Bus Overview - Keithley 6512 Instruction Manual

A.1 Introduction
This appendix provides an overview of the IEEE-488 bus.
For detailed Model 6512 programming information, refer to
Section 3.
A.2 Bus description
The IEEE-488 bus, which is also frequently referred to as the
GPIB (General Purpose Interface Bus), was designed as a
parallel transfer medium to optimize data transfer without
using an excessive number of bus lines. In keeping with this
goal, the bus has only eight data lines that are used for both
data and many commands. Five bus management lines and
three handshake lines round out the complement of bus sig-
nal lines.
A typical configuration for controlled operation is shown in
Figure A-1. The typical system will have at least one control-
ler and one or more devices to which commands are given
and, in most cases, from which data is received. Generally,
there are three categories that describe device operation: con-
troller, talker, and listener.
The controller does what its name implies: it controls other
devices on the bus. A talker sends data (usually to the con-
troller), while a listener receives data. Depending on the in-
strument, a particular device may be a talker only, a listener
only, or both a talker and a listener.
IEEE-488 Bus Overview
Figure A-1
IEEE-488 bus configuration
TO OTHER DEVICES
DEVICE 1
ABLE TO
TALK, LISTEN
AND CONTROL
(COMPUTER)
DEVICE 2
ABLE TO
TALK AND
LISTEN
(6512)
DEVICE 3
ONLY ABLE
TO LISTEN
(PRINTER)
DEVICE 4
ONLY ABLE
TO TALK
(DMM)
A
DATA BUS
DATA BYTE
TRANSFER
CONTROL
GENERAL
INTERFACE
MANAGEMENT
DI01....8 DATA (8 LINES
DAV
HANDSHAKE
NRFD
NDAC
IFC
ATN
SRQ
BUS
REN MANAGEMENT
EOI
A-1