© National Instruments Corp.
D-1
GPIB-232CT User Manual
Appendix D
Operation of the GPIB
The GPIB is a link, 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 250 kbytes/sec to 1 Mbytes/sec, 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
The GPIB carries device-dependent messages and interface messages.
•
Device-dependent messages, often called
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
tasks as initializing the bus, addressing and unaddressing devices, and
setting device modes for remote or local programming.
The term
command
as used here should not be confused with some device
instructions that can also be called commands. Such device-specific
instructions are actually data messages.
Talkers, Listeners, and Controllers
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.
