National Instruments GPIB-140 Series User manual

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© Copyright 1995 National Instruments Corporation.
All Rights Reserved.
GPIB-140
User Manual
June 1995 Edition
Part Number 320911B-01

National Instruments Corporate Headquarters
6504 Bridge Point Parkway
Austin, TX 78730-5039
[phone]
Technical support fax: [phone]
[phone]
Branch Offices:
Australia 03 9 879 9422, Austria 0662 45 79 90 0, Belgium 02 757 00 20,
Canada (Ontario) 519 622 9310, Canada (Québec) 514 694 8521,
Denmark 45 76 26 00, Finland 90 527 2321, France 1 48 14 24 24,
Germany 089 741 31 30, Hong Kong 2645 3186, Italy 02 48301892,
Japan 03 5472 2970, Korea 02 596 7456, Mexico 5 202 2544,
Netherlands 03480 33466, Norway 32 84 84 00, Singapore 2265886,
Spain 91 640 0085, Sweden 08 730 49 70, Switzerland 056 20 51 51,
Taiwan 02 377 1200, U.K. 01635 523545

Limited Warranty
The GPIB-140 and GPIB-140/2 are 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.

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.

© National Instruments Corp. vii GPIB-140 User Manual
Contents
About This Manual ............................................................................................... xi
Organization of This Manual........................................................................... xi
Conventions Used in This Manual................................................................... xii
Related Documentation ................................................................................... xiii
Customer Communication ............................................................................... xiii
Chapter 1
Introduction.............................................................................................................. 1-1
What Your Kit Should Contain ....................................................................... 1-1
Optional Equipment......................................................................................... 1-1
Hardware Description ...................................................................................... 1-2
Chapter 2
Connection ................................................................................................................ 2-1
Configure the DIP Switch................................................................................ 2-1
Connect the Hardware ..................................................................................... 2-1
Step 1. Connect the Cables............................................................... 2-1
Step 2. Switch On Your GPIB Extender .......................................... 2-2
Optional Self-Test............................................................................................ 2-3
Chapter 3
Configuration and Operation ........................................................................... 3-1
Data Transfer Modes ....................................................................................... 3-1
Unbuffered Mode .............................................................................. 3-1
Buffered Mode................................................................................... 3-1
Setting the Data Transfer Mode ........................................................ 3-1
HS488 Mode .................................................................................................... 3-2
HS488 Disabled................................................................................. 3-2
HS488 Enabled.................................................................................. 3-2
Setting the HS488 Mode ................................................................... 3-3
Parallel Poll Response (PPR) Modes............................................................... 3-3
Immediate PPR Mode ....................................................................... 3-4
Latched PPR Mode............................................................................ 3-4
Choosing the PPR Mode ................................................................... 3-4
Setting the PPR Mode ....................................................................... 3-5
Operating the Extension System...................................................................... 3-5
POWER LED .................................................................................... 3-5
LINK LED......................................................................................... 3-6
ERROR LED..................................................................................... 3-6

