IEEE-488 Bus Overview F-11
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 F-3 lists a typical bus sequence for sending the
addressed multiline 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 F-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 command string.
Table F-3
Typical addressed bus 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
?
’
EOT
3F
27
04
63
39
4
*Assumes primary address = 7.
Table F-4
Typical addressed common 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
?
’
*
R
S
T
3F
27
2A
52
53
54
63
39
42
82
83
84
*Assumes primary address = 7.
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