Instrument Model and Command Processing R&S SMB
1407.0806.32 5.20 E-2
The command for setting the FM deviation is rejected and an execution error is generated.
At the time when this command is processed, the previous setting of the RF frequency (60
MHz) is still valid, i.e. the value for the FM deviation is outside the permissible value range.
The two other commands are set.
3. The two first commands in one program message, the third command in a separate program
message.
:SOUR:FM:STAT ON; :SOUR:FM:DEV 1MHz
:SOUR:FREQ 100MHz
The command for setting the FM deviation is rejected and an execution error is generated.
At the time when this command is processed, the previous setting of the RF frequency (60
MHz) is still valid, i.e. the value for the FM deviation is outside the permissible value range.
The two other commands are executed.
This example shows that it is advisable to send interdependent commands in one program
message as in this case the sequence in which they are sent is irrelevant.
For further examples on command sequence see section "Command Sequence and Command
Synchronization", on page 5.20.
Before passing on the data to the hardware, the settling bit in the STATus:OPERation register is set
(see section Status Reporting System, page 5.23). The hardware executes the settings and resets the
bit again as soon as the new state has settled. This fact can be used to synchronize command
servicing.
Queries induce the data set management to send the desired data to the output unit.
Status Reporting System
The status reporting system collects information on the instrument state and makes it available to the
output unit on request. The exact structure and function are described in section "Status Reporting
System".
Output Unit
The output unit collects the information requested by the controller, which it receives from the data set
management. It processes it according to the SCPI rules and makes it available in the output buffer.
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 sends the error message "Query UNTERMINATED" to the
status reporting system. No data are sent on the IEC/IEEE bus or via the Ethernet, the controller waits
until it has reached its time limit. This behavior is specified by SCPI.
Command Sequence and Command Synchronization
IEEE 488.2 defines a distinction between overlapped and sequential commands:
- An overlapped command is one which does not automatically finish executing before the next
command starts executing. Overlapped commands allow the program to do other tasks while
being executed.
- A sequential command is one which always finishes before the next command starts executing.
Sequential commands are not implemented in the generator, however the execution time of
most commands is so short that they act as sequential commands.
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