Contents
GPIB-140 User Manual viii © National Instruments Corp.
Chapter 4
Theory of Operation ............................................................................................. 4-1
Message Interpreter Layer ............................................................................... 4-2
Packet Translation Layer ................................................................................. 4-3
Link Management Layer.................................................................................. 4-3
Parallel-to-Serial Translation Layer................................................................. 4-3
Physical Layer ................................................................................................. 4-3
Appendix A
Operation of the GPIB......................................................................................... A-1
Types of Messages........................................................................................... A-1
Talkers, Listeners, and Controllers .................................................................. A-1
The Controller-In-Charge and System Controllers.......................................... A-2
GPIB Signals and Lines................................................................................... A-2
Data Lines ......................................................................................... A-2
Handshake Lines ............................................................................... A-3
Interface Management Lines ............................................................. A-3
Physical and Electrical Characteristics ............................................................ A-4
Configuration Requirements............................................................................ A-5
Appendix B
Specifications ........................................................................................................... B-1
Appendix C
Introduction to HS488.......................................................................................... C-1
Objectives of HS488 ........................................................................................ C-1
Fast Transfer Rates ............................................................................ C-1
Compatibility with Existing IEEE 488.1 Devices............................. C-1
No Additional Software Overhead—Automatic HS488 Detection... C-1
No Changes to the IEEE 488.2 Standard........................................... C-1
No Added Cabling Restrictions beyond IEEE 488.1 ........................ C-2
IEEE 488.1 Requirements for Higher Speed Operation
(T1 Delay ≥350 ns)......................................................................................... C-2
Additional HS488 System Requirements ........................................................ C-2
Sequence of Events in Data Transfers ............................................................. C-2
Case 1: Talker and Listener are HS488 Capable ............................. C-4
Case 2: Talker Is HS488 Capable, But Listener Is Not HS488
Capable ............................................................................... C-5
Case 3: Talker Is Not HS488 Capable, But Listener Is HS488
Capable ............................................................................... C-6
System Configuration ...................................................................................... C-6
Appendix D
Multiline Interface Messages............................................................................. D-1

Contents
© National Instruments Corp. ix GPIB-140 User Manual
Appendix E
Customer Communication................................................................................. E-1
Glossary...................................................................................................................... G-1
Figures
Figure 1-1. Typical Extension System (Physical Configuration) ............................ 1-2
Figure 1-2. Typical Extension System (Logical Configuration) ............................. 1-2
Figure 2-1. DIP Switch Default Setting................................................................... 2-1
Figure 2-2. GPIB Extenders with Fiber Optic Cable Connected............................. 2-2
Figure 2-3. GPIB Extender Configured for Optional Self-Test............................... 2-3
Figure 3-1. Switch Setting for Buffered Data Transfer Mode................................. 3-2
Figure 3-2. Switch Setting for HS488 Mode (Enabled) .......................................... 3-3
Figure 3-3. Switch Setting for Immediate Parallel Poll Response (PPR) Mode ..... 3-5
Figure 4-1. GPIB Extender Block Diagram............................................................. 4-2
Figure A-1. GPIB Connector and the Signal Assignment ........................................ A-4
Figure A-2. Linear and Star System Configuration.................................................. A-5
Figure C-1. IEEE 488.1 and HS488 Transfers......................................................... C-3
Figure C-2. Talker and Listener are HS488 Capable ............................................... C-4
Figure C-3. Talker is HS488 Capable, But Listener Is Not HS488 Capable ........... C-5
Figure C-4. Talker is Not HS488 Capable, But Listener Is 488 Capable................. C-6
Tables
Table A-1. GPIB Handshake Lines......................................................................... A-3
Table A-2. GPIB Interface Management Lines....................................................... A-3
Table B-1. System Configuration ........................................................................... B-1
Table B-2. Performance Characteristics ................................................................. B-1
Table B-3. Operation Characteristics ...................................................................... B-2
Table B-4. Electrical Characteristics....................................................................... B-2
Table B-5. Environmental Characteristics .............................................................. B-2
Table B-6. Physical Characteristics ........................................................................ B-3

© National Instruments Corp. xi GPIB-140 User Manual
About This Manual
This manual describes how to install, configure, and operate the National Instruments
GPIB-140 or GPIB-140/2 bus extender.
Organization of This Manual
This manual is organized as follows:
• Chapter 1, Introduction, lists what your kit should contain and optional equipment
you can order, and gives a brief description of the GPIB extender.
• Chapter 2, Connection, describes how to connect the GPIB extender and verify that it
is operating properly.
• Chapter 3, Configuration and Operation, describes how to configure and operate a
GPIB-140 or GPIB-140/2 system.
• Chapter 4, Theory of Operation, describes how the GPIB extender circuitry operates.
• Appendix A, Operation of the GPIB, describes some basic concepts you should
understand to operate the GPIB. It also contains a description of the physical and
electrical characteristics and the configuration requirements of the GPIB.
• Appendix B, Specifications, lists the specifications of the GPIB extender.
• Appendix C, Introduction to HS488, describes HS488 and the sequence of events in
data transfers.
• Appendix D, Multiline Interface Messages, lists the multiline interface messages and
describes the mnemonics and messages that correspond to the interface functions.
• Appendix E, Customer Communication contains forms you can use to request help
from National Instruments or to comment on our products and manuals.
• The Glossary contains an alphabetical list and a description of terms used in this
manual, including abbreviations, acronyms, metric prefixes, mnemonics, and
symbols.

