National Instruments GPIB-120A Appendix A Operation of the GPIB

Appendix AOperation of the GPIB

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

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.

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.