National Instruments NI 9403 - Manual (Page 7)

© National Instruments Corp. 7 NI 9403 Operating Instructions and Specifications
Each channel has a DIO pin to which you can connect a digital
input or output device. The 32 DIO channels are internally
referenced to COM, so you can use any of the four COM lines as a
reference for the external signal.
You can independently configure each DIO channel in software for
input or output. The DIO channels have Schmitt trigger inputs and
are compatible with 5 V TTL logic devices. Each input channel has
hysteresis for improved performance with noisy and
non-monotonic input signals. Each channel also has a pull-down
resistor and includes overvoltage, overcurrent, and short-circuit
protection. Refer to the
Specifications section for more information
about input thresholds and overvoltage protection. Refer to the
Overcurrent/Short-Circuit Protection section for more
information about overcurrent and short-circuit protection.