Interface circuit for controlling output impedance of transmission circuit

An interface circuit includes: a first transmission circuit that outputs a first signal to a transmission line via a first transfer pad; and a second transmission circuit outputting a second signal to the transmission line through the second transfer pad, the first transmission circuit including a first terminal resistance block having a switch and a first terminal resistor connected between the first transfer pads, the second transmission circuit includes a second termination resistance block having a switch and a second termination resistor connected between the second transfer pads, and the second termination resistance block detects the first signal when the first transmission circuit outputs the first signal, and the second termination resistance block detects the second signal when the first transmission circuit is in a low-power operation mode. The second termination resistance block disconnects the second termination resistor when the first transmit circuit is in a high-speed data transfer mode, and c