Use external Sample Clock for PXI4472

[blinde2000]

Hi.

I am trying to use a PXI4472 with an external clock.

For the history we have some code working that used the comedi lib and we are now trying to port the code with DAQmx...

I have seen some examples where there is a call to

DAQmxCfgSamplClkTiming(taskHandle, "/Dev1/PFI7"... )

When I try this I have an error

Requested value is not a supported value for this property

Property : DAQmx_SamplClkSrc

You have requested: /Dev1/PFI7

You can select: OnboardClock

1. Does it mean that with DAQmx I only can use the OnboardClock for the 4472 ?

2. I have used PFI7 because I saw it in the example, but I have no idea if it is the right value or not. I didn't find anything about that in the DAQmx C reference Help... Should I use something else ?

Thanks

Chris

[LucaP.]

Hi Chris,

You cannot use an external clock with a PXI-4472, because it requires an oversample clock. You'll find more details in this KB: Can I Use an External Clock with My DSA Device?

[blinde2000]

Hi.

In fact we have a system where a board generates a clock.

This clock is dispatched on the pxi bus through our backplane.

This clock is a ~20Mhz.

So I want to use this clock (that indeed is an oversample clock).

I agree that the clock for the 4472 will always be generated in local.

I guess that I should try to synchronise my 4472 with the board generating the clock...

Need to check the API to see how to do that.

Chris

[blinde2000]

Hi

I am looking at the example in "/ansi_c/Synchronisation/Multi-Device/ContinuousAI" to see how I could make it work.

From my understanding, in the example we have:

Dev1 that is the master board. The oversample clock will be dispatched to others boards.

Dev10 is a slave board.

To configure Dev10, a call to DAQmxSetSampClkTimebaseSrc is done with /dev1/SampleClockTimebase

So the ClockTimebase for Dev10 is clearly the same that for Dev1

In my case, I have a custom board instead of the dev1 board.

This custom board generates the oversample clock just like a PXI4472 would do it (trusting hardware guys 🙂 )

But, in my soft,  how can I configure my slave board to use this generated oversample clock ?

As my board is not seen by DAQmx I have no dev1...

Any idea ?

Maybe a way to create a fake board with nidaqmxconfig ?

Thanks

Chris