National Instruments Data Acquisition Device E Series - Manual (Page 129)

Chapter 9 Bus Interface
© National Instruments Corporation 9-3 E Series User Manual
Changing Data Transfer Methods between DMA and IRQ
There are a limited number of DMA channels per device. Refer to
Appendix A,
Device-Specific Information , for the specifications document
for your device. Each operation (for example, AI, AO, and so on) that
requires a DMA channel uses that method until all of the DMA channels
are used. Once all of the DMA channels are used, you will get an error if
you try to run another operation requesting a DMA channel. If appropriate,
you can change one of the operations to use interrupts. For NI-DAQmx, use
the Data Transfer Mechanism property node. For Traditional NI-DAQ
(Legacy), use the Set DAQ Device Information VI or function.