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niDaqmx Sample written incorrect

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Hello Everyone,

 

something strange is going on with one of my analog output tasks. 

 

I am using a PXI 6723 card to output a simple sort sequence of voltages. Each change of the output is triggered on the PFI1 line.

Before starting the output, I write 6 samples per channel (4 channels) to the device. I then start the task, and the card starts outputing the correct voltages when the external sample clock pulses arrive on PFI1. 

 

On an osciloscope I see the trigger pulses, and the voltage output, and everything is fine. All samples are generated. Yet the "DAQmx Is Task Done.vi" never indicates that the task is complete. I then wired up a property node, and find the numbers "Total Samples per Channel generated", and another indicating the total number of samples per channel in the task. The samples written only counts up to 5, and the total number of samples in the task is 6. 

 

This is strange because I see all 6 samples outputed on the osciloscope (plus all 6 trigger pulses), yet the DAQmx driver seems to only know about 5 of those samples.

 

Anyone has any advise?

 

Another question I have is that on the PFI line I see 5 volts when the card is idle, is this normal? (The sample clock is configured to trigger on the rising edge of my external trigger pulses which are TTL pulses 0 to 5 volts.)

 

Thanks a lot,

Paul

 

p.s. I am using nidaqmx version 8.9.0f4.

 

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Solution
Accepted by topic author labJunky

Hi labJunky,

      I believe that the answer to what you are seeing is described in this post.  Additionally, in that same thread, this post is referenced, which gives a detailed explanation of the behavior you are seeing.  Have a great weekend!

 

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Thanks aNItaB, the referenced posts above explain everything!
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