IEEE-488 Bus Overview
C-7
C.4.7 Typical command sequences
For the various multiline commands, a specific bus sequence
must take place to properly send the command. In particular,
the correct listen address must be sent to the instrument
before it will respond to addressed commands. Table C-3
lists a typical bus sequence for sending the addressed multi-
line commands. In this instance, the SDC command is being
sent to the instrument. UNL is generally sent as part of the
sequence to ensure that no other active listeners are present.
Note that ATN is true for both the listen command and the
SDC command byte itself.
Table C-4 gives a typical common command sequence. In
this instance, ATN is true while the instrument is being
addressed, but it is set high while sending the common com-
mand string.
C.4.8 IEEE command groups
Command groups supported by the Model 708A are listed in
Table C-5.
Table C-3
Typical addressed command sequence
Step Command
ATN state
Data bus
ASCII
Hex
Decimal
1
2
3
4
UNL
LAG*
SDC
Set low
Stays low
Stays low
Returns high
?
0
EOT
3F
30
04
63
48
4
*Assumes primary address = 16.
Table C-4
Typical addressed command sequence
Step
Command
ATN state
Data bus
ASCII
Hex Decimal
1
2
3
4
5
6
UNL
LAG*
Data
Data
Data
Data
Set low
Stays low
Set high
Stays high
Stays high
Stays high
?
0
*
R
S
T
3F
30
2A
52
53
54
63
48
42
82
83
84
*Assumes primary address = 16.
Table C-5
IEEE command groups
HANDSHAKE COMMAND GROUP
NDAC = NOT DATA ACCEPTED
NRFD = NOT READY FOR DATA
DAV = DATA VALID
UNIVERSAL COMMAND GROUP
ATN = ATTENTION
DCL = DEVICE CLEAR
IFC = INTERFACE CLEAR
REN = REMOTE ENABLE
SPD = SERIAL POLL DISABLE
SPE = SERIAL POLL ENABLE
ADDRESS COMMAND GROUP
LISTEN
TALK
LAG = LISTEN ADDRESS GROUP
MLA = MY LISTEN ADDRESS
UNL = UNLISTEN
TAG = TALK ADDRESS GROUP
MTA = MY TALK ADDRESS
UNT = UNTALK
OTA = OTHER TALK ADDRESS
ADDRESSED COMMAND GROUP
ACG = ADDRESSED COMMAND GROUP
GTL = GO TO LOCAL
SDC = SELECTIVE DEVICE CLEAR
STATUS COMMAND GROUP
RQS = REQUEST SERVICE
SRQ = SERIAL POLL REQUEST
STB = STATUS BYTE
EOI = END
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