07-16-2014 09:55 AM
I have a PCI-6259 DAQ card (M-series card) that I am programming with DAQmx. I would like to know if there is a limit in terms of how close together you can use repeating triggers. I plan to use a 1us internal clock rate. An asynchronous external TTL signal will be used to trigger a finite digital output sequence from the 6259. The finite digital sequence is 4 samples long, so it will take 4us. The asynchronous trigger edges will occur about every 100us. I plan to use trigger property Start.Retriggerable = TRUE so that I can repeat this 4 sample generation every time the external TTL signal is recieved.
Is 100us too close together? Is there a limit to how close together you can repeat a hardware trigger when using Start.Retriggerable = TRUE?
Is there any way to know if my PCI-6259 card even supports the trigger property Start.Retriggerable?
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07-16-2014 04:07 PM
100 us will be fine (the re-arm time is on the order of a timebase tick or two, ~10s of ns).
However, the M Series does not directly support retriggerable digital output. Instead, configure a finite retriggerable counter output to generate 4 pulses at 1 MHz (this uses both onboard counters of the M Series). Use the internal counter output as the sample clock for a continuous digital output task that will repeat your 4 sample sequence.
07-16-2014 04:13 PM
Thanks for your response John. Do you know if a there is a LabVIEW DAQmx example of using counters to enable retriggerable triggers on m-series DAQ? I searched with the example finder and I have not found anything.
07-16-2014 04:38 PM - edited 07-16-2014 04:38 PM
I couldn't find a good example either (a lot of old/conflicting information out there too due to different behavior on various generations of hardware).
On your M Series you'll want to do something like this:
The low time is very small since the low time is used as the intial delay for retriggering on M Series (see here).