User manual

Addressed commands are multiline commands that must be preceded by the device lis-
ten 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 ad-
dress preceding it are sent with ATN true.
SDC (Selective Device Clear) — The SDC command performs essentially the same func-
tion as the DCL command except that only the addressed device responds. Generally, in-
struments 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). Al-
though GET is an addressed command, many devices respond to GET without addressing.
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
primary address and are used to address devices to listen. The actual command byte is ob-
tained 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 ad-
dressing capabilities. Many devices (including the Model 2000) do not use these 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 com-
mand.
UNT (Untalk) — Any previously commanded talkers will be placed in the talker idle
state by the UNT command.
E-10 IEEE-488 Bus Overview
2000-900 (J - Aug 2010) BOOK.fm Page 10 Wednesday, October 12, 2011 12:29 PM