National Instruments Network Router GPIB 120A User Manual

GPIB-120A  
User Manual  
October 1994 Edition  
Part Number 370893A-01  
© Copyright 1991, 1994 National Instruments Corporation.  
All Rights Reserved.  
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Limited Warranty  
The GPIB-120A is warranted against defects in materials and workmanship for a period of two 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.  
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 manual 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. CUSTOMER'S 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.  
Trademarks  
Product and company names listed are trademarks or trade names of their respective companies.  
WARNING REGARDING MEDICAL AND CLINICAL USE  
OF NATIONAL INSTRUMENTS PRODUCTS  
National Instruments products are not designed with components and testing intended to ensure a level of reliability  
suitable for use in treatment and diagnosis of humans. Applications of National Instruments products involving  
medical or clinical treatment can create a potential for accidental injury caused by product failure, or by errors on  
the part of the user or application designer. Any use or application of National Instruments products for or involving  
medical or clinical treatment must be performed by properly trained and qualified medical personnel, and all  
traditional medical safeguards, equipment, and procedures that are appropriate in the particular situation to prevent  
serious injury or death should always continue to be used when National Instruments products are being used.  
National Instruments products are NOT intended to be a substitute for any form of established process, procedure, or  
equipment used to monitor or safeguard human health and safety in medical or clinical treatment.  
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FCC/DOC Radio Frequency Interference Compliance  
This equipment generates and uses radio frequency energy and, if not installed and used in strict accordance with the  
instructions in this manual, may cause interference to radio and television reception. This equipment has been tested  
and found to comply with the following two regulatory agencies:  
Federal Communications Commission  
This device complies with Part 15 of the Federal Communications Commission (FCC) Rules for a Class A digital  
device. Operation is subject to the following two conditions:  
1. This device may not cause harmful interference in commercial environments.  
2. This device must accept any interference received, including interference that may cause undesired operation.  
Canadian Department of Communications  
This device complies with the limits for radio noise emissions from digital apparatus set out in the Radio  
Interference Regulations of the Canadian Department of Communications (DOC).  
Le présent appareil numérique n’émet pas de bruits radioélectriques dépassant les limites applicables aux appareils  
numériques de classe A prescrites dans le règlement sur le brouillage radioélectrique édicté par le ministère des  
communications du Canada.  
Instructions to Users  
These regulations are designed to provide reasonable protection against harmful interference from the equipment to  
radio reception in commercial areas. Operation of this equipment in a residential area is likely to cause harmful  
interference, in which case the user will be required to correct the interference at his own expense.  
There is no guarantee that interference will not occur in a particular installation. However, the chances of  
interference are much less if the equipment is installed and used according to this instruction manual.  
If the equipment does cause interference to radio or television reception, which can be determined by turning the  
equipment on and off, one or more of the following suggestions may reduce or eliminate the problem.  
Operate the equipment and the receiver on different branches of your AC electrical system.  
Move the equipment away from the receiver with which it is interfering.  
Reorient or relocate the receiver’s antenna.  
Be sure that the equipment is plugged into a grounded outlet and that the grounding has not been defeated with  
a cheater plug.  
Notice to user: Changes or modifications not expressly approved by National Instruments could void the user’s  
authority to operate the equipment under the FCC Rules.  
If necessary, consult National Instruments or an experienced radio/television technician for additional suggestions.  
The following booklet prepared by the FCC may also be helpful: How to Identify and Resolve Radio-TV  
Interference Problems. This booklet is available from the U.S. Government Printing Office, Washington, DC  
20402, Stock Number 004-000-00345-4.  
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Danger  
The GPIB-120A does not generate high voltages; however, you must use extreme caution  
if your system or application can cause high voltages on the shield or logic ground of the  
GPIB cable you attach to the electrically isolated connector (GPIB Port B) located on the  
rear panel of the GPIB-120A. Many GPIB cables use a metal shell to enclose the GPIB  
piggyback connectors. This metal shell is normally connected to the cable shield.  
Therefore, if the shield is at a high potential with respect to the chassis ground of the  
GPIB-120A, the high voltage is also present, in most cases, on the cable connector  
housing.  
The chassis, back panel, and front panel of the GPIB-120A are electrically connected to  
the earth ground pin of the AC power connector on the back panel. If the AC wiring in  
your building is installed correctly, you can safely operate the GPIB-120A. Because the  
EMI shield and jack screws of rear panel connector ‘GPIB A’ are electrically shorted to  
the rear panel, a GPIB cable attached to GPIB Port A has its shield and connector  
housing connected to earth ground, as well, and no danger should exist associated with  
GPIB Port A. There may be, however, a hazardous voltage between the cable connector  
housings of the GPIB cable attached to GPIB Port A and the GPIB cable attached to  
GPIB Port B.  
Do not touch the GPIB-120A case, power cord, or any GPIB cable connected to the  
GPIB-120A unless you are absolutely sure that there are no hazardous voltages present.  
In addition, never open the GPIB-120A case unless you have removed the power cord  
and all GPIB cables from the back panel.  
The GPIB-120A is not recommended for use when ground potential differences in excess  
of 30 V are present between the two rear panel GPIB connectors and associated cables,  
unless sufficient precautions are taken to ensure human safety.  
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Contents  
Introduction............................................................................................................................1-1  
Connection...............................................................................................................................2-1  
Theory of Operation ............................................................................................................3-1  
Operation of the GPIB........................................................................................................A-1  
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Contents  
Specifications..........................................................................................................................B-1  
Multiline Interface Messages ............................................................................................C-1  
Customer Communication.................................................................................................D-1  
Figures  
Tables  
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About This Manual  
This manual describes how to use the National Instruments GPIB-120A bus expander/isolator.  
