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