4-1. INTRODUCTION
The GPIB (general purpose interface bus) is an
instrumentation data bus with standards originally
adopted by the IEEE (Institute of Electrical and
Electronic Engineering) in 1975 and given the IEEE-
488 designation. In November 1987 the IEEE-488
document was revised, primarily for editorial classi-
fication and addendum, and the new document was
identified as IEEE-488-1978.
This document has been the standard for gen-
eral-purpose instrumentation bus (GPIB) which has
been adopted by worldwide instrumentation manu-
facturers. In June 1987 the IEEE approved a new
standard for programmable instruments and devices
IEEE Standard 488.2-1987 Codes, Formats, Proto-
cols, and Common Commands. The original docu-
ment, IEEE-488-1978, was re-titled IEEE-488.1.
The IEEE-488.2 standard was designed to make
the interface system easier to use by requiring that
all devices provide certain capabilities such as talk
and listen, respond to device clear commands, and
be capable of service requests. Other functions such
as parallel poll are left optional with the instrument
manufacturer. The Model 8020 complies with all of
the mandatory IEEE-488.1 and IEEE-488.2 require-
ments. Some of the issues which IEEE-488.2 Ad-
dresses are:
1. A required minimum set of IEEE-488.1 capa-
bilities.
2. Reliable transfer of messages between a talker
and listener and precise syntax in those messages.
3. A set of commands which would be useful in
all instruments.
4. Common serial poll status reporting.
5. Synchronization programming with instrument
functions.
This section contains general bus information as
well as detailed programming information and is
divided as follows:
1. General introductory information pertaining to
the IEEE-488 bus may be found primarily in para-
graphs 4-2 through 4-5.
2. Information necessary to connect the Model
8020 to the bus and to change the bus address is
contained in paragraphs 4-6 and 4-7.
3. Programming of the instrument with general
bus command is covered in paragraph 4-8.
4. Device-dependent command programming is
described in detail in paragraph 4-10. The commands
outlined in this section can be considered to be the
most important since they control virtually all instru-
ment functions.
5. Additional information pertaining to device status
reporting and error messages can be found in para-
graphs 4-13 and 4-15.
4-2. BUS DESCRIPTION
The IEEE-488 bus was designed as a parallel data
transfer medium to optimize data transfer without
using as excessive number of bus lines. In keeping
with this goal, the bus has only eight data lines
which are used for both data and most commands.
Five bus management lines and three handshake
lines round out the complement of signal lines. Since
the bus is of parallel design, all devices connected
to the bus have the same information available
simultaneously. Exactly what is done with the infor-
mation by each device depends on many factors,
including device capabilities.
A typical bus configuration for remote controlled
operation is shown in Figure 4-1. The typical system
will have one controller and one or more instruments
to which commands are given and from which data
is received. There are three categories that describe
device operation. These include: controller; talker;
listener.
The controller controls other devices on the bus.
A talker sends data, while a listener receives data.
an instrument, may be a talker only, a listener only,
or both a talker and listener.
SECTION 4
GPIB OPERATION
Model 8020 IEEE-488.2 Operation
Page 4-1
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