DIO function of NI 9401

[angelmcdoggie]

Hello Markie,

 When you mean "sync" in DI & DO, will the rising and falling edges of the clock occur at the same time?  Please refer to DI_DO_pulse train.jpg.  Second, does is it refer to DO generation and DI capture will occur at the same time?  Please refer to generation_capture.jpg.

Thanks for your patience.

A

[tnek]

Hi A,

Since the same exact sample clock will be used for the digital input and output, they will share the same rising and falling edges. This will also mean that the each acquisition and generation will occur at the same time.

Regards,
Kent
Applications Engineer

[angelmcdoggie]

Hello

My understanding of what you have mentioned is illustrated in the page 1 of the attachment.  At every active edge ( rising edge ) of the clock, the generation and acquisition occurs.

Specifically for my application as shown in page 2 of the attachment, the moment I generated the 1st desired setpoint,  the 1st sample readback will occur at the same time.  Is there an API or a code setup to achieve this?

Thanks again,

[tnek]

Hi A,

I am not quite sure what the difference between the two pictures that you have posted. It seems that it is the same signal but shifted in time. But regardless, both digital tasks will act at the same clock edge. As for the code, I believe that you are working on this on another post. As was discussed before on this thread, the only thing needed is to create a counter output task for the sample clock, and use this clock as the sample clock for both digital tasks.

Regards,
Kent
Applications Engineer

[angelmcdoggie]

Hello

I have completed the code for that without using a counter module.

Sorry for the confusion again.

Well anyway, both pictures are quite similar except that the 2nd picture, wherein I put emphasis on the 1st generation & 1st capture.

The moment I write the 1st sample, I want to acquire the 1st sample immedietely.  I am going to use this on a speed application that is < 10 ms, with a tolerance of +/- 1%.

Is there an API or something to achieve the immediete 1st sample acquisition?

Thanks for your patience.

Best regards,

A

[tnek]

Hi A,

If the sample clock begins after the digital tasks are started then both the first generation and first acquisition will occur at the first rising edge of the sample clock. If the sample clock is already running when the tasks are started, you can use a trigger to align the two. See this article for more information on triggering in DAQmx. There is also very good information about sample clocks and triggers in the DAQmx Help file.

Regards,
Kent
Applications Engineer

[angelmcdoggie]

Dear tnek,

you mean like this:

DOTask->Start();

DITask->Start();

....

....

....

DOTask->Timing...

DITask->Timing...

Best regards,

A

[tnek]

Hi A,

Here is an LabVIEW example which accomplishes this task. I have attached it as a screenshot so you can use it to structure your program. Note that the timing is set before the tasks are started.

Regards,
Kent
Applications Engineer


Message Edited by tnek on 06-26-2008 11:16 AM

[angelmcdoggie]

Dear K,

errrr..ooopss sorry I cannot open the attachment because I am using Visual C++.

Thanks,

[tnek]

Hi A,

The attachment is just a picture and should be viewable in your web browser. I just posted it so you can see how your task should be structured.

Regards,
Kent
Applications Engineer