Radio/Audio System Description and Operation
Radio/Audio System Description and Operation
The Entertainment System on this vehicle is configured with either a base or an uplevel system. Both the base and uplevel systems contain a radio, antenna, speakers, and an audio amplifier. Satellite digital radio (U2K) is available with the base and uplevel systems.
The following list shows the radios available for this vehicle:
* Base Radio (U2T) - AM/FM, CD, RDS, and BOSE(R) Amplifier
* Base Radio (U2R) - AM/FM, COX, RDS, and BOSE(R) Amplifier
* Uplevel Radio (U2S) - AM/FM, DVD, RDS, 40GB Hard Disk Drive (HDD) and BOSE(R) 5.1 Surround Sound Amplifier
* Uplevel Radio (UAV) - AM/FM, DVD, RDS, Navigation, and BOSE(R) 5.1 Surround Sound Amplifier (U.S. and Canada)
* Uplevel Radio (U2Y) - AM/FM, ICDX, RDS, Navigation, and BOSE(R) 5.1 Surround Sound Amplifier (Europe)
* Uplevel Radio (U2X) - AM/FM, ICDX, RDS, Navigation, and BOSE(R) 5.1 Surround Sound Amplifier (Japan)
Contents
Each item in the list below represents topics covered in detail below.
* Component Description
* Circuit Operation
* AM/FM Reception
* XM Reception
* XM Satellite Radio
* On-Board Diagnostics
* Theft Deterrent
* Radio Personalization w/Home and Away Feature
* Radio Data System (RDS)
* Steering Wheel Controls
Component Description
Radio
In order for any radio to operate two essential parts are needed; the transmitter and receiver. The radio transmitter encodes a message (audio, video, or data) onto a sine wave and transmits it with radio waves to the antenna. The radio waves are transmitted from the antenna into free space.
The radio receiver antenna captures as much of the transmitters power as possible and supplies it to the radio tuner. The radio receiver also processes information from recorded playback media (e.g., CD player, IPOD, MP3 playback device, etc.).
After the radio receives and decodes the message the signal is amplified and sent to the speakers, remote amplifier, or headphones.
The operator interfaces with the radio system through the buttons and control knobs located on the Infotainment Faceplate Control Module or faceplate. The operator is able to control system power, volume, fade, balance, bass, and treble equalizations. When the operator turns a knob or pushes a button, a module in the faceplate sends a signal to the radio on a UART - based bus called CAN Graphical Interface (CGI). The CGI bus circuit is part of a wiring harness that connects the faceplate and radio.
The radio is located in the instrument panel center stack area, behind the faceplate, and is fastened to the instrument panel by fasteners. A rear bullet type guide pin is provided to aid in aligning the radio. A 44-way connector is the main connector for all radios. The navigation radio has an additional 20-way connector and a connector for the color display. The USB cable connection to the radio is the USB Mini - A type. Three separate coaxial cables connect to the radio, one each for AM/FM, XM (if equipped), and GPS.
Radio amplifier outputs to the speakers are protected from damage should speaker leads become shorted to ground or shorted to vehicle power. The radio will sense these conditions and shut down the amplifier outputs in a non-destructive manner. After the short condition is removed, the radio will return to normal operation.
Hard Disk Drive (HDD) Radio
Radios with a hard disk drive (RPO U2S and UAV) are able to record songs from Audio CDs, MP3 / WMA discs, and USB mass storage devices. The hard drive has a 40GB memory capacity. A portion of the HDD is used for the storage of radio system files. The remainder of the HDD capacity is available for the storage of media files. Refer to the owner's manual on using the HDD feature.
Important:
* The audible.com(R) playback requires activation of the vehicle as a player for the downloaded content. The radio system activates the audible.com(R) system when information is found on either a CD inserted into the CD/DVD-A player or if a USB storage device is connected. The Vehicle Identification Number (VIN) number is required in order to activate your vehicle.
* If the radio needs to be replaced the hard drive needs to be cleared before sending the radio back to the Electronic Service Center. Use the scan tool to perform this function.
The radio is able to play back audio - book content downloaded from www.audible.com(R). This content can be transferred into the HDD by either burning it to a CD or copying it to a USB storage device and then recording it to the HDD.
Infotainment Faceplate Control Module
The Infotainment Faceplate Control Module or faceplate is a separate component from the radio chassis. The faceplate contains the radio control knobs and buttons for all audio functions. In addition, the HVAC head controls are part of the faceplate. If equipped with the heated seat option, the temperature control switches for the driver and passenger are part of the faceplate.
