Patent ID: 8443112

Claim:
An input/output signal controller comprising: a transmitting section that outputs a transmission signal to the side of a 2-wire transmission line connected to terminal end resistors of both ends; a first switching section that outputs the transmission signal transmitted from the transmitting section by switching ON/OFF of a battery power supplied from a unit power supply section, being the first switching section connected between a high potential side of the unit power supply section and one of the transmission line; a second switching section that outputs from the transmission line the transmission signal transmitted from the transmitting section by switching ON/OFF of the supplied battery power simultaneously with the first switching section, being the second switching section connected between the other line of the transmission line and a low potential side of the unit power supply section; a receiving section that receives the transmission signal from the transmission line; a first detecting section connected between the high potential side of the unit power supply section and one of the transmission line, for detecting an output of the transmission signal from the transmitting section flowing through the first switching section; a second detecting section connected between the other line of the transmission line and the low potential side of the unit power supply section, for detecting the output of the transmission signal from the transmitting section flowing through the second switching section; and a selecting section that selects the receiving section when the output of the transmission signal from the transmitting section is not detected by either one of the first and second detecting sections.