Luiart;
You are probably seeing that behavior because your aquisition task is probably a synchronous type. If you are running a synchronous acquisition, all the CPU time will be sucked up by the acquisition.
You need to set up a Asynchronous DAQ type which can be found at Search Examples->I/O Insterfaces->Data Acquisition->Analog Input->DAQ Occurrences.
Hope this helps.
Filipe