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