 to 1—These terminals supply the  
current output of AO channels 0 to 1.  
Note: AO <0..1> are isolated from earth ground and chassis  
ground.  
© National Instruments Corporation  
3-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 3  
Connector Information  
Table 3-1. I/O Connector Signals (Continued)  
Signal Name  
AO GND  
Reference  
Direction  
Description  
Analog Output Ground—AO GND is the reference for  
AO <0..1>. AI GND and AO GND are connected on the  
device.  
Note: AI GND and AO GND are isolated from earth ground,  
chassis ground, P0.GND, and P1.GND.  
PFI <0..5>/P0.<0..5>  
P0.GND  
Input  
Programmable Function Interface or Static Digital Input  
Channels 0 to 5—Each of these terminals can be individually  
configured as an input directional PFI terminal or a digital  
input terminal.  
As an input, each input PFI terminal can be used to supply an  
external source for AI or AO timing signals or counter/timer  
inputs.  
Note: PFI <0..5>/P0.<0..5> are isolated from earth ground,  
chassis ground, AI GND, AO GND, and P1.GND.  
PFI <6..9>/P1.<0..3>  
P1.GND  
Output  
Programmable Function Interface or Static Digital  
Output Channels 6 to 9—Each of these terminals can be  
individually configured as an output directional PFI terminal  
or a digital output terminal.  
As a PFI output, you can route many different internal AI or  
AO timing signals to each PFI terminal. You also can route the  
counter/timer outputs to each PFI terminal.  
Note: PFI <6..9>/P1.<0..3> are isolated from earth ground,  
chassis ground, AI GND, AO GND, and P0.GND.  
NC  
No connect—Do not connect signals to these terminals.  
P0.GND  
Digital Ground—P0.GND supplies the reference for input  
PFI <0..5>/P0.<0..5>.  
Note: P0.GND is isolated from earth ground, chassis ground,  
AI GND, AO GND, and P1.GND.  
P1.GND  
Digital Ground—P1.GND supplies the reference for output  
PFI <6..9>/P1.<0..3>.  
Note: P1.GND is isolated from earth ground, chassis ground,  
AI GND, AO GND, and P0.GND.  
P1.VCC  
Digital Output Power—P1.VCC supplies the power for  
digital output lines. The actual power consumed depends on  
the load connected between the digital output and P1.GND.  
Analog Output Power Supply—AO POWER SUPPLY  
supplies power to the analog current output terminals.  
NI 6238/6239 User Manual  
3-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Chapter 3  
Connector Information  
Table 3-1. I/O Connector Signals (Continued)  
Signal Name  
CAL+  
Reference  
Direction  
Description  
External Calibration Positive Reference—CAL+ supplies  
the positive reference during external calibration of the NI  
6238/6239.  
CAL–  
the negative reference during external calibration of the NI  
6238/6239.  
RTSI Connector Pinout  
Refer to the RTSI Connector Pinout section of Chapter 10, Digital Routing  
and Clock Generation, for information on the RTSI connector.  
© National Instruments Corporation  
3-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
4
Analog Input  
Figure 4-1 shows the analog input circuitry of NI 6238 and NI 6239  
devices.  
Isolation  
Barrier  
AI <0..7>+  
Mux  
AI Terminal  
Configuration  
Selection  
Digital  
Isolators  
AI FIFO  
NI-PGIA  
ADC  
AI Data  
AI <0..7>–  
Input Range  
Selection  
AI GND  
Figure 4-1. NI 6238/6239 Analog Input Circuitry  
I/O Connector  
You can connect analog input signals to the M Series device through the I/O  
connector. The proper way to connect analog input signals is outlined in the  
Connecting Analog Current Input Signals section. Also refer to  
Appendix A, Device-Specific Information, for device I/O connector  
pinouts.  
MUX  
Each M Series device has one analog-to-digital converter (ADC). The  
multiplexers (MUX) route one AI channel at a time to the ADC through the  
NI-PGIA.  
Instrumentation Amplifier (NI-PGIA)  
The NI programmable gain instrumentation amplifier (PGIA) is a  
measurement and instrument class amplifier that minimizes settling times  
© National Instruments Corporation  
4-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                 
Chapter 4  
Analog Input  
for all input ranges. The NI-PGIA can amplify or attenuate an AI signal to  
ensure that you use the maximum resolution of the ADC.  
M Series devices use the NI-PGIA to deliver high accuracy even when  
sampling multiple channels with small input ranges at fast rates. M Series  
devices can sample channels in any order at the maximum conversion rate,  
and you can individually program each channel in a sample with a different  
input range.  
A/D Converter  
The analog-to-digital converter (ADC) digitizes the AI signal by converting  
the analog voltage into a digital number.  
Isolation Barrier and Digital Isolators  
The digital isolators across the isolation barrier provide a ground break  
between the isolated analog front end and the earth/chassis/building  
ground.  
AI FIFO  
M Series devices can perform both single and multiple A/D conversions of  
a fixed or infinite number of samples. A large first-in-first-out (FIFO)  
buffer holds data during AI acquisitions to ensure that no data is lost.  
M Series devices can handle multiple A/D conversion operations with  
DMA, interrupts, or programmed I/O.  
Analog Input Range  
Input range refers to the set of input voltages or currents that an analog  
input channel can digitize with the specified accuracy. The NI-PGIA  
amplifies or attenuates the AI signal depending on the input range. You can  
individually program the input range of each AI channel on your M Series  
device.  
The input range affects the resolution of the M Series device for an AI  
channel. Resolution refers to the voltage or current of one ADC code.  
For example, a 16-bit ADC converts analog current inputs into one of  
65,536 (= 216) codes—that is, one of 65,536 possible digital values. These  
values are spread fairly evenly across the input range. So, for an input range  
of 20 mA, the current of each code of a 16-bit ADC is:  
NI 6238/6239 User Manual  
4-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 4  
Analog Input  
(20 mA – (–20 mA))  
216  
= 610 nA  
M Series devices use a calibration method that requires some codes  
(typically about 5% of the codes) to lie outside of the specified range. This  
calibration method improves absolute accuracy, but it increases the nominal  
resolution of input ranges by about 5% over what the formulas shown above  
would indicate.  
Choose an input range that matches the expected input range of your signal.  
A large input range can accommodate a large signal variation, but reduces  
the measurement resolution. Choosing a smaller input range improves the  
measurement resolution, but may result in the input signal going out of  
range.  
For more information on programming these settings, refer to the  
NI-DAQmx Help or the LabVIEW 8.x Help.  
Table 4-1 shows the input ranges and resolutions supported by the NI 6238  
and NI 6239 devices.  
Table 4-1. Input Ranges for NI 6238/6239  
Nominal Resolution Assuming  
Input Range  
5% Over Range  
20 mA  
640 nA  
Connecting Analog Current Input Signals  
When making signal connections, caution must be taken with the voltage  
level of the signal going into the device. There are two types of connections  
that can be made.  
Method 1  
Method 1, shown in Figure 4-2, connects AI + and AI – inputs at a voltage  
level with respect to AI GND. Verify that the voltage levels on the AI + and  
AI – side do not exceed the common-mode input range of 10 V.  
Common-mode input range is the voltage input range with respect to  
AI GND (AI + versus AI GND, AI – versus AI GND, or AI + versus AI –).  
© National Instruments Corporation  
4-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 4  
Analog Input  
Isolation  
Barrier  
AI +  
AI –  
+
+
V
AI GND  
AI GND  
Figure 4-2. Analog Current Input Connection Method 1  
Method 2  
Method 2, shown in Figure 4-3, ties the AI – input to AI GND. When  
measuring current up to 20 mA, this type of connection ensures that the  
voltage level on both the positive and negative side are within the  
common-mode input range for NI 6238/6239 devices.  
Isolation  
Barrier  
AI +  
+
AI –  
AI GND  
Figure 4-3. Analog Current Input Connection Method 2  
NI 6238/6239 User Manual  
4-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
Note that AI GND must always be connected to some voltage level.  
AI GND is the reference that NI 6238/6239 devices measure against.  
The NI 6238 and NI 6239 are isolated devices with isolation ratings up to  
60 VDC/30 Vrms. This allows for current measurement at high voltage  
levels provided that the common-mode input range requirement is satisfied.  
For example, in Figure 4-4, the node connected to AI GND can be at 50 V  
above the earth ground.  
Isolation  
Barrier  
AI +  
+
AI –  
AI GND  
+
= 50 V  
V
cm  
Figure 4-4. Current Measurement at High Voltage Levels  
The NI 6238/6239 device measures the voltage generated across the  
current input sense resistor during current input measurement. This voltage  
difference is then routed into the instrumentation amplifier (PGIA)  
differentially, as shown in Figure 4-5.  
© National Instruments Corporation  
4-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 4  
Analog Input  
Instrumentation  
Amplifier  
I
I
in+  
Current  
Sense  
Resistor  
+
PGIA  
Measured  
V
m
in–  
Voltage  
AI GND  
V
= I  
in R × Gain  
m
Figure 4-5. NI 6238/6239 PGIA  
Analog input ground-reference setting refers to the reference that the PGIA  
measures against. Differential is the only ground-reference setting for NI  
6238/6239 analog input signals, which means that the PGIA always  
measures the voltages between AI + and AI – generated across the input  
sense resistor, regardless of which analog input connection method is used.  
Refer to the Connecting Analog Current Input Signals section for allowable  
input connection methods.  
When measuring voltages internal to the device, such as the onboard  
reference, the signal is measured against AI GND. This measurement  
method is called referenced single-ended (RSE). The name is derived from  
the fact that one end of the measurement, the positive input of the PGIA, is  
connected to a signal, and the negative input of the PGIA is connected to  
the AI GND reference.  
Table 4-2 shows how signals are routed to the NI-PGIA.  
Table 4-2. Signals Routed to the NI-PGIA  
AI Ground-Reference  
Settings  
Signals Routed to the Positive  
Signals Routed to the Negative  
Input of the NI-PGIA (Vin+  
)
Input of the NI-PGIA (Vin–  
)
DIFF  
RSE  
AI <0..7>+  
AI <0..7>–  
Internal Channels  
AI GND  
Note On devices that allow multiple ground-reference settings, the settings are  
programmed on a per-channel basis.  
NI 6238/6239 User Manual  
4-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 4  
Analog Input  
Caution The maximum input voltages rating of AI signals with respect to AI GND (and  
for differential signals with respect to each other) and earth/chassis ground are listed in the  
Maximum Working Voltage section of the NI 6238/6239 Specifications. Exceeding the  
maximum input voltage or maximum working voltage of AI signals distorts the  
measurement results. Exceeding the maximum input voltage or maximum working voltage  
rating also can damage the device and the computer. Exceeding the maximum input voltage  
can cause injury and harm the user. NI is not liable for any damage or injuries resulting  
from such signal connections.  
AI ground-reference setting is sometimes referred to as AI terminal  
configuration.  
Configuring AI Ground-Reference Settings in  
Software  
You can program channels on an M Series device to acquire with different  
ground references.  
To enable multimode scanning in LabVIEW, use NI-DAQmx Create  
Virtual Channel.viof the NI-DAQmx API. You must use a new VI for  
each channel or group of channels configured in a different input mode. In  
Figure 4-6, channel 0 is configured in differential mode and  
aignd_vs_aignd reads the internal analog input ground-reference of the  
device.  
Figure 4-6. Enabling Multimode Scanning in LabVIEW  
To configure the input mode of your current measurement using the DAQ  
Assistant, use the Terminal Configuration drop-down list. Refer to the  
DAQ Assistant Help for more information on the DAQ Assistant.  
To configure the input mode of your current measurement using the  
NI-DAQmx C API, set the terminalConfig property. Refer to the  
NI-DAQmx C Reference Help for more information.  
© National Instruments Corporation  
4-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
Multichannel Scanning Considerations  
M Series devices can scan multiple channels at high rates and digitize the  
signals accurately. However, you should consider several issues when  
designing your measurement system to ensure the high accuracy of your  
measurements.  
In multichannel scanning applications, accuracy is affected by settling  
time. When your M Series device switches from one AI channel to another  
AI channel, the device configures the NI-PGIA with the input range of the  
new channel. The NI-PGIA then amplifies the input signal with the gain for  
the new input range. Settling time refers to the time it takes the NI-PGIA to  
amplify the input signal to the desired accuracy before it is sampled by the  
ADC. The NI 6238/6239 Specifications shows the device settling time.  
M Series devices are designed to have fast settling times. However, several  
factors can increase the settling time which decreases the accuracy of your  
measurements. To ensure fast settling times, you should do the following  
(in order of importance):  
Use short high-quality cabling  
Minimize current step between adjacent channels  
Avoid scanning faster than necessary  
Refer to the following sections for more information on these factors.  
Use Short High-Quality Cabling  
Using short high-quality cables can minimize several effects that degrade  
accuracy including crosstalk, transmission line effects, and noise. The  
capacitance of the cable also can increase the settling time.  
National Instruments recommends using individually shielded,  
twisted-pair wires that are 2 m or less to connect AI signals to the device.  
Refer to the Connecting Analog Current Input Signals section for more  
information.  
Minimize Current Step between Adjacent Channels  
When scanning between channels that have the same input range, the  
settling time increases with the current step between the channels. If you  
know the expected input range of your signals, you can group signals with  
similar expected ranges together in your scan list.  
NI 6238/6239 User Manual  
4-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 4  
Analog Input  
For example, suppose all channels in a system use a –20 to 20 mA input  
range. The signals on channels 0, 2, and 4 vary between 18 and 19 mA. The  
signals on channels 1, 3, and 5 vary between –18 and 0 mA. Scanning  
channels in the order 0, 2, 4, 1, 3, 5 will produce more accurate results than  
scanning channels in the order 0, 1, 2, 3, 4, 5.  
Avoid Scanning Faster Than Necessary  
Designing your system to scan at slower speeds gives the PGIA more time  
to settle to a more accurate level. Here are two examples to consider.  
Example 1  
Averaging many AI samples can increase the accuracy of the reading by  
decreasing noise effects. In general, the more points you average, the more  
accurate the final result will be. However, you may choose to decrease the  
number of points you average and slow down the scanning rate.  
Suppose you want to sample 10 channels over a period of 40 ms and  
average the results. You could acquire 500 points from each channel at a  
scan rate of 125 kS/s. Another method would be to acquire 1,000 points  
from each channel at a scan rate of 250 kS/s. Both methods take the same  
amount of time. Doubling the number of samples averaged (from 500 to  
1,000) decreases the effect of noise by a factor of 1.4 (the square root of 2).  
However, doubling the number of samples (in this example) decreases the  
time the PGIA has to settle from 8 µs to 4 µs. In some cases, the slower scan  
rate system returns more accurate results.  
Example 2  
If the time relationship between channels is not critical, you can sample  
from the same channel multiple times and scan less frequently. For  
example, suppose an application requires averaging 100 points from  
channel 0 and averaging 100 points from channel 1. You could alternate  
reading between channels—that is, read one point from channel 0, then one  
point from channel 1, and so on. You also could read all 100 points from  
channel 0 then read 100 points from channel 1. The second method  
switches between channels much less often and is affected much less by  
settling time.  
© National Instruments Corporation  
4-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 4  
Analog Input  
Analog Input Data Acquisition Methods  
When performing analog input measurements, you either can perform  
software-timed or hardware-timed acquisitions. Hardware-timed  
acquisitions can be buffered or non-buffered.  
Software-Timed Acquisitions  
With a software-timed acquisition, software controls the rate of the  
acquisition. Software sends a separate command to the hardware to initiate  
each ADC conversion. In NI-DAQmx, software-timed acquisitions are  
referred to as having on-demand timing. Software-timed acquisitions are  
also referred to as immediate or static acquisitions and are typically used  
for reading a single sample of data.  
Hardware-Timed Acquisitions  
With hardware-timed acquisitions, a digital hardware signal  
(ai/SampleClock) controls the rate of the acquisition. This signal can be  
generated internally on your device or provided externally.  
Hardware-timed acquisitions have several advantages over software-timed  
acquisitions.  
The time between samples can be much shorter.  
The timing between samples is deterministic.  
Hardware-timed acquisitions can use hardware triggering.  
Hardware-timed operations can be buffered or non-buffered. A buffer is a  
temporary storage in computer memory for to-be-generated samples.  
Buffered  
In a buffered acquisition, data is moved from the DAQ device’s onboard  
FIFO memory to a PC buffer using DMA or interrupts before it is  
transferred to application memory. Buffered acquisitions typically allow  
for much faster transfer rates than non-buffered acquisitions because data  
is moved in large blocks, rather than one point at a time.  
One property of buffered I/O operations is the sample mode. The sample  
mode can be either finite or continuous.  
Finite sample mode acquisition refers to the acquisition of a specific,  
predetermined number of data samples. After the specified number of  
NI 6238/6239 User Manual  
4-10  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 4  
Analog Input  
samples has been written out, the generation stops. If you use a reference  
trigger, you must use finite sample mode.  
Continuous acquisition refers to the acquisition of an unspecified number  
of samples. Instead of acquiring a set number of data samples and stopping,  
a continuous acquisition continues until you stop the operation. Continuous  
acquisition is also referred to as double-buffered or circular-buffered  
acquisition.  
If data cannot be transferred across the bus fast enough, the FIFO will  
become full. New acquisitions will overwrite data in the FIFO before it can  
be transferred to host memory. The device generates an error in this case.  
With continuous operations, if the user program does not read data out of  
the PC buffer fast enough to keep up with the data transfer, the buffer could  
reach an overflow condition, causing an error to be generated.  
Non-Buffered  
In non-buffered acquisitions, data is read directly from the FIFO on the  
device. Typically, hardware-timed, non-buffered operations are used to  
read single samples with known time increments between them and good  
latency.  
Analog Input Triggering  
Analog input supports three different triggering actions:  
Start trigger  
Reference trigger  
Pause trigger  
Refer to the AI Start Trigger Signal, AI Reference Trigger Signal, and AI  
Pause Trigger Signal sections for information on these triggers.  
A digital trigger can initiate these actions. NI 6238/6239 devices support  
digital triggering, but do not support analog triggering.  
Field Wiring Considerations  
Environmental noise can seriously affect the measurement accuracy of the  
device if you do not take proper care when running signal wires between  
signal sources and the device. The following recommendations apply  
© National Instruments Corporation  
4-11  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 4  
Analog Input  
mainly to AI signal routing to the device, although they also apply to signal  
routing in general.  
Minimize noise pickup and maximize measurement accuracy by using  
individually shielded, twisted-pair wires to connect AI signals to the  
device. With this type of wire, the signals attached to the positive and  
negative input channels are twisted together and then covered with a shield.  
You then connect this shield only at one point to the signal source ground.  
This kind of connection is required for signals traveling through areas with  
large magnetic fields or high electromagnetic interference.  
Refer to the NI Developer Zone document, Field Wiring and Noise  
Considerations for Analog Signals, for more information. To access this  
document, go to ni.com/infoand enter the info code rdfwn3.  
In order to provide all of the timing functionality described throughout this  
section, NI 6238/6239 devices have a flexible timing engine. Figure 4-7  
summarizes all of the timing options provided by the analog input timing  
engine. Also refer to the Clock Routing section of Chapter 10, Digital  
Routing and Clock Generation.  
PFI, RTSI  
PXI_STAR  
ai/Sample  
PFI, RTSI  
PXI_STAR  
Ctr n Internal Output  
SW Pulse  
ai/Sample  
Clock  
Timebase  
Clock  
Programmable  
20 MHz Timebase  
100 kHz Timebase  
PXI_CLK10  
Clock  
Divider  
PFI, RTSI  
PXI_STAR  
ai/Convert  
Clock  
ai/Convert  
Clock  
Ctr n Internal Output  
Timebase Programmable  
Clock  
Divider  
Figure 4-7. Analog Input Timing Options  
NI 6238/6239 User Manual  
4-12  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
M Series devices use ai/SampleClock and ai/ConvertClock to perform  
interval sampling. As Figure 4-8 shows, ai/SampleClock controls the  
sample period, which is determined by the following equation:  
1/Sample Period = Sample Rate  
Channel 0  
Channel 1  
Convert Period  
Sample Period  
Figure 4-8. Interval Sampling  
ai/ConvertClock controls the Convert Period, which is determined by the  
following equation:  
1/Convert Period = Convert Rate  
By default, the NI-DAQmx driver chooses the fastest Channel Clock rate  
possible while still allowing extra time for adequate amplifier settling time.  
At slower scan rates, 10 μs of delay is added to the fastest possible channel  
conversion rate of the device, which is the same as the maximum scan rate,  
to derive the Channel Clock.  
As the scan rate increases, there eventually will not be enough time to have  
a full 10 μs of additional delay time between channel conversions and to  
finish acquiring all channels before the next edge of the Scan Clock. At this  
point, NI-DAQmx uses round robin channel sampling, evenly dividing the  
time between scans by the number of channels being acquired to obtain the  
interchannel delay. In this case, you can calculate the Channel Clock by  
multiplying the scan rate by the number of channels being acquired.  
For example, the NI 623x M Series device has a maximum sampling rate of  
250 kS/s. At a slower acquisition rate, such as 10 kHz with 2 channels, the  
Convert Clock would be set to 71428.6 Hz. This rate is determined by  
taking the fastest channel conversion rate for the device and adding 10 μs,  
4 μs (1/250000) + 10 μs, which results in 14 μs or 71428.6 Hz.  
© National Instruments Corporation  
4-13  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Chapter 4  
Analog Input  
When this calculation results in the sampling rate exceeding 35 kHz, there  
is not enough time between samples to acquire both channels and still add  
a 10 μs delay per channel, so the Convert Clock rate becomes the sampling  
rate multiplied by the number of channels being acquired. For example, on  
the PCI-6220 M Series device, a sampling rate of 40 kHz for two channels  
would result in a Convert Clock rate of 80 kHz.  
Maximum settling time for the amplifier is also very important. For  
example, to ensure accuracy to within 1 LSB on an NI 623x M Series  
device, the device requires a minimum amplifier settling time of 6 μs even  
though the maximum channel conversion rate is 4 μs. Higher source  
impedance also increases amplifier settling time.  
Note The sampling rate is the fastest you can acquire data on the device and still achieve  
accurate results. For example, if an M Series device has a sampling rate of 250 kS/s, this  
sampling rate is aggregate—one channel at 250 kS/s or two channels at 125 kS/s per  
channel illustrates the relationship.  
Posttriggered data acquisition allows you to view only data that is acquired  
after a trigger event is received. A typical posttriggered DAQ sequence is  
shown in Figure 4-9. In this example, the DAQ device reads two channels  
five times. The sample counter is loaded with the specified number of  
posttrigger samples, in this example, five. The value decrements with each  
pulse on ai/SampleClock, until the value reaches zero and all desired  
samples have been acquired.  
ai/StartTrigger  
ai/SampleClock  
ai/ConvertClock  
Sample Counter  
4
3
2
1
0
Figure 4-9. Posttriggered Data Acquisition Example  
Pretriggered data acquisition allows you to view data that is acquired before  
the trigger of interest, in addition to data acquired after the trigger.  
Figure 4-10 shows a typical pretriggered DAQ sequence. ai/StartTrigger  
can be either a hardware or software signal. If ai/StartTrigger is set up to be  
a software start trigger, an output pulse appears on the ai/StartTrigger line  
when the acquisition begins. When the ai/StartTrigger pulse occurs, the  
sample counter is loaded with the number of pretriggered samples, in this  
NI 6238/6239 User Manual  
4-14  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Chapter 4  
Analog Input  
example, four. The value decrements with each pulse on ai/SampleClock,  
until the value reaches zero. The sample counter is then loaded with the  
number of posttriggered samples, in this example, three.  
ai/StartTrigger  
n/a  
ai/ReferenceTrigger  
ai/SampleClock  
ai/ConvertClock  
Scan Counter  
3
2
1
0
2
2
2
1
0
Figure 4-10. Pretriggered Data Acquisition Example  
If an ai/ReferenceTrigger pulse occurs before the specified number of  
pretrigger samples are acquired, the trigger pulse is ignored. Otherwise,  
when the ai/ReferenceTrigger pulse occurs, the sample counter value  
decrements until the specified number of posttrigger samples have been  
acquired.  
