A level shifting multiplexing circuit provides an interface between a two conductor full duplex bus (two conductor bus) and a single conductor bidirectional half duplex bus (single conductor bus) where the two conductor bus is operates at a first supply voltage and the single conductor bus operates at a second supply voltage. A first switching circuit connected between the single conductor bus and the reception conductor of the two conductor bus is configured to provide a low logic signal to the reception conductor when a first switching voltage threshold is exceeded and to provide a high logic signal, otherwise. A second switching circuit connected between the single conductor bus and the transmission conductor of the two conductor bus is configured to provide a voltage less than the first switching voltage threshold when voltage at the transmission conductor exceeds a second switching voltage threshold unless a high logic signal is received on the single conductor bus. The second switching circuit is further configured to provide a voltage greater than the first switching voltage when the transmission conductor voltage exceeds the second switching voltage threshold unless a low logic signal is received on the single conductor bus.