Data Acquisition

88.1 IntroductionThe communications standard now known as the GPIB (general purpose interface bus),was originally developed by Hewlett Packard in 1965 (when it was called the HewlettPackard interface bus – HPIB), to connect and control their programmable testinstruments. Due to its speed, flexibility, and usefulness in connecting programmableinstruments to computers, it gained widespread acceptance, and was adopted by differentmanufacturers for their own programmable instrumentation.It soon became clear that with the introduction of digital controllers and programmableinstruments from different manufacturers, a standard high-speed data communicationsinterface was required so that instruments from different manufacturers couldcommunicate with each other. Following a study by a committee of the IEEE, theinterface was published in 1975 as the IEEE Standard 488-1975. The standard wasupdated, with minor revisions, in 1978, to coincide with the international issue of thestandard as IEC-625, the latter designation being more commonly used in Europe. Thecurrent version of the same standard is referred to as the IEEE Standard 488.1-1987. Thisstandard greatly simplified the connection of programmable instrumentation by definingthe mechanical, electrical and hardware protocol specification of the communicationsinterface. For the first time, instruments from different manufacturers were connected bya standard cable. However, the standard did not address the data formats, status reporting,message exchange protocol, common configuration commands, or device-specific commands,all of which were subsequently implemented differently by different equipmentmanufacturers.In 1987, the IEEE Standard 488.2 was introduced to define data formats, statusreporting, controller functionality, error handling, and common commands. IEEE 488.2concentrates on software protocol issues and maintains full compatibility with devicesthat comply with the hardware-oriented IEEE 488.1 standard.EOI. In 1990, a group of instrument manufacturers announced a further extension ofthe standard, known as SCPI (standard commands for programmable instruments), whichuses IEEE 488.2 as a basis and defines a common command set that can be used for