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USB U2701A Checking Trigger Status

Question asked by swalpole on Jan 22, 2016

I have a U2701A USB Scope.  I'm trying to start a triggered acquisition and then use software to poll to see if a trigger has occurred.  I am using the IVI Com driver.  I have tried multiple approaches and I can't find a way to check if a trigger has occurred.  Here is a description of my latest attempt, what I see, and what I expect to see.  Thank you for any help!

1) AgilentU2701AClass::Initialize
2) IAgilentU2701ATrigger::Configure(AgilentU2701ATriggerEdge)
3) IAgilentU2701ATriggerEdge::Configure("EXT", 0, AgilentU2701TriggerSlopePositive)
4) IAgilentU2701AMeasurements::Initiate()
5) IAgilentU2701ASystem::WaitForOperationComplete(100)
6) IAgilentU2701AMeasurement::FetchWaveform()

What I see is:
1-4 occur without errors as expected.
5 (WaitForOperationComplete) takes 2-4ms to complete regardless of whether a trigger has occurred.
6 takes about 5 seconds before returning the WaveformArray that was last on the screen.  If a trigger does occur, then 6 occurs quickly and returns the new data.

What I expect to see is:
5 (WaitForOperationComplete) waits 100 miliseconds before completing if a trigger does not occur.  If a trigger does occur, then WaitForOperationComplete completes sooner.  

I have also tried reading the AgilentU2701AMeasurements::Status field.  Here I find that the value is always "AgilentU2701AAcqComplete".  I would expect the value to be "AgilentU2701AAcqInProgress" until a trigger occurs, and then the field to be "AgilentU2701AAcqComplete".