IEEE-488 Bus Overview
C-2
A device is placed in the talk or listen state by sending an
appropriate talk or listen command. These talk and listen
commands are derived from an instrument’s primary
address. The primary address may have any value between 0
and 31, and is generally set by rear panel DIP switches or
programmed in from the front panel of the instrument. The
actual listen address value sent out over the bus is obtained
by ORing the primary address with $20. For example, if the
primary address is $16, the actual listen address is $36 ($36
= $16 + $20). In a similar manner, the talk address is
obtained by ORing the primary address with $40. With the
present example, the talk address derived from a primary
address of $16 would be $56 ($56 = $16 + $40).
The IEEE-488 standards also include another addressing
mode called secondary addressing. Secondary addresses lie
in the range of $60-$7F. Note, however, that many devices,
including the Model 708A, do not use secondary addressing.
Once a device is addressed to talk or listen, the appropriate
bus transactions take place. For example, if the instrument is
addressed to talk, it places its data string on the bus one byte
at a time. The controller reads the information, and the
appropriate software can be used to direct the information to
the desired location.
DEVICE 1
ABLE TO
TALK, LISTEN
AND CONTROL
(COMPUTER)
DEVICE 3
ONLY ABLE
TO LISTEN
(PRINTER)
DEVICE 4
ONLY ABLE
TO TALK
DAV
NRFD
NDAC
IFC
ATN
SRQ
REN
EOI
D IO1 ... 8 DATA
(8 LINES)
HANDSHAKE
BUS
MANAGEMENT
DATA BUS
DATA BYTE
TRANSFER
CONTROL
GENERAL
INTERFACE
MANAGEMENT
DEVICE 2
ABLE TO
TALK AND
LISTEN
7001
TO OTHER DEVICES
Figure C-1
IEEE-488 bus configuration
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Summary of Contents for 708A
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