Organization of This Manual  
This manual is organized as follows:  
Chapter 1, Introduction, contains a description of the GPIB-120A, lists what you need to get  
started and optional equipment you can order, and explains how to unpack the GPIB-120A.  
Chapter 2, Connection, contains information for connecting your GPIB-120A.  
Chapter 3, Theory of Operation, describes the operational theory of the GPIB-120A.  
Appendix A, Operation of the GPIB, contains a brief history of the GPIB and describes the  
operation of the GPIB.  
Appendix B, Specifications, lists the specifications of the GPIB-120A.  
Appendix C, Multiline Interface Messages, contains an interface message reference list,  
which describes the mnemonics and messages that correspond to the interface functions.  
Appendix D, Customer Communication, contains forms you can use to request help from  
National Instruments or to comment on our products or manuals.  
The Glossary contains an alphabetical list and a description of terms used in this manual,  
including abbreviations, acronyms, metric prefixes, mnemonics, and symbols.  
Conventions Used in This Manual  
The following conventions are used in this manual.  
italic  
Italic text denotes emphasis, a cross reference, or an introduction to a key  
concept.  
bold italic  
Bold italic text denotes a note, caution, warning, or danger statement.  
Abbreviations, acronyms, metric prefixes, mnemonics, symbols, and terms are listed in the  
Glossary.  
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About This Manual  
Related Documentation  
The following document contains information that you may find helpful as you read this manual.  
ANSI/IEEE Standard 488.1-1987, IEEE Standard Digital Interface for Programmable  
Instrumentation  
Customer Communication  
National Instruments wants to receive your comments on our products and manuals. We are  
very interested in the applications you develop with our products, and we want to help if you  
have problems with them. To make it easy for you to contact us, this manual contains comment  
and configuration forms for to you complete. These forms are in Appendix D, Customer  
Communication, at the end of this manual.  
GPIB-120A User Manual  
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Chapter 1  
Introduction  
This chapter contains a description of the GPIB-120A, lists what you need to get started and  
optional equipment you can order, and explains how to unpack the GPIB-120A.  
Description of the GPIB-120A  
The GPIB-120A is a high-speed bus expander/isolator with the following features:  
It is transparent to user software.  
It electrically isolates two GPIB systems.  
It expands the GPIB to interface up to 28 devices.  
It extends the GPIB by effectively doubling the 20 m cable limit.  
It has optional rack-mount hardware.  
The high-speed GPIB-120A bus expander connects two GPIB (IEEE 488) bus systems in a  
functionally transparent manner.  
The two bus systems are electrically isolated from each other. Isolating an instrument or group  
of instruments from an IEEE 488 bus Controller can eliminate ground loop noise and induced  
common-mode noise, which may cause measurement problems in both analog and digital  
systems. The two isolated bus systems are physically separate, as shown in Figure 1-1; however,  
the devices logically appear to be located on the same bus, as shown in Figure 1-2.  
GPIB #1  
GPIB-120A  
GPIB #2  
Computer  
(Controller,  
Talker, and Listener)  
Printer  
(Listener)  
Multimeter  
(Talker and  
Listener)  
Signal Generator  
(Listener)  
Unit Under Test  
Figure 1-1. Typical GPIB-120A Extension System (Physical Configuration)  
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Introduction  
Chapter 1  
GPIB  
Computer  
(Controller,  
Talker, and Listener)  
Printer  
(Listener)  
Multimeter  
(Talker and  
Listener)  
Signal Generator  
(Listener)  
Unit Under Test  
Figure 1-2. Typical GPIB-120A Extension System (Logical Configuration)  
With the GPIB-120A, it is possible to overcome the following two configuration restrictions  
imposed by the ANSI/IEEE Standard 488.1-1987:  
An electrical loading limit of 15 devices per contiguous bus.  
A cable length limit of 20 m total per contiguous bus or 2 m times the number of devices on  
the bus, whichever is smaller.  
With each GPIB-120A, you can add up to 14 additional devices to the bus. The GPIB-120A  
appears as a device load on each side of the expansion; therefore, one GPIB-120A increases the  
maximum load limit from 15 devices to 28 devices. The cable length limit for the system is also  
increased an additional 4 m to 20 m, depending on the number of devices on that side of the  
expansion.  
All signal expansion is bidirectional, meaning that Controllers, Talkers, and Listeners can be on  
either side of the expander. The GPIB-120A front panel light-emitting diodes (LEDs) indicate  
the location of the System Controller, Active Controller, and Source Handshaker, with respect to  
the two sides of the expansion.  
Because the GPIB-120A is a functionally transparent expander, the same GPIB communications  
and control programs that work with an unexpanded system can work unmodified with an  
expanded system.  
GPIB-120A User Manual  
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Chapter 1  
Introduction  
What You Need to Get Started  
One of the following GPIB-120A Bus Expanders/Isolators:  
GPIB-120A (100 to 120 VAC)  
GPIB-120A (220 to 240 VAC)  
2.2 m, 125 VAC Power Cord (When connected to a power source, this cord connects the  
equipment chassis to power ground.)  
Optional Equipment  
You can contact National Instruments to order any of the following optional equipment.  
Rack-Mount Kit  
Single Rack-Mount Kit  
Dual Rack-Mount Kit  
Shielded GPIB cables*  
Type X1 single-shielded GPIB cables (1 m, 2 m, or 4 m)  
Type X2 double-shielded GPIB cables (1 m, 2 m, or 4 m)  
* To meet FCC emission limits for this Class A device, you must use a shielded (Type X1 or  
X2) GPIB cable. Operating this equipment with a non-shielded cable may cause interference  
to radio and television reception in commercial areas.  
Unpacking Your GPIB-120A  
Follow these steps when unpacking your GPIB-120A.  
1. Verify that the package you received contained everything you need to get started, as listed  
earlier in this chapter.  