NI 6238/6239 devices feature the following analog input timing signals.  
AI Sample Clock Signal  
AI Sample Clock Timebase Signal  
AI Convert Clock Signal  
AI Convert Clock Timebase Signal  
AI Hold Complete Event Signal  
AI Start Trigger Signal  
AI Reference Trigger Signal  
AI Pause Trigger Signal  
AI Sample Clock Signal  
Use the AI Sample Clock (ai/SampleClock) signal to initiate a set of  
measurements. Your M Series device samples the AI signals of every  
channel in the task once for every ai/SampleClock. A measurement  
acquisition consists of one or more samples.  
© National Instruments Corporation  
4-15  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
You can specify an internal or external source for ai/SampleClock. You also  
can specify whether the measurement sample begins on the rising edge or  
falling edge of ai/SampleClock.  
Using an Internal Source  
One of the following internal signals can drive ai/SampleClock.  
Counter n Internal Output  
AI Sample Clock Timebase (divided down)  
A pulse initiated by host software  
A programmable internal counter divides down the sample clock timebase.  
Several other internal signals can be routed to ai/SampleClock through  
RTSI. Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
Using an External Source  
Use one of the following external signals as the source of ai/SampleClock:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
Routing AI Sample Clock Signal to an Output  
Terminal  
You can route ai/SampleClock out to any output PFI <6..9> or RTSI <0..7>  
terminal. This pulse is always active high.  
You can specify the output to have one of two behaviors. With the pulse  
behavior, your DAQ device briefly pulses the PFI terminal once for every  
occurrence of ai/SampleClock.  
With level behavior, your DAQ device drives the PFI terminal high during  
the entire sample.  
PFI <0..5> terminals are fixed inputs. PFI <6..9> terminals are fixed  
outputs.  
NI 6238/6239 User Manual  
4-16  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
Other Timing Requirements  
Your DAQ device only acquires data during an acquisition. The device  
ignores ai/SampleClock when a measurement acquisition is not in progress.  
During a measurement acquisition, you can cause your DAQ device to  
ignore ai/SampleClock using the ai/PauseTrigger signal.  
A counter on your device internally generates ai/SampleClock unless you  
select some external source. ai/StartTrigger starts this counter and either  
software or hardware can stop it after a finite acquisition completes. When  
using an internally generated ai/SampleClock, you also can specify a  
configurable delay from ai/StartTrigger to the first ai/SampleClock pulse.  
By default, this delay is set to two ticks of the ai/SampleClockTimebase  
signal. When using an externally generated ai/SampleClock, you must  
ensure the clock signal is consistent with respect to the timing requirements  
of ai/ConvertClock. Failure to do so may result in ai/SampleClock pulses  
that are masked off and acquisitions with erratic sampling intervals. Refer  
to the AI Convert Clock Signal section for more information on the timing  
requirements between ai/ConvertClock and ai/SampleClock.  
Figure 4-11 shows the relationship of ai/SampleClock to ai/StartTrigger.  
ai/SampleClockTimebase  
ai/StartTrigger  
ai/SampleClock  
Delay  
From  
Start  
Trigger  
Figure 4-11. ai/SampleClock and ai/StartTrigger  
AI Sample Clock Timebase Signal  
You can route any of the following signals to be the AI Sample Clock  
Timebase (ai/SampleClockTimebase) signal:  
20 MHz Timebase  
100 kHz Timebase  
PXI_CLK10  
© National Instruments Corporation  
4-17  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 4  
Analog Input  
RTSI <0..7>  
Input PFI <0..5>  
PXI_STAR  
ai/SampleClockTimebase is not available as an output on the I/O connector.  
ai/SampleClockTimebase is divided down to provide one of the possible  
sources for ai/SampleClock. You can configure the polarity selection for  
ai/SampleClockTimebase as either rising or falling edge.  
AI Convert Clock Signal  
Caution Setting the conversion rate higher than the maximum rate specified for your  
device will result in errors.  
Use the AI Convert Clock (ai/ConvertClock) signal to initiate a single A/D  
conversion on a single channel. A sample, controlled by the AI Sample  
Clock, consists of one or more conversions.  
You can specify either an internal or external signal as the source of  
ai/ConvertClock. You also can specify whether the measurement sample  
begins on the rising edge or falling edge of ai/ConvertClock.  
With NI-DAQmx, the driver will choose the fastest conversion rate possible  
based on the speed of the A/D converter and add 10 µs of padding between  
each channel to allow for adequate settling time. This scheme enables the  
channels to approximate simultaneous sampling and still allow for  
adequate settling time. If the AI Sample Clock rate is too fast to allow for  
this 10 µs of padding, NI-DAQmx will choose the conversion rate so that  
the AI Convert Clock pulses are evenly spaced throughout the sample.  
To explicitly specify the conversion rate, use the AI Convert Clock Rate  
DAQmx Timing property node or function.  
Using an Internal Source  
One of the following internal signals can drive ai/ConvertClock:  
AI Convert Clock Timebase (divided down)  
Counter n Internal Output  
A programmable internal counter divides down the AI Convert Clock  
Timebase to generate ai/ConvertClock. The counter is started by  
ai/SampleClock and continues to count down to zero, produces an  
ai/ConvertClock, reloads itself, and repeats the process until the sample is  
NI 6238/6239 User Manual  
4-18  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
finished. It then reloads itself in preparation for the next ai/SampleClock  
pulse.  
Using an External Source  
Use one of the following external signals as the source of ai/ConvertClock:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
Routing AI Convert Clock Signal to an Output  
Terminal  
You can route ai/ConvertClock (as an active low signal) out to any output  
PFI <6..9> or RTSI <0..7> terminal.  
PFI <0..5> terminals are fixed inputs. PFI <6..9> terminals are fixed  
outputs.  
Using a Delay from Sample Clock to Convert Clock  
When using an internally generated ai/ConvertClock, you also can specify  
a configurable delay from ai/SampleClock to the first ai/ConvertClock  
pulse within the sample. By default, this delay is three ticks of  
ai/ConvertClockTimebase.  
Figure 4-12 shows the relationship of ai/SampleClock to ai/ConvertClock.  
© National Instruments Corporation  
4-19  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
ai/ConvertClockTimebase  
ai/SampleClock  
ai/ConvertClock  
Delay  
From  
Convert  
Period  
Sample  
Clock  
Figure 4-12. ai/SampleClock and ai/ConvertClock  
Other Timing Requirements  
The sample and conversion level timing of M Series devices work such that  
clock signals are gated off unless the proper timing requirements are met.  
For example, the device ignores both ai/SampleClock and ai/ConvertClock  
until it receives a valid ai/StartTrigger signal. When the device recognizes  
an ai/SampleClock pulse, it ignores subsequent ai/SampleClock pulses  
until it receives the correct number of ai/ConvertClock pulses.  
Similarly, the device ignores all ai/ConvertClock pulses until it recognizes  
an ai/SampleClock pulse. After the device receives the correct number of  
ai/ConvertClock pulses, it ignores subsequent ai/ConvertClock pulses until  
it receives another ai/SampleClock. Figure 4-13 shows timing sequences  
for a four-channel acquisition (using AI channels 0, 1, 2, and 3) and  
demonstrates proper and improper sequencing of ai/SampleClock and  
ai/ConvertClock.  
It is also possible to use a single external signal to drive both  
ai/SampleClock and ai/ConvertClock at the same time. In this mode, each  
tick of the external clock will cause a conversion on the ADC. Figure 4-13  
shows this timing relationship.  
NI 6238/6239 User Manual  
4-20  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 4  
Analog Input  
ai/SampleClock  
ai/ConvertClock  
0 1  
2
3
0 1 …  
0 1  
2
3
Channel Measured  
Sample #1 Sample #2 Sample #3  
• One External Signal Driving Both Clocks  
Figure 4-13. Single External Signal Driving ai/SampleClock and ai/ConvertClock  
Simultaneously  
AI Convert Clock Timebase Signal  
The AI Convert Clock Timebase (ai/ConvertClockTimebase) signal is  
divided down to provide on of the possible sources for ai/ConvertClock.  
Use one of the following signals as the source of  
ai/ConvertClockTimebase:  
ai/SampleClockTimebase  
20 MHz Timebase  
ai/ConvertClockTimebase is not available as an output on the I/O  
connector.  
AI Hold Complete Event Signal  
The AI Hold Complete Event (ai/HoldCompleteEvent) signal generates a  
pulse after each A/D conversion begins. You can route  
ai/HoldCompleteEvent out to any output PFI <6..9> or RTSI <0..7>  
terminal.  
The polarity of ai/HoldCompleteEvent is software-selectable, but is  
typically configured so that a low-to-high leading edge can clock external  
AI multiplexers indicating when the input signal has been sampled and can  
be removed.  
© National Instruments Corporation  
4-21  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 4  
Analog Input  
AI Start Trigger Signal  
Use the AI Start Trigger (ai/StartTrigger) signal to begin a measurement  
acquisition. A measurement acquisition consists of one or more samples. If  
you do not use triggers, begin a measurement with a software command.  
After the acquisition begins, configure the acquisition to stop under the  
following conditions:  
When a certain number of points are sampled (in finite mode)  
After a hardware reference trigger (in finite mode)  
With a software command (in continuous mode)  
An acquisition that uses a start trigger (but not a reference trigger) is  
sometimes referred to as a posttriggered acquisition.  
Using a Digital Source  
To use ai/StartTrigger with a digital source, specify a source and an edge.  
The source can be any of the following signals:  
Input PFI <0..5>  
RTSI <0..7>  
Counter n Internal Output  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
The source also can be one of several other internal signals on your DAQ  
device. Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
You also can specify whether the measurement acquisition begins on the  
rising edge or falling edge of ai/StartTrigger.  
Routing AI Start Trigger to an Output Terminal  
You can route ai/StartTrigger out to any output PFI <6..9> or RTSI <0..7>  
terminal.  
The output is an active high pulse.  
The device also uses ai/StartTrigger to initiate pretriggered DAQ  
operations. In most pretriggered applications, a software trigger generates  
ai/StartTrigger. Refer to the AI Reference Trigger Signal section for a  
NI 6238/6239 User Manual  
4-22  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 4  
Analog Input  
complete description of the use of ai/StartTrigger and ai/ReferenceTrigger  
in a pretriggered DAQ operation.  
AI Reference Trigger Signal  
Use a reference trigger (ai/ReferenceTrigger) signal to stop a measurement  
acquisition. To use a reference trigger, specify a buffer of finite size and a  
number of pretrigger samples (samples that occur before the reference  
trigger). The number of posttrigger samples (samples that occur after the  
reference trigger) desired is the buffer size minus the number of pretrigger  
samples.  
After the acquisition begins, the DAQ device writes samples to the buffer.  
After the DAQ device captures the specified number of pretrigger samples,  
the DAQ device begins to look for the reference trigger condition. If the  
reference trigger condition occurs before the DAQ device captures the  
specified number of pretrigger samples, the DAQ device ignores the  
condition.  
If the buffer becomes full, the DAQ device continuously discards the oldest  
samples in the buffer to make space for the next sample. This data can be  
accessed (with some limitations) before the DAQ device discards it. Refer  
to the KnowledgeBase document, Can a Pretriggered Acquisition be  
Continuous?, for more information. To access this KnowledgeBase, go to  
ni.com/infoand enter the info code rdcanq.  
When the reference trigger occurs, the DAQ device continues to write  
samples to the buffer until the buffer contains the number of posttrigger  
samples desired. Figure 4-14 shows the final buffer.  
Reference Trigger  
Pretrigger Samples  
Posttrigger Samples  
Complete Buffer  
Figure 4-14. Reference Trigger Final Buffer  
© National Instruments Corporation  
4-23  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 4  
Analog Input  
Using a Digital Source  
To use ai/ReferenceTrigger with a digital source, specify a source and an  
edge. The source can be any of the following signals:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
The source also can be one of several internal signals on your DAQ device.  
Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
You also can specify whether the measurement acquisition stops on the  
rising edge or falling edge of ai/ReferenceTrigger.  
Routing AI Reference Trigger Signal to an Output  
Terminal  
You can route ai/ReferenceTrigger out to any output PFI <6..9> or  
RTSI <0..7> terminal.  
AI Pause Trigger Signal  
You can use the AI Pause Trigger (ai/PauseTrigger) signal to pause and  
resume a measurement acquisition. The internal sample clock pauses while  
the external trigger signal is active and resumes when the signal is inactive.  
You can program the active level of the pause trigger to be high or low.  
Using a Digital Source  
To use ai/SampleClock, specify a source and a polarity. The source can be  
any of the following signals:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
The source also can be one of several other internal signals on your DAQ  
device. Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
NI 6238/6239 User Manual  
4-24  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 4  
Analog Input  
Routing AI Pause Trigger Signal to an Output  
Terminal  
You can route ai/PauseTrigger out to RTSI <0..7>.  
Note Pause triggers are only sensitive to the level of the source, not the edge.  
Getting Started with AI Applications in Software  
You can use the M Series device in the following analog input applications.  
Single-point analog input  
Finite analog input  
Continuous analog input  
You can perform these applications through DMA, interrupt, or  
programmed I/O data transfer mechanisms. Some of the applications also  
use start, reference, and pause triggers.  
Note For more information about programming analog input applications and triggers in  
software, refer to the NI-DAQmx Help or the LabVIEW 8.x Help.  
© National Instruments Corporation  
4-25  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
5
Analog Output  
NI 6238/6239 devices have two AO channels controlled by a single clock  
and capable of waveform generation. Figure 5-1 shows the analog current  
output circuitry of NI 6238 and NI 6239 devices.  
V-I Converter  
Isolation  
Barrier  
AO POWER SUPPLY  
AO 0  
DAC0  
DAC1  
Digital  
Isolators  
AO FIFO  
V-I Converter  
AO Sample Clock  
AO 1  
AO GND  
Figure 5-1. NI 6238/6239 Analog Current Output Circuitry  
Analog Output Circuitry  
DACs  
Digital-to-analog converters (DACs) convert digital codes to analog  
voltages.  
V-I Converter  
The V-I converter converts voltage (V) into current (I).  
AO FIFO  
The AO FIFO enables analog output waveform generation. It is a  
first-in-first-out (FIFO) memory buffer between the computer and the  
© National Instruments Corporation  
5-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                 
Chapter 5  
Analog Output  
DACs. It allows you to download the points of a waveform to your M Series  
device without host computer interaction.  
AO Sample Clock  
The AO Sample Clock signal reads a sample from the DAC FIFO and  
generates the AO voltage.  
Isolation Barrier and Digital Isolators  
The digital isolators across the isolation barrier provide a ground break  
between the isolated analog front end and the earth/chassis/building  
ground.  
Analog Output Data Generation Methods  
When performing an analog output operation, you either can perform  
software-timed or hardware-timed generations. Hardware-timed  
generations can be non-buffered or buffered.  
Software-Timed Generations  
With a software-timed generation, software controls the rate at which data  
is generated. Software sends a separate command to the hardware to initiate  
each DAC conversion. In NI-DAQmx, software-timed generations are  
referred to as on-demand timing. Software-timed generations are also  
referred to as immediate or static operations. They are typically used for  
writing a single value out, such as a constant DC current.  
Hardware-Timed Generations  
With a hardware-timed generation, a digital hardware signal controls the  
rate of the generation. This signal can be generated internally on your  
device or provided externally.  
Hardware-timed generations have several advantages over software-timed  
acquisitions:  
The time between samples can be much shorter.  
The timing between samples can be deterministic.  
Hardware-timed acquisitions can use hardware triggering.  
Hardware-timed operations can be buffered or non-buffered. A buffer is a  
temporary storage in computer memory for to-be-generated samples.  
NI 6238/6239 User Manual  
5-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 5  
Analog Output  
Non-Buffered  
In non-buffered acquisitions, data is written directly to the DACs on the  
device. Typically, hardware-timed, non-buffered operations are used to  
write single samples with good latency and known time increments  
between them.  
Buffered  
In a buffered acquisition, data is moved from a PC buffer to the DAQ  
device’s onboard FIFO using DMA or interrupts before it is written to the  
DACs one sample at a time. Buffered acquisitions typically allow for much  
faster transfer rates than non-buffered acquisitions because data is moved  
in large blocks, rather than one point at a time.  
One property of buffered I/O operations is the sample mode. The sample  
mode can be either finite or continuous.  
Finite sample mode generation refers to the generation of a specific,  
predetermined number of data samples. After the specified number of  
samples has been written out, the generation stops.  
Continuous generation refers to the generation of an unspecified number of  
samples. Instead of generating a set number of data samples and stopping,  
a continuous generation continues until you stop the operation. There are  
several different methods of continuous generation that control what data is  
written. These methods are regeneration, FIFO regeneration, and  
non-regeneration modes.  
Regeneration is the repetition of the data that is already in the buffer.  
Standard regeneration is when data from the PC buffer is continually  
downloaded to the FIFO to be written out. New data can be written to the  
PC buffer at any time without disrupting the output.  
With FIFO regeneration, the entire buffer is downloaded to the FIFO and  
regenerated from there. After the data is downloaded, new data cannot be  
written to the FIFO. To use FIFO regeneration, the entire buffer must fit  
within the FIFO size. The advantage of using FIFO regeneration is that it  
does not require communication with the main host memory after the  
operation is started, thereby preventing any problems that may occur due to  
excessive bus traffic.  
With non-regeneration, old data will not be repeated. New data must be  
continually written to the buffer. If the program does not write new data to  
© National Instruments Corporation  
5-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 5  
Analog Output  
the buffer at a fast enough rate to keep up with the generation, the buffer  
will underflow and cause an error.  
Analog Output Triggering  
Analog output supports two different triggering actions:  
Start trigger  
Pause trigger  
A digital trigger can initiate these actions. NI 6238/6239 devices support  
digital triggering, but do not support analog triggering. Refer to the AO  
Start Trigger Signal and AO Pause Trigger Signal sections for more  
information on these triggering actions.  
AO <0..1> are the current output signals for AO channels 0 and 1. AO GND  
is the ground reference for AO <0..1>.  
Figure 5-2 shows how to make analog current output connections to the  
device.  
AO Power  
NI 6238/6239  
Supply Pin  
Internal  
Voltage  
Drop  
User-  
Provided  
Power  
+
DAC  
Supply  
AO x  
User-  
Provided  
Load  
User-Provided  
AO GND  
AO GND  
Figure 5-2. Analog Current Output Connections  
Tip Internal voltage drop for the NI 6238/6239 devices is a maximum of 3 V relative to  
Caution The maximum output voltages rating of AO signals and input voltage ratings for  
AO power supply with respect to AO GND and earth/chassis ground are listed in the  
NI 6238/6239 User Manual  
5-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 5  
Analog Output  
Maximum Working Voltage section of the NI 6238/6239 Specifications. Exceeding the  
maximum input supply voltage or maximum working voltage of AO signals distorts the  
measurement results. Exceeding the maximum input supply voltage or maximum working  
voltage rating also can damage the device and the computer. Exceeding the maximum  
output voltage can cause injury and harm the user. NI is not liable for any damage or  
injuries resulting from such signal connections.  
Analog Output Timing Signals  
Figure 5-3 summarizes all of the timing options provided by the analog  
output timing engine.  
PFI, RTSI  
PXI_STAR  
PFI, RTSI  
PXI_STAR  
ao/Sample  
Clock  
ao/Sample  
Clock  
Ctr n Internal Output  
Timebase  
Programmable  
Clock  
Divider  
20 MHz Timebase  
100 kHz Timebase  
PXI_CLK10  
Figure 5-3. Analog Output Timing Options  
NI 6238/6239 devices feature the following AO (waveform generation)  
timing signals.  
AO Start Trigger Signal  
AO Pause Trigger Signal  
AO Sample Clock Signal  
AO Sample Clock Timebase Signal  
AO Start Trigger Signal  
Use the AO Start Trigger (ao/StartTrigger) signal to initiate a waveform  
generation. If you do not use triggers, you can begin a generation with a  
software command.  
© National Instruments Corporation  
5-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 5  
Analog Output  
Using a Digital Source  
To use ao/StartTrigger, specify a source and an edge. The source can be one  
of the following signals:  
A pulse initiated by host software  
Input PFI <0..5>  
RTSI <0..7>  
ai/ReferenceTrigger  
ai/StartTrigger  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
The source also can be one of several internal signals on your DAQ device.  
Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
You also can specify whether the waveform generation begins on the rising  
edge or falling edge of ao/StartTrigger.  
Routing AO Start Trigger Signal to an Output  
Terminal  
You can route ao/StartTrigger out to any output PFI <6..9> or RTSI <0..7>  
terminal.  
The output is an active high pulse.  
PFI <0..5> terminals are fixed inputs. PFI <6..9> terminals are fixed  
outputs.  
AO Pause Trigger Signal  
Use the AO Pause Trigger signal (ao/PauseTrigger) to mask off samples in  
a DAQ sequence. That is, when ao/PauseTrigger is active, no samples  
occur.  
ao/PauseTrigger does not stop a sample that is in progress. The pause does  
not take effect until the beginning of the next sample.  
When you generate analog output signals, the generation pauses as soon as  
the pause trigger is asserted. If the source of your sample clock is the  
NI 6238/6239 User Manual  
5-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 5  
Analog Output  
onboard clock, the generation resumes as soon as the pause trigger is  
deasserted, as shown in Figure 5-4.  
Pause Trigger  
Sample Clock  
Figure 5-4. ao/PauseTrigger with the Onboard Clock Source  
If you are using any signal other than the onboard clock as the source of  
your sample clock, the generation resumes as soon as the pause trigger is  
deasserted and another edge of the sample clock is received, as shown in  
Figure 5-5.  
Pause Trigger  
Sample Clock  
Figure 5-5. ao/PauseTrigger with Other Signal Source  
Using a Digital Source  
To use ao/PauseTrigger, specify a source and a polarity. The source can be  
one of the following signals:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
The source also can be one of several other internal signals on your DAQ  
device. Refer to Device Routing in MAX in the NI-DAQmx Help or the  
LabVIEW 8.x Help for more information.  
© National Instruments Corporation  
5-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 5  
Analog Output  
You also can specify whether the samples are paused when ao/PauseTrigger  
is at a logic high or low level.  
Routing AO Pause Trigger Signal to an Output  
Terminal  
You can route ao/PauseTrigger out to RTSI <0..7>.  
AO Sample Clock Signal  
Use the AO Sample Clock (ao/SampleClock) signal to initiate AO samples.  
Each sample updates the outputs of all of the DACs. You can specify an  
internal or external source for ao/SampleClock. You also can specify  
whether the DAC update begins on the rising edge or falling edge of  
ao/SampleClock.  
Using an Internal Source  
One of the following internal signals can drive ao/SampleClock.  
AO Sample Clock Timebase (divided down)  
Counter n Internal Output  
A programmable internal counter divides down the AO Sample Clock  
Timebase signal.  
Using an External Source  
Use one of the following external signals as the source of ao/SampleClock:  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
Routing AO Sample Clock Signal to an Output  
Terminal  
You can route ao/SampleClock (as an active low signal) out to any output  
PFI <6..9> or RTSI <0..7> terminal.  
NI 6238/6239 User Manual  
5-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 5  
Analog Output  
Other Timing Requirements  
A counter on your device internally generates ao/SampleClock unless you  
select some external source. ao/StartTrigger starts the counter and either the  
software or hardware can stop it after a finite generation completes. When  
using an internally generated ao/SampleClock, you also can specify a  
configurable delay from ao/StartTrigger to the first ao/SampleClock pulse.  
By default, this delay is two ticks of ao/SampleClockTimebase.  
Figure 5-6 shows the relationship of ao/SampleClock to ao/StartTrigger.  
ao/SampleClockTimebase  
ao/StartTrigger  
ao/SampleClock  
Delay  
From  
Start  
Trigger  
Figure 5-6. ao/SampleClock and ao/StartTrigger  
AO Sample Clock Timebase Signal  
The AO Sample Clock Timebase (ao/SampleClockTimebase) signal is  
divided down to provide a source for ao/SampleClock.  
