24, 72, and 120 channels of TTL digital I/O lines.

All I/O lines buffered by tristate transceivers. Outputs sink 24mA and source 15mA.

Four- and eight-bit groups independently selectable for I/O.

Pull-up resistors to provide CMOS and contact closure compatibility.

Cable crosstalk suppression by grounds on all even-numbered conductors.

50-pin connector for compatibility with Western Reserve Controls, Opto-22, Gordos, Potter and Brumfield, etc.

External interrupts.