2. Inspect the shipping container and contents for damage. If the container is damaged and the  
damage appears to have been caused in shipment, file a claim with the carrier. If the  
equipment is damaged, do not attempt to operate it. Contact National Instruments for  
instructions. Retain the shipping material for possible inspection by carrier or reshipment of  
the equipment.  
3. Verify that the voltage you will be using is the same as that marked on the rear panel of the  
GPIB-120A.  
Note: The GPIB-120A is shipped from the factory set at a certain operating voltage, either  
100 to 120 VAC or 220 to 240 VAC. Operating the unit at the wrong voltage can  
damage the unit. If the GPIB-120A is set at a voltage other than the one you will be  
using, contact National Instruments for further instructions.  
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Chapter 2  
Connection  
This chapter contains information for connecting your GPIB-120A.  
Danger: The GPIB-120A does not generate high voltages; however, you must use extreme  
caution if your system or application can cause high voltages on the shield or logic  
ground of the GPIB cable you attach to the electrically isolated connector (GPIB  
Port B) located on the rear panel of the GPIB-120A. Many GPIB cables use a  
metal shell to enclose the GPIB piggyback connectors. This metal shell is normally  
connected to the cable shield. Therefore, if the shield is at a high potential with  
respect to the chassis ground of the GPIB-120A, the high voltage is also present, in  
most cases, on the cable connector housing.  
The chassis, back panel, and front panel of the GPIB-120A are electrically  
connected to the earth ground pin of the AC power connector on the back panel. If  
the AC wiring in your building is installed correctly, you can safely operate the  
GPIB-120A. Because the EMI shield and jack screws of rear panel connector  
‘GPIB A’ are electrically shorted to the rear panel, a GPIB cable attached to GPIB  
Port A has its shield and connector housing connected to earth ground, as well,  
and no danger should exist associated with GPIB Port A. There may be, however,  
a hazardous voltage potential between the cable connector housings of the GPIB  
cable attached to GPIB Port A and the GPIB cable attached to GPIB Port B.  
Never touch the GPIB-120A case, power cord, or any GPIB cable connected to the  
GPIB-120A unless you are absolutely sure that there are no hazardous voltages  
present. In addition, never open the GPIB-120A case unless you have removed the  
power cord and all GPIB cables from the back panel.  
The GPIB-120A is not recommended for use when ground potential differences in  
excess of 30 V are present between the two rear panel GPIB connectors and  
associated cables unless sufficient precautions are taken to ensure human safety.  
Isolation Considerations  
Noise and ground loop problems are common when performing small signal analysis. You can  
solve such problems by isolating a group of sensitive GPIB instruments from other noisier  
instruments.  
Your GPIB-120A has two GPIB connectors that are electrically isolated from each other: Bus A  
and Bus B. Bus B is also isolated from the chassis and back panel of the GPIB-120A.  
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Connection  
Chapter 2  
Placing Your Instruments  
Identify the instruments or devices in your system that are sensitive to ground loop noise. In the  
next section, Connecting the GPIB-120A, you will connect these instruments or devices to Bus B  
of your GPIB-120A. Then, you will connect the other instruments or devices to Bus A. Usually  
you connect your computer or other device acting as the GPIB System Controller to Bus A.  
Connecting the GPIB-120A  
To connect the GPIB-120A, follow these instructions:  
1. Make sure that the power switch on the back panel is in the off position.  
2. Plug the utility power cord into an acceptable electrical outlet (100 to 120 VAC or 220 to  
240 VAC, depending upon which model of the GPIB-120A you have). Plug the other end  
of the power cord into the back panel of the GPIB.  
3. Link your GPIB instrument(s), board(s), and other device(s) to the GPIB-120A with  
appropriate cables (type X1 or X2). Use Bus A for devices that do not need to be electrically  
isolated. Use Bus B for devices that need to be electrically isolated from devices on Bus A.  
4. Move the power switch to the on position.  
Connecting to Hewlett-Packard Controllers  
To achieve very high data transfer rates and long cable spans between devices, many HP  
Controllers and computers, such as the 64000 series, use a preload technique on the unit  
designated Master Controller. When preloaded, the GPIB lines of the Master Controller are  
terminated to represent six device loads. HP has two types of preloading: Class A, in which all  
16 GPIB lines are loaded, and Class B, in which all lines, except NRFD and NDAC lines, are  
loaded.  
Preloading increases ringing on signal transitions and can cause improper operation of the  
GPIB-120A. If this happens, set all signals on the Master Controller to normal (1 unit) load.  
This is done using a back panel switch on your HP Controller. In addition, you must also strictly  
conform to the cabling rule of no more than two meters per device.  
Mounting the GPIB-120A  
The GPIB-120A is designed for table-top or rack-mount operation. Single- and dual-unit  
rack-mount kits are available from National Instruments. Refer to the Optional Equipment  
section of Chapter 1, Introduction, for ordering information on the rack-mount kits.  
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Chapter 3  
Theory of Operation  
This chapter describes the operational theory of the GPIB-120A. This chapter assumes that you  
have a basic knowledge of the GPIB. If you are a first-time user or you would like to review the  
basics, refer to Appendix A, Operation of the GPIB, for a history and the basic operation of the  
GPIB.  
Circuitry of the GPIB-120A  
The GPIB-120A consists of two sides: Bus A and Bus B. The circuitry for both sides is  
logically identical and the two sides are electrically isolated from each other. The only  
difference between the two sides is that logic ground on Bus A is connected to the chassis  
ground while the logic ground for Bus B is not. Thus, Bus B is the isolated side of the  
expansion. To reduce measurement problems caused by noise and ground loops, the  
measurement instruments must be located on the isolated Bus B and all other devices must be  
located on Bus A. A block diagram for the GPIB-120A is shown in Figure 3-1.  
