4.3.3 Parallel standards
The standard interface most commonly used for parallel communications
is IEEE-488. This was originally developed by Hewlett Packard to link
their computers and instruments and was known as the Hewlett Packard
Instrumentation Bus. It is now often termed the General Purpose
Instrument Bus. This bus provides a means of making interconnections so
that parallel data communications can take place between listeners, talkers
and controllers. Listeners are devices that accept data from the bus, talkers
place data, on request, on the bus and controllers manage the flow of data
on the bus and provide processing facilities. There is a total of 24 lines, of
which eight bi-directional lines are used to carry data and commands
between the various devices connected to the bus, five lines are used for
control and status signals, three are used for handshaking between devices
and eight are ground return lines (Figure 4.24).