
Keysight M8070A Programming Guide
87
SCPI Command Language
4
IEEE 488.2 Mandatory Commands
In order to comply with the SCPI model as described in IEEE 488.2, the
Serial BERT implements certain mandatory commands. Other commands
are implemented optionally. For more detail on the IEEE 488.2 mandatory
and optional commands, see
Overlapped and Sequential Commands
IEEE 488.2 defines the distinction between overlapped and sequential
commands. A sequential command is one which finishes executing before
the next command starts executing. An overlapped command is one which
does not finish executing before the next command starts executing.
Because these commands may allow the execution of more than one
command at a time, special programming techniques must be used to
ensure valid results. The common commands *OPC, *WAI and *OPC? can
be used for this purpose. They help synchronize a device controller with
the execution of overlapped commands.
The behaviors of these commands, in brief, are as follows:
• *OPC
The *OPC command sets the Operation Complete (OPC) bit of the Event
Register when the No Operation Pending flag is TRUE (No Operation
Pending flag is attached to each overlapped command). Until that time,
the controller may continue to parse and execute previous commands.
It is good technique, then, to periodically poll the OPC bit to determine
if the overlapped command has completed.
• *WAI
The *WAI command allows no further execution of commands or
queries until the No Operation Pending flag is true, or receipt of a
Device Clear (dcas) message, or a power on.
The *WAI command can be used for overlapped commands. It stops the
program execution until any pending overlapped commands have
finished. Specifically, it waits until the No Operation Pending flag is
TRUE, or receipt of a dcas message, or a power on.
NOTE
It is not reliable to use wait statements in the control program to
facilitate the use of overlapped commands.