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GPIB Basics
This appendix describes the basic concepts of GPIB, including its physical and electrical
characteristics, and configuration requirements.
The ANSI/IEEE Standard 488.1-1987, also known as General Purpose Interface Bus (GPIB),
describes a standard interface for communication between instruments and controllers from
various vendors. It contains information about electrical, mechanical, and functional
specifications. GPIB is a digital, 8-bit parallel communications interface with data transfer rates
of 1 Mbyte/s and higher, using a three-wire handshake. The bus supports one System Controller,
usually a computer, and up to 14 additional instruments. The ANSI/IEEE Standard 488.2-1992
extends IEEE 488.1 by defining a bus communication protocol, a common set of data codes and
formats, and a generic set of common device commands.
Types of Messages
Interconnected GPIB devices communicate by passing messages through the interface system,
including device-dependent messages and interface messages.
•
Device-dependent messages, also called
data
or
data messages
, contain device-specific
information, such as programming instructions, measurement results, machine status, and
data files.
•
Interface messages, also called
commands
or
command messages
, manage the bus itself.
Interface messages initialize the bus, address and unaddress devices, and set device modes
for remote or local programming.
The term
command
as used here does not refer to device instructions, which are also called
commands. Those device-specific instructions are data messages.
Talkers, Listeners, and Controllers
GPIB devices can be Talkers, Listeners, or Controllers. A Talker sends out data messages.
Listeners receive data messages. The Controller, usually a computer, manages the flow of
information on the bus. It defines the communication links and sends GPIB commands to
devices.
Some devices can play more than one role. A digital voltmeter, for example, can be a Talker and
a Listener. If your system has a National Instruments GPIB interface and software installed, it
can function as a Talker, Listener, and Controller.
