November 1985
Appendix D
Operation of the GPIB
National Instruments
The GPIB is a link, or bus, or interface system through which
interconnected electronic devices communicate. Hewlett-Packard
invented the GPIB, which they call the HP-IB, to connect and
control programmable instruments manufactured by them. Because
of its high system data rate ceilings of from 250K bytes to
byte
per second, the GPIB quickly became popular in other applications
such as intercomputer communication and peripheral control. It was
later accepted as the industry standard IEEE-488. The versatility of
the system prompted the name General Purpose Interface Bus.
Types of Messages
Devices on the GPIB communicate by passing messages through the
interface system. There are two types of messages:
* Device-dependent messages, often
data or data
messages, contain device-specific information such as
programming instructions, measurement results, machine
status, and data files.
* Interface messages manage the bus itself. They are usually
called commands or command messages. Interface messages
perform such functions as initializing the bus, addressing and
unaddressing devices, and setting devices for remote or local
programming.
The term command as used here should not be confused with
some device instructions which are also call commands.
Such device-specific instructions are actually data messages.
Talkers, Listeners, and Controllers
There are three types of GPIB communicators. A Talker sends data
messages to one or more Listeners. The Controller manages the flow
of information on the GPIB by sending commands to all devices.
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APPENDIX D OPERATION OF THE GPIB