About This Manual
GPIB-140 User Manual xii © National Instruments Corp.
Conventions Used in This Manual
The following conventions are used in this manual.
bold Bold text denotes light-emitting diodes (LEDs).
italic Italic text denotes emphasis, a cross reference, or an
introduction to a key concept.
bold italic Bold italic text denotes a note, caution, or warning.
monospace Text in this font denotes text or characters that are to be
literally input from the keyboard, sections of code,
programming examples, and syntax examples. This font is
also used for the proper names of disk drives, directories,
programs, subprograms, subroutines, device names, functions,
variables, field names and filenames.
<> Angle brackets enclose the name of a key on the keyboard—
for example, <Shift>.
- A hyphen between two or more key names enclosed in angle
brackets denotes that you should simultaneously press the
named keys—for example, <Control-Alt-Delete>.
GPIB-140 GPIB-140 refers to a National Instruments GPIB extender that
extends the GPIB to a maximum distance of 1 km.
GPIB-140/2 GPIB-140/2 refers to a National Instruments GPIB extender
that extends the GPIB to a maximum distance of 2 km.
GPIB extender GPIB extender refers generically to either the GPIB-140 or the
GPIB-140/2 in cases where the material can apply to either
extender.
IEEE 488 and IEEE 488 and IEEE 488.2 refer to the ANSI/IEEE Standard
IEEE 488.2 488.1-1987 and the ANSI/IEEE Standard 488.2-1992,
respectively, which define the GPIB.
Abbreviations, acronyms, metric prefixes, mnemonics, symbols, and terms are listed in
the Glossary.

About This Manual
© National Instruments Corp. xiii GPIB-140 User Manual
Related Documentation
The following documents contain information that you may find helpful as you read this
manual.
• ANSI/IEEE Standard 488.1-1987, IEEE Standard Digital Interface for
Programmable Instrumentation
• ANSI/IEEE Standard 488.2-1992, IEEE Standard Codes, Formats,
Protocols, and Common Commands
Customer Communication
National Instruments wants to receive your comments on our products and manuals. We
are 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 you to complete. These forms are in
Appendix E, Customer Communication, at the end of this manual.

© National Instruments Corp. 1-1 GPIB-140 User Manual
Chapter 1
Introduction
This chapter lists what your kit should contain and optional equipment you can order, and
gives a brief description of the GPIB extender.
What Your Kit Should Contain
Your kit should contain the following components.
One of the following GPIB-140 or GPIB-140/2 bus extenders:
U.S. 100-120 VAC
Switzerland 220-240 VAC
Australia 220-240 VAC
Universal European 220-240 VAC
North American 220-240 VAC
U.K. 220-240 VAC
One of the following standard 3-wire power cables:
100-120 VAC
220-240 VAC
Optional Equipment
You can contact National Instruments to order any of the following equipment to go with
your kit.
•Transmission cable:
Type T7 fiber optic cable – up to 1 km (used with GPIB-140)
Type T8 fiber optic cable – up to 2 km (used with GPIB-140/2)
•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.

