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Table 723 IEEE·488 bus signal (continued)
Bu,
Signal
Name
Functional
Group
Abbrev.
Description
Data
0101-8
Data input/
These signals represent the bits
output lines
of information on the data bus.
1 through 8
When a 010 signal is low, it
represents
1
and when high 0.
General
GND
Ground
Ground connections: There
are six control and manage-
ment signal ground returns,
one data 5"lgnal ground return
and one chassis shield ground
lead.
STATUS WORD (ST)
ST is a BASIC variable which can be used to check the outcome of INPUTfOUTPUT operations. ST can
have certain values over the range ·128 to 127. Table 7-24 shows the status code that appertains to the
IEEE·488 bus.
ST
Error
Explanation
1
Time
The IEEE device has not responded within the 65
out on
milliseconds time out inverval.
listener
2
Time
The IEEE device has
not
provided an active "data
out on
valid" signal (DAV low) within the 65 millisecond
talker
time out interval
64
End or
EOI has gone low {truel, on the last byte of data
identify
being transferred on IEEE bus. Note that all devices
(EOI)
do not generate an EOI signal. Consult relevant
instrument manual.
-128
Device
Device did not respond when addressed; this gen·
001
erates an error message and the operating system
present
returFls the PET to BASiC command level.
Table 7.24. ST status code for IEEE·488 bus.
IEEE-488 REGISTER ADDRESSES
Table 7-24 shows the IEEE-488 hardware addresses for the PET. An attempt to control the bus by means
of the PEEK and POKE commands will fail, jf the time out intervals for the 488 devices are exceeded.
Hox
Decimal
Bits
IEEE
Mode
Address
Address
E820
59424
0-7
0101-8
Input
- - - -
E822
59426
0-7
0101·8
Output
E821
59425
3
NDAC
Output
-
E823
59427
3
DAV
Input
7
SRQ
E810
59408
6
EOI
Input
E840
59456
0
NDAC
Input
1
NRFO
Output
2
ATN
Output
6
NRFO
Input
7
DAV
Output
Table 7.25. IEEE·488 hardware addresses and signal information.
88
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