Figure 1-2. Typical Gpib-120A Extension System (Logical Configuration) - National Instruments GPIB-120A User Manual

Introduction
Computer
(Controller,
Talker, and 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
GPIB
Printer Multimeter
(Listener) (Talker and
Listener)
1-2
Signal Generator
(Listener)
Unit Under Test
© National Instruments Corporation
Chapter 1