Provided is a digital transmitting module included in a host device connectable to a client device. The digital transmitting module may include: a clock generator which provides the host device with a clock whose one cycle is composed of T1, T2, T3 and T4 connected sequentially; and a voltage encoder which receives the clock from the clock generator, receives a digital bit from the host device, generates a voltage pulse by encoding the digital bit based on the clock, and then transmits the voltage pulse to the client device. Provided is a digital receiving module included in a client device connectable to a host device. The digital receiving module may include: an inpulse extractor which receives a voltage pulse from the host device and generates an inpulse signal by referring to an inpulse component of the voltage pulse; a voltage decoder which decodes a digital bit by referring to the inpulse signal; and a clock synchronizer which generates a clock synchronized with a clock signal of the host device by referring to the inpulse component existing in each cycle of the inpulse signal.