Controller  
Detection  
Controller  
Detection  
Source  
Handshake  
Detection  
Source  
Handshake  
Detection  
Data  
Direction  
Control  
Data  
Direction  
Control  
Parallel  
Poll  
Detection  
Parallel  
Poll  
Detection  
Side A  
Side B  
Figure 3-1. GPIB-120A Block Diagram  
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Theory of Operation  
Chapter 3  
The circuitry on each side of the expansion monitors local GPIB states and converts the signals  
monitored into X signals (for transmit) which drive the R signals (for receive) on the opposite  
side of the expansion. The X signals are optically isolated from the R signals. Each GPIB signal  
is sensed or driven depending on the System Controller, Active Controller, and Source  
Handshake states of each side of the expansion.  
The GPIB-120A Front Panel  
The GPIB-120A front panel has seven light-emitting diodes (LEDs). The POWER LED on the  
left-hand side of the front panel is lit whenever you power on the GPIB-120A.  
For each bus, an LED indicates the status of the System Controller, Active Controller, or Source  
Handshake state.  
Power On  
When you power on the GPIB-120A, all circuitry is cleared to an initialized state. The  
GPIB-120A expansion system is fully operational when you power on the GPIB-120A and your  
instruments are connected. Where there is GPIB activity, it is recommended that you keep at  
least two-thirds of the devices on both buses powered on.  
System Controller Detection  
After you power on, Bus A and Bus B System Controller states are false.  
If a GPIB device on Bus A asserts IFC or REN, the Bus A System Controller state becomes true  
and the Bus B System Controller state becomes false.  
If a GPIB device on Bus B asserts IFC or REN, the Bus B System Controller state becomes true  
and the Bus A System Controller state becomes false.  
Active Controller Detection  
After you power on, Bus A and Bus B Active Controller states are false.  
If a GPIB device on Bus A asserts ATN, the Bus A Active Controller state becomes true and the  
Bus B Active Controller state becomes false.  
If a GPIB device on Bus B asserts ATN, the Bus B Active Controller state becomes true and the  
Bus A Active Controller state becomes false.  
Source Handshake Detection  
A device is considered a source handshaker if it is an active Controller sourcing command bytes  
or if it is a Talker sourcing data bytes.  
After you power on, Bus A and Bus B Source Handshake states are false.  
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Chapter 3  
Theory of Operation  
If a GPIB device on Bus A asserts DAV, the Bus A Source Handshake state becomes true and  
the Bus B Source Handshake state becomes false.  
If a GPIB device on Bus B asserts DAV, the Bus B Source Handshake state becomes true and  
the Bus A Source Handshake state becomes false.  
Bus A and Bus B Source Handshake states also become false when a parallel poll begins or  
when the ATN signal changes states.  
Data Direction Control  
Bus B sends the data lines to Bus A if the Bus B Source Handshake state is true or if a Controller  
on Bus A is conducting a parallel poll.  
Bus A sends the data lines to Bus B if the Bus A Source Handshake state is true or if a Controller  
on Bus B is conducting a parallel poll.  
Parallel Poll Detection  
Controllers can conduct parallel polls on Bus A or Bus B with no modification of user software.  
Devices on both Bus A and Bus B can respond to parallel polls.  
If a Controller on Bus A conducts a parallel poll, the parallel poll detection circuitry on side B  
conducts a parallel poll on Bus B. The result of the parallel poll is driven on the data lines of  
Bus A.  
If a Controller on Bus B conducts a parallel poll, the parallel poll detection circuitry on side A  
conducts a parallel poll on Bus A. The result of the parallel poll is driven on the data lines of  
Bus B.  
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Theory of Operation  
Chapter 3  
Acceptable Identification Codes  
Bus A and Bus B of the GPIB-120A are each capable of appearing as a GPIB device having the  
GPIB capabilities listed in Table 3-1. For a complete description of each code, consult the  
ANSI/IEEE Standard 488.1-1987, IEEE Standard Digital Interface for Programmable  
Instrumentation.  
Table 3-1. IEEE 488 Capability Identification Codes  
Capability Code  
SH1  
Description  
Source Handshake  
AH1  
Acceptor Handshake  
Talker, Extended Talker  
Listener, Extended Listener  
Service Request  
Remote/Local  
T5, TE5  
L3, LE3  
SR1  
RL1  
PP1, PP2  
DC1  
Parallel Poll  
Device Clear  
DT1  
Device Trigger  
C1, C2, C3, C4, C5  
E1, E2  
Controller  
Three-state bus drivers with automatic switch  
to open collector during parallel poll  
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Appendix A  
Operation of the GPIB  
This appendix contains a brief history of the GPIB and describes the operation of the GPIB.  
History of the GPIB  
The original GPIB was designed by Hewlett-Packard (where it is called the HP-IB) to connect  
and control programmable instruments manufactured by Hewlett-Packard. Because of its high  
data transfer rates of up to 1 Mbytes/s, the GPIB quickly gained popularity in other applications  
such as intercomputer communication and peripheral control. It was later accepted as the  
industry standard IEEE 488. The versatility of the system prompted the name General Purpose  
Interface Bus.  
National Instruments expanded the use of the GPIB among users of computers manufactured  
by companies other than Hewlett-Packard. National Instruments specializes both in high-  
performance, high-speed hardware interfaces and in comprehensive, full-function software that  
helps users bridge the gap between their knowledge of instruments and computer peripherals and  
of the GPIB itself.  
GPIB Operation  
The GPIB is a link, or interface system, through which interconnected electronic devices  
communicate. Communication among interconnected GPIB devices is achieved by passing  
messages through the interface system.  
Types of Messages  
The GPIB carries device-dependent messages and interface messages.  
Device-dependent messages, often called data or data messages, contain device-specific  
information such as programming instructions, measurement results, machine status, and data  
files.  
