R&S®SML / R&S®SMV03 Instrument Model and Command Processing
1090.3123.12 E-6 5.15
Output Unit
The output unit collects the information requested by the controller and output by the data set
management. The output unit processes the information in accordance with the SCPI rules and makes it
available in the output buffer. The output buffer has a size of 256 characters. If the requested
information exceeds this size, it is made available in portions without this being recognized by the
controller.
If the instrument is addressed as a talker without the output buffer containing data or awaiting data from
the data set management, the output unit returns the error message "Query UNTERMINATED" to the
status reporting system. No data are sent on the IEC/IEEE bus. The controller waits until it has reached
its time limit. This procedure is specified by SCPI.
Command Sequence and Command Synchronization
As mentioned above, overlapping execution is possible for all commands. Likewise, the setting
commands of a command line are not necessarily processed in the order in which they are received.
To ensure that commands are carried out in a specific order, each command must be sent in a separate
command line, ie with a separate IBWRT() call.
To prevent overlapping execution of commands, one of commands *OPC, *OPC? or *WAI has to be
used. Each of the three commands causes a certain action to be triggered only after the hardware has
been set and has settled. The controller can be programmed to wait for the respective action to occur
(see Table 5-1).
Table 5-1 Synchronization by means of *OPC, *OPC? and *WAI
Command Action after the hardware has settled Programming of controller
*OPC Sets the operation-complete bits in the ESR - Setting of bit 0 in the ESE
- Setting of bit 5 in the SRE
– Waiting for a service request (SRQ)
*OPC? Writes a "1" into the output buffer Addressing of instrument as a talker
*WAI Continues the IEC/IEEE-bus handshake.
The handshake is not stopped.
Sending of next command
An example of command synchronization will be found in section 7, "Programming Examples".
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