Digital inputs are binary inputs (0 or 1, also called as high and low level) that are applied to the PLC. Binary inputs are basically voltages, varying from 5 V to 230 V 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 24 Vdc, 0 Vdc acts as the OFF state (Binary 0) and 24 Vdc acts as the ON state (Binary 1).