F-12 IEEE-488 Bus Overview Model 6485 Picoammeter Instruction Manual
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-4 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-5 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-4
Typical 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
2E
04
63
46
4
*Assumes primary address = 14.
Table F-5
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
?
.
*
R
S
T
3F
2E
2A
52
53
54
63
46
42
82
83
84
*Assumes primary address = 14.
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