Interface messages manage the bus itself. They are usually called commands or command  
messages. Interface messages perform such tasks as initializing the bus, addressing and  
unaddressing devices, and setting device modes for remote or local programming.  
The term command as used here should not be confused with some device instructions which can  
also be called commands. Such device-specific instructions are actually data messages.  
© National Instruments Corporation  
A-1  
GPIB-120A User Manual  
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Operation of the GPIB  
Appendix A  
Talkers, Listeners, and Controller  
There are three types of GPIB communicators: Talkers, Listeners, and Controllers. A Talker  
sends data messages to one or more Listeners. The Controller manages the flow of information  
on the GPIB by sending commands to all devices.  
Devices can be Listeners, Talkers, and/or Controllers. A digital voltmeter, for example, is a  
Talker and may be a Listener as well.  
The GPIB is a bus like an ordinary computer bus, except that the computer has its circuit cards  
interconnected via a backplane bus, whereas the GPIB has standalone devices interconnected via  
a cable bus.  
The role of the GPIB Controller can also be compared to the role of the CPU of a computer, but  
a better analogy is to the switching center of a city telephone system.  
The switching center (Controller) monitors the communications network (GPIB). When the  
center (Controller) notices that a party (device) wants to make a call (send a data message), it  
connects the caller (Talker) to the receiver (Listener).  
The Controller addresses a Talker and a Listener before the Talker can send its message to the  
Listener. After the message is transmitted, the Controller may unaddress both devices.  
Some bus configurations do not require a Controller. For example, one device may always be a  
Talker (called a Talk-only device) and there may be one or more Listen-only devices.  
A Controller is necessary when the active or addressed Talker or Listener must be changed. The  
Controller function is usually handled by a computer.  
With a GPIB interface board and its software, your personal computer plays all three roles.  
Controller – to manage the GPIB  
Talker – to send data  
Listener – to receive data  
The Controller-In-Charge and System Controller  
Although there can be multiple Controllers on the GPIB, only one Controller at a time is active  
or Controller-In-Charge (CIC). Active control can be passed from the current CIC to an idle  
Controller. Only one device on the bus, the System Controller, can make itself the CIC. A GPIB  
interface board in a computer is usually the System Controller.  
GPIB-120A User Manual  
A-2  
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Appendix A  
Operation of the GPIB  
GPIB Signals and Lines  
The interface system consists of 16 signal lines and 8 ground return or shield drain lines.  
The 16 signal lines are divided into the following three groups.  
Eight data lines  
Three handshake lines  
Five interface management lines  
Data Lines  
The eight data lines, DI01 through DI08, carry both data and command messages. All  
commands and most data use the 7-bit ASCII or ISO code set, in which case the eighth bit, DI08,  
is unused or used for parity.  
Handshake Lines  
Three lines asynchronously control the transfer of message bytes among devices. The process is  
called a three-wire interlocked handshake, and it guarantees that message bytes on the data lines  
are sent and received without transmission error.  
NRFD (Not Ready For Data)  
NRFD indicates when a device is ready or not ready to receive a message byte. The line is  
driven by all devices when receiving commands and by Listeners when receiving data messages.  
NDAC (Not Data Accepted)  
NDAC indicates when a device has or has not accepted a message byte. The line is driven by all  
devices when receiving commands and by Listeners when receiving data messages.  
DAV (Data Valid)  
DAV indicates when the signals on the data lines are stable (valid) and can be accepted safely by  
devices. The Controller drives DAV when sending commands and the Talker drives it when  
sending data messages.  
© National Instruments Corporation  
A-3  
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Operation of the GPIB  
Appendix A  
Interface Management Lines  
Five lines are used to manage the flow of information across the interface.  
ATN (Attention)  
The Controller drives ATN true when it uses the data lines to send commands and false when it  
allows a Talker to send data messages.  
IFC (Interface Clear)  
The System Controller drives the IFC line to initialize the bus and become CIC.  
REN (Remote Enable)  
The System Controller drives the REN line, which is used to place devices in remote or local  
program mode.  
SRQ (Service Request)  
Any device can drive the SRQ line to asynchronously request service from the Controller.  
EOI (End Or Identify)  
The EOI line has two purposes: the Talker uses the EOI line to mark the end of a message  
string, and the Controller uses the EOI line to tell devices to identify their response in a parallel  
poll.  
GPIB-120A User Manual  
A-4  
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Appendix A  
Operation of the GPIB  
Physical and Electrical Characteristics  
Devices are usually connected with a cable assembly consisting of a shielded 24 conductor cable  
with both a plug and receptacle connector at each end. With this design, devices can be linked in  
either a linear configuration (shown in Figure A-2) or a star configuration (shown in  
Figure A-3), or a combination of the two.  
The standard connector is the Amphenol or Cinch Series 57 Microribbon or Amp Champ type.  
An adapter cable using a non-standard cable and/or connector is used for special interconnecting  
applications.  
The GPIB uses negative logic with standard TTL logic levels. When DAV is true, for example,  
it is a TTL low level ( 0.8 V), and when DAV is false, it is a TTL high level ( 2.0 V).  
