Stanford Research Systems SR780, Руководство по эксплуатации и программированию

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Remote Programming 5-21
SR780 Network Signal Analyzer
However, some commands, such as file and print/plot commands and data transfer
operations, may require a long time to execute. In addition, the host program may need to
check that these operations executed without error. In these cases, after the command is
sent, the status should be queried.
When using the GPIB interface, serial polling may be used to check the IFC bit in the
Serial Poll status while an operation is in progress. After the IFC bit becomes set,
signaling the completion of the command, then the IERR bit may be checked to verify
successful completion of the command.
If the RS232 interface is used, or serial polling is not available, then the *STB? query
command may be used to read the Serial Poll status word. However, *STB NEVER
returns the IFC bit set (since *STB is itself a command).
Since the SR780 processes one command at a time, status queries will not be processed
until the previous operation is finished. Thus a response to a status query in itself signals
that the previous command is finished. The query response may then be checked for
various errors.
For example, the command line FSAV 0; ERRS ? <lf> will save the DisplayA data to
disk and return the Error Status word when finished. The Disk Error bit may be checked
to make sure that the FSAV (Display to Disk) command completed without error. Since
the FSAV command may take a long time to execute, it is important that the host
computer interface does not time out while waiting for the response to the ERRS ? query.
In the case where the host interface times out before the ERRS ? response, the host
program must wait before sending the ERRS ? query.
Data Synchronization
Changing measurement parameters often invalidates the display data. For example,
changing FFT spans or resolution requires some time before new data taken with the new
span or resolution is available. Another example is changing the FFT average mode while
averaging is on. In this case, the average is re-started and some time is required before a
new average is completed.
For these types of commands, simply waiting for IFC to be set does not ensure that the
display data reflects the operation just completed. Before querying or saving the display
data, the Display Status word needs to be queried until either NEW, AVG or STL is set
indicating new data is available, average completed or new settled data is available. This
will ensure that the display data has been updated since the previous operation.
Remember, these status bits are only reset when read. The status word needs to be cleared
before waiting for the desired bits to become set.
For example, to change the span and wait until new data is available, a program might
use the following procedure.
send (“*CLS; FSPN 0,6400”) *CLS clears all status words, FSPN changes
the span of DisplayA to 6.4 kHz.
query (“DSPS?”) DSPS? reads the Display Status