Keithley 6482, Reference Manual

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C-8 Return to
Section Topics
6482-901-01 Rev. A / August 2012
Appendix C: IEEE-488 Bus Overview Model 6482 Dual-Channel Picoammeter / Voltage Source Reference Manual
LLO (Local Lockout) : LLO is sent to the instrument to lock out the LOCAL key and thus all the
front panel controls.
DCL (Device Clear) : DCL is used to return instruments to some default state. Usually, instruments
return to the power-up conditions.
SPE (Serial Poll Enable) : SPE is the first step in the serial polling sequences, which is used to
determine which device has requested service.
SPD (Serial Poll Disable): SPD is used by the controller to remove all devices on the bus from
the serial poll mode and is generally the last command in the serial polling sequence.
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 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 primary
address and are used to address devices to listen. The actual command byte is obtained by ORing
the primary address with #H20.
TAG (Talk Address Group): The talk commands are derived from the primary address by ORing
the address with #H40. 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 6482) 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.
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.