You can route any of the following signals to be the AO Sample Clock  
Timebase (ao/SampleClockTimebase) signal:  
20 MHz Timebase  
100 kHz Timebase  
PXI_CLK10  
Input PFI <0..5>  
RTSI <0..7>  
PXI_STAR  
Note Refer to the NI 6238/6239 Specifications for the minimum allowable pulse width  
and the propagation delay of PFI <0..5>.  
© National Instruments Corporation  
5-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 5  
Analog Output  
ao/SampleClockTimebase is not available as an output on the I/O  
connector.  
You might use ao/SampleClockTimebase if you want to use an external  
sample clock signal, but need to divide the signal down. If you want to use  
an external sample clock signal but do not need to divide the signal, then  
you should use ao/SampleClock rather than ao/SampleClockTimebase.  
Getting Started with AO Applications in Software  
You can use an M Series device in the following analog output applications.  
Single-point (on-demand) generation  
Finite generation  
Continuous generation  
Waveform generation  
You can perform these generations through programmed I/O, interrupt, or  
DMA data transfer mechanisms. Some of the applications also use start  
triggers and pause triggers.  
Note For more information about programming analog output applications and triggers in  
software, refer to the NI-DAQmx Help or the LabVIEW 8.x Help.  
NI 6238/6239 User Manual  
5-10  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
6
Digital Input and Output  
NI 6238/6239 devices have six static digital input lines, P0.<0..5>. These  
lines also can be used as PFI inputs.  
In addition, the NI 6238/6239 devices have four static digital output lines,  
P1.<0..3>. These lines also can be used as PFI output.  
The voltage input and output levels and the current drive level of the DI and  
DO lines are listed in the NI 6238/6239 Specifications. Refer to Chapter 8,  
PFI, for more information on PFI inputs and outputs.  
I/O Protection  
Each DI, DO, and PFI signal is protected against overvoltage and  
undervoltage conditions as well as ESD events on NI 6238/6239 devices.  
Consult the device specifications for details. However, you should avoid  
these fault conditions by following these guidelines.  
Do not connect any digital output line to any external signal source,  
ground signal, or power supply.  
Understand the current requirements of the load connected to the  
digital output lines. Do not exceed the specified current output limits  
of the digital outputs. NI has several signal conditioning solutions for  
digital applications requiring high current drive.  
Do not drive the digital input lines with voltages or current outside of  
its normal operating range.  
Treat the DAQ device as you would treat any static sensitive device.  
Always properly ground yourself and the equipment when handling the  
DAQ device or connecting to it.  
Programmable Power-Up States  
By default, the digital output lines (P1.<0..3>/PFI <6..9>) are set to 0. They  
can be programmed to power up as 0 or 1.  
Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more  
information about setting power-up states in NI-DAQmx or MAX.  
© National Instruments Corporation  
6-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 6  
Digital Input and Output  
The DI signals P0.<0..5> are referenced to P0.GND and DO signals  
P1.<0..3> are referenced to P1.GND.  
Figures 6-1 and 6-2 show P0.<0..5> and P1.<0..3> on the NI 6238 and the  
NI 6239 device, respectively. Digital input and output signals can range  
from 0 to 30 V. Refer to the NI 6238/6239 Specifications for more  
information.  
P1.VCC  
P1.0  
P1.<0..3>  
Digital  
Isolators  
P1.1  
P1.GND  
P1.GND  
P0.0  
P0.GND  
P0.GND  
Figure 6-1. NI 6238 Digital I/O Connections (DO Source)  
NI 6238/6239 User Manual  
6-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 6  
Digital Input and Output  
P1.VCC  
P1.0  
Buffer  
P1.GND  
P1.1  
P1.<0..3>  
Digital  
Isolators  
P1.GND  
P1.GND  
P0.0  
P0.GND  
P0.GND  
Figure 6-2. NI 6239 Digital I/O Connections (DO Sink)  
Caution Exceeding the maximum input voltage or maximum working voltage ratings,  
which are listed in the NI 6238/6239 Specifications, can damage the DAQ device and the  
computer. NI is not liable for any damage resulting from such signal connections.  
Logic Conventions  
With NI 6238/6239 devices, logic “0” means that the Darlington output  
switch is open, while logic “1” means closed. Table 6-1 summarizes the  
expected behavior.  
© National Instruments Corporation  
6-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 6  
Digital Input and Output  
Table 6-1. NI 6238/6239 Logic Conventions  
Logic  
Device  
0
1
NI 6238 (Source)  
NI 6239 (Sink)  
P1.GND  
P1.VCC  
P1.VCC  
P1.GND  
Getting Started with DIO Applications in Software  
You can use NI 6238/6239 devices in the following digital I/O applications:  
Static digital input  
Static digital output  
Note For more information about programming digital I/O applications and triggers in  
software, refer to the NI-DAQmx Help or the LabVIEW 8.x Help.  
NI 6238/6239 User Manual  
6-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
7
Counters  
NI 6238/6239 devices have two general-purpose 32-bit counter/timers and  
one frequency generator, as shown in Figure 7-1. The general-purpose  
counter/timers can be used for many measurement and pulse generation  
applications.  
Caution When making measurements, take into account the minimum pulse width and  
time delay of the digital input and output lines. Refer to the NI 6238/6239 Specifications  
for more information.  
© National Instruments Corporation  
7-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Input Selection Muxes  
Counter 0  
Counter 0 Source (Counter 0 Timebase)  
Counter 0 Gate  
Counter 0 Internal Output  
Counter 0 Aux  
Counter 0 HW Arm  
Counter 0 A  
Counter 0 TC  
Counter 0 B (Counter 0 Up_Down)  
Counter 0 Z  
Input Selection Muxes  
Counter 1  
Counter 1 Source (Counter 1 Timebase)  
Counter 1 Gate  
Counter 0 Internal Output  
Counter 1 Aux  
Counter 1 HW Arm  
Counter 1 A  
Counter 0 TC  
Counter 1 B (Counter 1 Up_Down)  
Counter 1 Z  
Input Selection Muxes  
Frequency Generator  
Frequency Output Timebase  
Freq Out  
Figure 7-1. M Series Counters  
The counters have seven input signals, although in most applications only  
a few inputs are used.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
NI 6238/6239 User Manual  
7-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Chapter 7  
Counters  
Counter Input Applications  
Counting Edges  
In edge counting applications, the counter counts edges on its Source after  
the counter is armed. You can configure the counter to count rising or  
falling edges on its Source input. You also can control the direction of  
counting (up or down).  
The counter values can be read on demand or with a sample clock.  
Single Point (On-Demand) Edge Counting  
With single point (on-demand) edge counting, the counter counts the  
number of edges on the Source input after the counter is armed. On-demand  
refers to the fact that software can read the counter contents at any time  
without disturbing the counting process. Figure 7-2 shows an example of  
single point edge counting.  
Counter Armed  
SOURCE  
Counter Value  
0
1
2
3
4
5
Figure 7-2. Single Point (On-Demand) Edge Counting  
You also can use a pause trigger to pause (or gate) the counter. When the  
pause trigger is active, the counter ignores edges on its Source input. When  
the pause trigger is inactive, the counter counts edges normally.  
You can route the pause trigger to the Gate input of the counter. You can  
configure the counter to pause counting when the pause trigger is high or  
when it is low. Figure 7-3 shows an example of on-demand edge counting  
with a pause trigger.  
© National Instruments Corporation  
7-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 7  
Counters  
Counter Armed  
Pause Trigger  
(Pause When Low)  
SOURCE  
0
0
1
2
3
4
5
Counter Value  
Figure 7-3. Single Point (On-Demand) Edge Counting with Pause Trigger  
Buffered (Sample Clock) Edge Counting  
With buffered edge counting (edge counting using a sample clock), the  
counter counts the number of edges on the Source input after the counter is  
armed. The value of the counter is sampled on each active edge of a sample  
clock. A DMA controller transfers the sampled values to host memory.  
The count values returned are the cumulative counts since the counter  
armed event. That is, the sample clock does not reset the counter.  
You can route the counter sample clock to the Gate input of the counter. You  
can configure the counter to sample on the rising or falling edge of the  
sample clock.  
Figure 7-4 shows an example of buffered edge counting. Notice that  
counting begins when the counter is armed, which occurs before the first  
active edge on Gate.  
Counter Armed  
Sample Clock  
(Sample on Rising Edge)  
SOURCE  
Counter Value  
Buffer  
0
1
2
3
4
3
5
6
7
3
6
Figure 7-4. Buffered (Sample Clock) Edge Counting  
NI 6238/6239 User Manual  
7-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Non-Cumulative Buffered Edge Counting  
Non-cumulative edge counting is similar to buffered (sample clock) edge  
counting. However, the counter resets after each active edge of the Sample  
Clock. You can route the Sample Clock to the Gate input of the counter.  
Figure 7-5 shows an example of non-cumulative buffered edge counting.  
Counter  
Armed  
Sample Clock  
(Sample on Rising Edge)  
SOURCE  
Counter Value  
0
1
2
1
2
3
1
2
3
1
2
2
3
2
3
3
Buffer  
Figure 7-5. Non-Cumulative Buffered Edge Counting  
Notice that the first count interval begins when the counter is armed, which  
occurs before the first active edge on Gate.  
Notice that if you are using an external signal as the Source, at least one  
Source pulse should occur between each active edge of the Gate signal.  
This condition ensures that correct values are returned by the counter. If this  
condition is not met, consider using duplicate count prevention.  
Controlling the Direction of Counting  
In edge counting applications, the counter can count up or down. You can  
configure the counter to do the following.  
Always count up  
Always count down  
Count up when the Counter n B input is high; count down when it is  
low  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
© National Instruments Corporation  
7-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Pulse-Width Measurement  
In pulse-width measurements, the counter measures the width of a pulse on  
its Gate input signal. You can configure the counter to measure the width of  
high pulses or low pulses on the Gate signal.  
You can route an internal or external periodic clock signal (with a known  
period) to the Source input of the counter. The counter counts the number  
of rising (or falling) edges on the Source signal while the pulse on the Gate  
signal is active.  
You can calculate the pulse width by multiplying the period of the Source  
signal by the number of edges returned by the counter.  
A pulse-width measurement will be accurate even if the counter is armed  
while a pulse train is in progress. If a counter is armed while the pulse is in  
the active state, it will wait for the next transition to the active state to begin  
the measurement.  
Single Pulse-Width Measurement  
With single pulse-width measurement, the counter counts the number of  
edges on the Source input while the Gate input remains active. When the  
Gate input goes inactive, the counter stores the count in a hardware save  
register and ignores other edges on the Gate and Source inputs. Software  
then can read the stored count.  
Figure 7-6 shows an example of a single pulse-width measurement.  
GATE  
SOURCE  
Counter Value  
0
1
2
HW Save Register  
2
Figure 7-6. Single Pulse-Width Measurement  
Buffered pulse-width measurement is similar to single pulse-width  
measurement, but buffered pulse-width measurement takes measurements  
over multiple pulses.  
NI 6238/6239 User Manual  
7-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 7  
Counters  
The counter counts the number of edges on the Source input while the Gate  
input remains active. On each trailing edge of the Gate signal, the counter  
stores the count in a hardware save register. A DMA controller transfers the  
stored values to host memory.  
Figure 7-7 shows an example of a buffered pulse-width measurement.  
GATE  
SOURCE  
0
1
2
3
1
2
Counter Value  
Buffer  
3
3
2
3
2
Figure 7-7. Buffered Pulse-Width Measurement  
Note that if you are using an external signal as the Source, at least one  
Source pulse should occur between each active edge of the Gate signal.  
This condition ensures that correct values are returned by the counter. If this  
condition is not met, consider using duplicate count prevention.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Period Measurement  
In period measurements, the counter measures a period on its Gate input  
signal after the counter is armed. You can configure the counter to measure  
the period between two rising edges or two falling edges of the Gate input  
signal.  
You can route an internal or external periodic clock signal (with a known  
period) to the Source input of the counter. The counter counts the number  
of rising (or falling) edges occurring on the Source input between the two  
active edges of the Gate signal.  
You can calculate the period of the Gate input by multiplying the period of  
the Source signal by the number of edges returned by the counter.  
© National Instruments Corporation  
7-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Single Period Measurement  
With single period measurement, the counter counts the number of rising  
(or falling) edges on the Source input occurring between two active edges  
of the Gate input. On the second active edge of the Gate input, the counter  
stores the count in a hardware save register and ignores other edges on the  
Gate and Source inputs. Software then can read the stored count.  
Figure 7-8 shows an example of a single period measurement.  
GATE  
SOURCE  
Counter Value  
0
1
2
3
4
5
HW Save Register  
5
Figure 7-8. Single Period Measurement  
Buffered Period Measurement  
Buffered period measurement is similar to single period measurement, but  
buffered period measurement measures multiple periods.  
The counter counts the number of rising (or falling) edges on the Source  
input between each pair of active edges on the Gate input. At the end of  
each period on the Gate signal, the counter stores the count in a hardware  
save register. A DMA controller transfers the stored values to host memory.  
The counter begins when it is armed. The arm usually occurs in the middle  
of a period of the Gate input. So the first value stored in the hardware save  
register does not reflect a full period of the Gate input. In most applications,  
this first point should be discarded.  
Figure 7-9 shows an example of a buffered period measurement.  
NI 6238/6239 User Manual  
7-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
Counter Armed  
GATE  
SOURCE  
Counter Value  
1
2
1
2
3
1
2
3
1
2
3
3
2 (Discard)  
(Discard)  
2 (Discard)  
3
3
2
3
Buffer  
Figure 7-9. Buffered Period Measurement  
Note that if you are using an external signal as the Source, at least one  
Source pulse should occur between each active edge of the Gate signal.  
This condition ensures that correct values are returned by the counter. If this  
condition is not met, consider using duplicate count prevention.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Semi-Period Measurement  
In semi-period measurements, the counter measures a semi-period on its  
Gate input signal after the counter is armed. A semi-period is the time  
between any two consecutive edges on the Gate input.  
You can route an internal or external periodic clock signal (with a known  
period) to the Source input of the counter. The counter counts the number  
of rising (or falling) edges occurring on the Source input between two  
edges of the Gate signal.  
You can calculate the semi-period of the Gate input by multiplying the  
period of the Source signal by the number of edges returned by the counter.  
Single Semi-Period Measurement  
Single semi-period measurement is equivalent to single pulse-width  
measurement.  
© National Instruments Corporation  
7-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
Buffered Semi-Period Measurement  
In buffered semi-period measurement, on each edge of the Gate signal, the  
counter stores the count in a hardware save register. A DMA controller  
transfers the stored values to host memory.  
The counter begins counting when it is armed. The arm usually occurs  
between edges on the Gate input. So the first value stored in the hardware  
save register does not reflect a full semi-period of the Gate input. In most  
applications, this first point should be discarded.  
Figure 7-10 shows an example of a buffered semi-period measurement.  
Counter Armed  
GATE  
SOURCE  
Counter Value  
Buffer  
0
1
2
1
2
3
1
1
2
1
2
3
2
3
1
2
2
3
1
2
2
3
1
2
Figure 7-10. Buffered Semi-Period Measurement  
Note that if you are using an external signal as the Source, at least one  
Source pulse should occur between each active edge of the Gate signal.  
This condition ensures that correct values are returned by the counter. If this  
condition is not met, consider using duplicate count prevention.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Frequency Measurement  
You can use the counters to measure frequency in several different ways.  
You can choose one of the following methods depending on your  
application.  
Method 1—Measure Low Frequency with One  
In this method, you measure one period of your signal using a known  
timebase. This method is good for low frequency signals.  
NI 6238/6239 User Manual  
7-10  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 7  
Counters  
You can route the signal to measure (F1) to the Gate of a counter. You can  
route a known timebase (Ft) to the Source of the counter. The known  
timebase can be 80MHzTimebase. For signals that might be slower than  
0.02 Hz, use a slower known timebase.  
You can configure the counter to measure one period of the gate signal. The  
frequency of F1 is the inverse of the period. Figure 7-11 illustrates this  
method.  
Interval Measured  
F1  
F1  
Ft  
Gate  
1
2
3
N
Source  
Ft  
N
Single Period  
Measurement  
Period of F1 =  
Ft  
Ft  
N
Frequency of F1 =  
Figure 7-11. Method 1  
Method 1b—Measure Low Frequency with One  
Counter (Averaged)  
In this method, you measure several periods of your signal using a known  
timebase. This method is good for low to medium frequency signals.  
You can route the signal to measure (F1) to the Gate of a counter. You can  
route a known timebase (Ft) to the Source of the counter. The known  
timebase can be 80MHzTimebase. For signals that might be slower than  
0.02 Hz, use a slower known timebase.  
You can configure the counter to make K + 1 buffered period  
measurements. Recall that the first period measurement in the buffer should  
be discarded.  
Average the remaining K period measurements to determine the average  
period of F1. The frequency of F1 is the inverse of the average period.  
Figure 7-12 illustrates this method.  
© National Instruments Corporation  
7-11  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Intervals Measured  
T1  
T2  
TK  
F1  
Ft  
Gate  
F1  
Ft  
12...N11......N2  
1......NK  
Source  
Buffered Period  
Measurement  
N1 + N2 + …NK  
1
×
Average Period of F1 =  
Frequency of F1 =  
K
Ft  
K × Ft  
N1 + N2 + …NK  
Figure 7-12. Method 1b  
Method 2—Measure High Frequency with Two  
Counters  
In this method, you measure one pulse of a known width using your signal  
and derive the frequency of your signal from the result. This method is good  
for high frequency signals.  
In this method, you route a pulse of known duration (T) to the Gate of a  
counter. You can generate the pulse using a second counter. You also can  
generate the pulse externally and connect it to a PFI or RTSI terminal. You  
only need to use one counter if you generate the pulse externally.  
Route the signal to measure (F1) to the Source of the counter. Configure the  
counter for a single pulse-width measurement. Suppose you measure the  
width of pulse T to be N periods of F1. Then the frequency of F1 is N/T.  
Figure 7-13 illustrates this method. Another option would be to measure  
the width of a known period instead of a known pulse.  
NI 6238/6239 User Manual  
7-12  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Width of Pulse (T)  
Pulse  
Pulse  
F1  
Gate  
1
2
N
Source  
F1  
N
Pulse-Width  
Measurement  
Width of  
Pulse  
T =  
F1  
N
T
Frequency of F1 =  
Figure 7-13. Method 2  
Method 3—Measure Large Range of Frequencies  
Using Two Counters  
By using two counters, you can accurately measure a signal that might be  
high or low frequency. This technique is called reciprocal frequency  
measurement. In this method, you generate a long pulse using the signal to  
measure. You then measure the long pulse with a known timebase. The  
M Series device can measure this long pulse more accurately than the faster  
input signal.  
You can route the signal to measure to the Source input of Counter 0, as  
shown in Figure 7-14. Assume this signal to measure has frequency F1.  
Configure Counter 0 to generate a single pulse that is the width of N periods  
of the source input signal.  
© National Instruments Corporation  
7-13  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Signal to  
Measure (F1)  
SOURCE  
COUNTER 0  
OUT  
Signal of Known  
Frequency (F2)  
SOURCE  
OUT  
COUNTER 1  
GATE  
2
0
1
3
N  
CTR_0_SOURCE  
(Signal to Measure)  
CTR_0_OUT  
(CTR_1_GATE)  
Interval  
to Measure  
CTR_1_SOURCE  
Figure 7-14. Method 3  
Then route the Counter 0 Internal Output signal to the Gate input of  
Counter 1. You can route a signal of known frequency (F2) to the Counter  
1 Source input. F2 can be 80MHzTimebase. For signals that might be  
slower than 0.02 Hz, use a slower known timebase. Configure Counter 1 to  
perform a single pulse-width measurement. Suppose the result is that the  
pulse width is J periods of the F2 clock.  
From Counter 0, the length of the pulse is N/F1. From Counter 1, the length  
of the same pulse is J/F2. Therefore, the frequency of F1 is given by  
F1 = F2 * (N/J).  
Choosing a Method for Measuring Frequency  
The best method to measure frequency depends on several factors including  
the expected frequency of the signal to measure, the desired accuracy, how  
many counters are available, and how long the measurement can take.  
Method 1 uses only one counter. It is a good method for many  
applications. However, the accuracy of the measurement decreases as  
the frequency increases.  
Consider a frequency measurement on a 50 kHz signal using an  
80 MHz Timebase. This frequency corresponds to 1600 cycles of the  
NI 6238/6239 User Manual  
7-14  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 7  
Counters  
80 MHz Timebase. Your measurement may return 1600 1 cycles  
depending on the phase of the signal with respect to the timebase. As  
your frequency becomes larger, this error of 1 cycle becomes more  
significant; Table 7-1 illustrates this point.  
Table 7-1. Frequency Measurement Method 1  
Task  
Equation  
Example 1  
50 kHz  
Example 2  
5 MHz  
Actual Frequency to Measure  
Timebase Frequency  
F1  
Ft  
80 MHz  
1600  
80 MHz  
16  
Actual Number of Timebase  
Periods  
Ft/F1  
Worst Case Measured Number of (Ft/F1) – 1  
Timebase Periods  
1599  
15  
Measured Frequency  
Error  
Ft F1/(Ft – F1)  
50.125 kHz  
125 kHz  
0.06%  
5.33 MHz  
333 kHz  
6.67%  
[Ft F1/(Ft – F1)] – F1  
[Ft/(Ft – F1)] – 1  
Error %  
Method 1b (measuring K periods of F1) improves the accuracy of the  
measurement. A disadvantage of Method 1b is that you have to take  
K + 1 measurements. These measurements take more time and  
consume some of the available PCI or PXI bandwidth.  
Method 2 is accurate for high frequency signals. However, the  
accuracy decreases as the frequency of the signal to measure  
decreases. At very low frequencies, Method 2 may be too inaccurate  
for your application. Another disadvantage of Method 2 is that it  
requires two counters (if you cannot provide an external signal of  
known width). An advantage of Method 2 is that the measurement  
completes in a known amount of time.  
Method 3 measures high and low frequency signals accurately.  
However, it requires two counters.  
Table 7-2 summarizes some of the differences in methods of measuring  
frequency.  
© National Instruments Corporation  
7-15  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Chapter 7  
Counters  
Table 7-2. Frequency Measurement Method Comparison  
Measures High  
Frequency  
Signals  
Measures Low  
Frequency  
Signals  
Number of  
Measurements  
Returned  
Number of  
Counters Used  
Method  
Accurately  
Accurately  
1
1b  
2
1
1
1
Many  
1
Poor  
Fair  
Good  
Good  
Poor  
1 or 2  
2
Good  
Good  
3
1
Good  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Position Measurement  
You can use the counters to perform position measurements with  
quadrature encoders or two-pulse encoders. You can measure angular  
position with X1, X2, and X4 angular encoders. Linear position can be  
measured with two-pulse encoders. You can choose to do either a single  
point (on-demand) position measurement or a buffered (sample clock)  
position measurement. You must arm a counter to begin position  
measurements.  
Measurements Using Quadrature Encoders  
The counters can perform measurements of quadrature encoders that use  
X1, X2, or X4 encoding.  
A quadrature encoder can have up to three channels—channels A, B, and Z.  
X1 Encoding  
When channel A leads channel B in a quadrature cycle, the counter  
increments. When channel B leads channel A in a quadrature cycle, the  
counter decrements. The amount of increments and decrements per cycle  
depends on the type of encoding—X1, X2, or X4.  
Figure 7-15 shows a quadrature cycle and the resulting increments and  
decrements for X1 encoding. When channel A leads channel B, the  
increment occurs on the rising edge of channel A. When channel B leads  
channel A, the decrement occurs on the falling edge of channel A.  
NI 6238/6239 User Manual  
7-16  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 7  
Counters  
Ch A  
Ch B  
Counter Value  
6
7
7
6
5
5
Figure 7-15. X1 Encoding  
X2 Encoding  
The same behavior holds for X2 encoding except the counter increments or  
decrements on each edge of channel A, depending on which channel leads  
the other. Each cycle results in two increments or decrements, as shown in  
Figure 7-16.  
Ch A  
Ch B  
Counter Value  
5
6
7
8
9
9
8
7
6
5
Figure 7-16. X2 Encoding  
X4 Encoding  
Similarly, the counter increments or decrements on each edge of  
channels A and B for X4 encoding. Whether the counter increments or  
decrements depends on which channel leads the other. Each cycle results in  
four increments or decrements, as shown in Figure 7-17.  
