Programmer’s Guide 6-11
Trace Data Transfers
Taking Sweeps
Taking Sweeps
When making measurements and querying traces, your program should
perform the following steps:
1. Place the analyzer's sweep in hold.
2. Initiate a single sweep.
3. Wait for the sweep to complete.
4. Query the measurement trace.
Use the following program lines to perform these steps:
10 OUTPUT @Hp8711;"ABORT;:INIT1:CONT OFF"
20 OUTPUT @Hp8711;"INIT1"
30 OUTPUT @Hp8711;"*OPC?"
35 ENTER @Hp8711;Opc
40 OUTPUT @Hp8711;"TRACE:DATA? CH1FDATA"
45 ENTER @Hp8711;Fmt(*)
If you query the measurement trace while the analyzer is in continuous
sweep, the query will still work, but the data may not be correct. Using
INIT and *OPC? ensures that a complete sweep has finished before you
query the measurement data. In many cases, you can also use the
command "*WAI" in place of the "*OPC?" query, replacing lines 30 and 35
above with:
30 OUTPUT @Hp8711;"*WAI"
However, there are cases where "*WAI" will produce incorrect results.
One case is when using IBASIC's high-speed subprograms to query the
trace data. "*WAI" only ensures that the SCPI commands following the
"*WAI" are not executed until the commands before the "*WAI" are
complete. Since IBASIC subprograms don't use SCPI commands to
access the trace data, "*WAI" is ineffective, and "*OPC?" should be
used.
When using "*OPC?", the ENTER statement following the "*OPC?" will
wait until the previous SCPI commands are complete, preventing your
program from executing beyond the ENTER statement. When using
"*WAI", your program can continue to run and send SCPI commands,
and the analyzer will buffer them and act upon them in order.
Chapter 2, “Synchronizing the Analyzer and a Controller,” provides
additional details.
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