continuous digital waveform

[Elizabeth Reynolds]

Hi,

I'm trying to write a continuous digital waveform to lines 0 and 1 of port 0; I have the PCI-6229 and am using MS Visual C# express edition. I have successfully used this set-up to do single-sample writes to these lines on port 0, but I can't figure out how to generate a continuous (repeating) waveform. I have attached the code I am using; it will compile and run without generating exceptions, but when I monitor the output lines on the DAQ card, I see nothing. I don't see even a single run-through of the waveform data, much less a continuous stream of data. Does anyone know what I'm doing wrong?

Thanks,
Elizabeth

public void GrayEncoderWrite(double periodS)
{
    uint nSamples = (uint)(1 << 2);
    /* Mask the data to the 2 LSBs */
    uint mask = nSamples - 1;

     /* Create a new task */
    doTask = new Task(); // Task doTask is a data member of the form
   
    /* Attach an output channel to the task */
    doTask.DOChannels.CreateChannel("dev1/port0/line0:1",
        "", ChannelLineGrouping.OneChannelForAllLines);

    /* Configure timing for channel: sample rate is 1/periodS */
    doTask.Timing.ConfigureSampleClock("/dev1/pfi0", 1.0 / periodS,
        SampleClockActiveEdge.Rising,
        SampleQuantityMode.ContinuousSamples);

    /* Configure channel writer */
    DigitalSingleChannelWriter dWriter =
        new DigitalSingleChannelWriter(doTask.Stream);

    /* Create waveform to write
     * Turn the Gray-encoded initial state into an index integer
     */
    uint[] grayWaveformUint = new uint[nSamples];
    for (uint i = 0; i < nSamples; i++)
        grayWaveformUint[i & mask] = i^(i>>1);

    /* Do a Gray-encoded waveform starting at the initial state
     */
    DigitalWaveform grayWaveform = DigitalWaveform.FromPort(grayWaveformUint, (byte)mask);
    grayWaveform.Timing = WaveformTiming.CreateWithRegularInterval(TimeSpan.FromSeconds(periodS));

    /* Write waveform to channel */
    dWriter.WriteWaveform(true, grayWaveform);

    /* Write the initial state and start the clock */
    writingSqWave_ = true;
}

// the task is stopped/disposed of in another function

[Nick_F1]

Hi Elizabeth,

Thank you for posting on the National Instruments forums.
Is your application currently outputting the waveform that you want?  Is it just not doing it continously?

[Elizabeth Reynolds]

Hi Nick,

Thanks for your response.

Yesterday, it was not putting out any waveform at all. Today I found out that if I commented out the ConfigureSampleClock, then the card will write a single iteration of the pattern at 800kHz (1.25us between each sample). I can change the doTask.Timing parameter to anything I want; it will not affect the rate of the output. If I put the ConfigureSampleClock line back into the code, the code will again not write any output.

As you can imagine, I am very frustrated with this! I noticed that there are no measurement studio examples (for .NET languages) that show how to output a digital waveform--all of the examples are single-sample writes. This puzzles me a bit, since it seems to me that writing a digital waveform should be a basic function of a DAQ card.

I have found and run a few examples of a digital waveform output, but have not been able to get any of them to run successfully.

Any suggestions you have would be greatly welcome.

Thanks,
Elizabeth

[Elizabeth Reynolds]

It is all working now...thanks.

[Matt Allen]

I am having the same problem and was wondering if you could post what you did to fix this.

Thanks
Matt

[Elizabeth Reynolds]

My problem was understanding the digital I/O clock--there isn't one. Instead, you can either tie it to one of the analog clocks, use the counter clock, or provide a clock on one of the PFIs. I think there might be a couple other options, but I used the analog input clock. The key then is realizing that the analog input task must be running the entire time that you want your digital I/O running.

So I created a task, added an analog input channel, and started the task. This started the analog input clock, which I then used for my digital I/O. I didn't actually have to be continuously reading data from the task, I just had to have the task running.

Once the analog task was going, I could create another task and add a digital output channel. I used the ConfigureSampleClock function to set up the digital output channel timing, and made the first argument to the function "ai/SampleClock". Then I could create a digital channel writer, and my waveform wrote correctly.

Let me know if this helps and if you have any more questions about what I did.

[Mark Doyle]

Elizabeth,

Thanks a lot for your post. I was having the same problem and didn't realize I needed to create an analog task to provide the clock. After about half a day of trial and error I got the waveform output on the digital IO to work. Would be nice if they had provided an example, but your post provided the clue I need.

Mark Doyle

[Zenon_Cyganek]

Hi, Elizabeth,

Thanks for your explaining. I have the same problem, and Your post was very helpful.
But I also use Visual Studio and I have problem with implementation. I try to generate digital waveform with MAX and everything goes ok (as You wrote in last message). Unfortunately, when I do the same (I think the same) in Visual Studio, nothing happend. I think I use some wrong argument or something like this...

Every example I found in NI Zone are written in LabView.
Could You show your C# code to generate digital waveform?
Thanks
Best regards
Zenon Cyganek