Vehicle Communication Unit (VCU)

The VCU is a 3 watt transceiver that connects the OnStar(R) system to the cellular carrier's communication system. The VCU handles all cellular communications. The cellular antenna plugs into the VCU. The VIU provides power and ground to the VCU. The VCU receives power from VIU on the battery positive voltage circuit. The VIU also supplies ignition voltage to the VCU over the ignition 1 voltage circuit. The VCU communicates with the VIU by using the OnStar(R) serial data (-) circuit, OnStar(R) serial data (+) circuit and the OnStar(R) serial data return circuit. The callers voice is carried to the VCU using the microphone signal circuit and the drain wire circuit. The audio signal is carried from the VCU to the VIU on the audio return signal circuit and the audio low reference circuit.