Cellular Phone: Description and Operation

VEHICLE INTERFACE UNIT (VIU)
The Vehicle Interface Unit (VIU) is powered by a fused battery positive voltage circuit, connected through vehicle wiring to the 3 button assembly, radio, microphone and the Vehicle Communication Unit. It is also attached by means of a coax cable to the GPS antenna. Ground for the module is accomplished by means of dedicated circuits that are routed with body wiring systems to chassis ground points. The VIU also houses the cellular and GPS modems to process data from the GPS satellite system and VCU. The VIU communicates with the rest of the vehicle over the class 2 serial data bus. Power moding for the VIU is accomplished over the class 2 serial data bus on some vehicles or the ignition 1 voltage circuit on others. The VIU also has the capability of commanding the horn, door unlock and exterior lamps using class 2 messages. For vehicles without this capability, the VIU uses specific, discrete circuits for commanding these features. When an OnStar(R) keypress is made, a class 2 message is sent to the audio system to mute all radio functions and transmit OnStar(R) originated audio. On vehicles that do not use class 2 to communicate with the audio system the VIU uses the entertainment and comfort (E & C) serial data circuit. After the audio system is muted, the OnStar(R) audio is transmitted to the vehicle audio system on the remote audio right signal circuit, the remote audio left signal circuit, and remote audio output (-).

VEHICLE COMMUNICATION UNIT (VCU)
The Vehicle Communication Unit (VCU) is a 3 watt cellular transceiver that connects the OnStar(R) system to the cellular carrier's communication system. This module handles all cellular operations, sending and receiving all communications over the cellular antenna and cellular antenna coax. Power and ground for the VCU is provided by the VIU on the battery positive voltage and ground circuits. 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.