IEEE-488 Bus Overview F-9
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 question. Note that only the
addressed device will respond to these commands. Both the commands and the address preced-
ing 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 responds. 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 remove instruments from the remote
mode. With some instruments, GTL also unlocks front panel controls if they were previously
locked out with the LLO command.
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 include:
LAG (Listen Address Group) — These listen commands are derived from an instrument’s pri-
mary address and are used to address devices to listen. The actual command byte is obtained by
ORing the primary address with $20.
TAG (Talk Address Group) — The talk commands are derived from the primary address by
ORing the address with $40. Talk commands are used to address devices to talk.
SCG (Secondary Command Group) — Commands in this group provide additional address-
ing capabilities. Many devices (including the Model 6514) do not use these commands.
Unaddress commands
The two unaddress commands are used by the controller to remove any talkers or listeners
from the bus. ATN is true when these commands are asserted.
UNL (Unlisten) — Listeners are placed in the listener idle state by the UNL command.
UNT (Untalk) — Any previously commanded talkers will be placed in the talker idle state by
the UNT command.
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