DIO1  
DIO2  
DIO3  
DIO4  
EOI  
DAV  
NRFD  
NDAC  
IFC  
SRQ  
ATN  
1
2
3
4
5
6
7
8
9
13  
14  
15  
16  
17  
18  
19  
20  
21  
DIO5  
DIO6  
DIO7  
DIO8  
REN  
GND (TW PAIR W/DAV)  
GND (TW PAIR W/NRFD)  
GND (TW PAIR W/NDAC)  
GND (TW PAIR W/IFC)  
GND (TW PAIR W/SRQ)  
10 22  
11 23  
12 24  
GND (TW PAIR W/ATN)  
SIGNAL GROUND  
SHIELD  
Figure A-1. GPIB Connector and the Signal Assignment  
© National Instruments Corporation  
A-5  
GPIB-120A User Manual  
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Operation of the GPIB  
Appendix A  
Figure A-2. Linear Configuration of the GPIB Devices  
GPIB-120A User Manual  
A-6  
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Appendix A  
Operation of the GPIB  
Figure A-3. Star Configuration of the GPIB Devices  
© National Instruments Corporation  
A-7  
GPIB-120A User Manual  
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Operation of the GPIB  
Appendix A  
Configuration Restrictions: The Role of Expanders and Extenders  
To achieve the high data transfer rate for which the GPIB is designed, the physical distance  
between devices and the number of devices on the bus are limited.  
The following restrictions are typical:  
A maximum separation of 4 m between any two devices and an average separation of 2 m  
over the entire bus.  
A maximum total cable length of 20 m.  
No more than 15 devices connected to each bus, with at least two-thirds of the devices  
powered on.  
It is usually possible to connect a cluster of lab instruments without exceeding these restrictions,  
but many applications require longer cable spans or additional loading. From the time the GPIB  
was invented, the need has existed for bus extenders and expanders (repeaters).  
Extenders connect two separate buses via a transmission medium and the distance between the  
buses can be quite long. Expanders generally buffer one bus from an adjacent bus, allowing a  
doubling of the total cable and loading limits.  
National Instruments offers several products that accept longer cable spans. These extenders can  
functionally connect GPIB systems separated by distances from 20 m to over 2 km. For more  
information about which extender may be right for your application, contact National  
Instruments.  
The GPIB-120A is a high-speed bus expander which allows up to 14 additional devices to be  
connected to the bus and 20 m of cable to be added to the system. In addition, the two connected  
GPIBs are optically isolated to prevent ground loop and noise problems. Only one GPIB-120A  
is required per expansion.  
Related Document  
For more information on topics covered in this appendix, consult the ANSI/IEEE Standard  
488.1-1987, IEEE Standard Digital Interface for Programmable Instrumentation.  
GPIB-120A User Manual  
A-8  
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Appendix B  
Specifications  
This appendix lists the specifications of the GPIB-120A.  
Table B-1. System Configuration  
Configuration  
Loading per expansion  
Specification  
Up to 14 additional devices  
No restrictions  
GPIB driver output circuit and T1 timing  
of source device  
Note: T1 is the data settling time (DIO valid to DAV) and varies according to the type  
of drivers and the system configuration used.  
Table B-2. Performance Characteristics  
Characteristic  
Data transfer rate degradation  
Propagation delay  
Specification  
250 ns per byte, typical  
All signals except DAV  
140 ns typical for signal assertion edge  
180 ns typical for signal unassertion edge  
200 ns maximum  
DAV (first byte)  
2.5 µs typical for signal assertion edge  
180 ns typical for signal unassertion edge  
DAV (subsequent bytes)  
140 ns typical for signal assertion edge  
180 ns typical for signal unassertion edge  
200 ns maximum  
Transfer Rate  
Read from isolated GPIB instrument  
Write to isolated GPIB instrument  
GPIB commands to isolated GPIB  
800 kbytes/s maximum  
800 kbytes/s maximum  
in3s2t0rukmbeyntets/s maximum  
© National Instruments Corporation  
B-1  
GPIB-120A User Manual  
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Specifications  
Appendix B  
Table B-3. Electrical Characteristics  
Characteristic Specification  
Isolation  
60 V operating  
1600 V breakdown  
Power supply selectable  
90 to 130 VAC, 235 mA, (250 mA, 250 V,  
slow blow), 50 to 60 Hz or  
180 to 260 VAC, 120 mA, (200 mA,  
250 V, slow blow), 50 to 60 Hz  
GPIB interface load  
Power  
One standard load, AC and DC  
27 VA typical  
Table B-4. Environmental Characteristics  
Characteristic Specification  
Operating temperature  
Humidity  
0° to 45° C  
5% to 95% noncondensing conditions  
FCC Class A Verified  
EMI  
Table B-5. Physical Characteristics  
Characteristic Specification  
Case style  
Case size  
CS2  
89 mm by 216 mm by 330 mm  
(3.5 in. by 8.5 in. by 13 in.)  
Case material  
UL94V-0 flame retardant polystyrene  
DOW 60875F or Noryl FN-215  
GPIB-120A User Manual  
B-2  
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Appendix C  
Multiline Interface Messages  
This appendix contains an interface message reference list, which describes the mnemonics and  
messages that correspond to the interface functions. These multiline interface messages are sent  
and received with ATN TRUE.  
For more information on these messages, refer to the ANSI/IEEE Standard 488.1-1987,  
IEEE Standard Digital Interface for Programmable Instrumentation.  
© National Instruments Corporation  
C-1  
GPIB-120A User Manual  
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Multiline Interface Messages  
Appendix C  
Multiline Interface Messages  
Hex Oct Dec ASCII Msg  
Hex Oct Dec  
ASCII Msg  
00  
01  
02  
03  
04  
05  
06  
07  
000  
001  
002  
003  
004  
005  
006  
007  
0
1
2
3
4
5
6
7
NUL  
SOH  
STX  
ETX  
EOT  
ENQ  
ACK  
BEL  
20  
21  
22  
23  
24  
25  
26  
27  
040  
041  
042  
043  
044  
045  
046  
047  
32  
33  
34  
35  
36  
37  
38  
39  
SP  
!
