R&S ZNB Series User Manual page 822

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R&S ZNB/ZNBT
nition when the input buffer is full or when it receives a delimiter, <PROGRAM MESSAGE
TERMINATOR>, as defined in IEEE 488.2, or the interface message DCL.
If the input buffer is full, the message data traffic is stopped and the data received up to
then is processed. Subsequently the traffic is continued. If, however, the buffer is not
yet full when receiving the delimiter, the input unit can already receive the next com-
mand during command recognition and execution. The receipt of a DCL clears the input
buffer and immediately initiates a message to the command recognition.
6.4.2 Command recognition
The command recognition stage analyzes the data received from the input unit. It pro-
ceeds in the order in which it receives the data. Only a DCL is serviced with priority,
e.g. a GET (Group Execute Trigger) is only executed after the commands received
before. Each recognized command is immediately transferred 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 still
executed, if possible. After the syntax check, the range of the numerical parameters is
checked, if necessary.
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).
6.4.3 Data base and instrument hardware
The expression instrument hardware denotes the part of the instrument fulfilling the
actual instrument function – signal generation, measurement etc. The controller is not
included. The data base manages all the parameters and associated settings required
for 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, it only passes them
on to the hardware when requested by the command recognition. This can only occur
at the end of a command line, therefore the order of the setting commands in the com-
mand line is not relevant.
The commands are only checked for their compatibility among each other and with the
instrument hardware immediately before they are transmitted to the instrument hard-
ware. If the instrument detects that execution is not possible, an execution error is sig-
naled 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 (example: simultaneous
activation of a frequency and a power sweep). At the end of the command line, how-
ever, a permissible instrument state must have been reached again.
User Manual 1173.9163.02 ─ 62
Remote control
Command processing
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