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PXIe-6556 large data Acquisition Problem

Hi Guys,

I'm developing a method that could capture large quantity of samples/data from ADC products and I would like to use the PXIe-6556 for this.

 

I'm attaching below I2C pattern that I'll be using to capture output data from my ADC. This pattern contains about 500 vectors if I'll run the PXIe-6556 at 2MHz. If the clock rate is faster, the pattern needs to be adjusted and the number of vectors will increase.

 

In this pattern (which composes of 500vectors @ 2MHz clock) I'll only need 16bits (or vertors) of data. The location of those 16 bits are at the thin pulses of the red plot. My problem during acquisition is that, the 6556 or generally all HSDIO of NI, will capture data on every vector. So instead of 16data capture, I'll be capturing 500 data on every single run of this pattern.

 

If I'll fully utilize the onboard memory of 6556 (say 8Mb), I can only loop this pattern for about 16000 times. The problem is, I need to loop the pattern for 100000 times.

 

So my question; is there a way to configure PXie-6556 such that it will only capture on those thin red pulses? Or in general, can I command the 6556 to capture only when I want, not on every vector of the whole pattern?

 

Thanks in advance.

 

Regards,

 

i2c read pattern.PNG

 

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Hi Jeep26,

 

Do you know exactly when the desired data will occur each time? If so, you can set up a trigger to start just before the desired data occurs and read in a finite amount of samples upon receiving the trigger.

 

Kaitlin N.
National Instruments
Applications Engineer
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Hi Kaitlin,

Yes I know when the desired data occurs but how to setup the acquisition trigger just before that? Could you let me know which, on the hsdio VIs, sets this up?

Thanks!

 

Regards,

Jessy

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Hi Jessy,

 

There are a couple ways that you can go about this. The attached example shows how to use a digital edge trigger and a pattern match trigger. If you know the pattern that occurs just before the desired data then you can use this type of trigger. If you use an edge start trigger you will need to generate a signal that you can use for the trigger. This signal will need to have a frequency such that the first falling or rising edge occurs just before the desired data. For example, if you know the desired data begins at .5sec, then you can generate a 1Hz signal and trigger off of the falling edge of that signal. This VI is in LV 2012, please let me know if you are using another version of LabVIEW and I can try to find a similar example.

 

Regards,

Kaitlin N.
National Instruments
Applications Engineer
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Hi Kaitlin,

It took a while...

I didn't have much time to make the PXIe6556 work on my setup so we I temporarily used other DIO just to complete my project.

 

Now I need to go back to 6556 and I'd like to look at the solution you've posted below. Could you send me LV2010 version of the vi please?

 

Thanks!

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Hi jeep26,

 

Here is the LabVIEW 2010 version of the VI.

Regards,

 

Kaitlin N.
National Instruments
Applications Engineer
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