To provide a system for determining property of a device in a semiconductor device to which two or more different types of devices are connected.

A first switch SW1 is provided between a determination unit 14 and a signal line 12. The first switch SW1 is turned on while the determination unit 14 determines the device 4 and thereafter turned off. A second switch SW2 is turned off while the determination unit 14 determines the device 4 and thereafter turned on. The signal line 12 connects a communication interface port P2 connectable with two or more different types of devices 4 and a communication terminal P2 of a processor which performs data communication with the device 4. The determination unit 14 monitors the electric state of the signal line to determine the device 4 connected to the port.