CVI-AOGenerateWaveforms problem

[Niranjan]

Hi,
We have a data acquition application in CVI-labwindows where we acquire upto 8 input channels using NI daq functions such as SCAN_Start. We have NI PCI-MIO-16E-1 DAQ board. While acquiring, we also inject (analog output) on one of the two output channels. We output a sine or pulse wave using AOGenerateWaveforms function. When we acquire more than 2 input channels, the length of injected output sine wave decreases. I mean AOGenerateWaveforms or board inject sine wave of lesser period than what we have set. Ex: we want to inject 100 points of sine wave then it will inject (output) approx 95 points instead of 100. The shape of sine wave remains same and correct. We have no idea why is this happening. We give correct length of buffer to AOGe
nerateWaveforms function for generating output. But it probably slows down and inject for lesser period. And this happens only when we incerase number acquired input channels. If we acquire only one input channel then it works fine. Does anyone has any idea abt it?
cheers
Niranjan

[Filipe A.]

Hello;

That is probably happening because you are using synchronous NI-DAQ functions to configure the Analog Input task. Those syncrhonous functions hold the CPU time until the Input buffer is ready to be retrieved. That might prevent the CPU to handle the Analog Output task, therefore, missing some update points.

The way to go is to execute a asynchronous Analog Input task. The DAQ_Event NI-DAQ function is the one you might want to take a look at. There are also some examples using that function and showing how to configure an asynchronous Analog Input operation.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[Niranjan]

Hi Filipe,
Thanks for reply.

Are u talking abt function called Config_DAQ_Event_Message?
Can you please tell me where can I find the example for configuring Asynchronous analog input operation.

cheers
Niranjan