From Academic Kids

The Hewlett-Packard Instrument Bus (HP-IB), is a short-range digital communications cable standard developed by Hewlett-Packard (HP) in the 1970s for connecting electronic test and measurement devices (e.g. digital multimeters and logic analyzers) to control devices such as computers. Other manufacturers copied HP-IB, calling their implementation the General Purpose Instrumentation Bus (GPIB). In 1978 the bus was standardized by the Institute of Electrical and Electronics Engineers as the IEEE Standard Digital Interface for Programmable Instrumentation, IEEE-488-1978 (now 488.1).

IEEE-488 allows up to 15 intelligent devices to share a single bus by daisy-chaining, with the slowest device participating in the control and data transfer handshakes to determine the speed of the transaction. The maximum data rate is about one megabyte per second. Paraphrasing the 1989 HP Test & Measurement Catalog: HP-IB has a party-line structure wherein all devices on the bus are connected in parallel. The 16 signal lines within the passive interconnecting HP-IB cable are grouped into three clusters according to their functions: Data Bus, Data Byte Transfer Control Bus, and General Interface Management Bus.

In addition to the IEEE several other standards committees have adopted HP-IB. The American National Standards Institute's corresponding standard is known as ANSI Standard MC 1.1, and the International Electrotechnical Commission has its IEC Publication 625-1. In June 1987 the IEEE approved a revised standard for programmable instruments called IEEE-488-1987 (now 488.2): Codes, Formats, Protocols, and Common Commands. Hewlett-Packard's HP-IB implementation, however, still concurs to the aforementioned IEEE-488.1 version.

Not specifically planned for at the outset by HP-IB's designers was the use of IEEE-488 as a standard peripheral interface by general-purpose computers. Such applications of the bus were made by the Commodore PET/CBM range of educational/home/personal computers, whose disk drives, printers, modems, etc, were daisy-chain connected to the (host) computer, 'talking' and 'listening' on the designated bus lines to perform their jobs. All of Commodore's post-PET/CBM 8-bit machines, from the VIC-20 to the C128, utilized a proprietary 'serial IEEE-488' for peripherals, with round DIN connectors instead of the heavy-duty HP-IB plugs.

Tektronix's computer family (the 405x series) also used IEEE-488 as a peripheral interface. Hewlett-Packard's business computer group also used the HP-IB bus to control computer peripheral devices such as tape drives, printers etc. HP used standard HP-IB hardware and a protocol called 'CS-80' in their business computers. Additionally, some of HP's advanced pocket calculators/computers of the 1980s, such as the HP-41 and HP-71 series, could work with various instrumentation via an optional HB-IB interface. The interface would connect to the calculator via an HP-IL module (Hewlett-Packard Instrument Loop, also optional).

External links

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.



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