GPIB was formalized in 1975 as IEEE-488 -- Later renamed IEEE-488.1. A 1978 Update is primarily grammatical and does not include major revisions. A 1990 Supplement -- IEEE-488.2 -- defines minimum device capabilities, standard codes and formats, standard messaging protocols and standard message reporting. IEEE-488.2 includes a document called Standard Commands for Programmable Instrumentation (SCPI) which defines classes of instruments and the minimum command set each class must recognize. IEEE488.2 is backward compatible with IEEE-481.1, but the presence of IEEE-488.1 instruments on the bus may limit the capabilities of IEEE-488.2 instruments.
Computers interface to GPIB using GPIB controllers. Multiple controllers on one bus are permitted, but only one can control the bus at any time. 16 addresses are available to controllers and devices on the bus. (But references are inconsistent about whether 14 or 15 instruments are allowed). Multiple separate buses can be driven by one computer using multiple controllers. Usage of each bus is ultimately managed by a CIC -- Controller in Charge.
The physical GPIB is an 8 bit parallel bus operating at speeds to 1MByte/sec. Faster variants (e.g 8MByte/sec) have been deployed. It is unclear whether the GPIB specification has ever been changed to permit this.
Return To Index Copyright 1994-2002 by Donald Kenney.