Large output buffer on NI 9264 device?

[Winther79]

Hi.

I am working on an application which uses an NI 9264 16ch AO device. I connect to the module with a NI 9181 Ethernet chassis.

In the application I start a single task that outputs variations of sinewaves on all 16 channels. While the outputs are running I want to be able to change amplitude and frequency settings of the sinewaves se this chage on the actual outputs shortly after.

I have built this application and it works just as I want it to except for one thing. There seems to be a large output buffer in the 9264 module, so that when I change the signal settings it takes a long time for the changes to take effekt because it has to run through this large output buffer.

When using 20kS/s it takes a little more than 20 seconds for the buffer to run through - so it must be above 400.000 samples.

I have added a small VI that should illustrate my issue. I do not use DAQ assistant as in the example but the behaviour is the same.

Setting a value with "DAQmx Configure Output Buffer.vi" does not make a difference. And if I read out this buffer value without trying to change it, it is no where near the 400.000 samples.

If regeneration mode is set to "Do not allow regeneration" you will se the example run fast through the first iterations while filling up the buffer, and then continuing with one iteration every second.

If regeneration mode is set to "Allow regeneration" then the first iterations will not run fast but the buffer is still filled, it still takes a long time for changes to get through. I suspect it then uses the first dataset to fill the buffer.

Am I completely missing something here?

What is this buffer that cannot be set with "DAQmx Configure Output Buffer.vi"?

Or can someone tell me if it is possible to change the size of it?

Hope you can help.

Stephan.