106 Chapter 7 Using GPIB Interface
Bus commands
The IEEE-488.1 standard defines bus commands, which are sent to the 802 with ATN
true. The following table lists bus commands supported by the generator. For more
detailed descriptions of these commands, see the IEEE-488.1 and 488.2 standards.

Remote/local operation

The 802 has complete remote/local operation as defined by the IEEE-488.1 standard. All
four remote/local states (REMS, LOCS, RWLS and LWLS) are supported.
In the remote state (REMS), the 802 is under remote control and messages are processed
as received. The generator enters the remote with lockout state (RWLS) if the controller
issues the local lockout (LLO) message to the 802. The generator enters the local state
(LOCS) when the REN line goes false or the controller issues the go to local (GTL)
message to the generator, or a front panel control is actuated.
Event Status bit Definition
OPC Operation complete. Indicates that all operations have been completed.
RQC Request control. Indicates that a device is requesting control. The generator will
never request control, so this bit will always be 0.
QYE Query error. Indicates that a query request was made while the generator was in
deadlock.
DDE Device dependent error. Indicates that the generator encountered an error exe-
cuting a command.
EXE Execution error. Indicates that there was an error parsing a parameter.
CME Command error. Indicates that there was an unrecognizable command.
URQ User request. Indicates that a front panel key has been pressed or that the front
panel knob has been turned.
PON Power on. Indicates that power has been turned off and on. This bit will always
be 0 in the generator.
Command Description
DCL Device clear. Clears the input buffer and output queue, and stops parsing any
commands.
SDC Selected device clear. Same as DCL.
GTL Go to local. Enters the local state. See “Remote/local op eration” on page 106.
LLO Lo cal lockout. Enters the lockout state. See “Remote/local operation” on page
106.
SPE Serial poll enable. Enables transmission of the Status Byte.
SPD Serial poll disable. Exits the serial poll state.