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Appendix D: IEEE-488 bus overview
Model 6517B Electrometer Reference Manual
D-8
6517B-901-01 Rev. C / August 2015
Addressed multiline commands
Addressed commands are multiline commands that must be preceded by the device listen address
before that instrument responds to the command in question. Note that only the addressed device
responds 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 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.
Addressed 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 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 6517B) 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 are placed in the talker idle state by the
UNT
command.
Common Commands
Common commands are commands that are common to all devices on the bus. These commands
are designated and defined by the IEEE-488.2 standard.
Generally, these commands are sent as one or more ASCII characters that tell the device to perform
a common operation, such as reset. The IEEE-488 bus treats these commands as data because
ATN
is false when the commands are transmitted.
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