©
National Instruments Corporation
A-1
GPIB-120B User Manual
A
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.