Introduction Chapter 1
GPIB-140 User Manual 1-2 © National Instruments Corp.
Hardware Description
The GPIB-140 and GPIB-140/2 are high-speed bus extenders that are used in pairs with
fiber optic cable to connect two separate GPIB (IEEE 488) bus systems in a functionally
transparent manner.
Although the two bus systems are physically separate, as shown in Figure 1-1, devices
logically appear to be located on the same bus, as shown in Figure 1-2.
POWER LINK ERROR
GPIB-140
FUSE
POWER LINK ERROR
GPIB-140
FUSE
Printer
(Listener) Computer
(System Controller,
Talker, and Listener)
GPIB-140 or 
GPIB-140/2 GPIB Cable
GPIB Cable
GPIB Cable
Multimeter
(Talker and Listener)
Signal Generator
(Listener) Unit Under Test
Fiber Optic Cable
GPIB-140 or 
GPIB-140/2
Figure 1-1. Typical Extension System (Physical Configuration)
Computer
(System Controller,
Talker, and Listener) Printer
(Listener)
GPIB
Multimeter
(Talker and Listener) Signal Generator (Listener)
Unit Under Test
Figure 1-2. Typical Extension System (Logical Configuration)

Chapter 1 Introduction
© National Instruments Corp. 1-3 GPIB-140 User Manual
The GPIB-140 and GPIB-140/2 bus extenders comply with the specifications of the
ANSI/IEEE Standard 488.1-1987 and the ANSI/IEEE Standard 488.2-1992, including the
Find Listeners protocol. With the GPIB extenders, you can overcome the following two
configuration restrictions imposed by ANSI/IEEE Standard 488.1-1987:
• 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.
• An electrical loading limit of 15 devices per contiguous bus.
Each GPIB-140 system extends the GPIB to a maximum distance of 1 km, and each
GPIB-140/2 system extends the GPIB to a maximum distance of 2 km. Both types of
systems extend the loading limit to 28 devices (including the GPIB extenders), without
sacrificing speed or performance. These point-to-point extension systems can be
connected in series for longer distances or in star patterns for additional loading.
The maximum data transfer rate over the extension is 2.2 Mbytes/s using HS488
protocol. The GPIB extender uses a buffered transfer technique with a serial extension
bus to get maximum performance while keeping the cabling cost at a minimum.
Furthermore, there is no speed degradation for transfers between devices on the same side
of the extension. The GPIB extender also has error-checking capabilities to ensure
successful data transmission over the fiber optic link.
Because the GPIB-140 and the GPIB-140/2 are functionally transparent extenders, the
same GPIB communications and control programs that work with an unextended system
can work with an extended system. The Parallel Poll Response (PPR) Modes section of
Chapter 3, Configuration and Operation, discusses one minor exception to this
transparency in conducting parallel polls.

© National Instruments Corp. 2-1 GPIB-140 User Manual
Chapter 2
Connection
This chapter describes how to connect the GPIB extender and verify that it is operating
properly.
Configure the DIP Switch
The 3-bit DIP switch selects the operation mode of the GPIB extender. Each GPIB
extender is shipped from the factory with the DIP switch set for unbuffered transfer
mode, latched parallel poll (PPR) response, and HS488 disabled mode. Figure 2-1 shows
the factory default setting of the DIP switch. Refer to Chapter 3, Configuration and
Operation, for information on setting the operating mode for your application.
OFF
ON
PARALLEL POLL IMMEDIATE
HS488 ENABLE
BUFFERED TRANSFER
Figure 2-1. DIP Switch Default Setting
Connect the Hardware
Step 1. Connect the Cables
Follow these steps to connect the cables to both GPIB extenders:
1. Make sure that the power switch on each GPIB extender is in the OFF position.
2. Connect the fiber optic cable to both GPIB extenders. The fiber optic cable has two
connectors on each end. Connect the connector marked T (transmit) to the connector
marked TRANS on the side panel of the GPIB extender. Connect the connector
marked R (receive) to the connector marked RCVR on the side panel of the GPIB
extender.

