A-3
A1
A
Figure A-1 IEEE 488 Bus
Two types of messages are transferred over the bus:
Interface messages - for bus management
Device-dependent messages - for device control and data
transfer
Devices connected to the bus may act as talkers, listeners, controllers,
or combinations of the three functions, depending upon their internal
capability. The system controller is a controller that becomes active
at power turn-on. It is the Bus manager and the initial controller-in-
charge.
A controller can send interface messages to manage the other
devices, address devices to talk or listen and command specific
actions within devices.
A talker sends device dependent messages, i.e., data, status.
A listener accepts interface messages, bus commands and device-
dependent messages, i.e., setup commands, data.
Bus systems can be as simple as two devices; one a talker always
sending data to a second device which listens to the data. Larger
systems can have one or more controllers and many devices (the IEEE
488 driver specifications limit the total number of units on one bus
DEVICE B
Able to Talk
and to Listen
e.g. DVM
DEVICE C
Able to Listen
e.g. Signal
generator
IFC
ATN
SRQ
REN
EOI
DAV
NRFD
NDAC
DIO1-8
Bus Control
Lines
Byte Transfer
Control Lines
Data Bus
(8 Lines)
DEVICE A
Able to Talk,
Listen and Control
e.g. Computer
