GPIB / IEEE 488 Basics Tutorial

- an overview or tutorial describing the basics of GPIB - General Purpose Interface Bus - or IEEE 488 bus, how it operates, how the GPIB interface can be used and tips for successful, trouble free operation.

GPIB tutorial includes:

    •  GPIB / IEEE 488 tutorial & basics
    •  GPIB / IEEE 488 operation
    •  Using GPIB / IEEE 488
    •  GPIB cables and connectors

The GPIB or General Purpose Interface Bus or IEEE 488 bus is still one of the more popular and versatile interface standards available today. GPIB is widely used for enabling electronics test equipment to be controlled remotely, although it us also used in a many other applications including data acquisition. Today most bench electronics test equipment has either a GPIB option or are fitted with it as standard.

Originally GPIB was named the HP-IB (Hewlett Packard Interface Bus) when it was first introduced, it has gained a number of other names over the years. GPIB has been adopted by a number of major institutions that have given it their numbers. The Institute of Electrical and Electronic Engineers in the U.S.A. have given it their specification number 488, and as a result it is sometimes referred to as the IEEE 488 bus or IEEE488 bus. Other organisations have also adopted it. The American National Standards Institute as has the European IEC. Despite the proliferation of names and numbers for it, the specifications are all virtually the same and can be used interchangeably. However of all the names GPIB is the most common, followed by IEEE 488 bus.

Basic GPIB concept

The GPIB or IEEE 488 bus is a very flexible system, allowing data to flow between any of the instruments on the bus, at a speed suitable for the slowest active instrument. Up to fifteen instruments may be connected together with a maximum bus length not exceeding 20 m. There must also be no more than 2 m between any two instruments. It is possible to purchase GPIB cards to incorporate into computers that do not have the interface fitted. As GPIB cards are relatively cheap, this makes the inclusion of a GPIB card into the system a very cost effect method of installing it.

The connector used for the IEEE 488 bus is standardised as a 24-way Amphenol 57 series type. This provides an ideal physical interface for the standard. The IEEE 488 or GPIB connector is very similar in format to those that were used for parallel printer ports on PCs although the type used for the GPIB has the advantage it has been changed so that several connectors can be piggy-backed. This helps the physical setting up of the bus and prevents complications with special connection boxes or star points.

Within IEEE 488, the equipment on the bus falls into three categories. There are controllers, talkers and listeners, although any piece of equipment may be able to fulfil more than one function. For example a voltmeter which is controlled over the bus will act as a listener when it is being set up, and then when it is returning the data, it will act as a talker. As such it is known as a talker / listener. A printer will only be able to listen, as it will only need to accept data to print out on the paper.

The IEEE 488 or GPIB controller has the most crucial role on the bus. It is usually a computer and signals that instruments are to perform the various functions. The GPIB controller also ensures that no conflicts occur on the bus. If two talkers tried to talk at the same time then data would become corrupted and the operation of the whole system would be seriously impaired. Often GPIB cards can be used in a variety of roles, but these GPIB cards are most often used as controllers as they tend to reside in the controlling computer. Most test instruments that might be intended for use with the GBIP interface would have this fitted as standard and would therefore not require and additional GPIB card.

GPIB / IEEE 488 today

The GPIB has been available for over thirty years, but despite its age, it is still a valuable tool that is widely used throughout the industry. Most bench instruments have GPIB fitted as standard or as an option making it easy to use test equipment in a variety of applications apart from being dedicated to use in an ATE test stack. Additionally GPIB or IEEE 488 is used in a wide number of other applications including data acquisition.

Although computers tend not to have GPIB interfaces fitted as standard today, a GPIB card may be bought and installed. In view of its flexibility and convenience and it is likely to remain in widespread use for many years to come.

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