Ch A  
Ch B  
Counter Value  
5
6
7
8
9
10 11 12 13 13 12 11 10  
9
8
7
6
5
Figure 7-17. X4 Encoding  
Channel Z Behavior  
Some quadrature encoders have a third channel, channel Z, which is also  
referred to as the index channel. A high level on channel Z causes the  
counter to be reloaded with a specified value in a specified phase of the  
quadrature cycle. You can program this reload to occur in any one of the  
four phases in a quadrature cycle.  
© National Instruments Corporation  
7-17  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 7  
Counters  
Channel Z behavior—when it goes high and how long it stays  
high—differs with quadrature encoder designs. You must refer to the  
documentation for your quadrature encoder to obtain timing of channel Z  
with respect to channels A and B. You must then ensure that channel Z is  
high during at least a portion of the phase you specify for reload. For  
instance, in Figure 7-18, channel Z is never high when channel A is high  
and channel B is low. Thus, the reload must occur in some other phase.  
In Figure 7-18, the reload phase is when both channel A and channel B are  
low. The reload occurs when this phase is true and channel Z is high.  
Incrementing and decrementing takes priority over reloading. Thus, when  
the channel B goes low to enter the reload phase, the increment occurs first.  
The reload occurs within one maximum timebase period after the reload  
phase becomes true. After the reload occurs, the counter continues to count  
as before. Figure 7-18 channel Z reload with X4 decoding.  
Ch A  
Ch B  
Ch Z  
Max Timebase  
Counter Value  
5
6
7
8
9
0
1
2
3
4
A = 0  
B = 0  
Z = 1  
Figure 7-18. Channel Z Reload with X4 Decoding  
Measurements Using Two Pulse Encoders  
The counter supports two pulse encoders that have two channels—channels  
A and B.  
The counter increments on each rising edge of channel A. The counter  
decrements on each rising edge of channel B, as shown in Figure 7-19.  
Ch A  
Ch B  
Counter Value 2  
3
4
5
4
3
4
Figure 7-19. Measurements Using Two Pulse Encoders  
NI 6238/6239 User Manual  
7-18  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Two-Signal Edge-Separation Measurement  
Two-signal edge-separation measurement is similar to pulse-width  
measurement, except that there are two measurement signals—Aux and  
Gate. An active edge on the Aux input starts the counting and an active edge  
on the Gate input stops the counting. You must arm a counter to begin a two  
edge separation measurement.  
After the counter has been armed and an active edge occurs on the Aux  
input, the counter counts the number of rising (or falling) edges on the  
Source. The counter ignores additional edges on the Aux input.  
The counter stops counting upon receiving an active edge on the Gate input.  
The counter stores the count in a hardware save register.  
You can configure the rising or falling edge of the Aux input to be the active  
edge. You can configure the rising or falling edge of the Gate input to be  
the active edge.  
Use this type of measurement to count events or measure the time that  
occurs between edges on two signals. This type of measurement is  
sometimes referred to as start/stop trigger measurement, second gate  
measurement, or A-to-B measurement.  
Single Two-Signal Edge-Separation Measurement  
With single two-signal edge-separation measurement, the counter counts  
the number of rising (or falling) edges on the Source input occurring  
between an active edge of the Gate signal and an active edge of the Aux  
signal. The counter then stores the count in a hardware save register and  
ignores other edges on its inputs. Software then can read the stored count.  
Figure 7-20 shows an example of a single two-signal edge-separation  
measurement.  
© National Instruments Corporation  
7-19  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Counter  
Armed  
Measured Interval  
AUX  
GATE  
SOURCE  
Counter Value  
0
0
0
0
1
2
3
4
5
6
7
8
8
8
HW Save Register  
8
Figure 7-20. Single Two-Signal Edge-Separation Measurement  
Buffered Two-Signal Edge-Separation Measurement  
Buffered and single two-signal edge-separation measurements are similar,  
but buffered measurement measures multiple intervals.  
The counter counts the number of rising (or falling) edges on the Source  
input occurring between an active edge of the Gate signal and an active  
edge of the Aux signal. The counter then stores the count in a hardware save  
register. On the next active edge of the Gate signal, the counter begins  
another measurement. A DMA controller transfers the stored values to host  
memory.  
Figure 7-21 shows an example of a buffered two-signal edge-separation  
measurement.  
AUX  
GATE  
SOURCE  
Counter Value  
1
2
3
1
2
3
1
2
3
3
3
3
3
3
3
Buffer  
Figure 7-21. Buffered Two-Signal Edge-Separation Measurement  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
NI 6238/6239 User Manual  
7-20  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Counter Output Applications  
Simple Pulse Generation  
Single Pulse Generation  
The counter can output a single pulse. The pulse appears on the Counter n  
Internal Output signal of the counter.  
You can specify a delay from when the counter is armed to the beginning  
of the pulse. The delay is measured in terms of a number of active edges of  
the Source input.  
You can specify a pulse width. The pulse width is also measured in terms  
of a number of active edges of the Source input. You also can specify the  
active edge of the Source input (rising or falling).  
Figure 7-22 shows a generation of a pulse with a pulse delay of four and a  
pulse width of three (using the rising edge of Source).  
Counter Armed  
SOURCE  
OUT  
Figure 7-22. Single Pulse Generation  
Single Pulse Generation with Start Trigger  
The counter can output a single pulse in response to one pulse on a  
hardware Start Trigger signal. The pulse appears on the Counter n Internal  
Output signal of the counter.  
You can route the Start Trigger signal to the Gate input of the counter. You  
can specify a delay from the Start Trigger to the beginning of the pulse. You  
also can specify the pulse width. The delay and pulse width are measured  
in terms of a number of active edges of the Source input.  
After the Start Trigger signal pulses once, the counter ignores the Gate  
input.  
Figure 7-23 shows a generation of a pulse with a pulse delay of four and a  
pulse width of three (using the rising edge of Source).  
© National Instruments Corporation  
7-21  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                 
Chapter 7  
Counters  
GATE  
(Start Trigger)  
SOURCE  
OUT  
Figure 7-23. Single Pulse Generation with Start Trigger  
Retriggerable Single Pulse Generation  
The counter can output a single pulse in response to each pulse on a  
hardware Start Trigger signal. The pulses appear on the Counter n Internal  
Output signal of the counter.  
You can route the Start Trigger signal to the Gate input of the counter. You  
can specify a delay from the Start Trigger to the beginning of each pulse.  
You also can specify the pulse width. The delay and pulse width are  
measured in terms of a number of active edges of the Source input.  
The counter ignores the Gate input while a pulse generation is in progress.  
After the pulse generation is finished, the counter waits for another Start  
Trigger signal to begin another pulse generation.  
Figure 7-24 shows a generation of two pulses with a pulse delay of five and  
a pulse width of three (using the rising edge of Source).  
GATE  
(Start Trigger)  
SOURCE  
OUT  
Figure 7-24. Retriggerable Single Pulse Generation  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
NI 6238/6239 User Manual  
7-22  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Pulse Train Generation  
Continuous Pulse Train Generation  
This function generates a train of pulses with programmable frequency and  
duty cycle. The pulses appear on the Counter n Internal Output signal of the  
counter.  
You can specify a delay from when the counter is armed to the beginning  
of the pulse train. The delay is measured in terms of a number of active  
edges of the Source input.  
You specify the high and low pulse widths of the output signal. The pulse  
widths are also measured in terms of a number of active edges of the Source  
input. You also can specify the active edge of the Source input (rising or  
falling).  
The counter can begin the pulse train generation as soon as the counter is  
armed, or in response to a hardware Start Trigger. You can route the Start  
Trigger to the Gate input of the counter.  
You also can use the Gate input of the counter as a Pause Trigger (if it is not  
used as a Start Trigger). The counter pauses pulse generation when the  
Pause Trigger is active.  
Figure 7-25 shows a continuous pulse train generation (using the rising  
edge of Source).  
SOURCE  
OUT  
Counter Armed  
Figure 7-25. Continuous Pulse Train Generation  
Continuous pulse train generation is sometimes called frequency division.  
If the high and low pulse widths of the output signal are M and N periods,  
then the frequency of the Counter n Internal Output signal is equal to the  
frequency of the Source input divided by M + N.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
© National Instruments Corporation  
7-23  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
Frequency Generation  
You can generate a frequency by using a counter in pulse train generation  
mode or by using the frequency generator circuit.  
The frequency generator can output a square wave at many different  
frequencies. The frequency generator is independent of the two  
general-purpose 32-bit counter/timer modules on M Series devices.  
Figure 7-26 shows a block diagram of the frequency generator.  
Frequency  
Output  
Timebase  
20 MHz Timebase  
100 kHz Timebase  
÷ 2  
Frequency Generator  
Freq Out  
Divisor  
(1–16)  
Figure 7-26. Frequency Generator Block Diagram  
The frequency generator generates the Frequency Output signal. The  
Frequency Output signal is the Frequency Output Timebase divided by a  
number you select from 1 to 16. The Frequency Output Timebase can be  
either the 20 MHz Timebase divided by 2 or the 100 kHz Timebase.  
The duty cycle of Frequency Output is 50% if the divider is either 1 or an  
even number. For an odd divider, suppose the divider is set to D. In this  
case, Frequency Output is low for (D + 1)/2 cycles and high for (D – 1)/2  
cycles of the Frequency Output Timebase.  
Figure 7-27 shows the output waveform of the frequency generator when  
the divider is set to 5.  
Frequency  
Output  
Timebase  
Freq Out  
Figure 7-27. Frequency Generator Output Waveform  
NI 6238/6239 User Manual  
7-24  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 7  
Counters  
Frequency Output can be routed out to any output PFI <6..9> or  
RTSI <0..7> terminal. All PFI terminals are set to high-impedance at  
In software, program the frequency generator as you would program one of  
the counters for pulse train generation.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
The counters can generate a signal with a frequency that is a fraction of an  
input signal. This function is equivalent to continuous pulse train  
generation.  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Pulse Generation for ETS  
In this application, the counter produces a pulse on the output a specified  
delay after an active edge on Gate. After each active edge on Gate, the  
counter cumulatively increments the delay between the Gate and the pulse  
on the output by a specified amount. Thus, the delay between the Gate and  
the pulse produced successively increases.  
Note ETS = Equivalent Time Sampling.  
The increase in the delay value can be between 0 and 255. For instance, if  
you specify the increment to be 10, the delay between the active Gate edge  
and the pulse on the output will increase by 10 every time a new pulse is  
generated.  
Suppose you program your counter to generate pulses with a delay of 100  
and pulse width of 200 each time it receives a trigger. Furthermore, suppose  
you specify the delay increment to be 10. On the first trigger, your pulse  
delay will be 100, on the second it will be 110, on the third it will be 120;  
the process will repeat in this manner until the counter is disarmed. The  
counter ignores any Gate edge that is received while the pulse triggered by  
the previous Gate edge is in progress.  
The waveform thus produced at the counter’s output can be used to provide  
timing for undersampling applications where a digitizing system can  
sample repetitive waveforms that are higher in frequency than the Nyquist  
© National Instruments Corporation  
7-25  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
frequency of the system. Figure 7-28 shows an example of pulse generation  
for ETS; the delay from the trigger to the pulse increases after each  
subsequent Gate active edge.  
GATE  
OUT  
D1  
D2 = D1 + ΔD  
D3 = D1 + 2ΔD  
Figure 7-28. Pulse Generation for ETS  
For information on connecting counter signals, refer to the Default Counter  
Terminals section.  
Counter Timing Signals  
M Series devices feature the following counter timing signals.  
Counter n Source  
Counter n Gate  
Counter n Aux  
Counter n A  
Counter n B  
Counter n Z  
Counter n Up_Down  
Counter n HW Arm  
Counter n Internal Output  
Counter n TC  
Frequency Output  
In this section, n refers to either Counter 0 or 1. For example, Counter n  
Source refers to two signals—Counter 0 Source (the source input to  
Counter 0) and Counter 1 Source (the source input to Counter 1).  
The selected edge of the Counter n Source signal increments and  
decrements the counter value depending on the application the counter is  
NI 6238/6239 User Manual  
7-26  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
performing. Table 7-3 lists how this terminal is used in various  
applications.  
Table 7-3. Counter Applications and Counter n Source  
Application  
Pulse Generation  
Purpose of Source Terminal  
Counter Timebase  
One Counter Time Measurements Counter Timebase  
Two Counter Time Measurements Input Terminal  
Non-Buffered Edge Counting  
Buffered Edge Counting  
Two-Edge Separation  
Input Terminal  
Input Terminal  
Counter Timebase  
Routing a Signal to Counter n Source  
Each counter has independent input selectors for the Counter n Source  
signal. Any of the following signals can be routed to the Counter n Source  
input.  
80 MHz Timebase  
20 MHz Timebase  
100 kHz Timebase  
RTSI <0..7>  
Input PFI <0..5>  
PXI_CLK10  
PXI_STAR  
In addition, Counter 1 TC or Counter 1 Gate can be routed to  
Counter 0 Source. Counter 0 TC or Counter 0 Gate can be routed to  
Counter 1 Source.  
Some of these options may not be available in some driver software.  
Routing Counter n Source to an Output Terminal  
You can route Counter n Source out to any output PFI <6..9> or  
RTSI <0..7> terminal. All PFIs are set to high-impedance at startup.  
© National Instruments Corporation  
7-27  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
Counter n Gate Signal  
The Counter n Gate signal can perform many different operations  
depending on the application including starting and stopping the counter,  
and saving the counter contents.  
Routing a Signal to Counter n Gate  
Each counter has independent input selectors for the Counter n Gate signal.  
Any of the following signals can be routed to the Counter n Gate input.  
RTSI <0..7>  
Input PFI <0..5>  
ai/ReferenceTrigger  
ai/StartTrigger  
ai/SampleClock  
ai/ConvertClock  
ao/SampleClock  
PXI_STAR  
In addition, Counter 1 Internal Output or Counter 1 Source can be routed to  
Counter 0 Gate. Counter 0 Internal Output or Counter 0 Source can be  
routed to Counter 1 Gate.  
Some of these options may not be available in some driver software.  
Routing Counter n Gate to an Output Terminal  
You can route Counter n Gate out to any output PFI <6..9> or RTSI <0..7>  
terminal. All PFIs are set to high-impedance at startup.  
Counter n Aux Signal  
The Counter n Aux signal indicates the first edge in a two-signal  
edge-separation measurement.  
Routing a Signal to Counter n Aux  
Each counter has independent input selectors for the Counter n Aux signal.  
Any of the following signals can be routed to the Counter n Aux input.  
RTSI <0..7>  
Input PFI <0..5>  
ai/ReferenceTrigger  
NI 6238/6239 User Manual  
7-28  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 7  
Counters  
ai/StartTrigger  
PXI_STAR  
In addition, Counter 1 Internal Output, Counter 1 Gate, Counter 1 Source,  
or Counter 0 Gate can be routed to Counter 0 Aux. Counter 0 Internal  
Output, Counter 0 Gate, Counter 0 Source, or Counter 1 Gate can be routed  
to Counter 1 Aux.  
Some of these options may not be available in some driver software.  
Counter n A, Counter n B, and Counter n Z Signals  
Counter n B can control the direction of counting in edge counting  
applications.  
Use the A, B, and Z inputs to each counter when measuring quadrature  
encoders or measuring two pulse encoders.  
Routing Signals to A, B, and Z Counter Inputs  
Each counter has independent input selectors for each of the A, B, and Z  
inputs. Any of the following signals can be routed to each input.  
RTSI <0..7>  
Input PFI <0..5>  
PXI_STAR  
Routing Counter n Z Signal to an Output Terminal  
You can route Counter n Z out to RTSI <0..7>.  
Counter n Up_Down Signal  
Counter n Up_Down is another name for the Counter n B signal.  
Counter n HW Arm Signal  
The Counter n HW Arm signal enables a counter to begin an input or output  
function.  
To begin any counter input or output function, you must first enable, or arm,  
the counter. In some applications, such as buffered semi-period  
measurement, the counter begins counting when it is armed. In other  
applications, such as single pulse-width measurement, the counter begins  
© National Instruments Corporation  
7-29  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 7  
Counters  
waiting for the Gate signal when it is armed. Counter output operations can  
use the arm signal in addition to a start trigger.  
Software can arm a counter or configure counters to be armed on a  
hardware signal. Software calls this hardware signal the Arm Start Trigger.  
Internally, software routes the Arm Start Trigger to the Counter n HW Arm  
input of the counter.  
Routing Signals to Counter n HW Arm Input  
Any of the following signals can be routed to the Counter n HW Arm input.  
RTSI <0..7>  
Input PFI <0..5>  
ai/ReferenceTrigger  
ai/StartTrigger  
PXI_STAR  
Counter 1 Internal Output can be routed to Counter 0 HW Arm. Counter 0  
Internal Output can be routed to Counter 1 HW Arm.  
Some of these options may not be available in some driver software.  
Counter n Internal Output and Counter n TC Signals  
Counter n TC is an internal signal that asserts when the counter value is 0.  
The Counter n Internal Output signal changes in response to Counter n TC.  
The two software-selectable output options are pulse on TC and toggle  
output polarity on TC. The output polarity is software-selectable for both  
options.  
Routing Counter n Internal Output to an Output  
Terminal  
You can route Counter n Internal Output to any output PFI <6..9> or  
RTSI <0..7> terminal. All output PFIs are set to high-impedance at startup.  
Frequency Output Signal  
The Frequency Output (FREQ OUT) signal is the output of the frequency  
output generator.  
NI 6238/6239 User Manual  
7-30  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 7  
Counters  
Routing Frequency Output to a Terminal  
You can route Frequency Output to any output PFI <6..9> terminal. All  
PFIs are set to high-impedance at startup.  
Default Counter Terminals  
By default, NI-DAQmx routes the counter/timer inputs and outputs to the  
PFI pins, shown in Table 7-4.  
Table 7-4. NI 6238/6239 Device Default NI-DAQmx Counter/Timer Pins  
Counter/Timer Signal  
CTR 0 SRC  
Default Pin Number (Name)  
13 (PFI 0)  
Port  
P0.0  
P0.1  
P0.2  
P1.0  
P0.0  
P0.1  
P0.2  
P0.3  
P0.4  
P0.5  
P1.1  
P0.3  
P0.4  
P0.5  
CTR 0 GATE  
CTR 0 AUX  
CTR 0 OUT  
CTR 0 A  
32 (PFI 1)  
33 (PFI 2)  
17 (PFI 6)  
13 (PFI 0)  
CTR 0 Z  
32 (PFI 1)  
CTR 0 B  
33 (PFI 2)  
CTR 1 SRC  
CTR 1 GATE  
CTR 1 AUX  
CTR 1 OUT  
CTR 1 A  
15 (PFI 3)  
34 (PFI 4)  
16 (PFI 5)  
36 (PFI 7)  
15 (PFI 3)  
CTR 1 Z  
34 (PFI 4)  
CTR 1 B  
16 (PFI 5)  
You can use these defaults or select other sources and destinations for the  
counter/timer signals in NI-DAQmx. Refer to Connecting Counter Signals  
in the NI-DAQmx Help or the LabVIEW 8.x Help for more information on  
how to connect your signals for common counter measurements and  
generations. M Series default PFI lines for counter functions are listed in  
Physical Channels in the NI-DAQmx Help or the LabVIEW 8.x Help.  
© National Instruments Corporation  
7-31  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
Counter Triggering  
Counters support three different triggering actions—arm start, start, and  
pause.  
Arm Start Trigger  
To begin any counter input or output function, you must first enable, or arm,  
the counter. Software can arm a counter or configure counters to be armed  
on a hardware signal. Software calls this hardware signal the Arm Start  
Trigger. Internally, software routes the Arm Start Trigger to the Counter n  
HW Arm input of the counter.  
For counter output operations, you can use it in addition to the start and  
pause triggers. For counter input operations, you can use the arm start  
trigger to have start trigger-like behavior. The arm start trigger can be used  
for synchronizing multiple counter input and output tasks.  
Start Trigger  
For counter output operations, a start trigger can be configured to begin a  
finite or continuous pulse generation. After a continuous generation has  
triggered, the pulses continue to generate until you stop the operation in  
software. For finite generations, the specified number of pulses is generated  
and the generation stops unless you use the retriggerable attribute. When  
you use this attribute, subsequent start triggers cause the generation to  
restart.  
When using a start trigger, the start trigger source is routed to the Counter  
n Gate signal input of the counter.  
Counter input operations can use the arm start trigger to have start  
trigger-like behavior.  
Pause Trigger  
You can use pause triggers in edge counting and continuous pulse  
generation applications. For edge counting acquisitions, the counter stops  
counting edges while the external trigger signal is low and resumes when  
the signal goes high or vice versa. For continuous pulse generations, the  
counter stops generating pulses while the external trigger signal is low and  
resumes when the signal goes high or vice versa.  
When using a pause trigger, the pause trigger source is routed to the  
Counter n Gate signal input of the counter.  
NI 6238/6239 User Manual  
7-32  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                 
Chapter 7  
Counters  
Other Counter Features  
Cascading Counters  
signal of each counter to the Gate inputs of the other counter. By cascading  
two counters together, you can effectively create a 64-bit counter. By  
cascading counters, you also can enable other applications. For example, to  
improve the accuracy of frequency measurements, use reciprocal frequency  
measurement, as described in the Method 3—Measure Large Range of  
Frequencies Using Two Counters section.  
Counter Filters  
You can enable a programmable debouncing filter on each PFI, RTSI, or  
PXI_STAR signal. When the filters are enabled, your device samples the  
input on each rising edge of a filter clock. M Series devices use an onboard  
oscillator to generate the filter clock with a 40 MHz frequency.  
Note NI-DAQmx only supports filters on counter inputs.  
The following is an example of low-to-high transitions of the input signal.  
High-to-low transitions work similarly.  
Assume that an input terminal has been low for a long time. The input  
terminal then changes from low-to-high, but glitches several times. When  
the filter clock has sampled the signal high on N consecutive edges, the  
low-to-high transition is propagated to the rest of the circuit. The value of  
N depends on the filter setting; refer to Table 7-5.  
Table 7-5. Filters  
N (Filter  
Pulse Width  
Pulse Width  
ClocksNeeded Guaranteedto Guaranteedto  
Filter Setting  
125 ns  
to Pass Signal)  
Pass Filter  
125 ns  
Not Pass Filter  
100 ns  
5
257  
6.425 µs  
2.55 ms  
6.425 µs  
2.55 ms  
6.400 µs  
2.54 ms  
~101,800  
Disabled  
© National Instruments Corporation  
7-33  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 7  
Counters  
The filter setting for each input can be configured independently. On power  
up, the filters are disabled. Figure 7-29 shows an example of a low-to-high  
transition on an input that has its filter set to 125 ns (N = 5).  
RTSI, PFI, or  
Filtered input goes high  
when terminal is sampled  
high on five consecutive  
filter clocks.  
PXI_STAR Terminal  
1
1
2
3
4
1
2
3
4
5
Filter Clock  
(40 MHz)  
Filtered Input  
Figure 7-29. Filter Example  
Enabling filters introduces jitter on the input signal. For the 125 ns and  
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the  
jitter is up to 10.025 µs.  
When a PFI input is routed directly to RTSI, or a RTSI input is routed  
directly to PFI, the M Series device does not use the filtered version of the  
input signal.  
Refer to the KnowledgeBase document, Digital Filtering with M Seriesand  
CompactDAQ, for more information about digital filters and counters. To  
access this KnowledgeBase, go to ni.com/infoand enter the info code  
rddfms.  
Prescaling  
Prescaling allows the counter to count a signal that is faster than the  
maximum timebase of the counter. M Series devices offer 8X and 2X  
prescaling on each counter (prescaling can be disabled). Each prescaler  
consists of a small, simple counter that counts to eight (or two) and rolls  
over. This counter can run faster than the larger counters, which simply  
count the rollovers of this smaller counter. Thus, the prescaler acts as a  
frequency divider on the Source and puts out a frequency that is one-eighth  
(or one-half) of what it is accepting.  
