IEEE-488 Bus Overview D-3
There are two categories of controllers: system controller and basic controller. Both are able
to control other instruments, but only the system controller has the absolute authority in the
system. In a system with more than one controller, only one controller may be active at any
given time. Certain protocol is used to pass control from one controller to another.
The IEEE-488 bus is limited to 15 devices, including the controller. Thus, any number of
talkers and listeners up to that limit may be present on the bus at one time. Although several
devices may be commanded to listen simultaneously, the bus can have only one active talker, or
communications would be scrambled.
DEVICE 1
ABLE TO
TALK, LISTEN
AND CONTROL
(COMPUTER)
DEVICE 2
ABLE TO
TALK AND
LISTEN
(6430)
DEVICE 3
ONLY ABLE
TO LISTEN
(PRINTER)
DEVICE 4
ONLY ABLE
TO TALK
DAV
NRFD
NDAC
IFC
ATN
SRQ
REN
EOI
DATA BUS
DATA BYTE
TRANSFER
CONTROL
GENERAL
INTERFACE
MANAGEMENT
DIO 1–8 DATA
(8 LINES)
HANDSHAKE
BUS
MANAGEMENT
TO OTHER DEVICES
igure D-1
EEE-488 bus
configuration
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