NI 6221 Sample Clock rate

[plg]

Hello guys!

Considering this :

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http://zone.ni.com/devzone/cda/epd/p/id/4167

With DAQmx, the sample clock rate (for Analog input and output) can be changed after the start has been called[...]

Hardware Model: PCI-6221 (37-Pin), PCI-6221

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Why does it generates me an exception when I try to change a task timing when the task is already started? It works fine on a serie X (6321) but it fails on a 6221.

Test method TestDevices.IODevices.Tasks.AIAOTest.ChangeReadingDelayOfAnInputTask threw exception:
NationalInstruments.DAQmx.DaqException: Specified property cannot be set while the task is running.

Set the property prior to starting the task, or stop the task prior to setting the property.

Property: NationalInstruments.DAQmx.Timing.SampleClockRate

Task Name: _unnamedTask<43>

Status Code: -200557

It is stated in the above document that it's supposed to work on a 6221. Is there something I missed?

Thanks in advance for you enlightenment.

PL

[Kevin_Price]

I'm afraid that doc is (at least partly) wrong.  I haven't done much exploring on recent versions of DAQmx, but I *am* sure that M-series boards did *not* allow a direct change in sample clock rate on a running AI task as of DAQmx 8.0

I'm also sure that such a rate change *was* allowed for AO tasks.  Further, it was also quite possible to change an AI sample rate *indirectly* by using a separate continuous pulse train task as the AI task's sample clock.

If it's an AI task throwing the exception, that's expected for M-series boards.  It's actually news to me that X-series supports such a feature - cool!   If it's an AO task throwing the exception, then I for one am surprised and hopefully someone else can enlighten you further.

-Kevin P

[plg]

Thanks Kevin for your input. That's what I think too, I'm just waiting for an official answer from NI.

It's indeed on an Analog Input task, so I'm experiencing exactly what you are saying.

Have a nice day!

PL

[Paul_M. · Accepted solution]

Hi plg,

What Kevin said is correct. The sample rate property can be changed during AO tasks but not AI tasks for E, M  or S series devices. I'll take a look at the document that you linked and make the appropriate edits. Thanks for bringing that to our attention.

Paul M

[plg]

Excellent!

Many thanks for the confirmation.