GPIB-120A
User Manual
October 1994 Edition
Part Number 370893A-01
© Copyright 1991, 1994 National Instruments Corporation.
All Rights Reserved.
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Switzerland 056/20 51 51, Taiwan 02 377 1200, U.K. 0635 523545
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
OF
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
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.
. CUSTOMER'S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART
NATIONAL INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER.
. This limitation of the liability of National Instruments will apply regardless of the form of action,
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.
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.
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.
Contents
About This Manual...............................................................................................................ix
Organization of This Manual...........................................................................................ix
Conventions Used in This Manual...................................................................................ix
Related Documentation....................................................................................................x
Customer Communication ...............................................................................................x
Chapter 1
Introduction
Description of the GPIB-120A ........................................................................................1-1
What You Need to Get Started ........................................................................................1-3
Optional Equipment.........................................................................................................1-3
Unpacking Your GPIB-120A...........................................................................................1-3
Chapter 2
Connection
Isolation Considerations...................................................................................................2-1
Placing Your Instruments.................................................................................................2-2
Connecting the GPIB-120A.............................................................................................2-2
Mounting the GPIB-120A................................................................................................2-2
............................................................................................................................1-1
...............................................................................................................................2-1
Connecting to Hewlett-Packard Controllers........................................................2-2
Chapter 3
Theory of Operation
Circuitry of the GPIB-120A.............................................................................................3-1
The GPIB-120A Front Panel............................................................................................3-2
Power On..............................................................................................................3-2
System Controller Detection................................................................................3-2
Active Controller Detection.................................................................................3-2
Source Handshake Detection...............................................................................3-2
Data Direction Control.........................................................................................3-3
Parallel Poll Detection .........................................................................................3-3
Acceptable Identification Codes......................................................................................3-4
............................................................................................................3-1
Appendix A
Operation of the GPIB
History of the GPIB .........................................................................................................A-1
GPIB Operation................................................................................................................A-1
Types of Messages...............................................................................................A-1
Talkers, Listeners, and Controllers......................................................................A-2
The Controller-In-Charge and System Controller ...............................................A-2
GPIB Signals and Lines.......................................................................................A-3
Data Lines................................................................................................A-3
Handshake Lines......................................................................................A-3
........................................................................................................A-1
NRFD (Not Ready For Data).......................................................A-3
© National Instruments Corporation vii GPIB-120A User Manual
Contents
NDAC (Not Data Accepted)........................................................A-3
DAV (Data Valid)........................................................................A- 3
Interface Management Lines....................................................................A-4
ATN (Attention)...........................................................................A-4
IFC (Interface Clear)....................................................................A-4
REN (Remote Enable) .................................................................A-4
SRQ (Service Request) ................................................................A-4
EOI (End Or Identify)..................................................................A-4
Physical and Electrical Characteristics................................................................A-5
Configuration Restrictions: The Role of Expanders and Extenders...................A-8
Related Document............................................................................................................A- 8
Appendix B
Specifications
..........................................................................................................................B-1
Appendix C
Multiline Interface Messages
Appendix D
Customer Communication
.................................................................................................D-1
............................................................................................C-1
Figures
Figure 1-1. Typical GPIB-120A Extension System (Physical Configuration) .....................1-1
Figure 1-2. Typical GPIB-120A Extension System (Logical Configuration).......................1-2
Figure 3-1. GPIB-120A Block Diagram ...............................................................................3-1
Figure A-1. GPIB Connector and the Signal Assignment......................................................A-5
Figure A-2. Linear Configuration of the GPIB Devices ........................................................A-6
Figure A-3. Star Configuration of the GPIB Devices............................................................A-7
Tables
Table 3-1. IEEE 488 Capability Identification Codes .........................................................3-4
Table B-1. System Configuration.........................................................................................B-1
Table B-2. Performance Characteristics...............................................................................B-1
Table B-3. Electrical Characteristics....................................................................................B-2
Table B-4. Environmental Characteristics............................................................................B-2
Table B-5. Physical Characteristics......................................................................................B-2
GPIB-120A User Manual viii © National Instruments Corporation
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.
© National Instruments Corporation ix GPIB-120A User Manual
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 x © National Instruments Corporation
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-120AGPIB #1 GPIB #2
Computer
(Controller,
Talker, and Listener)
Figure 1-1. Typical GPIB-120A Extension System (Physical Configuration)
© National Instruments Corporation 1-1 GPIB-120A User Manual
Printer
(Listener)
Multimeter
(Talker and
Listener)
Unit Under Test
Signal Generator
(Listener)
Introduction Chapter 1
GPIB
Computer
(Controller,
Talker, and Listener)
Printer
(Listener)
Multimeter
(Talker and
Listener)
Unit Under Test
Signal Generator
(Listener)
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 1-2 © National Instruments Corporation
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