1. An integral digital signal interface for interfacing between an electronic control unit (ECU) and external electrical process equipment (EEPE), said interface having input terminals for receiving control signals from said ECU and output terminals for transmitting signals for controlling said EEPE, said digital signal interface comprising: control means for receiving mode select signals from said ECU for selectively programming the interface to operate in digital output/input modes and for receiving threshold input values from said ECU to perform a plurality of functions for controlling the interface and for providing operating functions with respect to controlling said EEPE; said control means including: at least one multiplexor for receiving at least one of said mode select signals and at least one of said threshold input values from said ECU; a first current limit regulator responsive to an output of said at least one multiplexor, power MOSFET circuits (PMCs) responsive to an output of said first current limit regulator for selectively switching said interface into respective digital input (DI) and digital output (DO) modes, and the interface is correspondingly set to receive input data/control signals from the ECU or to function to generate respective output signals for controlling the EEPE.