Accessing sampling clock from BNC-2110 in from PCI-6110 using NiDAQ MMX

[Biologist2009]

Hi,

I'm trying to access the sampling/pixel clock from a PCI-6110 card. I'm using a BNC-2110 board and I'm sampling an analog signal at 0.5-1 MHz. I want to get access to this signal so that I can control some integrating electronics downstream.

[Biologist2009]

I should also mention that I'm using Visual Studio 2008 C# with NiDAQ mx. I am unsure of what commands/syntax I need to export the signal to a terminal on the BNC-2110 (preferably one of the user-defined signals). I would prefer the SCAN_CLK signal because I like its 450 ns width, but maybe the Convert or Start_Scan signal would be okay...

Message Edited by Biologist2009 on 01-05-2010 03:55 PM

[John_P1]

Hi Biologist2009,

I believe you are looking for the following function:

 

In this case, signal would be SampleClock and the output terminal would be something along the lines of /Dev1/PFI7 where "Dev1" is the name of your DAQ device.  You should use PFI 7 since this is the direct route to the AI Sample clock on the 6110 (you can find this in the device routes tab of Measurement and Automation Explorer).

The 6110 is simultaneous so it doesn't have an independent convert clock signal (although you can export the start trigger in this way if so desired).

Best Regards,

John

Message Edited by John P on 01-05-2010 06:07 PM

[Biologist2009]

Hi John,

Thanks for the reply. The pin you reference below as the Sample Clock is the START SCAN pin of the NI DAQ, correct? Is there any way to get the SCAN CLK output (or AI Hold Complete as I believe it's referred to in NIDAQmx) in NI DAQmx? If I just connect a wire to pin 46 on the 68-pin connector (pg. 33 of http://www.ni.com/pdf/manuals/321759d.pdf), would I be able to access the sampling clock directly (i.e., is the sampling clock hard-wired to pin 46 or do I have to set it in software)?

Thanks.

---

John P wrote:

Hi Biologist2009,

I believe you are looking for the following function:

 

In this case, signal would be SampleClock and the output terminal would be something along the lines of /Dev1/PFI7 where "Dev1" is the name of your DAQ device.  You should use PFI 7 since this is the direct route to the AI Sample clock on the 6110 (you can find this in the device routes tab of Measurement and Automation Explorer).

The 6110 is simultaneous so it doesn't have an independent convert clock signal (although you can export the start trigger in this way if so desired).

Best Regards,

John

Message Edited by John P on 01-05-2010 06:07 PM

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[Biologist2009]

To add to my post above, if I try to export the signal AIHoldCompleteEvent in C# .NET with NIDAQmx, I get an exception raised "SignalType requested to be exported is not supported for the specified task...". I also tried probing pin 46 (referenced to DGND), and I just get a constant high voltage signal instead of the 450 ns pulses I would have expected to see.

[John_P1]

You should export the signal the way I mentioned in my other post--the 6110 hardware manual still uses the old terminology but the Scan Clock is now referred to as Sample Clock in the newer DAQmx Terminology.

You have to explicitly export the signal, the clock will not be on PFI 7 (pin 46) unless you call the ExportSignal to export the Sample Clock.

Best Regards,

[Biologist2009]

Hi John,

I can export the STARTSCAN signal (pin 38) to PFI7, but not the SCANCLOCK (pin 46). As I understand, the order of signals for an acquisition is STARTSCAN, followed by CONVERT (50-100 ns in length), followed by SCANCLOCK (450 ns wide). I would like to get the SCANCLOCK (which I believe is referred as AIHoldComplete in NiDAQmx terminology) instead of the STARTSCAN (referred to as SampleClock in NiDAQms terminology).

 Thanks.

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John P wrote:

You should export the signal the way I mentioned in my other post--the 6110 hardware manual still uses the old terminology but the Scan Clock is now referred to as Sample Clock in the newer DAQmx Terminology.

You have to explicitly export the signal, the clock will not be on PFI 7 (pin 46) unless you call the ExportSignal to export the Sample Clock.

Best Regards,

---

[John_P1]

Hi Biologist,

I understand what you are saying now--there are in fact two distinct signals with similar names:  Scan Clock (aka STARTSCAN) and SCANCLK.  These two signals are now known respectively as AI Sample Clock and AI Hold Complete Event in DAQmx (the names are supposed to be more intuitive in DAQmx).  Here's a better link for DAQmx terminology changes.

In addition to the two above signals, there is also the Convert Clock which functions pretty much as you've described it.  

DAQmx does allow the user to export the AI Hold Complete Event and the Convert Clock using the Export Signal function on E, M, and X Series boards.  However, DAQmx does not seem to recognize the AI Hold Complete Event or the Convert Clock as a valid signal to export for the 6110--this is likely true for all of the 611x boards.  I'm going to file this as a bug to our DAQ Software Group (at the very least documentation needs to be updated to make this behavior more clear).

Could you tell us a bit more about what you need to use the SCANCLOCK for?  There are two user-accessible counters on the 6110 that might also be an option (e.g. you could one of them to generate a pulse of configurable width with a configurable delay after the sample clock).  The timebase for the counters is 20 MHz so you would have a 50 ns resolution on your times for both your pulse width and delay from Sample Clock.

Best Regards,

[KimKimBo]

Dear John,

However, DAQmx does not seem to recognize the AI Hold Complete Event or the Convert Clock as a valid signal to export for the 6110--this is likely true for all of the 611x boards.  I'm going to file this as a bug to our DAQ Software Group (at the very least documentation needs to be updated to make this behavior more clear).

Has this bug been fixed? I need the AI Hold Complete Event to drive some legacy hardware.

The bug is still there in NIDAQmx 9.1. It would be great if it is fixed in 9.2.2 ...

Thanks

[enderWiggin10]

Hi KimKimBo,

I will look into this and get back to you about the bug documentation.  You can always check the release notes/readme of the new driver to see what bugs have been addressed.

Best,