National Instruments NI 9401

Each channel has a DIO pin to which you can connect a digital

input or output device. The eight DIO channels are internally

referenced to COM, so you can use any of the nine COM lines as

a reference for the external signal.

The DIO channels are grouped in two ports, one containing

channels 0, 1, 2, and 3, and one containing channels 4, 5, 6, and 7.

You can independently configure each digital port in software for

input or output. Note that all four channels in the port must share

the same line direction. Refer to the software help for information

about configuring ports on the NI 9401.

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 Protection

section for more information about overcurrent protection.