Patent ID: 7626421

Claim:
An interface circuit for expanding at least one output port of a micro processing unit, the interface circuit comprising: an input port electrically connected to one of the output port of the micro processing unit for receiving analog control signals therefrom; a plurality of output ports electrically connected to a plurality of external circuits respectively, one of the plurality of output ports being selectively driven to control one of the corresponding external circuits by inputting the analog control signals to the input port with different analog voltage values; a voltage-providing unit configured for providing a series of reference voltages; a comparing unit electrically connected to the voltage-providing unit, the comparing unit configured for receiving the analog control signals output from the input port of the interface circuit, and receiving the reference voltages output from the voltage-providing unit; and a switching unit electrically connected to the comparing unit, the switching unit configured for receiving the analog control signals outputted from the input port and the output ports, and receiving an output signal from the comparing unit.