NI 6238/6239 User Manual  
7-34  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 7  
Counters  
External Signal  
Prescaler Rollover  
(Used as Source  
by Counter)  
Counter Value  
0
1
Figure 7-30. Prescaling  
Prescaling is intended to be used for frequency measurement where the  
measurement is made on a continuous, repetitive signal. The prescaling  
counter cannot be read; therefore, you cannot determine how many edges  
have occurred since the previous rollover. Prescaling can be used for event  
counting provided it is acceptable to have an error of up to seven (or one).  
Prescaling can be used when the counter Source is an external signal.  
Prescaling is not available if the counter Source is one of the internal  
timebases (80MHzTimebase, 20MHzTimebase, or 100kHzTimebase).  
Duplicate Count Prevention  
Duplicate count prevention (or synchronous counting mode) ensures that a  
counter returns correct data in applications that use a slow or non-periodic  
external source. Duplicate count prevention applies only to buffered  
counter applications such as measuring frequency or period. In such  
buffered applications, the counter should store the number of times an  
external Source pulses between rising edges on the Gate signal.  
Example Application That Works Correctly (No  
Duplicate Counting)  
Figure 7-31 shows an external buffered signal as the period measurement  
Source.  
© National Instruments Corporation  
7-35  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
Rising Edge  
of Gate  
Counter detects rising edge  
of Gate on the next rising  
edge of Source.  
Gate  
Source  
Counter Value  
Buffer  
6
7
1
2
1
7
2
7
Figure 7-31. Duplicate Count Prevention Example  
On the first rising edge of the Gate, the current count of 7 is stored. On the  
next rising edge of the Gate, the counter stores a 2 since two Source pulses  
occurred after the previous rising edge of Gate.  
The counter synchronizes or samples the Gate signal with the Source  
signal, so the counter does not detect a rising edge in the Gate until the next  
Source pulse. In this example, the counter stores the values in the buffer on  
the first rising Source edge after the rising edge of Gate. The details of  
when exactly the counter synchronizes the Gate signal vary depending on  
the synchronization mode. Synchronization modes are described in the  
Synchronization Modes section.  
Example Application That Works Incorrectly  
(Duplicate Counting)  
In Figure 7-32, after the first rising edge of Gate, no Source pulses occur.  
So the counter does not write the correct data to the buffer.  
NI 6238/6239 User Manual  
7-36  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 7  
Counters  
No Source edge, so no  
value written to buffer.  
Gate  
Source  
Counter Value  
Buffer  
6
7
1
7
Figure 7-32. Duplicate Count Example  
Example Application That Prevents Duplicate Count  
With duplicate count prevention enabled, the counter synchronizes both the  
Source and Gate signals to the 80 MHz Timebase. By synchronizing to the  
timebase, the counter detects edges on the Gate even if the Source does not  
pulse. This enables the correct current count to be stored in the buffer even  
if no Source edges occur between Gate signals, as shown in Figure 7-33.  
Counter detects  
rising Gate edge.  
Counter value  
increments only  
one time for each  
Source pulse.  
Gate  
Source  
80 MHz Timebase  
Counter Value  
Buffer  
6
7
0
1
7
0
7
Figure 7-33. Duplicate Count Prevention Example  
Even if the Source pulses are long, the counter increments only once for  
each Source pulse.  
Normally, the counter value and Counter n Internal Output signals change  
synchronously to the Source signal. With duplicate count prevention, the  
© National Instruments Corporation  
7-37  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 7  
Counters  
counter value and Counter n Internal Output signals change synchronously  
to the 80 MHz Timebase.  
Note that duplicate count prevention should only be used if the frequency  
of the Source signal is 20 MHz or less.  
When To Use Duplicate Count Prevention  
You should use duplicate count prevention if the following conditions are  
true.  
You are making a counter measurement  
You are using an external signal (such as PFI <0..5>) as the counter  
Source  
The frequency of the external source is 20 MHz or less  
You can have the counter value and output to change synchronously  
with the 80 MHz Timebase  
In all other cases, you should not use duplicate count prevention.  
Enabling Duplicate Count Prevention in NI-DAQmx  
You can enable duplicate count prevention in NI-DAQmx by setting the  
Enable Duplicate Count Prevention attribute/property. For specific  
information on finding the Enable Duplicate Count Prevention  
attribute/property, refer to the help file for the API you are using.  
Synchronization Modes  
The 32-bit counter counts up or down synchronously with the Source  
signal. The Gate signal and other counter inputs are asynchronous to the  
Source signal, so M Series devices synchronize these signals before  
presenting them to the internal counter.  
M Series devices use one of three synchronization methods:  
80 MHz source mode  
Other internal source mode  
External source mode  
In DAQmx, the device uses 80 MHz source mode if the user performs the  
Performs a position measurement  
Selects duplicate count prevention  
NI 6238/6239 User Manual  
7-38  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 7  
Counters  
Otherwise, the mode depends on the signal that drives Counter n Source.  
Table 7-6 describes the conditions for each mode.  
Table 7-6. Synchronization Mode Conditions  
Duplicate  
Count  
Prevention  
Enabled  
SignalDriving  
Counter n  
Source  
Type of  
Measurement  
Synchronization  
Mode  
Yes  
No  
Any  
Any  
Any  
80 MHz Source  
80 MHz Source  
Position  
Measurement  
No  
No  
Any  
80 MHz  
Timebase  
80 MHz Source  
All Except  
Position  
Measurement  
20 MHz  
Other Internal  
Source  
Timebase, 100  
kHz Timebase,  
or PXI_CLK10  
No  
All Except  
Position  
Any Other  
Signal (such as  
PFI or RTSI)  
External Source  
80 MHz Source Mode  
In 80 MHz source mode, the device synchronizes signals on the rising edge  
of the source, and counts on the following rising edge of the source, as  
shown in Figure 7-34.  
Source  
Synchronize  
Count  
Figure 7-34. 80 MHz Source Mode  
Other Internal Source Mode  
In other internal source mode, the device synchronizes signals on the  
falling edge of the source, and counts on the following rising edge of the  
source, as shown in Figure 7-35.  
© National Instruments Corporation  
7-39  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 7  
Counters  
Source  
Synchronize  
Count  
Figure 7-35. Other Internal Source Mode  
External Source Mode  
In external source mode, the device generates a delayed Source signal by  
delaying the Source signal by several nanoseconds. The device  
synchronizes signals on the rising edge of the delayed Source signal, and  
counts on the following rising edge of the source, as shown in Figure 7-36.  
Source  
Synchronize  
Delayed Source  
Count  
Figure 7-36. External Source Mode  
NI 6238/6239 User Manual  
7-40  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
8
PFI  
NI 6238/6239 devices have 10 Programmable Function Interface (PFI)  
signals—six input signals and four output signals.  
Each PFI <0..5>/P0.<0..5> can be configured as a timing input signal for  
AI or counter/timer functions or a static digital input. Each PFI input also  
has a programmable debouncing filter.  
Caution When making measurements, take into account the minimum pulse width and  
time delay of the digital input and output lines.  
Figure 8-1 shows the circuitry of one PFI input line. Each PFI line is  
similar.  
Isolation  
Barrier  
Static DI  
Digital  
Isolators  
PFI <0..5>/P0.<0..5>  
To Input Timing  
Signal Selectors  
PFI  
Filters  
Figure 8-1. NI 6238/6239 PFI Input Circuitry  
Each PFI <6..9>/P1.<0..3> can be configured as a timing output signal  
from AI, AO, or counter/timer functions or a static digital output.  
Figure 8-2 shows the circuitry of one PFI output line. Each PFI line is  
similar.  
© National Instruments Corporation  
8-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 8  
PFI  
Isolation  
Barrier  
Timing Signals  
Digital  
PFI <6..9>/P1.<0..3>  
Isolators  
Static DO  
Buffer  
Figure 8-2. NI 6238/6239 PFI Output Circuitry  
When a terminal is used as a timing input or output signal, it is called PFI x  
(where x is an integer from 0 to 9). When a terminal is used as a static digital  
input or output, it is called P0.x or P1.x.  
The voltage input and output levels and the current drive levels of the PFI  
signals are listed in the NI 6238/6239 Specifications.  
Using PFI Terminals as Timing Input Signals  
Use PFI <0..5> terminals to route external timing signals to many different  
M Series functions. Each input PFI terminal can be routed to any of the  
following signals.  
AI Convert Clock  
AI Sample Clock  
AI Start Trigger  
AI Reference Trigger  
AI Pause Trigger  
AI Sample Clock Timebase  
AO Start Trigger  
AO Sample Clock  
AO Sample Clock Timebase  
AO Pause Trigger  
Counter input signals for either counter—Source, Gate, Aux,  
Most functions allow you to configure the polarity of PFI inputs and  
whether the input is edge or level sensitive.  
NI 6238/6239 User Manual  
8-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 8  
PFI  
Exporting Timing Output Signals Using PFI Terminals  
You can route any of the following timing signals to any PFI <6..9>  
terminal.  
AI Hold Complete Event  
Counter n Source  
Counter n Gate  
Counter n Internal Output  
Frequency Output  
PXI_STAR  
RTSI <0..7>  
Note Short pulses on the signal might not be observable by the user or another instrument.  
Refer to the Digital Output (Port 1) section of the NI 6238/6239 Specifications for more  
information.  
Using PFI Terminals as Static Digital Inputs and Outputs  
When a terminal is used as a static digital input or output, it is called P0.x  
or P1.x. On the I/O connector, each terminal is labeled PFI x/P0.x or  
PFI x/P1.x.  
Connecting PFI Input Signals  
All PFI input connections are referenced to P0.GND. Figure 8-3 shows this  
reference, and how to connect an external PFI 0 source and an external  
PFI 2 source to two PFI terminals.  
© National Instruments Corporation  
8-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
             
Chapter 8  
PFI  
I/O Connector  
PFI 0  
PFI 2  
PFI 0  
Source  
PFI 2  
Source  
P0.GND  
M Series Device  
Figure 8-3. PFI Input Signals Connections  
PFI Filters  
You can enable a programmable debouncing filter on each PFI, RTSI, or  
PXI_STAR signal. When the filters are enabled, your device samples the  
input on each rising edge of a filter clock. M Series devices use an onboard  
oscillator to generate the filter clock with a 40 MHz frequency.  
Note NI-DAQmx only supports filters on counter inputs.  
The following is an example of low-to-high transitions of the input signal.  
High-to-low transitions work similarly.  
Assume that an input terminal has been low for a long time. The input  
terminal then changes from low-to-high, but glitches several times. When  
the filter clock has sampled the signal high on N consecutive edges, the  
low-to-high transition is propagated to the rest of the circuit. The value of  
N depends on the filter setting; refer to Table 8-1.  
NI 6238/6239 User Manual  
8-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 8  
PFI  
Table 8-1. Filters  
N (Filter Pulse Width  
Pulse Width  
ClocksNeeded Guaranteedto Guaranteedto  
Filter Setting  
125 ns  
to Pass Signal)  
Pass Filter  
Not Pass Filter  
5
257  
125 ns  
100 ns  
6.425 µs  
2.55 ms  
6.425 µs  
2.55 ms  
6.400 µs  
2.54 ms  
~101,800  
Disabled  
The filter setting for each input can be configured independently. On power  
up, the filters are disabled. Figure 8-4 shows an example of a low-to-high  
transition on an input that has its filter set to 125 ns (N = 5).  
RTSI, PFI, or  
Filtered input goes high  
when terminal is sampled  
high on five consecutive  
filter clocks.  
PXI_STAR Terminal  
1
1
2
3
4
1
2
3
4
5
Filter Clock  
(40 MHz)  
Filtered Input  
Figure 8-4. Filter Example  
Enabling filters introduces jitter on the input signal. For the 125 ns and  
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the  
jitter is up to 10.025 µs.  
When a PFI input is routed directly to RTSI, or a RTSI input is routed  
directly to PFI, the M Series device does not use the filtered version of the  
input signal.  
Refer to the KnowledgeBase document, Digital Filtering with M Series  
and CompactDAQ, for more information about digital filters and counters.  
To access this KnowledgeBase, go to ni.com/infoand enter the info  
code rddfms.  
I/O Protection  
Each DI, DO, and PFI signal is protected against overvoltage and  
undervoltage conditions as well as ESD events on NI 6238/6239 devices.  
© National Instruments Corporation  
8-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 8  
PFI  
Consult the device specifications for details. However, you should avoid  
these fault conditions by following these guidelines.  
Do not connect any digital output line to any external signal source,  
ground signal, or power supply.  
Understand the current requirements of the load connected to the  
digital output lines. Do not exceed the specified current output limits  
of the digital outputs. NI has several signal conditioning solutions for  
digital applications requiring high current drive.  
Do not drive the digital input lines with voltages or current outside of  
its normal operating range.  
Treat the DAQ device as you would treat any static sensitive device.  
Always properly ground yourself and the equipment when handling the  
DAQ device or connecting to it.  
Programmable Power-Up States  
By default, the digital output lines (P1.<0..3>/PFI <6..9>) are set to 0. They  
can be programmed to power up as 0 or 1.  
Refer to the NI-DAQmx Help or the LabVIEW 8.x Help for more  
information about setting power-up states in NI-DAQmx or MAX.  
The DI signals P0.<0..5> are referenced to P0.GND and DO signals  
P1.<0..3> are referenced to P1.GND.  
Figures 8-5 and 8-6 show P0.<0..5> and P1.<0..3> on the NI 6238 and the  
NI 6239 device, respectively. Digital input and output signals can range  
from 0 to 30 V. Refer to the NI 6238/6239 Specifications for more  
information.  
NI 6238/6239 User Manual  
8-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 8  
PFI  
P1.VCC  
P1.0  
P1.<0..3>  
Digital  
Isolators  
P1.1  
P1.GND  
P1.GND  
P0.0  
P0.GND  
P0.GND  
Figure 8-5. NI 6238 Digital I/O Connections (DO Source)  
© National Instruments Corporation  
8-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Chapter 8  
PFI  
P1.VCC  
P1.0  
Buffer  
P1.GND  
P1.1  
P1.<0..3>  
Digital  
Isolators  
P1.GND  
P1.GND  
P0.0  
P0.GND  
P0.GND  
Figure 8-6. NI 6239 Digital I/O Connections (DO Sink)  
Caution Exceeding the maximum input voltage or maximum working voltage ratings,  
which are listed in the NI 6238/6239 Specifications, can damage the DAQ device and the  
computer. NI is not liable for any damage resulting from such signal connections.  
NI 6238/6239 User Manual  
8-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
9
NI 6232/6233 devices are isolated data acquisition devices. As shown in  
Figure 9-1, the analog input, analog output, counters, and PFI/static DIO  
circuitry are referenced to an isolated ground. The bus interface circuitry,  
RTSI, digital routing, and clock generation are all referenced to a  
non-isolated ground. Refer to Table 9-1 for an example of the symbols for  
isolated ground and non-isolated ground.  
Table 9-1. Ground Symbols  
Isolated Ground  
Non-Isolated Ground  
A
Isolation  
Barrier  
Analog Input  
AI GND  
A
A
Digital  
Routing  
and Clock  
Generation  
Analog Output  
Bus  
Bus  
Interface  
AO GND  
Digital  
Isolators  
Counters  
RTSI  
PFI/Static DI  
P0  
P1  
P0.GND  
P1.GND  
PFI/Static DO  
Figure 9-1. General NI 6238/6239 Block Diagram  
© National Instruments Corporation  
9-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 9  
Isolation and Digital Isolators  
The non-isolated ground is connected to the chassis ground of the PC or  
chassis where the device is installed.  
Each isolated ground is not connected to the chassis ground of the PC or  
isolated ground signal.  
Each isolated ground is an input to the NI 6238/6239 device. The user must  
connect this ground to the ground of system being measured or controlled.  
Refer to the Connecting Analog Current Input Signals section of Chapter 4,  
Analog Input, the Connecting Analog Current Output Signals section of  
Chapter 5, Analog Output, the Connecting Digital I/O Signals section of  
Chapter 6, Digital Input and Output, and the Connecting PFI Input Signals  
section of Chapter 8, PFI, for more information.  
Digital Isolation  
The NI 6238/6239 uses digital isolators. Unlike analog isolators, digital  
isolators do not introduce any analog error in the measurements taken by  
the device. The A/D converter, used for analog input, is on the isolated side  
of the device. The analog inputs are digitized before they are sent across the  
isolation barrier. Similarly, the D/A converters, used for analog output, are  
on the isolated side of the device.  
Benefits of an Isolated DAQ Device  
With isolation, engineers can safely measure a small current in the presence  
of a large common-mode voltage signal. Some advantages of isolation are  
as follows:  
Improved rejection—Isolation increases the ability of the  
measurement system to reject common-mode voltages when the  
common-mode voltage is applied to the isolated ground.  
Common-mode voltage is the signal that is present or “common” to  
both the positive and negative input of a measurement device, but is not  
part of the signal to be measured.  
Improved accuracy—Isolation improves measurement accuracy by  
physically preventing ground loops. Ground loops, a common source  
of error and noise, are the result of a measurement system having  
multiple grounds at different potentials.  
NI 6238/6239 User Manual  
9-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 9  
Isolation and Digital Isolators  
Improved safety—Isolation creates an insulation barrier so you can  
make measurements at elevated voltages while protecting against large  
transient voltage spikes.  
Reducing Common-Mode Noise  
Isolated products require an isolated power supply to deliver power to the  
isolated side from the non-isolated side. Isolated power supplies work by  
switching voltages through a transformer with high-speed transistors.  
Switching voltages through the transformer causes charging and  
discharging of the parasitic capacitances and inductances in the switching  
power supplies that occur on every switch cycle, resulting in high-speed  
currents flowing through the isolated side and returning to the non-isolated  
side, which is earth ground.  
These parasitic currents interact with parasitic and non-parasitic resistances  
causing voltage spikes. These voltage spikes are called common-mode  
noise, a noise source that travels in the ground and is therefore common to  
both the ground and any signal referenced to the ground, such as AI, AO,  
and digital signals. Common-mode noise appears at the harmonics of the  
switching power supply frequency and can corrupt measurements  
depending on the system setup.  
To reduce common-mode noise:  
Better grounding from the front connector can reduce common-mode  
noise. Use low resistance cabling and connections and verify that all  
ground connections are kept short. Keep the number of connections to  
a minimum. If the device’s isolated ground is being connected back to  
earth ground, verify that this is done in the most direct way possible.  
Reduce source impedances if possible. The parasitic currents react  
with these impedances.  
© National Instruments Corporation  
9-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
10  
Digital Routing and Clock  
Generation  
The digital routing circuitry has the following three main functions.  
Manages the flow of data between the bus interface and the  
acquisition/generation sub-systems (analog input, analog output,  
digital I/O, and the counters). The digital routing circuitry uses FIFOs  
(if present) in each sub-system to ensure efficient data movement.  
Routes timing and control signals. The acquisition/generation  
sub-systems use these signals to manage acquisitions and generations.  
These signals can come from the following sources.  
Your M Series device  
Other devices in your system through RTSI  
User input through the PFI terminals  
User input through the PXI_STAR terminal  
Routes and generates the main clock signals for the M Series device.  
Clock Routing  
Figure 10-1 shows the clock routing circuitry of an M Series device.  
Onboard  
80 MHz  
Oscillator  
10 MHz RefClk  
(To RTSI <0..7>  
Output Selectors)  
÷ 8  
External  
Reference  
80 MHz Timebase  
RTSI <0..7>  
PXI_CLK10  
Clock  
PLL  
20 MHz Timebase  
÷
4
PXI_STAR  
÷
200  
100 kHz Timebase  
Figure 10-1. M Series Clock Routing Circuitry  
© National Instruments Corporation  
10-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 10  
Digital Routing and Clock Generation  
Caution RTSI signals are not isolated from the chassis.  
80 MHz Timebase  
The 80 MHz Timebase can be used as the Source input to the 32-bit  
general-purpose counter/timers.  
The 80 MHz Timebase can be generated from either of the following.  
Onboard oscillator  
External signal (by using the external reference clock)  
20 MHz Timebase  
100 kHz Timebase  
The 20 MHz Timebase normally generates many of the AI and AO timing  
signals. The 20 MHz Timebase also can be used as the Source input to the  
32-bit general-purpose counter/timers.  
Your device generates 20 MHz Timebase by dividing down the 80 MHz  
Timebase.  
The 100 kHz Timebase can be used to generate many of the AI and AO  
timing signals. The 100 kHz Timebase also can be used as the Source input  
to the 32-bit general-purpose counter/timers.  
The 100 kHz Timebase is generated by dividing down the 20 MHz  
Timebase by 200.  
External Reference Clock  
The external reference clock can be used as a source for the internal  
timebases (80 MHz Timebase, 20 MHz Timebase, and 100 kHz Timebase)  
on an M Series device. By using the external reference clock, you can  
synchronize the internal timebases to an external clock.  
The following signals can be routed to drive the external reference clock.  
RTSI <0..7>  
PXI_CLK10  
PXI_STAR  
The external reference clock is an input to a Phase-Lock Loop (PLL). The  
PLL generates the internal timebases.  
NI 6238/6239 User Manual  
10-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
               
Chapter 10  
Digital Routing and Clock Generation  
10 MHz Reference Clock  
The 10 MHz reference clock can be used to synchronize other devices to  
your M Series device. The 10 MHz reference clock can be routed to the  
RTSI <0..7> terminals. Other devices connected to the RTSI bus can use  
this signal as a clock input.  
The 10 MHz reference clock is generated by dividing down the onboard  
oscillator.  
Synchronizing Multiple Devices  
With the RTSI bus and the routing capabilities of M Series devices, there  
are several ways to synchronize multiple devices depending on your  
application.  
To synchronize multiple devices to a common timebase, choose one  
device—the initiator—to generate the timebase. The initiator device routes  
its 10 MHz reference clock to one of the RTSI <0..7> signals.  
All devices (including the initiator device) receive the 10 MHz Reference  
Clock from RTSI. This signal becomes the external reference clock. A PLL  
on each device generates the internal timebases synchronous to the external  
reference clock.  
On PXI systems, you also can synchronize devices to PXI_CLK10. In this  
application the PXI chassis acts as the initiator. Each PXI module routes  
PXI_CLK10 to its external reference clock.  
Another option in PXI systems is to use PXI_STAR. The Star Trigger  
controller device acts as the initiator and drives PXI_STAR with a clock  
signal. Each target device routes PXI_STAR to its external reference clock.  
When all of the devices are using or referencing a common timebase, you  
can synchronize operations across them by sending a common start trigger  
out across the RTSI bus and setting their sample clock rates to the same  
value.  
Real-Time System Integration Bus (RTSI)  
Real-Time System Integration (RTSI) is set of bused signals among devices  
that allow you to do the following.  
Use a common clock (or timebase) to drive the timing engine on  
multiple devices  
© National Instruments Corporation  
10-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 10  
Digital Routing and Clock Generation  
Share trigger signals between devices  
Many National Instruments DAQ, motion, vision, and CAN devices  
support RTSI.  
In a PCI system, the RTSI bus consists of the RTSI bus interface and a  
ribbon cable. The bus can route timing and trigger signals between several  
functions on as many as five DAQ, vision, motion, or CAN devices in the  
computer. In a PXI system, the RTSI bus consists of the RTSI bus interface  
and the PXI trigger signals on the PXI backplane. This bus can route timing  
and trigger signals between several functions on as many as seven DAQ  
devices in the system.  
RTSI Connector Pinout  
Figure 10-2 shows the RTSI connector pinout and Table 10-1 describes the  
RTSI signals. The RTSI signals are referenced to earth/chassis ground; they  
are not isolated.  
Terminal 34  
Terminal 33  
Terminal 2  
Terminal 1  
Figure 10-2. NI 6238/6239 RTSI Pinout  
NI 6238/6239 User Manual  
10-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 10  
Digital Routing and Clock Generation  
Table 10-1. RTSI Signal Descriptions  
RTSI Bus Signal  
Terminal  
RTSI 7  
RTSI 6  
RTSI 5  
RTSI 4  
RTSI 3  
RTSI 2  
RTSI 1  
RTSI 0  
34  
32  
30  
28  
26  
24  
22  
20  
Not Connected. Do not connect signals  
to these terminals.  