There are two faceplate designs with several button configurations (options XM radio, heated seat, heated and vented seat, and hot-shot):
* Non-navigation radios include a monochrome main display
* Navigation radios do not include a main display. The display is separate and mounts to the Display Module Actuator.
The faceplate communicates with the radio through the CAN Graphical Interface (CGI) bus. When the operator rotates a radio knob, to change a radio station or to increase the volume, a message is sent to the radio over the CGI bus. The request is completed after the radio receives the message.
Other messages communicated on the CGI bus between the radio and faceplate includes the following:
* Radio provides the content for the monochrome display
* Faceplate communicates button presses / knob rotations to the radio
* Radio commands the state of indicators / telltales on the faceplate
* Radio communicates the dimming level of the monochrome display
The Hazard, Hot Shot, and Traction buttons are not read by the faceplate and communicated to the radio. These switches are wired directly to their respective modules. The faceplate is responsible for backlighting of these switches.
Amplifier
Two types of amplifiers are available for this vehicle:
* Bose(R) sound system. The 8 channel non-GMLAN amplifier is mounted in the trunk.
* Bose(R) 5.1 Cabin Surround sound system. It includes Bose Audio Pilot(R) noise compensation technology. When activated, a microphone monitors interior ambient noise allowing the amplifier to continuously adjust the audio system equalization to compensate for background noise. It is most effective at lower radio volume settings where background noise can affect how well the music is heard. At higher volume settings, where the music is much louder than the background noise, there might be little or no adjustments made. The 10 channel GMLAN amplifier is mounted in the trunk.
Speakers
Two available speaker systems are available for this vehicle:
* UQA - The base speaker system consists of eight speakers. Two 1 inch speakers one mounted in each A - pillar. One 80 mm speaker mounted in the center IP. Two 6.5 inch speakers one mounted in each front door. Two 5.25 inch speakers one mounted in each rear door. One 10 inch subwoofer speaker mounted to the rear shelf.
* UQS - The up level speaker system consists of ten speakers. Three 80 mm speakers mounted in the IP. One mounted in the center and one each on the outside. Two 9 inch speakers one mounted in each front door. Two 5.25 inch speakers one mounted in each rear door. Two 80 mm speakers mounted to the rear shelf. One power subwoofer mounted to the center rear shelf.
Diversity Antenna System
The diversity antenna system uses both front and back windows with an integral antenna built between the glass layers of the windshield and as an appliqué to the rear glass. Any damage to the antenna requires replacing the glass.
The diversity antenna system is designed the best signal reception possible. Two antennas are used to form a diversity system. The primary antenna is part of the rear window and looks similar to the defogger grid. This antenna receives both AM and FM signals. The secondary antenna is part of the front windshield and receives only FM signals.
The antenna reception signals are sorted by the radio antenna module. The radio antenna module is enabled when the radio is turned on. When the AM or FM band is selected on the radio, the antenna module connects the rear window antenna directly to the radio. In addition, when the FM band is selected an enable signal is sent to the antenna module. Superimposed on this enable signal is the strength of the signal being received by the radio tuner. The antenna module now performs two functions. It switches between the front and rear antenna, monitoring the radio signal strength and combines both signals and phase aligns them to create one strong signal.
Remote Auxiliary Jack/USB Adapter
A remote 3.5 mm auxiliary stereo jack and USB connector allows playback of audio signals from remote devices (e.g., laptop computer, IPOD, MP3 player, etc.). The Aux jack is a five wire connector interface. The USB is a four wire plus shield USB cable interface. The USB connector uses the USB standards, 1.1 and 2.0. This type of connector supports rates for low speed (1.5 Mb/s), full speed (12 Mb/s), and high speed (480 Mb/s). The remote Aux jack/USB adapter is located in the rear console bin.
The radio detects the presence or absence of an audio mini-plug through the AuxJackDetect input. When the audio mini-plug is inserted in the Aux Detect Switch the mechanical switch closes. When removed the switch is open.
Circuit Operation
CAN Graphical Interface (CGI)
The CAN Graphical Interface (CGI) is a high-speed UART link used to transfer high - rate display graphics to the faceplate. Two-baud rates define CGI, a low-speed, and a high-speed. The low-speed rate is 28,000 bits/second. The high-speed rate is 625,000 bits/second. The UART communication format for both speeds is bi-directional.
CGI communications include the following:
* The radio provides the dimming levels for the display and communicates this information to the faceplate via the CGI circuit.
