Solution
NI offers two kinds of C Series and TestScale Digital I/O devices:
Serial digital I/O modules: NI 9375, NI 9403, NI 9425, NI 9426, NI 9476, NI 9477, NI 9478, TS-15120, and TS-15130.
Parallel digital I/O modules: NI 9344, NI 9401, NI 9402, NI 9411, NI 9421, NI 9422, NI 9423, NI 9435, NI 9436, NI 9437, NI 9472, NI 9474, NI 9475, NI 9481, NI 9482, NI 9485, and TS-15050 DIO P0.
On a serial module, you can only do hardware timing in one direction at a time. Therefore, at a time, a serial module can perform hardware-timed input
or hardware-timed output, but not both at the same time. See
Digital I/O Considerations for C Series and TestScale Devices for more details.