Digital inputs are binary inputs (0 or 1) that are applied to the PLC. Binary inputs are basically voltages, varying from 5V to 230V depending upon the type of card used. In simple words, any push-button, switches or sensors produces digital inputs to a PLC. Digital inputs are used to check the status of any devices whether it is ON or OFF. For an Input module of 24Vdc, 0Vdc acts as OFF state (Binary 0) and 24Vdc acts as ON state (Binary 1).