D-10
IEEE-488 Bus Overview
Model 6487 Reference Manual
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
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 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 per-
form 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 instru-
ment’s primary 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
addressing capabilities. Many devices (including the Model 6487) 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.
