Patent ID: 8594214

Claim:
An input module of a programmable logic controller (PLC), the input module comprising: a plurality of detection units each configured to: receive a pulse signal via a channel, the pulse signal applied from a load having a plurality of channels; detect rising and falling edges of the pulse signal; and transmit an output signal that is a result of detecting rising and falling edges of the pulse signal; a decision unit configured to: receive a plurality of output signals each transmitted from one of the plurality of detection units, detect edges of each of the plurality of channels; and transmit a detection signal that is a result of detecting edges of each of the plurality of channels; and a control unit configured to identify the occurrence of an interrupt using the detection signal transmitted from the decision unit and perform a counting process using the pulse signal when the interrupt occurs, wherein each of the plurality of detection units comprises: a first edge detector configured to receive the pulse signal as a clock signal and output a low signal when the rising edge is detected in the pulse signal; an inverter configured to invert the pulse signal; and a second edge detector configured to receive the inverted pulse signal as a clock signal and output a low signal when the rising edge is detected in the pulse signal.