Connection Chapter 2
GPIB-140 User Manual 2-2 © National Instruments Corp.
a. Remove the caps on the connectors.
b. Align the notch on each cable connector to the slot on the side panel connector.
c. Firmly push in the cable connector and rotate clockwise until the sleeve locks on
to the side notch of the side panel connector.
GPIB-140 or
GPIB-140/2
GPIB-140 or
GPIB-140/2
Fiber Optic Cable
T
TRANS
RCVR
TRANS
RCVR
T
R
R
Figure 2-2. GPIB Extenders with Fiber Optic Cable Connected
3. Connect a GPIB cable to each GPIB extender and tighten the thumb screws on the
connector. Connect the other end to your GPIB system. Be sure to follow all
IEEE 488.1 cabling restrictions. Refer to the Configuration Requirements section of
Appendix A, Operation of the GPIB, for typical restrictions.
4. Plug the utility power cord of each GPIB extender into an AC outlet of the correct
voltage. Then plug the other end of the power cord into the GPIB-140.
Step 2. Switch On Your GPIB Extender
Power on each GPIB extender. The POWER LED should come on immediately. The
LINK LED comes on only when both extenders are on and the fiber optic cable has been
properly connected between them.
If the POWER LED does not come on immediately, check to make sure that power is
supplied to the extender.

Chapter 2 Connection
© National Instruments Corp. 2-3 GPIB-140 User Manual
Optional Self-Test
Each GPIB extender is equipped with a self-test that determines if the GPIB extender
receivers, transmitters, and packet transmission and reception circuitry are operating
correctly.
Complete the following steps to run the self-test with the fiber optic cable.
1. Turn the GPIB extender power switch to the OFF position.
2. Disconnect the fiber optic cable from the GPIB extender.
3. Turn the GPIB extender power switch to the ON position.
At this point, the POWER LED lights up, indicating that power is supplied to the
extender. The LINK LED remains off.
4. Connect the connector marked T (transmit) on one end of the fiber optic cable to the
connector marked TRANS on the side panel of the GPIB extender.
5. Connect the connector marked R (receive) on the opposite end of the fiber optic
cable to the connector marked RCVR on the side panel of the GPIB extender.
GPIB-140 or
GPIB-140/2
Fiber Optic 
Cable
TRANS
RCVR
R
R
T
T
Figure 2-3. GPIB Extender Configured for Optional Self-Test
At this point, the LINK LED should light up, indicating that the cable has been
connected. The ERROR LED should remain off to show that the GPIB extender is
operating properly.

© National Instruments Corp. 3-1 GPIB-140 User Manual
Chapter 3
Configuration and Operation
This chapter describes how to configure and operate a GPIB-140 or GPIB-140/2 system.
Data Transfer Modes
The GPIB extender has two data transfer modes: unbuffered mode and buffered mode.
The data transfer mode determines how data is transmitted across the extension.
Unbuffered Mode
In unbuffered mode, each data byte is transmitted using the GPIB double-interlocked
handshaking protocol. For long data streams, transfers using unbuffered mode are slower
than transfers using buffered mode. However, the GPIB extension is transparent in
unbuffered mode.
Buffered Mode
In buffered mode, the GPIB extenders use FIFO (first-in-first-out) buffers to buffer data
between the remote and local units. For long data streams, you can obtain a much higher
data throughput with buffered mode than with unbuffered mode.
Consider the following situation: a GPIB device on the local side of the extension is
addressed to talk, another device on the remote side is addressed to listen. When the
talking device sources data bytes, the GPIB extenders accept the data bytes and store
them in a FIFO buffer. At the same time, the GPIB extenders read data from the FIFO
buffer and source data bytes to the Listener. Whenever the FIFO buffer contains data, the
number of bytes sourced by the Talker differs from the number of bytes accepted by the
Listener. Because of this behavior, a few applications may not operate properly in
buffered mode.
GPIB command bytes are not stored in the FIFO buffers; they are transmitted using the
GPIB double-interlocked handshaking protocol.
Setting the Data Transfer Mode
The two GPIB extenders in the extension system do not need to be set to the same data
transfer mode. Use switch position 1 on the DIP switch of each GPIB extender to set the
data transfer mode. Slide the switch down to the ON position to set buffered mode; slide
the switch up to set unbuffered mode. See Figure 3-1.