IEEE-488 or GPIB explaination

Introduction to IEEE-488 or GPIB

IEEE-488 stands to the Institute of Electrical and Electronics Engineers (IEEE) Standard number 488. IEEE-488 is also known as GPIB (General purpose interface bus). IEEE 488 was created as HP-IB (Hewlett-Packard Interface Bus).

IEEE 488 is an 8-bit, electrically parallel bus. The bus has sixteen signal lines — eight used for bi-directional data transfer, three for handshake, and five for bus management — plus eight ground return lines.

Every device on the bus has a unique 5-bit primary address, in the range from 0 to 30 (31 total possible addresses), no two instruments on the same bus should have the same address. The addresses on the instruments can be changed and this may typically be done via the front panel, or by using switches often located on the rear panel.

The standard allows up to 15 devices to share a single physical bus of up to 20 meters total cable length.

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.

In IEEE-488, the equipment on the bus falls into three categories, although items can fulfil more than one function:

Controller:  The controller controls the operation of the bus. It is usually a computer and it determines 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. It is possible for multiple controllers to share the same bus; but only one can act as a controller at any particular time.

Listener:   A listener is connected to the bus that accepts instructions from the bus. An example of a listener is an item such as a printer that only accepts data from the bus

Talker:   This is on the bus that issues instructions / data onto the bus.