"
#
$
%
&
'
MLA0  
MLA1  
MLA2  
MLA3  
MLA4  
MLA5  
MLA6  
MLA7  
GTL  
SDC  
PPC  
08  
09  
0A  
0B  
0C  
0D  
0E  
0F  
010  
011  
012  
013  
014  
015  
016  
017  
8
9
BS  
HT  
LF  
VT  
FF  
CR  
SO  
SI  
GET  
TCT  
28  
29  
2A  
2B  
2C  
2D  
2E  
2F  
050  
051  
052  
053  
054  
055  
056  
057  
40  
41  
42  
43  
44  
45  
46  
47  
(
)
*
+
,
-
.
MLA8  
MLA9  
10  
11  
12  
13  
14  
15  
MLA10  
MLA11  
MLA12  
MLA13  
MLA14  
MLA15  
/
10  
11  
12  
13  
14  
15  
16  
17  
020  
021  
022  
023  
024  
025  
026  
027  
16  
17  
18  
19  
20  
21  
22  
23  
DLE  
DC1  
DC2  
DC3  
DC4  
NAK  
SYN  
ETB  
30  
31  
32  
33  
34  
35  
36  
37  
060  
061  
062  
063  
064  
065  
066  
067  
48  
49  
50  
51  
52  
53  
54  
55  
0
1
2
3
4
5
6
7
MLA16  
MLA17  
MLA18  
MLA19  
MLA20  
MLA21  
MLA22  
MLA23  
LLO  
DCL  
PPU  
18  
19  
1A  
1B  
1C  
1D  
1E  
1F  
030  
031  
032  
033  
034  
035  
036  
037  
24  
25  
26  
27  
28  
29  
30  
31  
CAN  
EM  
SUB  
ESC  
FS  
GS  
RS  
SPE  
SPD  
38  
39  
3A  
3B  
3C  
3D  
3E  
3F  
070  
071  
072  
073  
074  
075  
076  
077  
56  
57  
58  
59  
60  
61  
62  
63  
8
9
:
MLA24  
MLA25  
MLA26  
MLA27  
MLA28  
MLA29  
MLA30  
UNL  
;
<
=
>
?
US  
Message Definitions  
DCL  
GET  
GTL  
LLO  
MLA  
Device Clear  
Group Execute Trigger  
Go To Local  
Local Lockout  
My Listen Address  
MSA  
My Secondary Address  
My Talk Address  
Parallel Poll Configure  
Parallel Poll Disable  
MTA  
PPC  
PPD  
GPIB-120A User Manual  
C-2  
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Appendix C  
Multiline Interface Messages  
Multiline Interface Messages  
Hex Oct Dec ASCII Msg  
Hex Oct Dec ASCII Msg  
40  
41  
42  
43  
44  
45  
46  
47  
100  
101  
102  
103  
104  
105  
106  
107  
64  
65  
66  
67  
68  
69  
70  
71  
@
A
B
C
D
E
MTA0  
MTA1  
MTA2  
MTA3  
MTA4  
MTA5  
MTA6  
MTA7  
60  
61  
62  
63  
64  
65  
66  
67  
140  
141  
142  
143  
144  
145  
146  
147  
96  
97  
98  
`
MSA0,PPE  
MSA1,PPE  
MSA2,PPE  
MSA3,PPE  
MSA4,PPE  
MSA5,PPE  
MSA6,PPE  
MSA7,PPE  
a
b
c
d
e
f
99  
100  
101  
102  
103  
F
G
g
48  
49  
4A  
4B  
4C  
4D  
4E  
4F  
110  
111  
112  
113  
114  
115  
116  
117  
72  
73  
74  
75  
76  
77  
78  
79  
H
I
J
K
L
M
N
O
MTA8  
MTA9  
68  
69  
6A  
6B  
6C  
6D  
6E  
6F  
150  
151  
152  
153  
154  
155  
156  
157  
104  
105  
106  
107  
108  
109  
110  
111  
h
i
j
k
l
m
n
o
MSA8,PPE  
MSA9,PPE  
MSA10,PPE  
MSA11,PPE  
MSA12,PPE  
MSA13,PPE  
MSA14,PPE  
MSA15,PPE  
MTA10  
MTA11  
MTA12  
MTA13  
MTA14  
MTA15  
50  
51  
52  
53  
54  
55  
56  
57  
120  
121  
122  
123  
124  
125  
126  
127  
80  
81  
82  
83  
84  
85  
86  
87  
P
MTA16  
MTA17  
MTA18  
MTA19  
MTA20  
MTA21  
MTA22  
MTA23  
70  
71  
72  
73  
74  
75  
76  
77  
160  
161  
162  
163  
164  
165  
166  
167  
112  
113  
114  
115  
116  
117  
118  
119  
p
q
r
s
t
u
v
w
MSA16,PPD  
MSA17,PPD  
MSA18,PPD  
MSA19,PPD  
MSA20,PPD  
MSA21,PPD  
MSA22,PPD  
MSA23,PPD  
Q
R
S
T
U
V
W
58  
59  
5A  
5B  
5C  
5D  
5E  
5F  
130  
131  
132  
133  
134  
135  
136  
137  
88  
89  
90  
91  
92  
93  
94  
95  
X
Y
Z
[
\
]
MTA24  
MTA25  
MTA26  
MTA27  
MTA28  
MTA29  
MTA30  
UNT  
78  
79  
7A  
7B  
7C  
7D  
7E  
7F  
170  
171  
172  
173  
174  
175  
176  
177  
120  
121  
122  
123  
124  
125  
126  
127  
x
y
z
{
|
}
~
DEL  
MSA24,PPD  
MSA25,PPD  
MSA26,PPD  
MSA27,PPD  
MSA28,PPD  
MSA29,PPD  
MSA30,PPD  
^
_
PPE  
PPU  
SDC  
SPD  
Parallel Poll Enable  
Parallel Poll Unconfigure  
Selected Device Clear  
Serial Poll Disable  
SPE  
Serial Poll Enable  
Take Control  
Unlisten  
TCT  
UNL  
UNT  
Untalk  
© National Instruments Corporation  
C-3  
GPIB-120A User Manual  
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Appendix D  
Customer Communication  
For your convenience, this appendix contains forms to help you gather the information necessary  
to help us solve technical problems you might have as well as a form you can use to comment on  
the product documentation. Filling out a copy of the Technical Support Form before contacting  
National Instruments helps us help you better and faster.  
