General Purpose Interface Bus (GPIB) or Hewlett-Packard Interface Bus (HP-IB) is a short-range digital communications 8-bit parallel multi-master interface bus specification originally developed by Hewlett-Packard and standardized in IEEE 488.1-2003. It subsequently became the subject of several standards. Although the bus was originally created to connect together automated test equipment, it also had some success as a peripheral bus for early microcomputers, notably the Commodore PET. Newer standards have largely replaced IEEE 488 for computer use, but it is still used by test equipment.
History In the 1960s, Hewlett-Packard (HP) manufactured various automated test and measurement instruments, such as digital multimeters and logic analyzers. They developed the HP Interface Bus (HP-IB) to enable easier interconnection between instruments and controllers (computers and other instruments). This part of HP was later (c. 1999) spun off as Agilent Technologies, and in 2014 Agilent's test and measurement division was spun off as Keysight Technologies. The bus was relatively easy to implement using the technology at the time, using a simple parallel bus and several individual control lines. For example, the HP 59501 Power Supply Programmer and HP 59306A Relay Actuator were both relatively simple HP-IB peripherals implemented in TTL, without the need for a microprocessor. HP licensed the HP-IB patents for a nominal fee to other manufacturers. It became known as the General Purpose Interface Bus (GPIB), and became a de facto standard for automated and industrial instrument control. As GPIB became popular, it was formalized by various standards organizations. In 1975, the IEEE standardized the bus as Standard Digital Interface for Programmable Instrumentation, IEEE 488; it was revised in 1978 (producing IEEE 488-1978). The standard was revised in 1987, and redesignated as IEEE 488.1 (IEEE 488.1-1987). These standards formalized the mechanical, electrical, and basic protocol parameters of GPIB, but said nothing about the format of commands or data. In 1987, IEEE introduced Standard Codes, Formats, Protocols, and Common Commands, IEEE 488.2. It was revised in 1992. IEEE 488.2 provided for basic syntax and format conventions, as well as device-independent commands, data structures, error protocols, and the like. IEEE 488.2 built on IEEE 488.1 without superseding it; equipment can conform to IEEE 488.1 without following IEEE 488.2. While IEEE 488.1 defined the hardware and IEEE 488.2 defined the protocol, there was still no standard for instrument-specific commands. Commands to control the same class of instrument, e.g., multimeters, varied between manufacturers and even models. The United States Air Force, and later Hewlett-Packard, recognized this as a problem. In 1989, HP developed their Test Measurement Language (TML) or Test and Measurement Systems Language (TMSL) which was the forerunner to Standard Commands for Programmable Instrumentation (SCPI), introduced as an industry standard in 1990. SCPI added standard generic commands, and a series of instrument classes with corresponding class-specific commands. SCPI mandated the IEEE 488.2 syntax, but allowed other (non-IEEE 488.1) physical transports. The IEC developed their own standards in parallel with the IEEE, with IEC 60625-1 and IEC 60625-2 (IEC 625), later replaced by IEC 60488-2. National Instruments introduced a backward-compatible extension to IEEE 488.1, originally known as HS-488. It increased the maximum data rate to 8 Mbyte/s, although the rate decreases as more devices are connected to the bus. This was incorporated into the standard in 2003 (IEEE 488.1-2003), over HP's objections. In 2004, the IEEE and IEC combined their respective standards into a "Dual Logo" IEEE/IEC standard IEC 60488-1, Standard for Higher Performance Protocol for the Standard Digital Interface for Programmable Instrumentation - Part 1: General, replaces IEEE 488.1/IEC 60625-1, and IEC 60488-2,Part 2: Codes, Formats, Protocols and Common Commands, replaces IEEE 488.2/IEC 60625-2. The Linux kernel got support for GPIB with version 6.19, after Greg Kroah-Hartman merged the code.
Characteristics IEEE 488 is an 8-bit, electrically parallel bus which employs sixteen signal lines — eight used for bi-directional data transfer, three for handshake, and five for bus management — plus eight ground return lines. The bus supports 31 five-bit primary device addresses numbered from 0 to 30, allocating a unique address to each device on the bus. The standard allows up to 15 devices to share a single physical bus of up to 20 metres (66 ft) total cable length. The physical topology can be linear or star (forked). Active extenders allow longer buses, with up to 31 devices theoretically possible on a logical bus. Control and data transfer functions are logically separated; a controller can address one device as a "talker" and one or more devices as "listeners" without having to participate in the data transfer. It is possible for multiple controllers to share the same bus, but only one can be the "Controller In Charge" at a time. In the original protocol, transfers use an interlocked, three-wire ready–valid–accepted handshake. The maximum data rate is about one megabyte per second. The later HS-488 extension relaxes the handshake requirements, allowing up to 8 Mbyte/s. The slowest participating device determines the speed of the bus.
Connectors
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