1–18  
GND  
19, 21, 23, 25, 27, 29, 31, 33  
Note: RTSI <0..7> and GND are earth/chassis ground-referenced. They are not isolated.  
Using RTSI as Outputs  
RTSI <0..7> are bidirectional terminals. As an output, you can drive any of  
the following signals to any RTSI terminal.  
ai/StartTrigger  
ai/ReferenceTrigger  
ai/ConvertClock*  
ai/SampleClock  
ai/PauseTrigger  
ao/SampleClock*  
ao/StartTrigger  
ao/PauseTrigger  
10 MHz Reference Clock  
Counter n Source, Gate, Z, Internal Output  
FREQ OUT  
Input PFI <0..5>  
Note Signals with a * are inverted before being driven on the RTSI terminals.  
© National Instruments Corporation  
10-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
     
Chapter 10  
Digital Routing and Clock Generation  
Using RTSI Terminals as Timing Input Signals  
You can use RTSI terminals to route external timing signals to many  
different M Series functions. Each RTSI terminal can be routed to any of  
the following signals.  
AI Convert Clock  
AI Sample Clock  
AI Start Trigger  
AI Reference Trigger  
AI Pause Trigger  
AI Sample Clock Timebase  
AO Start Trigger  
AO Sample Clock  
AO Sample Clock Timebase  
AO Pause Trigger  
Counter input signals for either counter—Source, Gate, Aux,  
HW_Arm, A, B, or Z  
Most functions allow you to configure the polarity of PFI inputs and  
whether the input is edge or level sensitive.  
RTSI Filters  
You can enable a programmable debouncing filter on each PFI, RTSI, or  
PXI_STAR signal. When the filters are enabled, your device samples the  
input on each rising edge of a filter clock. M Series devices use an onboard  
oscillator to generate the filter clock with a 40 MHz frequency.  
Note NI-DAQmx only supports filters on counter inputs.  
The following is an example of low-to-high transitions of the input signal.  
High-to-low transitions work similarly.  
Assume that an input terminal has been low for a long time. The input  
terminal then changes from low-to-high, but glitches several times. When  
the filter clock has sampled the signal high on N consecutive edges, the  
low-to-high transition is propagated to the rest of the circuit. The value of  
N depends on the filter setting; refer to Table 10-2.  
NI 6238/6239 User Manual  
10-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 10  
Digital Routing and Clock Generation  
Table 10-2. Filters  
N (Filter  
Pulse Width  
Pulse Width  
ClocksNeeded Guaranteedto Guaranteedto  
Filter Setting  
125 ns  
to Pass Signal)  
Pass Filter  
125 ns  
Not Pass Filter  
100 ns  
5
257  
6.425 µs  
2.55 ms  
6.425 µs  
2.55 ms  
6.400 µs  
2.54 ms  
~101,800  
Disabled  
The filter setting for each input can be configured independently. On power  
up, the filters are disabled. Figure 10-3 shows an example of a low-to-high  
transition on an input that has its filter set to 125 ns (N = 5).  
RTSI, PFI, or  
Filtered input goes high  
when terminal is sampled  
high on five consecutive  
filter clocks.  
PXI_STAR Terminal  
1
1
2
3
4
1
2
3
4
5
Filter Clock  
(40 MHz)  
Filtered Input  
Figure 10-3. Filter Example  
Enabling filters introduces jitter on the input signal. For the 125 ns and  
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the  
jitter is up to 10.025 µs.  
When a PFI input is routed directly to RTSI, or a RTSI input is routed  
directly to PFI, the M Series device does not use the filtered version of the  
input signal.  
Refer to the KnowledgeBase document, Digital Filtering with M Series  
and CompactDAQ, for more information about digital filters and counters.  
To access this KnowledgeBase, go to ni.com/infoand enter the info  
code rddfms.  
PXI Clock and Trigger Signals  
Note PXI clock and trigger signals are only available on PXI devices. Other devices use  
RTSI.  
© National Instruments Corporation  
10-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 10  
Digital Routing and Clock Generation  
PXI_CLK10  
PXI_CLK10 is a common low-skew 10 MHz clock reference clock for  
synchronization of multiple modules in a PXI measurement or control  
system. The PXI backplane is responsible for generating PXI_CLK10  
independently to each peripheral slot in a PXI chassis.  
PXI Triggers  
A PXI chassis provides eight bused trigger lines to each module in a  
system. Triggers may be passed from one module to another, allowing  
precisely timed responses to asynchronous external events that are being  
monitored or controlled. Triggers can be used to synchronize the operation  
of several different PXI peripheral modules.  
On M Series devices, the eight PXI trigger signals are synonymous with  
RTSI <0..7>.  
Note that in a PXI chassis with more than eight slots, the PXI trigger lines  
may be divided into multiple independent buses. Refer to the  
documentation for your chassis for details.  
PXI_STAR Trigger  
In a PXI system, the Star Trigger bus implements a dedicated trigger line  
between the first peripheral slot (adjacent to the system slot) and the other  
peripheral slots. The Star Trigger can be used to synchronize multiple  
devices or to share a common trigger signal among devices.  
A Star Trigger controller can be installed in this first peripheral slot to  
provide trigger signals to other peripheral modules. Systems that do not  
require this functionality can install any standard peripheral module in this  
first peripheral slot.  
An M Series device receives the Star Trigger signal (PXI_STAR) from a  
Star Trigger controller. PXI_STAR can be used as an external source for  
many AI, AO, and counter signals.  
An M Series device is not a Star Trigger controller. An M Series device  
may be used in the first peripheral slot of a PXI system, but the system will  
not be able to use the Star Trigger feature.  
You can enable a programmable debouncing filter on each PFI, RTSI, or  
PXI_STAR signal. When the filters are enabled, your device samples the  
NI 6238/6239 User Manual  
10-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                       
Chapter 10  
Digital Routing and Clock Generation  
input on each rising edge of a filter clock. M Series devices use an onboard  
oscillator to generate the filter clock with a 40 MHz frequency.  
Note NI-DAQmx only supports filters on counter inputs.  
The following is an example of low-to-high transitions of the input signal.  
High-to-low transitions work similarly.  
Assume that an input terminal has been low for a long time. The input  
terminal then changes from low-to-high, but glitches several times. When  
the filter clock has sampled the signal high on N consecutive edges, the  
low-to-high transition is propagated to the rest of the circuit. The value of  
N depends on the filter setting; refer to Table 10-3.  
Table 10-3. Filters  
N (Filter  
Pulse Width  
Pulse Width  
ClocksNeeded Guaranteedto Guaranteedto  
Filter Setting  
125 ns  
to Pass Signal)  
Pass Filter  
125 ns  
Not Pass Filter  
100 ns  
5
257  
6.425 µs  
2.55 ms  
6.425 µs  
2.55 ms  
6.400 µs  
2.54 ms  
~101,800  
Disabled  
The filter setting for each input can be configured independently. On power  
up, the filters are disabled. Figure 10-4 shows an example of a low-to-high  
transition on an input that has its filter set to 125 ns (N = 5).  
RTSI, PFI, or  
Filtered input goes high  
when terminal is sampled  
high on five consecutive  
filter clocks.  
PXI_STAR Terminal  
1
1
2
3
4
1
2
3
4
5
Filter Clock  
(40 MHz)  
Filtered Input  
Figure 10-4. Filter Example  
Enabling filters introduces jitter on the input signal. For the 125 ns and  
6.425 µs filter settings, the jitter is up to 25 ns. On the 2.55 ms setting, the  
jitter is up to 10.025 µs.  
© National Instruments Corporation  
10-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Chapter 10  
Digital Routing and Clock Generation  
When a PFI input is routed directly to RTSI, or a RTSI input is routed  
directly to PFI, the M Series device does not use the filtered version of the  
input signal.  
Refer to the KnowledgeBase document, Digital Filtering with M Series  
and CompactDAQ, for more information about digital filters and counters.  
To access this KnowledgeBase, go to ni.com/infoand enter the info  
code rddfms.  
NI 6238/6239 User Manual  
10-10  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
11  
Bus Interface  
The bus interface circuitry of NI 6238/6239 devices efficiently moves data  
between host memory and the measurement and acquisition circuits.  
NI 6238/6239 devices are available for the following platforms.  
PCI  
PXI  
NI 6238/6239 devices are jumperless for complete plug-and-play  
operation. The operating system automatically assigns the base address,  
interrupt levels, and other resources.  
NI 6238/6239 devices incorporate PCI-MITE technology to implement a  
high-performance PCI interface.  
DMA Controllers  
NI 6238/6239 devices have four fully-independent DMA controllers for  
high-performance transfers of data blocks. One DMA controller is  
available for each measurement and acquisition block.  
Analog input  
Analog output  
Counter 0  
Counter 1  
Each DMA controller channel contains a FIFO and independent processes  
for filling and emptying the FIFO. This allows the buses involved in the  
transfer to operate independently for maximum performance. Data is  
transferred simultaneously between the ports. The DMA controller  
supports burst transfers to and from the FIFO.  
Each DMA controller acts as a PCI Master device. The DMA controllers  
support scatter-gather operations to and from host memory. Memory  
buffers may be used in linear or circular fashion.  
© National Instruments Corporation  
11-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
Chapter 11  
Bus Interface  
Each DMA controller supports packing and unpacking of data through the  
FIFOs to connect different size devices and optimize PCI bus utilization  
and automatically handles unaligned memory buffers.  
PXI Considerations  
PXI Clock and Trigger Signals  
Refer to the PXI_CLK10, PXI Triggers, PXI_STAR Trigger, and  
PXI_STAR Filters sections of Chapter 10, Digital Routing and Clock  
Generation, for more information on PXI clock and trigger signals.  
PXI and PXI Express  
NI PXI-6238/6239 modules can be installed in any PXI chassis and most  
slots of PXI Express chassis.  
PXI specifications are developed by the PXI System Alliance  
(www.pxisa.org). Using the terminology of the PXI specifications,  
NI PXI-6238/6239 devices are 3U Hybrid Slot-Compatible PXI-1  
Peripheral Modules.  
3U designates devices that are 100 mm tall (as opposed to the taller 6U  
modules).  
Hybrid slot-compatible defines where the device can be installed.  
PXI-6238/6239 devices can be installed in the following chassis and slots:  
PXI chassis—PXI-6238/6239 devices can be installed in any  
peripheral slot of a PXI chassis.  
PXI Express chassis—PXI-6238/6239 devices can be installed in the  
following PXI Express chassis slots:  
PXI-1 slots—Accepts all PXI modules  
PXI hybrid slots—Accepts PXI or PXI Express modules.  
PXI-1 devices use PCI signaling to communicate to the host controller (as  
Peripheral devices are installed in peripheral slots and are not system  
controllers.  
NI 6238/6239 User Manual  
11-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 11  
Bus Interface  
Using PXI with CompactPCI  
Using PXI-compatible products with standard CompactPCI products is an  
important feature provided by PXI Hardware Specification Revision 2.1. If  
you use a PXI-compatible plug-in module in a standard CompactPCI  
chassis, you cannot use PXI-specific functions, but you can still use the  
basic plug-in device functions. For example, the RTSI bus on a PXI  
M Series device is available in a PXI chassis, but not in a CompactPCI  
chassis.  
The CompactPCI specification permits vendors to develop sub-buses that  
coexist with the basic PCI interface on the CompactPCI bus. Compatible  
operation is not guaranteed between CompactPCI devices with different  
sub-buses nor between CompactPCI devices with sub-buses and PXI. The  
standard implementation for CompactPCI does not include these  
sub-buses. The PXI M Series device works in any standard CompactPCI  
chassis adhering to the PICMG CompactPCI 2.0 R3.0 core specification.  
PXI-specific features are implemented on the J2 connector of the  
CompactPCI bus. The PXI device is compatible with any CompactPCI  
chassis with a sub-bus that does not drive the lines used by that device. Even  
if the sub-bus is capable of driving these lines, the PXI device is still  
compatible as long as those terminals on the sub-bus are disabled by default  
and never enabled.  
Caution Damage can result if these lines are driven by the sub-bus. NI is not liable for any  
damage resulting from improper signal connections.  
Data Transfer Methods  
There are three primary ways to transfer data across the PCI bus—direct  
memory access (DMA), interrupt request (IRQ), and programmed I/O.  
Direct Memory Access (DMA)  
DMA is a method to transfer data between the device and computer  
memory without the involvement of the CPU. This method makes DMA  
the fastest available data transfer method. National Instruments uses DMA  
hardware and software technology to achieve high throughput rates and to  
increase system utilization. DMA is the default method of data transfer for  
DAQ devices that support it.  
© National Instruments Corporation  
11-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Chapter 11  
Bus Interface  
Interrupt Request (IRQ)  
IRQ transfers rely on the CPU to service data transfer requests. The device  
notifies the CPU when it is ready to transfer data. The data transfer speed  
is tightly coupled to the rate at which the CPU can service the interrupt  
requests. If you are using interrupts to transfer data at a rate faster than the  
rate the CPU can service the interrupts, your systems may start to freeze.  
Programmed I/O is a data transfer mechanism where the user’s program is  
responsible for transferring data. Each read or write call in the program  
initiates the transfer of data. Programmed I/O is typically used in  
software-timed (on-demand) operations. Refer to the Software-Timed  
Generations section of Chapter 5, Analog Output, for more information.  
Changing Data Transfer Methods between DMA and IRQ  
On PCI or PXI M Series devices, each measurement and acquisition circuit  
(that is, AI, AO, and so on) has a dedicated DMA channel. So in most  
applications, all data transfers use DMA.  
However, NI-DAQmx allows you to disable DMA and use interrupts. To  
change your data transfer mechanism between DMA and interrupts in  
NI-DAQmx, use the Data Transfer Mechanism property node.  
NI 6238/6239 User Manual  
11-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
12  
Triggering  
A trigger is a signal that causes an action, such as starting or stopping the  
want to produce the trigger and the action you want the trigger to cause.  
NI 6238/6239 devices support internal software triggering, as well as  
external digital triggering. For information about the different actions  
triggers can perform for each sub-system of the device, refer to the  
following sections:  
The Analog Input Triggering section of Chapter 4, Analog Input  
The Analog Output Triggering section of Chapter 5, Analog Output  
The Counter Triggering section of Chapter 7, Counters  
Triggering with a Digital Source  
Your DAQ device can generate a trigger on a digital signal. You must  
specify a source and an edge. The digital source can be any of the PFI,  
RTSI, or PXI_STAR signals.  
The edge can be either the rising edge or falling edge of the digital signal.  
A rising edge is a transition from a low logic level to a high logic level. A  
falling edge is a high to low transition.  
Figure 12-1 shows a falling-edge trigger.  
High  
Digital Trigger  
0 V  
Falling Edge Initiates Acquisition  
Figure 12-1. Falling-Edge Trigger  
© National Instruments Corporation  
12-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Chapter 12  
Triggering  
You also can program your DAQ device to perform an action in response to  
a trigger from a digital source. The action can affect the following.  
Analog input acquisition  
Analog output generation  
Counter behavior  
NI 6238/6239 User Manual  
12-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Device-Specific Information  
This appendix contains device pinouts, specifications, cable and accessory  
choices, and other information for the NI 6238 and NI 6239 M Series  
isolated devices.  
To obtain documentation for devices not listed here, refer to  
ni.com/manuals.  
NI 6238  
NI 6238 Pinout  
Figure A-1 shows the pinout of the NI 6238.  
For a detailed description of each signal, refer to the I/O Connector Signal  
Descriptions section of Chapter 3, Connector Information.  
© National Instruments Corporation  
A-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
           
Appendix A  
Device-Specific Information  
1
2
3
4
5
6
7
8
9
AI 0+/CAL+  
AI 1–  
20  
21  
22  
23  
24  
25  
26  
27  
28  
AI 0–  
AI 1+  
AI 2+  
AI 3–  
AI GND  
AI 4–  
AI 5+  
AI 6+  
AI 7+  
AI GND  
AI 2–  
AI 3+  
AI 4+  
AI 5–  
CAL–  
AI 6–  
10 AI 7–  
AO POWER SUPPLY 29  
11 NC  
AO 0  
30  
31  
32  
33  
34  
35  
36  
37  
12 AO 1  
AO GND  
13 PFI 0/P0.0 (Input)  
PFI 1/P0.1 (Input)  
PFI 2/P0.2 (Input)  
PFI 4/P0.4 (Input)  
P1.VCC  
P0.GND  
14  
15  
16  
17  
18  
19  
PFI 3/P0.3 (Input)  
PFI 5/P0.5 (Input)  
PFI 6/P1.0 (Output)  
PFI 8/P1.2 (Output)  
P1.GND  
PFI 7/P1.1 (Output)  
PFI 9/P1.3 (Output)  
NC = No Connect  
Figure A-1. NI 6238 Pinout  
Table A-1. NI 6238 Device Default NI-DAQmx Counter/Timer Pins  
Counter/Timer Signal  
CTR 0 SRC  
Default Pin Number (Name)  
13 (PFI 0)  
Port  
P0.0  
P0.1  
P0.2  
P1.0  
P0.0  
P0.1  
P0.2  
P0.3  
P0.4  
P0.5  
CTR 0 GATE  
CTR 0 AUX  
CTR 0 OUT  
CTR 0 A  
32 (PFI 1)  
33 (PFI 2)  
17 (PFI 6)  
13 (PFI 0)  
CTR 0 Z  
32 (PFI 1)  
CTR 0 B  
33 (PFI 2)  
CTR 1 GATE  
CTR 1 AUX  
15 (PFI 3)  
34 (PFI 4)  
16 (PFI 5)  
NI 6238/6239 User Manual  
A-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Appendix A  
Device-Specific Information  
Table A-1. NI 6238 Device Default NI-DAQmx Counter/Timer Pins (Continued)  
Counter/Timer Signal  
CTR 1 OUT  
Default Pin Number (Name)  
36 (PFI 7)  
Port  
P1.1  
P0.3  
P0.4  
P0.5  
CTR 1 A  
CTR 1 Z  
CTR 1 B  
15 (PFI 3)  
34 (PFI 4)  
16 (PFI 5)  
Note For more information about default NI-DAQmx counter inputs, refer to Connecting  
Counter Signals in the NI-DAQmx Help or the LabVIEW 8.x Help.  
NI 6238 Specifications  
Refer to the NI 6238/6239 Specifications, available on the NI-DAQ Device  
Document Browser or ni.com/manuals, for more detailed information  
on the NI 6238 device.  
NI 6238 Accessory and Cabling Options  
This section describes some cable and accessory options for the NI 6238  
device. Refer to ni.comfor other accessory options including new devices.  
Screw Terminal  
National Instruments offers several styles of screw terminal connector  
blocks. Use an SH37F-37M cable to connect an NI 6238 device to a  
connector block, such as the following:  
CB-37F-HVD—37-pin DIN rail screw terminal block, UL  
Recognized derated to 30 Vrms, 42.4 Vpk, or 60 VDC  
CB-37FH—Horizontal DIN-mountable terminal block with 37 screw  
terminals  
CB-37FVVertical DIN-mountable terminal block with 37 screw  
terminals  
CB-37F-LP—Low profile terminal block with 37 screw terminals  
TB-2621—37-pin PXI screw terminal block, UL Recognized derated  
to 30 Vrms, 42.4 Vpk, or 60 VDC  
RTSI  
Use RTSI bus cables to connect timing and synchronization signals among  
PCI devices, such as M Series, E Series, CAN, and other measurement,  
© National Instruments Corporation  
A-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Appendix A  
Device-Specific Information  
vision, and motion devices. Since PXI devices use PXI backplane signals  
for timing and synchronization, no cables are required.  
Cables  
In most applications, you can use the following cables:  
SH37F-37M-x—37-pin female-to-male shielded I/O cable, UL Listed  
derated to 30 Vrms, 42.4 Vpk, or 60 VDC  
R37F-37M-1—37-pin female-to-male ribbon I/O cable  
SH37F-P-4—37-pin female-to-pigtails shielded I/O cable  
Custom Cabling and Connectivity  
Refer to the Custom Cabling section of Chapter 2, DAQ System Overview,  
for more information about custom cabling solutions.  
NI 6239  
NI 6239 Pinout  
Figure A-2 shows the pinout of the NI 6239.  
For a detailed description of each signal, refer to the I/O Connector Signal  
Descriptions section of Chapter 3, Connector Information.  
NI 6238/6239 User Manual  
A-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Appendix A  
Device-Specific Information  
1
AI 0+/CAL+  
20  
21  
22  
23  
24  
25  
26  
27  
28  
AI 0–  
AI 1+  
AI 2+  
AI 3–  
AI GND  
AI 4–  
AI 5+  
AI 6+  
AI 7+  
2
3
4
5
6
7
8
9
AI 1–  
AI GND  
AI 2–  
AI 3+  
AI 4+  
AI 5–  
CAL–  
AI 6–  
10 AI 7–  
AO POWER SUPPLY 29  
11 NC  
AO 0  
30  
31  
32  
33  
34  
35  
36  
37  
12 AO 1  
AO GND  
13 PFI 0/P0.0 (Input)  
PFI 1/P0.1 (Input)  
PFI 2/P0.2 (Input)  
PFI 4/P0.4 (Input)  
P1.GND  
P0.GND  
14  
15  
16  
17  
18  
19  
PFI 3/P0.3 (Input)  
PFI 5/P0.5 (Input)  
PFI 6/P1.0 (Output)  
PFI 8/P1.2 (Output)  
P1.VCC  
PFI 7/P1.1 (Output)  
PFI 9/P1.3 (Output)  
NC = No Connect  
Figure A-2. NI 6239 Pinout  
Table A-2. NI 6239 Device Default NI-DAQmx Counter/Timer Pins  
Counter/Timer Signal  
CTR 0 SRC  
Default Pin Number (Name)  
13 (PFI 0)  
Port  
P0.0  
P0.1  
P0.2  
P1.0  
P0.0  
P0.1  
P0.2  
P0.3  
P0.4  
P0.5  
CTR 0 GATE  
CTR 0 AUX  
CTR 0 OUT  
CTR 0 A  
32 (PFI 1)  
33 (PFI 2)  
17 (PFI 6)  
13 (PFI 0)  
CTR 0 Z  
32 (PFI 1)  
CTR 0 B  
33 (PFI 2)  
CTR 1 SRC  
CTR 1 GATE  
CTR 1 AUX  
15 (PFI 3)  
34 (PFI 4)  
16 (PFI 5)  
© National Instruments Corporation  
A-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Appendix A  
Device-Specific Information  
Table A-2. NI 6239 Device Default NI-DAQmx Counter/Timer Pins (Continued)  
Counter/Timer Signal  
CTR 1 OUT  
Default Pin Number (Name)  
36 (PFI 7)  
Port  
P1.1  
P0.3  
P0.4  
P0.5  
CTR 1 A  
CTR 1 Z  
CTR 1 B  
15 (PFI 3)  
34 (PFI 4)  
16 (PFI 5)  
Note For more information about default NI-DAQmx counter inputs, refer to Connecting  
Counter Signals in the NI-DAQmx Help or the LabVIEW 8.x Help.  
NI 6239 Specifications  
Refer to the NI 6239 Specifications, available on the NI-DAQ Device  
Document Browser or ni.com/manuals, for more detailed information  
on the NI 6239 device.  
NI 6239 Accessory and Cabling Options  
This section describes some cable and accessory options for the NI 6239  
device. Refer to ni.comfor other accessory options including new devices.  
Screw Terminal  
National Instruments offers several styles of screw terminal connector  
blocks. Use an SH37F-37M cable to connect an NI 6239 device to a  
connector block, such as the following:  
CB-37F-HVD—37-pin DIN rail screw terminal block, UL  
Recognized derated to 30 Vrms, 42.4 Vpk, or 60 VDC  
CB-37FH—Horizontal DIN-mountable terminal block with 37 screw  
terminals  
CB-37FVVertical DIN-mountable terminal block with 37 screw  
terminals  
CB-37F-LP—Low profile terminal block with 37 screw terminals  
TB-2621—37-pin PXI screw terminal block, UL Recognized derated  
to 30 Vrms, 42.4 Vpk, or 60 VDC  
Use RTSI bus cables to connect timing and synchronization signals among  
PCI devices, such as M Series, E Series, CAN, and other measurement,  
NI 6238/6239 User Manual  
A-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Appendix A  
Device-Specific Information  
vision, and motion devices. Since PXI devices use PXI backplane signals  
for timing and synchronization, no cables are required.  
