R&S SMB Instrument Model and Command Processing
1407.0806.32 5.19 E-2
Command Recognition
The command recognition analyses the data received from the input unit. It proceeds in the order in
which it receives the data. Only a DCL is serviced with priority, a GET (Group Execute Trigger), e.g., is
only executed after the commands received before. Each recognized command is immediately
transmitted to the data set but not executed immediately.
The command recognition detects syntax errors in the commands and transfers them to the status
reporting system. The rest of a command line after a syntax error is analyzed further if possible and
serviced. After the syntax test, the value range of the parameter is checked, if required.
If the command recognition detects a delimiter or a DCL, it also requests the data set to perform the
necessary instrument hardware settings. Subsequently it is immediately prepared to process further
commands. This means that new commands can already be serviced while the hardware is still being
set ("overlapping execution").
Database and Instrument Hardware
The expression "instrument hardware" denotes the part of the instrument fulfilling the actual instrument
function - signal generation etc. The controller is not included. The term "database" denotes a database
that manages all the parameters and associated settings required for setting the instrument hardware.
Setting commands lead to an alteration in the data set. The data set management enters the new
values (e.g. frequency) into the data set, however, only passes them on to the hardware when
requested by the command recognition. As this is only ever effected at the end of a command line, the
order of the setting commands in the command line is not relevant.
The data are only checked for their compatibility among each other and with the instrument hardware
immediately before they are transmitted to the instrument hardware. If the detection is made that
execution is not possible, an "execution error" is signaled to the status reporting system. All alterations
of the data set are canceled, the instrument hardware is not reset. Due to the delayed checking and
hardware setting, however, impermissible instrument states can be set for a short period of time within
one command line without this leading to an error message. At the end of the command line, however,
a permissible instrument state must have been reached again.
Example:
With Frequency Modulation, the settable FM deviation depends on the set RF frequency and
the FM mode. The Signal Generator responds as follows:
Assuming the set RF frequency is 60 MHz and normal FM mode is set, i.e. the maximum value
for FM deviation is 650 kHz. A deviation of 1 MHz should be set. To do so, the RF frequncy has
to be changed to e.g. 100 MHz. The following commands are sent:
1. All commands in one program message:
:SOUR:FM:STAT ON; :SOUR:FM:DEV 1MHz; :SOUR:FREQ 100MHz
This command line yields the desired setting. Since a valid state is obtained at the end of the
program message, no error message is issued.
2. Each command in a separate program message:
:SOUR:FM:STAT ON
:SOUR:FM:DEV 1MHz
:SOUR:FREQ 100MHz
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