Appendix A Operation Of The Gpib; History Of The Gpib; Gpib Operation; Types Of Messages - National Instruments GPIB-120A User Manual

Appendix A
Operation of the GPIB
This appendix contains a brief history of the GPIB and describes the operation of the GPIB.

History of the GPIB

The original GPIB was designed by Hewlett-Packard (where it is called the HP-IB) to connect
and control programmable instruments manufactured by Hewlett-Packard. Because of its high
data transfer rates of up to 1 Mbytes/s, the GPIB quickly gained popularity 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.
National Instruments expanded the use of the GPIB among users of computers manufactured
by companies other than Hewlett-Packard. National Instruments specializes both in high-
performance, high-speed hardware interfaces and in comprehensive, full-function software that
helps users bridge the gap between their knowledge of instruments and computer peripherals and
of the GPIB itself.

GPIB Operation

The GPIB is a link, or interface system, through which interconnected electronic devices
communicate. Communication among interconnected GPIB devices is achieved by passing
messages through the interface system.

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 which can
also be called commands. Such device-specific instructions are actually data messages.
© National Instruments Corporation A-1 GPIB-120A User Manual