User manual

Part 5: IEEE 488.2 Programming Reference
Timing and Synchronization
Depending on how your remote program is written, it may be affected by timing changes between
different oscilloscopes. Most timing and synchronization problems are related to changing acquisitions, or
the completion of analysis after an acquisition occurs.
Say that you change the Offset of C1 while the oscilloscope is in Auto trigger mode, and then use the
PAVA? query to read a parameter computed on C1. In newer oscilloscopes, the processing is overlapped
with the next acquisition and, as a consequence, the PAVA? result may have come from the acquisition
prior to the offset change.
There are several ways to ensure your program provides correct results when remotely controlling the
oscilloscope.
Control the Trigger Mode
When in Single trigger mode, acquisitions do not overlap. You can use the status registers available in the
instrument, or the *OPC? query and the WAIT command to detect acquisition and processing completion.
When you arm the oscilloscope by sending the TRMD SINGLE command, the instrument automatically
performs any necessary calibrations before it acquires any data. These calibrations may take several
seconds, so if you query the status immediately after sending the TRMD SINGLE command, set the GPIB
(or remote) timeout to least 10 seconds and prevent a timeout before receiving the correct results.
A case where you may need to use Normal or Auto trigger mode involves the accumulation of many
acquisitions for averaging or histogramming functions. In this case, it is best to stop the acquisitions, set
up the oscilloscope, and then set the trigger mode to Normal when acquiring the data.
A possible alternative would be to use Sequence trigger mode. It is faster, but does require knowing how
many acquisitions to accumulate. This number can be specified and captured using sequence mode.
Reduce Calibrations
When operating in Dynamic Calibration mode, the default on older MAUI oscilloscopes, calibrations are
performed whenever your program changes some acquisition settings such as Volts/Div or the number of
active channels. Calibrations are also performed if the oscilloscope temperature significantly changed.
The calibrations may be disabled by sending the AUTO_CALIBRATE OFF command. While oscilloscope
performance may be degraded if the temperature changes and does not self-calibrate, a calibration can
always be forced by issuing the *CAL? command.
Using this forced calibration technique allows you to control their timing so they do not interfere while
acquiring important data.
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