Charging system and digital interface circuit thereof

The utility model discloses a charging system and a digital interface circuit thereof. In one embodiment, the charging system comprises an AC-DC converting circuit, a load, a battery, a system management bus host, a control circuit, a first switch, and a second switch. The control circuit comprises the digital interface circuit consisting of a control register which is an N bit register. The N bit register comprises a principle state machine located in a first partial location and giving instructions on working states of the system management bus host; and a subordinate state machine located in a second partial location and giving instructions on data transmission digits of control commands of the system management bus host The charging system and the digital interface circuit thereof disclosed by the utility model reduces the number of the control register in the digital interface circuit and the cost, and increases the integrated level.