A peripheral connector includes a peripheral signal terminal set and a test signal terminal set for respectively electrically connecting a peripheral interface and a boundary scan interface of a microcomputer. A socket is selectively connectable to a peripheral device for data transmission between the peripheral device and the microcomputer or a test module for conducting a boundary scan test on the microcomputer. A converting unit has a logic circuit and a transmission circuit. The logic circuit converts an electric potential, which is transmitted from the socket and corresponds to one of the peripheral device and the test module that is connected to the socket, into a digital control signal for controlling enablement or disablement of the transmission circuit. The test module is able to conduct a boundary scan test on the microcomputer only when the transmission circuit is enabled.