Control & Measurement EUPP Modules - Digital Input Board The main board contains three digital input ports, one 6 input high speed port, and two 8 bit standard speed ports. All these ports connect to the external equipment via a standard digital input port board. These input boards are linked to the main board with a 10 way ribbon cable. These boards provide isolation via opto- isolators and the input circuit is tailored to the customer requirements. The digital inputs are accessed via a 15 way D-type plug connector.