© National Instruments Corporation 1-1 GPIB-120A User Manual
Chapter 1IntroductionThis 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.
Printer
(Listener) Multimeter
(Talker and
Listener)
Signal Generator
(Listener)
Computer
(Controller,
Talker, and Listener)
Unit Under Test
GPIB-120AGPIB #1 GPIB #2
Figure 1-1. Typical GPIB-120A Extension System (Physical Configuration)