Cables  
In most applications, you can use the following cables:  
SH37F-37M-x—37-pin female-to-male shielded I/O cable, UL Listed  
derated to 30 Vrms, 42.4 Vpk, or 60 VDC  
R37F-37M-1—37-pin female-to-male ribbon I/O cable  
SH37F-P-4—37-pin female-to-pigtails shielded I/O cable  
Custom Cabling and Connectivity  
Refer to the Custom Cabling section of Chapter 2, DAQ System Overview,  
for more information about custom cabling solutions.  
© National Instruments Corporation  
A-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
B
Troubleshooting  
This section contains some common questions about M Series devices. If  
your questions are not answered here, refer to the National Instruments  
KnowledgeBase at ni.com/kb. It contains thousands of documents that  
answer frequently asked questions about NI products.  
Analog Input  
I am seeing crosstalk when sampling multiple channels. What does this  
mean?  
You may be experiencing a phenomenon called charge injection, which  
occurs when you sample a series of high-output impedance sources with a  
multiplexer. Multiplexers contain switches, usually made of switched  
capacitors. When a channel, for example AI 0, is selected in a multiplexer,  
those capacitors accumulate charge. When the next channel, for example  
AI 1, is selected, the accumulated current (or charge) leaks backward  
through channel 1. If the output impedance of the source connected to AI 1  
is high enough, the resulting reading can somewhat affect the voltage in  
AI 0. To circumvent this problem, use a voltage follower that has  
operational amplifiers (op-amps) with unity gain for each high-impedance  
source before connecting to an M Series device. Otherwise, you must  
Another common cause of channel crosstalk is due to sampling among  
multiple channels at various gains. In this situation, the settling times can  
increase. For more information on charge injection and sampling channels  
at different gains, refer to the Multichannel Scanning Considerations  
section of Chapter 4, Analog Input.  
I am using my device in differential analog input ground-reference  
mode and I have connected a differential input signal, but my readings  
are random and drift rapidly. What is wrong?  
Check to make sure that the AI GND terminal is tied to a certain voltage  
level and verify that your input current signals are at voltage levels within  
the common-mode input range for this device. Refer to the NI 6238/6239  
Specifications for more information about common-mode input range.  
© National Instruments Corporation  
B-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Appendix B  
Troubleshooting  
In an isolated device, leaving the AI GND terminal unconnected will cause  
the signal to drift and eventually rail.  
How can I use the AI Sample Clock and AI Convert Clock signals on  
an M Series device to sample the AI channel(s)?  
M Series devices use ai/SampleClock and ai/ConvertClock to perform  
interval sampling. As Figure B-1 shows, ai/SampleClock controls the  
sample period, which is determined by the following equation:  
1/sample period = sample rate  
Channel 0  
Channel 1  
Convert Period  
Sample Period  
Figure B-1. ai/SampleClock and ai/ConvertClock  
ai/ConvertClock controls the convert period, which is determined by the  
following equation:  
1/convert period = convert rate  
This method allows multiple channels to be sampled relatively quickly in  
relationship to the overall sample rate, providing a nearly simultaneous  
effect with a fixed delay between channels.  
Analog Output  
I am seeing glitches on the output signal. How can I minimize it?  
When you use a DAC to generate a waveform, you may observe glitches on  
the output signal. These glitches are normal; when a DAC switches from  
one voltage to another, it produces glitches due to released charges. The  
largest glitches occur when the most significant bit of the DAC code  
changes. You can build a lowpass deglitching filter to remove some of these  
glitches, depending on the frequency and nature of the output signal. Visit  
ni.com/supportfor more information on minimizing glitches.  
NI 6238/6239 User Manual  
B-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
         
Appendix B  
Troubleshooting  
Counters  
When multiple sample clocks on my buffered counter measurement  
occur before consecutive edges on my source, I see weird behavior.  
Why?  
Duplicate count prevention ensures that the counter returns correct data for  
counter measurement in some applications where a slow or non-periodic  
external source is used.  
Refer to the Duplicate Count Prevention section of Chapter 7, Counters,  
for more information.  
How do I connect counter signals to my M Series device?  
The Default Counter Terminals section of Chapter 7, Counters, has  
information on counter signal connections.  
© National Instruments Corporation  
B-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
       
C
Technical Support and  
Professional Services  
Visit the following sections of the National Instruments Web site at  
ni.comfor technical support and professional services:  
Support—Online technical support resources at ni.com/support  
include the following:  
Self-Help Resources—For answers and solutions, visit the  
award-winning National Instruments Web site for software drivers  
and updates, a searchable KnowledgeBase, product manuals,  
step-by-step troubleshooting wizards, thousands of example  
programs, tutorials, application notes, instrument drivers, and  
so on.  
Free Technical Support—All registered users receive free Basic  
Service, which includes access to hundreds of Application  
Engineers worldwide in the NI Developer Exchange at  
ni.com/exchange. National Instruments Application Engineers  
make sure every question receives an answer.  
For information about other technical support options in your  
area, visit ni.com/servicesor contact your local office at  
ni.com/contact.  
Training and Certification—Visit ni.com/trainingfor  
self-paced training, eLearning virtual classrooms, interactive CDs,  
and Certification program information. You also can register for  
instructor-led, hands-on courses at locations around the world.  
System Integration—If you have time constraints, limited in-house  
technical resources, or other project challenges, National Instruments  
Alliance Partner members can help. To learn more, call your local  
NI office or visit ni.com/alliance.  
Declaration of Conformity (DoC)—A DoC is our claim of  
compliance with the Council of the European Communities using  
the manufacturer’s declaration of conformity. This system affords  
the user protection for electronic compatibility (EMC) and product  
safety. You can obtain the DoC for your product by visiting  
ni.com/certification.  
© National Instruments Corporation  
C-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
                     
Appendix C  
Technical Support and Professional Services  
Calibration Certificate—If your product supports calibration,  
you can obtain the calibration certificate for your product at  
ni.com/calibration.  
If you searched ni.comand could not find the answers you need, contact  
your local office or NI corporate headquarters. Phone numbers for our  
worldwide offices are listed at the front of this manual. You also can visit  
the Worldwide Offices section of ni.com/niglobalto access the branch  
office Web sites, which provide up-to-date contact information, support  
phone numbers, email addresses, and current events.  
NI 6238/6239 User Manual  
C-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
Numbers/Symbols  
%
Percent.  
+
Positive of, or plus.  
Negative of, or minus.  
Plus or minus.  
Less than.  
<
>
/
Greater than.  
Less than or equal to.  
Greater than or equal to.  
Per.  
º
Degree.  
Ω
Ohm.  
A
A
Amperes—the unit of electric current.  
Analog-to-Digital. Most often used as A/D converter.  
Alternating current.  
A/D  
AC  
accuracy  
A measure of the capability of an instrument or sensor to faithfully indicate  
the value of the measured signal. This term is not related to resolution;  
however, the accuracy level can never be better than the resolution of the  
instrument.  
ADE  
Application development environment.  
© National Instruments Corporation  
G-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
AI  
1. Analog input.  
2. Analog input channel signal.  
AI GND  
Analog input ground signal.  
AI SENSE  
analog  
Analog input sense signal.  
A signal whose amplitude can have a continuous range of values.  
analog input signal  
An input signal that varies smoothly over a continuous range of values,  
rather than in discrete steps.  
analog output signal  
analog signal  
An output signal that varies smoothly over a continuous range of values,  
rather than in discrete steps.  
A signal representing a variable that can be observed and represented  
continuously.  
analog trigger  
A trigger that occurs at a user-selected point on an incoming analog signal.  
Triggering can be set to occur at a specific level on either an increasing or  
a decreasing signal (positive or negative slope). Analog triggering can be  
implemented either in software or in hardware. When implemented in  
software (LabVIEW), all data is collected, transferred into system memory,  
and analyzed for the trigger condition. When analog triggering is  
implemented in hardware, no data is transferred to system memory until the  
trigger condition has occurred.  
AO  
Analog output.  
AO 0  
Analog channel 0 output signal.  
Analog channel 1 output signal.  
Analog channel 2 output signal.  
Analog channel 3 output signal.  
Analog output ground signal.  
AO 1  
AO 2  
AO 3  
AO GND  
application  
arm  
A software program that creates an end-user function.  
The process of getting an instrument ready to perform a function. For  
example, the trigger circuitry of a digitizer is armed, meaning that it is  
ready to start acquiring data when an appropriate trigger condition is met.  
NI 6238/6239 User Manual  
G-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
ASIC  
Application-specific integrated circuit—A proprietary semiconductor  
component designed and manufactured to perform a set of specific  
functions for a specific customer.  
asynchronous  
1. Hardware—A property of an event that occurs at an arbitrary time,  
without synchronization to a reference clock.  
2. Software—A property of a function that begins an operation and  
returns prior to the completion or termination of the operation.  
B
b
Bit—One binary digit, either 0 or 1.  
B
Byte—Eight related bits of data, an eight-bit binary number. Also used to  
denote the amount of memory required to store one byte of data.  
block diagram  
BNC  
A pictorial description or representation of a program or algorithm.  
Bayonet-Neill-Concelman—A type of coaxial connector used in situations  
requiring shielded cable for signal connections and/or controlled  
impedance applications.  
buffer  
1. Temporary storage for acquired or generated data.  
2. A memory device that stores intermediate data between two devices.  
bus, buses  
The group of electrical conductors that interconnect individual circuitry in  
a computer. Typically, a bus is the expansion vehicle to which I/O or other  
devices are connected. Examples of PC buses are the PCI, AT(ISA), and  
EISA bus.  
C
C
Celsius.  
calibration  
The process of determining the accuracy of an instrument. In a formal  
sense, calibration establishes the relationship of an instrument’s  
measurement to the value provided by a standard. When that relationship is  
known, the instrument may then be adjusted (calibrated) for best accuracy.  
calibrator  
A precise, traceable signal source used to calibrate instruments.  
© National Instruments Corporation  
G-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
cascading  
Process of extending the counting range of a counter chip by connecting to  
the next higher counter.  
CE  
European emissions control standard.  
channel  
Pin or wire lead to which you apply or from which you read the analog or  
digital signal. For digital signals, you group channels to form ports. Ports  
usually consist of either four or eight digital channels.  
clock  
Hardware component that controls timing for reading from or writing to  
groups.  
CMOS  
CMRR  
Complementary metal-oxide semiconductor.  
Common-mode rejection ratio—A measure of the ability of a differential  
amplifier to reject interference from a common-mode signal, usually  
expressed in decibels (dB).  
common-mode rejection The ability of an electronic system to cancel any electronic noise pick-up  
that is common to both the positive and negative polarities of the input leads  
to the instrument front end. Common mode rejection is only a relevant  
specification for systems having a balanced or differential input.  
common-mode signal  
1. Any voltage present at the instrumentation amplifier inputs with  
respect to amplifier ground.  
2. The signal, relative to the instrument chassis or computer’s ground, of  
the signals from a differential input. This is often a noise signal, such  
as 50 or 60 Hz hum.  
connector  
1. A device that provides electrical connection.  
2. A fixture (either male or female) attached to a cable or chassis for  
quickly making and breaking one or more circuits. A symbol that  
connects points on a flowchart.  
convert rate  
count  
Reciprocal of the interchannel delay.  
The number of events, such as zero crossings, pulses, or cycles.  
NI 6238/6239 User Manual  
G-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
counter  
1. Software. A memory location used to store a count of certain  
occurrences.  
2. Hardware. A circuit that counts events. When it refers to an instrument,  
it refers to a frequency counter.  
counter/timer  
A circuit that counts external pulses or clock pulses (timing).  
D
D GND  
Digital ground signal.  
A serial connector.  
D-SUB connector  
DAC  
Digital-to-Analog Converter—An electronic device, often an integrated  
circuit, that converts a digital number into a corresponding analog voltage  
or current.  
In the instrumentation world, DACs can be used to generate arbitrary  
waveform shapes, defined by the software algorithm that computes the  
digital data pattern, which is fed to the DAC.  
DAQ  
1. Data acquisition—The process of collecting and measuring electrical  
signals from sensors, transducers, and test probes or fixtures and  
inputting them to a computer for processing.  
2. Data acquisition—The process of collecting and measuring the same  
kinds of electrical signals with A/D and/or DIO devices plugged into a  
computer, and possibly generating control signals with D/A and/or  
DIO devices in the same computer.  
DAQ device  
A device that acquires or generates data and can contain multiple channels  
and conversion devices. DAQ devices include plug-in devices, PCMCIA  
cards, and DAQPad devices, which connect to a computer USB or 1394  
®
(FireWire ) port. SCXI modules are considered DAQ devices.  
DAQ-STC2  
Data acquisition system timing controller chip.  
data acquisition  
The general concept of acquiring data, as in begin data acquisition or data  
acquisition and control. See also DAQ.  
© National Instruments Corporation  
G-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
data transfer  
A technique for moving digital data from one system to another.  
Options for data transfer are DMA, interrupt, and programmed I/O. For  
programmed I/O transfers, the CPU in the PC reads data from the DAQ  
device whenever the CPU receives a software signal to acquire a single data  
point. Interrupt-based data transfers occur when the DAQ device sends an  
interrupt to the CPU, telling the CPU to read the acquired data from the  
DAQ device. DMA transfers use a DMA controller, instead of the CPU, to  
move acquired data from the device into computer memory. Even though  
high-speed data transfers can occur with interrupt and programmed I/O  
transfers, they require the use of the CPU to transfer data. DMA transfers  
are able to acquire data at high speeds and keep the CPU free for  
performing other tasks at the same time.  
dB  
Decibel—The unit for expressing a logarithmic measure of the ratio of two  
signal levels: dB = 20log10 V1/V2, for signals in volts.  
DC  
Direct current—although the term speaks of current, many different types  
of DC measurements are made, including DC Voltage, DC current, and DC  
power.  
device  
A plug-in data acquisition product, card, or pad that can contain multiple  
channels and conversion devices. Plug-in products, PCMCIA cards, and  
devices such as the DAQPad-1200, which connects to your computer  
parallel port, are all examples of DAQ devices. SCXI modules are distinct  
from devices, with the exception of the SCXI-1200, which is a hybrid.  
DIFF  
Differential mode—An analog input mode consisting of two terminals,  
both of which are isolated from computer ground, whose difference is  
measured.  
differential input  
An input circuit that actively responds to the difference between two  
terminals, rather than the difference between one terminal and ground.  
Often associated with balanced input circuitry, but also may be used with  
an unbalanced source.  
digital I/O  
The capability of an instrument to generate and acquire digital signals.  
Static digital I/O refers to signals where the values are set and held, or  
rarely change. Dynamic digital I/O refers to digital systems where the  
signals are continuously changing, often at multi-MHz clock rates.  
digital isolator  
Provides voltage isolation between its input and output.  
NI 6238/6239 User Manual  
G-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
digital signal  
A representation of information by a set of discrete values according to a  
prescribed law. These values are represented by numbers.  
digital trigger  
DIO  
A TTL level signal having two discrete levels—a high and a low level.  
Digital input/output.  
DMA  
Direct Memory Access—A method by which data can be transferred to/  
from computer memory from/to a device or memory on the bus while the  
processor does something else. DMA is the fastest method of transferring  
data to/from computer memory.  
DMA controller chip  
driver  
Performs the transfers between memory and I/O devices independently of  
the CPU.  
Software unique to the device or type of device, and includes the set of  
commands the device accepts.  
E
edge detection  
A technique that locates an edge of an analog signal, such as the edge of a  
square wave.  
EEPROM  
encoder  
Electrically Erasable Programmable Read-Only Memory—ROM that can  
be erased with an electrical signal and reprogrammed. Some SCXI modules  
contain an EEPROM to store measurement-correction coefficients.  
A device that converts linear or rotary displacement into digital or pulse  
signals. The most popular type of encoder is the optical encoder, which uses  
a rotating disk with alternating opaque areas, a light source, and a  
photodetector.  
external trigger  
EXTREF  
A voltage pulse from an external source that causes a DAQ operation to  
begin.  
External reference signal.  
© National Instruments Corporation  
G-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
F
FIFO  
First-In-First-Out memory buffer—A data buffering technique that  
functions like a shift register where the oldest values (first in) come out  
first. Many DAQ products and instruments use FIFOs to buffer digital data  
from an A/D converter, or to buffer the data before or after bus  
transmission.  
The first data stored is the first data sent to the acceptor. FIFOs are often  
used on DAQ devices to temporarily store incoming or outgoing data until  
that data can be retrieved or output. For example, an analog input FIFO  
stores the results of A/D conversions until the data can be retrieved into  
system memory, a process that requires the servicing of interrupts and often  
the programming of the DMA controller. This process can take several  
milliseconds in some cases. During this time, data accumulates in the FIFO  
for future retrieval. With a larger FIFO, longer latencies can be tolerated. In  
the case of analog output, a FIFO permits faster update rates, because the  
waveform data can be stored on the FIFO ahead of time. This again reduces  
the effect of latencies associated with getting the data from system memory  
to the DAQ device.  
filter  
A physical device or digital algorithm that selectively removes noise from  
a signal, or emphasizes certain frequency ranges and de-emphasizes others.  
Electronic filters include lowpass, band-pass, and highpass types. Digital  
filters can operate on numeric data to perform equivalent operations on  
digitized analog data or to enhance video images.  
filtering  
floating  
A type of signal conditioning that allows you to filter unwanted frequency  
components from the signal you are trying to measure.  
The condition where a common mode voltage exists, or may exist, between  
earth ground and the instrument or circuit of interest. Neither the high, nor  
the low side of a circuit is at earth potential.  
floating signal sources  
Signal sources with voltage signals that are not connected to an absolute  
reference of system ground. Also called non-referenced signal sources.  
Some common examples of floating signal sources are batteries,  
transformers, and thermocouples.  
FREQ OUT  
frequency  
Frequency Output signal.  
The number of alternating signals that occur per unit time.  
NI 6238/6239 User Manual  
G-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
ft  
Feet.  
function  
1. A built-in execution element, comparable to an operator, function, or  
statement in a conventional language.  
2. A set of software instructions executed by a single line of code that may  
have input and/or output parameters and returns a value when executed.  
G
glitch  
GND  
ground  
An unwanted signal excursion of short duration that is usually unavoidable.  
See ground.  
1. A pin.  
2. An electrically neutral wire that has the same potential as the  
surrounding earth. Normally, a noncurrent-carrying circuit intended for  
safety.  
3. A common reference point for an electrical system.  
H
hardware  
The physical components of a computer system, such as the circuit boards,  
plug-in devices, chassis, enclosures, peripherals, and cables.  
hardware triggering  
Hz  
A form of triggering where you set the start time of an acquisition and  
gather data at a known position in time relative to a trigger signal.  
1. Hertz—The SI unit for measurement of frequency. One hertz (Hz)  
equals one cycle per second.  
2. The number of scans read or updates written per second.  
I
I/O  
Input/Output—The transfer of data to/from a computer system involving  
communications channels, operator interface devices, and/or data  
acquisition and control interfaces.  
© National Instruments Corporation  
G-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
impedance  
1. The electrical characteristic of a circuit expressed in ohms and/or  
capacitance/inductance.  
2. Resistance.  
Inch or inches.  
in.  
instrument driver  
A set of high-level software functions that controls a specific GPIB, VXI,  
or RS232 programmable instrument or a specific plug-in DAQ device.  
Instrument drivers are available in several forms, ranging from a function  
callable language to a virtual instrument (VI) in LabVIEW.  
instrumentation  
amplifier  
A circuit whose output voltage with respect to ground is proportional to the  
difference between the voltages at its two inputs. An instrumentation  
amplifier normally has high-impedance differential inputs and high  
common-mode rejection.  
interchannel delay  
Amount of time that passes between sampling consecutive channels in an  
AI scan list. The interchannel delay must be short enough to allow sampling  
of all the channels in the channel list, within the sample interval. The  
greater the interchannel delay, the more time the PGIA is allowed to settle  
before the next channel is sampled. The interchannel delay is regulated by  
ai/ConvertClock.  
interface  
Connection between one or more of the following: hardware, software, and  
the user. For example, hardware interfaces connect two other pieces of  
hardware.  
interrupt, interrupt  
request line  
1. A means for a device to notify another device that an event occurred.  
2. A computer signal indicating that the CPU should suspend its current  
task to service a designated activity.  
I
I
Current, output high.  
OH  
Current, output low.  
OL  
IRQ  
See interrupt, interrupt request line.  
An electrical break between any two signals or planes up to a given voltage.  
isolation  
isolation barrier  
An electrical break between two electrical planes providing a given or set  
amount of electrical isolation. Current does not flow or transfer between the  
two sides of the isolation barrier.  
NI 6238/6239 User Manual  
G-10  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
   
Glossary  
K
3
kHz  
Kilohertz—A unit of frequency; 1 kHz = 10 = 1,000 Hz.  
kS  
1,000 samples.  
L
LabVIEW  
A graphical programming language.  
LED  
Light-Emitting Diode—A semiconductor light source.  
lowpass filter  
A filter that passes signals below a cutoff frequency while blocking signals  
above that frequency.  
LSB  
Least Significant Bit.  
Meter.  
M
m
M Series  
An architecture for instrumentation-class, multichannel data acquisition  
devices based on the earlier E Series architecture with added new features.  
measurement  
The quantitative determination of a physical characteristic. In practice,  
measurement is the conversion of a physical quantity or observation to a  
domain where a human being or computer can determine the value.  
measurement device  
DAQ devices, such as the M Series multifunction I/O (MIO) devices, SCXI  
signal conditioning modules, and switch modules.  
6
MHz  
Megahertz—A unit of frequency; 1 MHz = 10 Hz = 1,000,000 Hz.  
–6  
micro (μ)  
MIO  
The numerical prefix designating 10 .  
Multifunction I/O—DAQ module. Designates a family of data acquisition  
products that have multiple analog input channels, digital I/O channels,  
timing, and optionally, analog output channels. An MIO product can be  
considered a miniature mixed signal tester, due to its broad range of signal  
types and flexibility. Also known as multifunction DAQ.  
© National Instruments Corporation  
G-11  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
MITE  
MXI Interface To Everything—A custom ASIC designed by National  
Instruments that implements the PCI bus interface. The MITE supports bus  
mastering for high-speed data transfers over the PCI bus.  
module  
A board assembly and its associated mechanical parts, front panel, optional  
shields, and so on. A module contains everything required to occupy one or  
more slots in a mainframe. SCXI and PXI devices are modules.  
monotonicity  
multichannel  
A characteristic of a DAC in which the analog output always increases as  
the values of the digital code input to it increase.  
Pertaining to a radio-communication system that operates on more than one  
channel at the same time. The individual channels might contain identical  
information, or they might contain different signals.  
multifunction DAQ  
multiplex  
See MIO.  
To assign more than one signal to a channel. See also mux.  
mux  
Multiplexer—A set of semiconductor or electromechanical switches  
arranged to select one of many inputs to a single output. The majority of  
DAQ cards have a multiplexer on the input, which permits the selection of  
one of many channels at a time.  
A switching device with multiple inputs that sequentially connects each of  
its inputs to its output, typically at high speeds, in order to measure several  
signals with a single analog input channel.  
N
NI  
National Instruments.  
NI-DAQ  
The driver software needed to use National Instruments DAQ devices and  
SCXI components. Some devices use Traditional NI-DAQ (Legacy); others  
use NI-DAQmx.  
NI-DAQmx  
The latest NI-DAQ driver with new VIs, functions, and development tools  
for controlling measurement devices. The advantages of NI-DAQmx over  
earlier versions of NI-DAQ include the DAQ Assistant for configuring  
channels and measurement tasks for your device for use in LabVIEW,  
LabWindows/CVI, and Measurement Studio; increased performance such  
as faster single-point analog I/O; and a simpler API for creating DAQ  
applications using fewer functions and VIs than earlier versions of NI-  
DAQ.  
