PFI comedi

[sanny]

Hi All,

I have a PCI-6052E data acquisition board that I control using the comedi drivers. Now, I need to digitise the output of a multiplexer while controlling the switching on the multiplexer. The multiplexer has 16 inputs and 1 output. I control the switching on the multiplexer using a 4 bit counter. Now, I need to increment the counter at a frequency of 320KHz, so that I sample the inputs at the rate of 20KHz. I need to send a 320KHz digital signal from the DAQ board. The multiplexer settling time is about 1us and so I need to trigger the analog acquisition off the 320KHz signal with a delay of 1us to account for the multiplexer settling time. Does anyone know how to do this or have any ideas on how I should do it. Any help would be greatly appreciated! 

Also, can I monitor the analog input conversion times on one of the PFI outputs?

Thank you very much for any help,

Raghav 

[John_P1]

Hi Raghav,

Thanks for posting!  Unfortunately, I am not familiar with the Comedi drivers for our DAQ products (they are not officially supported on this forum).  However, there are at least two possible ways that the hardware would allow you to implement this delay.

1.  Analog input tasks use a convert clock to actually sample the data.  By default, this occurs two timebase ticks after the sample clock edge.  I am not sure if the Comedi drivers expose the functionality, but the hardware is capable of setting a different number of timebase ticks to delay the convert clock.  More information about the convert clock can be found in the E series user manual (page 2-43).
2. If this is not an option, you could try to configure the analog input task to sample on the falling edge of your clock signal.  Again, I am not sure if the Comedi drivers expose the functionality.

If the Comedi driver allows you to route signals, you should be able to connect the Convert Clock to PFI 2 without reserving the Trigger Bus:

Again, I am not familiar with the Comedi driver, so you may need to try to find support through their website: http://www.comedi.org/.  Perhaps somebody else on these forums may have more experience with Comedi.

-John 

Message Edited by John P on 04-23-2009 07:26 PM

Message Edited by John P on 04-23-2009 07:27 PM

[sanny]

Thanks for the suggestions.

I don't think Comedi lets me control the number of ticks or trigger of a falling edge. But, I could ensure that my digital signal is 1us wide and then invert it and trigger the acquisition of the inverted signal.

I did figure out how to route the sample clock signal to the PFI inputs using the comedi drivers.

Thanks,

Raghav

[John_P1]

Hi Raghav,

This should work perfectly--sorry that you have to resort to external circuitry but hopefully it shouldn't be too complicated to implement.  Programming the DAQ card to do this itself should be doable with the DAQmx driver, but the functions required are more advanced features that don't seem to be currently available on the Comedi driver.

-John

[sanny]

Hi John,

Is the DAQmx driver supported on 64bit machines with Linux - Mandriva 2008? Is NI going to support this?

Thanks,
Raghav

[John_P1]

Hi Raghav,

I should have asked which OS you are running.  Currently the only 64-bit OS that DAQmx supports is Vista, so it sounds like you have a special case that requires you to use another driver (such as Comedi).  You can also try posting to the Driver Development Kit forums if you want to dive into Register Level Programming. 

I can't comment on the status of any upcoming releases--our R&D team has many items on their plate and we try to offer support for the most customers possible.  We are aware that many customers use Linux (with a growing number switching to 64-bit), but it couldn't hurt to formally post a Product Suggestion.  These are reviewed by R&D to assess the demand for specific features in upcoming releases. 

For now it sounds like the best option for you may be to continue to use the Comedi driver; it sounds like you are very close to getting everything working.  I hope all is well, and the best of luck with your application!

-John 

[sanny]

Hi John,

Thanks for the reply. I will post a suggestion and work with Comedi for the moment!

Thanks again for the help,

Raghav