Global Positioning System: Description and Operation

ONSTAR DESCRIPTION AND OPERATION

This vehicle uses the Generation 5 version of the OnStar(R) system. This system consists of the following components:
- Vehicle Communication Interface Module (VCIM)
- OnStar(R) button assembly
- Microphone
- Cellular antenna
- Navigation antenna

This system also interfaces with the factory installed vehicle audio system.

Vehicle Communication Interface Module (VCIM)
The VCIM is a 3-watt cellular device that allows the user to communicate data and voice signals over the national cellular network. It is powered by a fused, battery positive voltage circuit, connected through vehicle wiring to the 3-button assembly and the radio, and attached by means of coax cables to the cellular and navigation antennas. Ground for the module is accomplished by means of dedicated circuits that are routed with body wiring systems to chassis ground points. The module houses two modems, one to process GPS data, and the other for cellular information. Satellites orbiting earth are constantly transmitting signals of their current location, from which the OnStar(R) system is able to pinpoint its own location. The navigation antenna receives these GPS signals and provides the data to the VCIM to be processed. The Vehicle Communication Interface Module communicates with the rest of the vehicle over the class 2 serial data bus. Ignition state is determined by the VCIM through class 2 messaging. The module also has the capability of commanding the horn and operating the exterior lamps using the class 2 serial data circuit. This vehicle uses a dedicated driver door lock switch unlock signal circuit for operating the remote door unlock feature. 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. After the audio system is muted, the OnStar(R) signals are transmitted to the audio system on the cellular telephone voice signal circuit, and returned to the module on the cellular telephone voice low reference circuit. The cellular modem connects the OnStar (R) system to the cellular carrier's communication system by interacting with the national cellular infrastructure. The module sends and receives all cellular communications over the cellular antenna and cellular antenna coax.

OnStar(R) Button Assembly
The OnStar(R) button assembly may be part of the rearview mirror on some vehicles or a separate unit on others. The button assembly is comprised of 3 buttons and a status LED. The buttons are defined as follows:
- The Answer/End Call button, which is black with a white "dot" allows the user to answer and end calls or initiate the personal calling feature, if equipped.
- The blue OnStar(R) Call Center button, which displays the OnStar(R) logo, allows the user to connect to the OnStar(R) call center.
- The Emergency button, which will display either a red or white cross, sends a high priority emergency call to the OnStar(R) call center when pressed.

The OnStar(R) button assembly receives 10 volts on the keypad supply voltage circuit. When pressed, each button completes a circuit across a resister allowing a specific voltage to be returned to the VCIM on the keypad signal circuit. Depending upon the voltage range returned, the VCIM is able to identify which button has been pressed.

The OnStar(R) status LED is located to the right of the emergency button on a mirror-mounted assembly and to the left of the answer/end call button when the assembly is mounted on the dash or overhead console. The LED is green when the system is on and operating normally. When the status LED is green and flashing, it is an indication that a call is in progress. When the LED is red, this indicates a system malfunction is present. In the event there is a system malfunction and the OnStar(R) system is still able to make a call, the LED will flash red during the call. The OnStar(R) LED is controlled by the VCIM over the keypad red LED signal circuit and the keypad green LED signal circuit.