NI 6238/6239 User Manual  
G-12  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
NI-PGIA  
See instrumentation amplifier.  
non-referenced signal  
sources  
Signal sources with voltage signals that are not connected to an absolute  
reference or system ground. Also called floating signal sources. Some  
common example of non-referenced signal sources are batteries,  
transformers, or thermocouples.  
NRSE  
Non-Referenced Single-Ended mode—All measurements are made with  
respect to a common (NRSE) measurement system reference, but the  
voltage at this reference can vary with respect to the measurement system  
ground.  
O
offset  
The unwanted DC voltage due to amplifier offset voltages added to a signal.  
P
PCI  
Peripheral Component Interconnect—A high-performance expansion bus  
architecture originally developed by Intel to replace ISA and EISA. It offers  
a theoretical maximum transfer rate of 132 MB/s.  
period  
The period of a signal, most often measured from one zero crossing to the  
next zero crossing of the same slope. The period of a signal is the reciprocal  
of its frequency (in Hz). Period is designated by the symbol T.  
periods  
The number of periods of a signal.  
Programmable Function Interface.  
Programmable Gain Instrumentation Amplifier.  
See channel.  
PFI  
PGIA  
physical channel  
Plug and Play devices  
Devices that do not require DIP switches or jumpers to configure resources  
on the devices. Also called switchless devices port.  
1. A communications connection on a computer or a remote controller;  
2. A digital port, consisting of four or eight lines of digital input and/or  
output.  
posttriggering  
The technique used on a DAQ device to acquire a programmed number of  
samples after trigger conditions are met.  
© National Instruments Corporation  
G-13  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
power source  
An instrument that provides one or more sources of AC or DC power. Also  
known as power supply.  
ppm  
Parts per million.  
pretriggering  
The technique used on a DAQ device to keep a continuous buffer filled with  
data, so that when the trigger conditions are met, the sample includes the  
data leading up to the trigger condition.  
pulse  
A signal whose amplitude deviates from zero for a short period of time.  
The time from the rising to the falling slope of a pulse (at 50% amplitude).  
pulse width  
PXI  
A rugged, open system for modular instrumentation based on CompactPCI,  
with special mechanical, electrical, and software features. The PXIbus  
standard was originally developed by National Instruments in 1997, and is  
now managed by the PXIbus Systems Alliance.  
PXI Express  
PXI_STAR  
PCI Express eXtensions for Instrumentation—The PXI implementation of  
PCI Express, a scalable full-simplex serial bus standard that operates at 2.5  
Gbps and offers both asynchronous and isochronous data transfers.  
A special set of trigger lines in the PXI backplane for high-accuracy device  
synchronization with minimal latencies on each PXI slot. Only devices in  
the PXI Star controller Slot 2 can set signal on this line. For additional  
information concerning PXI star signal specifications and capabilities,  
refer to the PXI Specification located at www.pxisa.org/specs.  
Q
quadrature encoder  
An encoding technique for a rotating device where two tracks of  
information are placed on the device, with the signals on the tracks offset  
by 90° from each other. This makes it possible to detect the direction of the  
motion.  
R
range  
The maximum and minimum parameters between which a sensor,  
instrument, or device operates with a specified set of characteristics. This  
may be a voltage range or a frequency range.  
NI 6238/6239 User Manual  
G-14  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
real time  
1. Displays as it comes in; no delays.  
2. A property of an event or system in which data is processed and acted  
upon as it is acquired instead of being accumulated and processed at a  
later time.  
3. Pertaining to the performance of a computation during the actual time  
that the related physical process transpires so results of the  
computation can be used in guiding the physical process.  
RSE  
Referenced Single-Ended configuration—All measurements are made with  
respect to a common reference measurement system or a ground. Also  
called a grounded measurement system.  
RTSI  
Real-Time System Integration.  
RTSI bus  
Real-Time System Integration bus—The National Instruments timing bus  
that connects DAQ devices directly, by means of connectors on top of the  
devices, for precise synchronization of functions.  
S
s
Seconds.  
Samples.  
S
sample counter  
The clock that counts the output of the channel clock, in other words, the  
number of samples taken. On devices with simultaneous sampling, this  
counter counts the output of the scan clock and hence the number of scans.  
scan  
One or more analog or digital input samples. Typically, the number of input  
samples in a scan is equal to the number of channels in the input group. For  
example, one pulse from the scan clock produces one scan which acquires  
one new sample from every analog input channel in the group.  
scan interval  
Controls how often a scan is initialized; is regulated by the AI Sample  
Clock signal.  
scan rate  
SCC  
Reciprocal of the scan interval.  
Signal Conditioning Carriers—A compact, modular form factor for signal  
conditioning modules.  
© National Instruments Corporation  
G-15  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
SCXI  
Signal Conditioning eXtensions for Instrumentation—The National  
Instruments product line for conditioning low-level signals within an  
external chassis near sensors so that only high-level signals are sent to DAQ  
devices in the noisy PC environment.  
sensor  
A device that responds to a physical stimulus (heat, light, sound, pressure,  
motion, flow, and so on), and produces a corresponding electrical signal.  
Primary characteristics of sensors are sensitivity, frequency range, and  
linearity.  
signal conditioning  
1. Electronic equipment that makes transducer or other signals suitable in  
level and range to be transmitted over a distance, or to interface with  
voltage input instruments.  
2. The manipulation of signals to prepare them for digitizing.  
signal source  
signals  
A generic term for any instrument in the family of signal generators.  
Signals are waveforms containing information. Although physical signals  
can be in the form of mechanical, electromagnetic, or other forms, they are  
most often converted to electronic form for measurement.  
single trigger mode  
single-buffered  
When the arbitrary waveform generator goes through the staging list only  
once.  
Describes a device that acquires a specified number of samples from one or  
more channels and returns the data when the acquisition is complete.  
single-ended input  
single-ended output  
software applications  
A circuit that responds to the voltage on one input terminal and ground. See  
also differential input.  
A circuit whose output signal is present between one output terminal and  
ground.  
The programs that run on your computer and perform a specific user-  
oriented function, such as accounting, program development,  
measurement, or data acquisition. In contrast, operating system functions  
basically perform the generic ‘housekeeping’ of the machine, which is  
independent of any specific application. Operating system functions  
include the saving of data (file system), handling of multiple programs at  
the same time (multi-tasking), network interconnection, printing, and  
keyboard/user interface interaction.  
software triggering  
A method of triggering in which you simulate an analog trigger using  
software. Also called conditional retrieval.  
NI 6238/6239 User Manual  
G-16  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
source impedance  
synchronous  
A parameter of signal sources that reflects current-driving ability of voltage  
sources (lower is better) and the voltage-driving ability of current sources  
(higher is better).  
1. Hardware—A property of an event that is synchronized to a reference  
clock.  
2. Software—A property of a function that begins an operation and  
returns only when the operation is complete. A synchronous process is,  
therefore, locked and no other processes can run during this time.  
T
task  
In NI-DAQmx, a collection of one or more channels, timing, and triggering  
and other properties that apply to the task itself. Conceptually, a task  
represents a measurement or generation you want to perform.  
TC  
See terminal count.  
terminal  
terminal count  
An object or region on a node through which data passes.  
The highest value of a counter.  
Gate hold time.  
t
t
t
gh  
Gate setup time.  
gsu  
gw  
Gate pulse width.  
Timebase  
The reference signals for controlling the basic accuracy of time or  
frequency-based measurements. For instruments, timebase refers to the  
t
Output delay time.  
out  
transducer  
A device that responds to a physical stimulus (heat, light, sound, pressure,  
motion, flow, and so on), and produces a corresponding electrical signal.  
See also sensor.  
© National Instruments Corporation  
G-17  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Glossary  
trigger  
1. Any event that causes or starts some form of data capture.  
2. An external stimulus that initiates one or more instrument functions.  
Trigger stimuli include a front panel button, an external input voltage  
pulse, or a bus trigger command. The trigger may also be derived from  
attributes of the actual signal to be acquired, such as the level and slope  
of the signal.  
t
t
Source clock period.  
Source pulse width.  
sc  
sp  
TTL  
Transistor-Transistor Logic—A digital circuit composed of bipolar  
transistors wired in a certain manner. A typical medium-speed digital  
technology. Nominal TTL logic levels are 0 and 5 V.  
U
USB  
Universal Serial Bus—A 480 Mbit/s serial bus with up to 12-Mbps  
bandwidth for connecting computers to keyboards, printers, and other  
peripheral devices. USB 2.0 retains compatibility with the original USB  
specification.  
V
V
Volts.  
V
V
V
V
V
V
V
V
V
Common-mode voltage.  
Ground loop voltage.  
Volts, input high.  
Volts, input low.  
Volts in.  
cm  
g
IH  
IL  
in  
Measured voltage.  
Volts, output high.  
Volts, output low.  
Volts out.  
m
OH  
OL  
out  
NI 6238/6239 User Manual  
G-18  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Glossary  
V
Signal source voltage.  
s
virtual channel  
See channel.  
W
waveform  
1. The plot of the instantaneous amplitude of a signal as a function of  
time.  
2. Multiple voltage readings taken at a specific sampling rate.  
© National Instruments Corporation  
G-19  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
ai/PauseTrigger, 4-24  
ai/ReferenceTrigger, 4-22  
analog input  
Symbols  
Numerics  
10 MHz reference clock, 10-3  
100 kHz Timebase, 10-2  
20 MHz Timebase, 10-2  
80 MHz Timebase, 10-2  
circuitry, 4-1  
A
A/D converter, 4-2  
software, 4-25  
ground-reference settings, 4-5  
accessories, 2-4, A-3, A-6  
choosing for your device, 1-2  
acquisitions  
and AI Convert Clock, B-2  
AI Convert Clock signal, 4-18  
AI Convert Clock Timebase signal, 4-21  
AI data acquisition methods, 4-10  
AI FIFO, 4-2  
sampling channels with AI Sample Clock  
and AI Convert Clock, B-2  
timing signals, 4-12  
triggering, 4-11  
AI Hold Complete Event signal, 4-21  
AI Pause Trigger signal, 4-24  
AI Reference Trigger signal, 4-22  
AI Sample Clock signal, 4-15  
AI Sample Clock Timebase signal, 4-17  
AI Start Trigger signal, 4-21  
AI timing signals, 4-12  
ai/ConvertClock, 4-18  
ai/ConvertClockTimebase, 4-21  
ai/HoldCompleteEvent, 4-21  
data generation methods, 5-2  
getting started with applications in  
software, 5-10  
signals, 5-5  
timing signals, 5-5  
trigger signals, 5-4  
© National Instruments Corporation  
I-1  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
 
Index  
triggering, 5-4  
troubleshooting, B-2  
ANSI C documentation, xvii  
AO FIFO, 5-1  
cables, 2-4, A-3, A-6  
custom, 2-4  
AO Pause Trigger signal, 5-6  
AO Sample Clock signal, 5-8  
AO Sample Clock Timebase signal, 5-9  
AO Start Trigger signal, 5-5  
ao/PauseTrigger, 5-6  
ao/SampleClock, 5-8  
ao/SampleClockTimebase, 5-9  
ao/StartTrigger, 5-5  
and IRQ, 11-4  
AI Convert Clock, B-2  
charge injection, B-1  
applications  
counter input, 7-3  
counter output, 7-21  
edge counting, 7-3  
circular-buffered acquisition, 4-11  
clock  
10 MHz reference, 10-3  
external reference, 10-2  
generation, 10-1  
arm start trigger, 7-32  
PXI, and trigger signals, 10-7  
software, 4-5  
B
block diagram  
PFI input circuitry, 8-1  
PFI output circuitry, 8-2  
buffered  
connecting  
edge counting, 7-4  
analog current input signals, 4-3  
analog current output signals, 5-4  
counter signals, B-3  
digital I/O signals, 6-2, 8-6  
PFI input signals, 8-3  
non-cumulative, 7-5  
hardware-timed generations, 5-3  
semi-period measurement, 7-10  
two-signal edge-separation  
measurement, 7-20  
connector, A-1, A-4  
information, 3-1  
RTSI, 3-3, 10-4  
considerations  
bus  
for field wiring, 4-11  
for multichannel scanning, 4-8  
for PXI, 11-2  
interface, 11-1  
RTSI, 10-3  
continuous pulse train generation, 7-23  
controllers, DMA, 11-1  
controlling counting direction, 7-3  
NI 6238/6239 User Manual  
I-2  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
conventions used in the manual, xiii  
Counter n A signal, 7-29  
Counter n Aux signal, 7-28  
Counter n B signal, 7-29  
Counter n Gate signal, 7-28  
Counter n HW Arm signal, 7-29  
Counter n Internal Output signal, 7-30  
Counter n Source signal, 7-26  
Counter n TC signal, 7-30  
Counter n Up_Down signal, 7-29  
Counter n Z signal, 7-29  
counter output applications, 7-21  
counter signals  
trigger, 7-21  
timing signals, 7-26  
triggering, 7-32  
crosstalk when sampling multiple  
connecting analog output, 5-4  
Counter n A, 7-29  
Counter n Aux, 7-28  
Counter n B, 7-29  
DACs, 5-1  
hardware, 2-1  
system, 2-1  
DAQ-STC2, 2-2  
acquisition methods, 4-10  
generation methods, 5-2  
data transfer methods, 11-3  
changing, 11-4  
DMA, 11-3  
Counter n Gate, 7-28  
Counter n HW Arm, 7-29  
Counter n Internal Output, 7-30  
Counter n Source, 7-26  
Counter n TC, 7-30  
Counter n Up_Down, 7-29  
FREQ OUT, 7-30  
Frequency Output, 7-30  
counter terminals, default, 7-31  
counters  
cascading, 7-33  
duplicate count prevention, 7-35  
edge counting, 7-3  
IRQ, 11-4  
programmed I/O, 11-4  
Declaration of Conformity (NI resources), C-1  
default counter terminals, 7-31  
device  
filters, 7-33  
generation, 7-21  
prescaling, 7-34  
pulse train generation, 7-23  
retriggerable single pulse  
generation, 7-22  
simple pulse generation, 7-21  
single pulse generation, 7-21  
information, A-1  
multiple synchronization, 10-3  
specifications, 1-2  
diagnostic tools (NI resources), C-1  
differential, analog input  
(troubleshooting), B-1  
© National Instruments Corporation  
I-3  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
digital  
NI-DAQmx, 7-38  
input and output, 6-1  
encoders, quadrature, 7-16  
encoding  
isolation, 9-3  
isolators, 9-1  
X1, 7-16  
routing, 10-1  
X2, 7-17  
X4, 7-17  
source, triggering, 12-1  
examples (NI resources), C-1  
exporting timing output signals using PFI  
terminals, 8-3  
digital I/O  
circuitry, 6-1  
getting started with applications in  
software, 6-4  
external  
source mode, 7-40  
I/O protection, 6-1, 8-5  
programmable power-up states, 6-1, 8-6  
triggering, 12-1  
digital isolators, 4-2, 5-2  
DMA  
field wiring considerations, 4-11  
filters  
as a transfer method, 11-3  
changing data transfer methods, 11-4  
controllers, 11-1  
counter, 7-33  
PFI, 8-4  
PXI_STAR, 10-8  
RTSI, 10-6  
documentation  
conventions used in manual, xiii  
NI resources, C-1  
related documentation, xiv  
double-buffered acquisition, 4-11  
drivers (NI resources), C-1  
duplicate count prevention, 7-35  
FREQ OUT signal, 7-30  
frequency  
division, 7-25  
generation, 7-24  
generator, 7-24  
E
edge counting, 7-3  
buffered, 7-4  
analog output data, 5-2  
buffered hardware-timed, 5-3  
clock, 10-1  
continuous pulse train, 7-23  
frequency, 7-24  
non-cumulative buffered, 7-5  
sample clock, 7-4  
buffered two-signal, 7-20  
single two-signal, 7-19  
hardware-timed, 5-2  
NI 6238/6239 User Manual  
I-4  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
non-buffered hardware-timed, 5-3  
pulse for ETS, 7-25  
interrupt request, as a transfer method, 11-4  
IRQ  
pulse train, 7-23  
as a transfer method, 11-4  
retriggerable single pulse, 7-22  
simple pulse, 7-21  
single pulse, 7-21  
changing data transfer methods, 11-4  
isolated DAQ devices, 9-1  
benefits, 9-3  
single pulse with start trigger, 7-21  
software-timed, 5-2  
getting started, 1-1  
isolation barrier, 4-2, 5-2  
isolators, 9-1  
AI applications in software, 4-25  
AO applications in software, 5-10  
DIO applications in software, 6-4  
ground-reference  
K
KnowledgeBase, C-1  
H
LabWindows/CVI documentation, xvi  
hardware  
DAQ, 2-1  
installing, 1-1  
hardware-timed  
M
M Series  
information, A-1  
specifications, xvii  
Measurement Studio documentation, xvi  
buffered period, 7-8  
I
buffered pulse-width, 7-6  
buffered semi-period, 7-10  
buffered two-signal edge-separation, 7-20  
frequency, 7-10  
period, 7-7  
position, 7-16  
I/O connector, 3-1  
NI 6238 pinout, A-1  
NI 6239 pinout, A-4  
I/O protection, 6-1, 8-5  
input signals  
pulse-width, 7-6  
semi-period, 7-9  
single period, 7-8  
using PFI terminals as, 8-2  
using RTSI terminals as, 10-6  
installation  
single pulse-width, 7-6  
single semi-period, 7-9  
single two-signal edge-separation, 7-19  
two-signal edge-separation, 7-19  
hardware, 1-1  
NI-DAQ, 1-1  
other software, 1-1  
instrument drivers (NI resources), C-1  
interface, bus, 11-1  
© National Instruments Corporation  
I-5  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
measuring  
high frequency with two counters, 7-12  
other internal source mode, 7-39  
other software, 1-1  
averaged, 7-11  
methods, data transfer, 11-3  
minimizing output signal glitches  
(troubleshooting), B-2  
multiple device synchronization, 10-3  
P
pause trigger, 7-32  
N
services, C-1  
filters, 8-4  
NI 6238  
signals, 8-2  
accessory options, A-3  
cabling options, A-3  
information, A-1  
pinout, A-1  
specifications, A-3  
pin assignments. See pinouts  
pinouts, 1-1  
device, 1-1  
NI 6238, A-1  
NI 6239, A-4  
NI 6239  
accessory options, A-6  
cabling options, A-6  
information, A-1  
pinout, A-4  
specifications, A-6  
RTSI connector, 3-3, 10-4  
position measurement, 7-16  
prescaling, 7-34  
NI-DAQ documentation, xiv  
NI-DAQmx, enabling duplicate count  
prevention, 7-38  
acquisitions, 4-11  
generations, 5-3  
non-cumulative buffered edge counting, 7-5  
programmable function interface, 8-1  
programmable power-up states, 6-1, 8-6  
programmed I/O, 11-4  
programming devices in software, 2-5  
programming examples (NI resources), C-1  
pulse  
encoders, measurements using two, 7-18  
generation for ETS, 7-25  
train generation, 7-23  
continuous, 7-23  
NI 6238/6239 User Manual  
I-6  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
pulse-width measurement, 7-6  
buffered, 7-6  
sample clock edge counting, 7-4  
scanning speed, 4-9  
buffered, 7-10  
single, 7-6  
PXI  
and PXI Express, 11-2  
clock, 11-2  
clock and trigger signals, 10-7  
considerations, 11-2  
trigger signals, 11-2  
triggers, 10-8  
single, 7-9  
settings, analog input ground-reference, 4-5  
short high-quality cabling, 4-8  
signal descriptions, 3-1  
signal routing, RTSI bus, 10-3  
signals  
using with CompactPCI, 11-3  
PXI Express chassis compatibility, 11-2  
PXI_CLK10, 10-8  
PXI_STAR  
AI Convert Clock, 4-18  
AI Convert Clock Timebase, 4-21  
AI Hold Complete Event, 4-21  
AI Pause Trigger, 4-24  
filters, 10-8  
trigger, 10-8  
AI Reference Trigger, 4-22  
AI Sample Clock, 4-15  
AI Sample Clock Timebase, 4-17  
AI Start Trigger, 4-21  
Q
analog input, 4-12  
analog output, 5-5  
AO Pause Trigger, 5-6  
AO Sample Clock, 5-8  
AO Sample Clock Timebase, 5-9  
AO Start Trigger, 5-5  
R
range, analog input, 4-2  
real-time system integration bus, 10-3  
reciprocal frequency measurement, 7-13  
reference clock  
connecting analog current input, 4-3  
connecting analog current output, 5-4  
connecting counter, B-3  
connecting digital I/O, 6-2, 8-6  
connecting PFI input, 8-3  
Counter n A, 7-29  
Counter n Aux, 7-28  
Counter n B, 7-29  
Counter n Gate, 7-28  
Counter n HW Arm, 7-29  
Counter n Internal Output, 7-30  
Counter n Source, 7-26  
Counter n TC, 7-30  
Counter n Up_Down, 7-29  
10 MHz, 10-3  
external, 10-2  
related documentation, xiv  
retriggerable single pulse generation, 7-22  
routing  
clock, 10-1  
digital, 10-1  
RTSI, 10-3  
connector pinout, 3-3, 10-4  
filters, 10-6  
using as outputs, 10-5  
using terminals as timing input  
signals, 10-6  
© National Instruments Corporation  
I-7  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
Counter n Z, 7-29  
counters, 7-26  
synchronous counting mode, 7-35  
exporting timing output using PFI  
terminals, 8-3  
FREQ OUT, 7-30  
T
technical support, xviii, C-1  
Timebase  
Frequency Output, 7-30  
minimizing output glitches, B-2  
simple pulse generation, 7-21  
single  
terminals, 8-3  
training, xvii  
training and certification (NI resources), C-1  
transducers, 2-3  
period measurement, 7-8  
retriggerable, 7-22  
with start trigger, 7-21  
software  
triggering, 12-1  
analog input, 4-11  
counter, 7-32  
with a digital source, 12-1  
triggers, 12-1  
settings, 4-7  
NI resources, C-1  
AI Pause Trigger signal, 4-24  
AI Reference Trigger signal, 4-22  
AI Start Trigger signal, 4-21  
AO Pause Trigger signal, 5-6  
AO Start Trigger signal, 5-5  
arm start, 7-32  
programming devices, 2-5  
timed acquisitions, 4-10  
software-timed  
acquisitions, 4-10  
generations, 5-2  
specifications, A-3, A-6  
device, 1-2  
pause, 7-32  
PXI, 10-8  
start trigger, 7-32  
PXI_STAR, 10-8  
static  
Star Trigger, 10-8  
digital input, 6-1  
start, 7-32  
digital output, 6-1  
troubleshooting  
DIO, using PFI terminals as, 8-3  
support  
analog input, B-1  
analog output, B-2  
counters, B-3  
technical, C-1  
synchronization modes, 7-38  
external source, 7-40  
other internal source, 7-39  
NI resources, C-1  
two-signal edge-separation measurement  
buffered, 7-20  
single, 7-19  
NI 6238/6239 User Manual  
I-8  
ni.com  
Download from Www.Somanuals.com. All Manuals Search And Download.  
Index  
U
W
using PFI terminals  
as static digital I/Os, 8-3  
as timing input, 8-2  
wiring, field, 4-11  
to export timing output signals, 8-3  
using RTSI  
X
as outputs, 10-5  
X1 encoding, 7-16  
X2 encoding, 7-17  
X4 encoding, 7-17  
terminals as timing input signals, 10-6  
using short high-quality cabling, 4-8  
V
V-I Converter, 5-1  
© National Instruments Corporation  
I-9  
NI 6238/6239 User Manual  
Download from Www.Somanuals.com. All Manuals Search And Download.  

Milwaukee Sander Heavy Duty Sanders and Grinders User Manual
NCR Scanner 7837 User Manual
NEC Marine Instruments P521 User Manual
NETGEAR Network Router R7500 User Manual
NuTone Door LA500K User Manual
Olympus Film Camera IS 1 User Manual
Onkyo Stereo System TX SR574 User Manual
Panasonic All in One Printer KX FC175AL User Manual
ParaBody Home Gym 493 User Manual
Paradyne Network Card SAM2000GV 12 User Manual