IEEE-488 Bus Overview
D-5
Addressed multiline commands
Addressed commands are multiline commands that
must be preceded by the device listen address before
that instrument will respond to the command in ques-
tion. Note that only the addressed device will respond
to these commands. Both the commands and the ad-
dress preceding it are sent with ATN true.
SDC (Selective Device Clear) — The SDC command
performs essentially the same function as the DCL
command except that only the addressed device re-
sponds. Generally, instruments return to their power-
up default conditions when responding to the SDC
command.
GTL (Go To Local) — The GTL command is used to re-
move instruments from the remote mode. With some
instruments, GTL also unlocks front panel controls if
Table D-1
IEEE-488 bus command summary
Command
type Command
State of
ATN
line Comments
Uniline REN (Remote Enable)
EOI
IFC (Interface Clear)
ATN (Attention)
SRQ
X
X
X
Low
X
Set up devices for remote operation.
Marks end of transmission.
Clears interface.
Defines data bus contents.
Controlled by external device.
Multiline
Universal LLO (Local Lockout)
DCL (Device Clear)
SPE (Serial Enable)
SPD (Serial Poll Disable)
Low
Low
Low
Low
Locks our local operation.
Returns device to default conditions.
Enables serial polling.
Disables serial polling.
Addressed SDC (Selective Device Clear)
GTL (Go To Local)
Low
Low
Returns unit to default conditions.
Returns device to local.
Unaddressed UNL (Unlisten)
UNT (Untalk)
Low
Low
Removes all listeners from the bus.
Removes any talkers from the bus.
Common — High Programs IEEE-488.2 compatible instruments for
common operations.
SCPI — High Programs SCPI compatible instruments for partic-
ular operations.
they were previously locked out with the LLO com-
mand.
GET (Group Execute Trigger) — The GET command is
used to trigger devices to perform a specific action that
depends on device configuration (for example, take a
reading). Although GET is an addressed command,
many devices respond to GET without addressing.
Address commands
Addressed commands include two primary command
groups and a secondary address group. ATN is true
when these commands are asserted. The commands in-
clude:
LAG (Listen Address Group) — These listen com-
mands are derived from an instrument’s primary ad-
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