National Instruments provides comprehensive technical assistance around the world. In the U.S.  
and Canada, applications engineers are available Monday through Friday from 8:00 a.m. to  
6:00 p.m. (central time). In other countries, contact the nearest branch office. You may fax  
questions to us at any time.  
Corporate Headquarters  
(512) 795-8248  
Technical support fax: (800) 328-2203  
(512) 794-5678  
Branch Offices  
Australia  
Austria  
Belgium  
Denmark  
Finland  
France  
Germany  
Italy  
Phone Number  
(03) 879 9422  
(0662) 435986  
02/757.00.20  
45 76 26 00  
(90) 527 2321  
(1) 48 14 24 00  
089/741 31 30  
02/48301892  
(03) 3788-1921  
95 800 010 0793  
03480-33466  
32-848400  
Fax Number  
(03) 879 9179  
(0662) 437010-19  
02/757.03.11  
45 76 71 11  
(90) 502 2930  
(1) 48 14 24 14  
089/714 60 35  
02/48301915  
(03) 3788-1923  
95 800 010 0793  
03480-30673  
32-848600  
Japan  
Mexico  
Netherlands  
Norway  
Singapore  
Spain  
Sweden  
Switzerland  
Taiwan  
2265886  
2265887  
(91) 640 0085  
08-730 49 70  
056/20 51 51  
02 377 1200  
0635 523545  
(91) 640 0533  
08-730 43 70  
056/20 51 55  
02 737 4644  
0635 523154  
U.K.  
© National Instruments Corporation  
D-1  
GPIB-120A User Manual  
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Technical Support Form  
___________________________________________________  
Photocopy this form and update it each time you make changes to your software or hardware, and use the completed  
copy of this form as a reference for your current configuration. Completing this form accurately before contacting  
National Instruments for technical support helps our applications engineers answer your questions more efficiently.  
If you are using any National Instruments hardware or software products related to this problem, include the  
configuration forms from their user manuals. Include additional pages if necessary.  
Name  
Company  
Address  
Fax (  
Computer brand  
Operating system  
)
Phone (  
Model  
)
Processor  
Speed  
MHz  
RAM  
no  
MB  
Display adapter  
Mouse  
yes  
Other adapters installed  
Brand  
Hard disk capacity  
Instruments used  
MB  
National Instruments hardware product model  
Configuration  
Revision  
National Instruments software product  
Configuration  
Version  
The problem is  
List any error messages  
The following steps will reproduce the problem  
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GPIB-120A Hardware and Software  
Configuration Form  
Record the settings and revisions of your hardware and software on the line located to the right  
of each item. Complete this form each time you revise your software or hardware configuration,  
and use this form as a reference for your current configuration. Completing this form accurately  
before contacting National Instruments for technical support helps our applications engineers  
answer your questions efficiently.  
National Instruments Products  
GPIB Software Revision Number on Disk  
Programming Language Interface Revision  
Types of National Instruments GPIB boards installed in your computer and their respective hardware settings:  
Interrupt Line  
Setting  
DMA Channel  
Setting  
Base I/O Address  
Setting  
Board Type  
Other Products  
Computer Make and Model  
Other GPIB Devices or Instruments  
Application Programming Language (BASICA, QuickBASIC, C, Pascal, and so on)  
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Documentation Comment Form  
National Instruments encourages you to comment on the documentation supplied with our products. This  
information helps us provide quality products to meet your needs.  
Title: GPIB-120A User Manual  
Edition Date:  
Part Number:  
October 1994  
370893A-01  
Please comment on the completeness, clarity, and organization of the manual.  
If you find errors in the manual, please record the page numbers and describe the errors.  
Thank you for your help.  
Name  
Title  
Company  
Address  
Phone  
(
)
Mail to:  
Technical Publications  
Fax to:  
Technical Publications  
National Instruments Corporation  
MS 53-02  
National Instruments Corporation  
6504 Bridge Point Parkway, MS 53-02  
Austin, TX 78730-5039  
(512) 794-5678  
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Glossary  
___________________________________________________  
Prefix  
Meaning  
Value  
-9  
n-  
nano-  
micro-  
milli-  
kilo-  
10  
-6  
µ-  
10  
-3  
m-  
k-  
10  
3
10  
6
M-  
mega-  
10  
°
%
degrees  
percent  
A
AC  
amperes  
alternating current  
ANSI  
ASCII  
ATN  
C
CIC  
CPU  
DAV  
DC  
American National Standards Institute  
American Standard Code for Information Interchange  
Attention  
Celsius  
Controller-In-Charge  
central processing unit  
Data Valid  
direct current  
DIO  
EMI  
EOI  
FCC  
GPIB  
Hz  
Data Input/Output  
electromagnetic interference  
End Or Identify  
Federal Communications Commission  
General Purpose Interface Bus  
hertz  
IFC  
in.  
Interface Clear  
inches  
ISO  
LED  
m
MB  
NDAC  
NRFD  
RAM  
REN  
s
International Standards Organization  
light-emitting diode  
meters  
megabytes of memory  
Not Data Accepted  
Not Ready For Data  
random-access memory  
Remote Enable  
seconds  
SRQ  
TTL  
V
Service Request  
transistor-transistor logic  
volts  
VA  
volt amperes  
VAC  
volts alternating current  
© National Instruments Corporation  
G-1  
GPIB-120A User Manual  
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