A complex programmable logic device includes a SGPIO analyzing circuit, a I2C analyzing circuit and a first multiplexer. The SGPIO analyzing circuit has a plurality of port analyzing circuits, a detecting circuit and a processing circuit. Each port analyzing circuit receives an input signal and outputs a first data. The detecting circuit detects the input signal of the first port analyzing circuit to output a detecting signal. The processing circuit captures port information of the first data outputted by at least part of the port analyzing circuits as a first control signal according to the detecting signal. The I2C analyzing circuit analyzes a data flow for outputting a second control signal according to an address command related to an address message, a control command and an input data. The first multiplexer selects the first control signal or the second control to be outputted according to a testing signal.