Solution
The externally powered USB M Series devices use the
STC 2 ASIC that provides for correlated digital I/O. Correlated digital I/O refers to the ability to provide a sample clock to digital input or output tasks. This clock can come from a number of possible sources; you may refer to the device routes tab in Measurement & Automation Explorer for a full list. Externally powered M Series USB DAQ devices are numbered 622x, 625x, and 628x.
Bus-powered USB M Series devices (621x) do
not support correlated Digital I/O. These devices do not use the same STC 2 chip as other M Series devices. Much of the functionality of the STC 2 is implemented on these devices through an on-board FPGA, but correlated Digital I/O is not included in this feature list.