Hello,
Your DAQPad-6020E (for USB) works for interrupt data transfer, that is to say, the CPU is responsible of the data transfer.
During "buffered count operations", one sample need to be transfer each time the GATE signal falls. As this time, an interrupt request is generated. The CPU must stop all its current tasks in order to process this interrupt request. If your CPU is too slow or too busy, he will not have enough time to process the IRQ and some samples will not be transferred.
The counter of the DAQPad-6020E can count events from its internal timebase (20 MHz) and the count register is correctly incremented each time the SOURCE clock provides a rising edge but you cannot transfer all the samples (count register) to the RAM of your computer so fast due to the limitation of interrupt transfer.
With other DAQ hardware devices like DAQPad for firewire for example, DMA transfer is possible so that the CPU is not involved in the data transfer so transfer can be performed faster.
Here is a technical note on error 1920:
* Why Do I Get Error -10920 When Doing Buffered Counter Operations?
http://digital.ni.com/public.nsf/websearch/8FB9091CB9BB452B8525642000554799?OpenDocument
Hope this helps.
Matthieu Gourssies
National Instruments France.
