How to control two different processes with one DAQ output board

[PMCR]

Hi Neil,

Yes, what you have described is exactly what I want to do: a waveform generation on a single channel in one task (eg. channel 0), and several other tasks with single-point outputs on other channels (eg. channels 1-7). I believe this is indeed what Otis' example implements -- a waveform generation task on one channel and a simultaneous single-point write on another.

The problem with both his example and my own applications is that running them gives error -200963 (error described in full above).  From what I understand from your and Otis' posts, so long as I only have a waveform generation on one channel and single-point writes on the others, there shouldn't be any timing engine issues, contrary to the error message I'm getting. I don't get any errors when I just have several single-point tasks and no waveform generation task (eg. if I run the modified version of his example that I attached above).

Patrick

[Salvador_Santolucito]

Hi Patrick,

The PXI-6722 uses a serial DAC.  This means that it is not capable of outputting a waveform and simultaneously doing a single point update.  Unfortunately, this is a limitation of the hardware.  However, our other analog output products use parallel DACs and do have this capability.  The 671x and 673x boards are able to do simultaneous waveform and single point output.  Another option would be to use one of our M Series boards.  The 6229 has 4 analog output channels.  Depending on how many channels you need, the M Series might be the most cost effective option.

I apologize for any inconvenience this may have caused you.

Salvador Santolucito
Product Support Engineer
National Instruments

[beakdan]

    Heya -

this response may be a bit late, but depending on the time scales onvolved, you can get around this problem by

1) using the "ControlTask" vi to unreserve your single-point AOs
2) running your waveform
3) using "Control Task" again to reserve the resources for your single-point channels

I can use this technique because I take short data runs of only a few seconds, so I can pause my perdiodic updates, write my waveform, then resume my updates.

Hope that helps!

Dan

[ebalci]

Hi!

From the discussion I understand that I can NOT have 2 continious waveforms from 2 separate analog output channels of my PCI-6733 simultaneously. And there is NO "workaround" for doing that.

And if a waveform generation is in process, we have to "stop" the task and "clear" it in order to start waveform generation in another output. It does not suffice just to "stop" the initial waveform task. Am I right?

Is there any NI harware capable of doing that. I mean, multiple output FIFOs and multiple internal clocks for parallel waveform output?

Thanks.

Note: I am using CVI by the way. So I mean the DAQmxStopTask, DAQmxClearTask functions when I say "stop" and "clear" a task.

Message Edited by ebalci on 07-03-2006 04:34 PM

[Laura F.]

Hello S. Eren BALCI,

It is only the PXI-6722 that does not have this functionality.  Since you have a PCI-6733, you can have one task performing multiple channels of waveform generation and then other tasks performing single-point analog output simultaneously.  The limitation is that you cannot have two separate tasks doing waveform generation.  However, in one task, the waveforms on the multiple channels do not have to be identical, but they do use the same sample clock.  To workaround this limitation, you would choose sample clock based on your waveform with the highest frequency and then create waveforms to output to the other channels based on this rate.

Please take a look at this KnowledgeBase article and the linked example program about using hardware-timed and single-point analog output tasks simultaneously. 

Let us know if you have additional questions.

Regards,
Laura