A communication circuit facilitating communication between a first equipment and a second equipment including a conversion circuit, an input port, an output port, and a communication port is disclosed. The conversion circuit converts an input signal to a first intermediate signal, and converts a second intermediate signal to an output signal. The input port inputs the input signal to the first conversion circuit. The output port outputs the output signal to the control unit. The communication port inputs the second intermediate signal to the conversion circuit, and outputs the first intermediate signal to the second equipment. A voltage of the first intermediate signal is determined based on a voltage of a power source if the first intermediate signal is logic high, and a voltage of the second intermediate signal is determined based on the voltage of the power source if the second intermediate signal is logic high.