The Hp-Ib Interface; General Structure - HP 9000 Series 300 Tutorials Manual

The HP-IB Interface
The Hewlett-Packard Interface Bus (HP-IB) was developed at HP as the
solution to an expanding need for a universal interfacing technique that
could be readily adapted to a wide variety of electronic instruments. It was
later expanded to include high-speed disc drives and other high-performance
computer peripherals. The HP-IB architecture was subsequently proposed
to and accepted by the Institute of Electrical and Electronic Engineers
(IEEE) and is now widely used throughout the electronic industry. HP-IB is
compatible with IEEE standard 488-1978. The number of devices that can
be connected to a given HP-IB interface depends on the loading factor of
each device, but in general up to 15 devices (including the interface) can be
connected together while still maintaining electrical, mechanical, and timing
compatibility requirements on the bus.
General Structure
IEEE Standard 488-1978 defines a set of communication rules called "bus
protocol" that governs data and control operations on the bus. The defined
protocol is necessary in order to ensure orderly information traffic over the bus.
Each device (peripheral or computer interface) that is connected to the HP-IB
can function in one or more of the following roles:
System Controller Master controller of the HP-IB. The computer interface
is usually the bus controller when all peripheral devices
on the bus are slaves to the system computer. However,
any other device can become the active controller if it is
equipped to act as a controller and control is passed to
it by the System Controller. The System Controller is
always the active bus controller at power-up.
Active Controller Current controller of the HP-IB. At power-up or
whenever IFC (Inter Face Clear) is asserted by the System
Controller, the System Controller is the active controller.
Under certain conditions, the System controller may pass
control to another device that is capable of managing the
bus in which case that device becomes the new active
controller. The active controller can then pass control to
Interfacing Concepts 1-9