Hameg HO88, Manual

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Operation of test instruments using the IEEE-488 bus
The IEEE-488 bus, also known as the General Purpose Interface Bus (GPIB), is a
standardized interface system through which interconnected test instruments (e.g.
multimeters, power supplies, etc.) or peripherals (e.g. printers, plotters, etc.) and a
controller (which can be a computer) can communicate. There are two types of data
which can be transferred over the bus: socalled interface messages and device-
dependent messages.
The Controller can instruct a device to receive data or transmit data. Devices able to
receive data are designated as Listeners. Devices that can transmit data are called
Talkers. A given device can be a Listener, a Talker, or both. The designations „Talker“
and „Listener“ are defined in the IEEE-488 standard, and will be used here as well to
indicate the different device states.
History of the IEEE-488 bus
Originally designed by Hewlett-Packard as the Hewlett-Packard Interface-Bus (HP-IB)
and marketed from 1965 on for interconnection and control of programmable instru-
ments, the HPIB standard was adopted in 1975 by the IEEE committee in the United
States as the IEEE-488 standard, being officially labelled the General Purpose Interface
Bus, and in 1977 in Europe as the IEC 625-1 standard. The European and American
standards use different connectors:
• IEC 625-1: 25-pin connector
• IEEE-488: 24-pin connector
However, in spite of their different names and choice of connector types, the European
IEC 625-1 bus, the American IEEE-488 or GPIB bus, and the HP-IB bus are fully com-
patible with one another as regards electrical levels and connections, and where
programming is concerned. Adapters are available for mating IEEE-488 connectors
with IEC-625 connectors. In the following, the term IEEE-488 bus will be used, since
the 24-pin connector specified by the American standard is used by HAMEG’s test
instruments .
Capabilities of the IEEE-488 bus
For operation of a number of devices connected to a bus, each device is assigned a
unique address called the primary address between 0 and 30. On HAMEG equipment,
the primary address is selected using DIP switches. The System Controller uses these
primary addresses to route information and commands over the bus to the proper
instrument or device. In order to instruct a device to begin sending data, the System
Controller addresses it as a Talker. To enable an instrument’s receiver function, it is
addressed as a Listener.
Not every instrument has both Talker and Listener functions, like multimeters, for
instance. Some devices can only act as Listeners (e.g. printers), and some only have
Talker capabilities (such as a voltmeter that only sends measurements). Only one
device at a time on an IEEE-488 bus may be enabled as a Talker, while any number can
be Listeners at once. If two or more computers are connected to a bus, only one of
them may act as the System Controller at any given time. It then has active controller
status, and is referred to as the Controller-in-Charge (CIC). It can also address the
other computers and instruct them to send or receive data, or transfer active control
to another computer and become an idle controller, i.e. it can then be instructed to
send or receive data as a Talker or Listener by the new CIC.
It is also possible for data to be sent over the bus even without the mediation of a
controller. This works if the transmitting device has „Talk-only“ status, and if the
receiving device (or devices) has „ Listen-only“ status. Data may then be passed from
the former to the latter without their being addressed first.
Physical configuration of the IEEE-488 bus
The IEEE-488 bus uses 16 signal lines, 7 ground return lines and one shield drain line.
Both of the valid standards - IEC- 625 of the International Electrotechnical Commission