Characteristics
IEEE-488 is an 8-bit, electrically parallel bus. The bus employs 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).
The standard allows up to 15 devices to share a single physical bus of up to 20 meters 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.
Read more about this topic: IEEE-488