National Instruments Data Acquisition Device NI USB-621x - Changing Data Transfer Methods

Chapter 11 Bus Interface
NI USB-621x User Manual 11-2 ni.com
Output Data Generation Methods section of Chapter 5, Analog
Output, for more information.
Changing Data Transfer Methods
USB-621x devices have four dedicated USB Signal Stream channels. To
change your data transfer mechanism between USB Signal Streams and
programmed I/O, use the Data Transfer Mechanism property node
function in NI-DAQmx.