* Button presses and knob rotations are communicated from the faceplate to the radio via the CGI circuit.
* HVAC control button presses from the faceplate are communicated over the CGI circuit to the radio. The radio places the information on the GMLAN circuit which is sent to the electronic climate control (ECC) module.
* If equipped with the Heated Seats option, a warmer or cooler seat request is made and the message is communicated over the CGI circuit to the radio. The radio places the information on the GMLAN circuit which is sent to the memory seat module (MSM).
* The radio commands the state of faceplate indicators and telltales over the CGI circuit.
Wake and Reset
When the infotainment system is active, the radio asserts and holds the CntrStackWake circuit in order to wake up and control the power state of the faceplate.
The faceplate monitors the buttons on the faceplate during the OFF power state. After a local wakeup event (e.g., a button press), the faceplate detects the event and asserts the CntrStackWake circuit waking up the radio. The other buttons required to wake up the system are:
* Power On (center push feature of the volume knob)
* Eject
* Load
* Display/Info
* Buttons that initiate Bench Mode
Radio Power
A 15A RADIO fuse, located in the rear BEC, supplies the main radio power. The radio does not require a discrete ignition feed circuit for power moding. The power moding is accomplished using a structure of Virtual Networks (VN). The Power Mode Master (PMM) transmits the GMLAN power mode signals.
The radio supports the following signals:
* System Power Mode
* Infotainment Operation Allowed
The radio also supports the following GMLAN Vehicle Power Modes:
* OFF
* ACCESSORY
* RUN
* CRANK REQUEST
Radio Ground
A wire in the main radio connector connects to ground G850 which is located around the left rear body area. Resistance between the ground pin and the vehicle battery negative terminal must not exceed 0.05 ohms.
Faceplate Display Dimming
GMLAN signal data received by the radio determines the dimming and backlighting levels of the faceplate. The radio sets the backlight and display dimming to the value indicated by the interior dimming level and interior dimming display level signals in the GMLAN dimming information frame. The radio provides faceplate and control/graphics backlighting in the OFF (RAP inactive) when the exterior lighting virtual network (VN) is activated. The faceplate display is consistent then with the surrounding devices that use analog PWM dimming to backlight their control/graphics when the power mode is OFF and the park lights are ON.
Amplifier Interface (Non - GMLAN)
A 30A AMPLIFIER fuse, located in the rear BEC, provides the main amplifier power for the amplifier. The radio remote enable circuit provides a switched 12-volt output to the non-GMLAN amplifier. This output controls the power - state of the amplifier. To respond quickly to audio input and control signals, the amplifier is ON in all vehicle power modes except OFF and CRANK Request. However, when the amplifier is asleep it still must allow chime functionality. The internal amplifier bridges are fully powered and unmuted when the amplifier receives the switched 12-volt input.
The radio provides a amp control output circuit to control overall muting of the non-GMLAN amplifiers. The amplifier receives PWM signals on the circuit at varying duty cycle percentages for controlling the muted and unmuted functions of the amplifier. The radio monitors the remote amp control circuit for faults and sets the appropriate DTC when detected.
The function table below shows the four possible amplifier mute functions.
Amplifier Interface (GMLAN)
A 30A AMPLIFIER fuse, located in the rear BEC, provides the main amplifier power for the amplifier. The amplifier does not require a remote enable circuit for power moding. The power moding is accomplished using a structure of Virtual Networks (VN).
The amplifier supports the following signals:
* System Power Mode
* Infotainment Operation Allowed
The amplifier also supports the following GMLAN Vehicle Power Modes:
* OFF
* ACCESSORY
* RUN
* CRANK REQUEST
The radio controls the overall muting of the amplifier and commands the amplifier to perform the following via serial data (GMLAN) messaging:
* Volume
* Balance
* Fade
* Bass
* Midrange
* Treble
* DSP Modes
* Volume Compensation
* Chime Output
Amplifier Radio Speaker Inputs
The low-level audio signals (LF, RF, LR, and RR) from the radio are the inputs to the amplifier. The amplifier boosts these inputs and outputs them to the vehicle speakers. If one speaker plus or minus low level audio signal circuit is open between the radio and the amplifier, the input to the amplifier is approximately half. The speakers for that channel then operate at approximately half the normal volume or in some cases no volume.
The low level audio signals from the radio to the amplifier typically measure in the 4-5V range.
Amplifier Speaker Outputs
At a low volume, the plus (+) and minus (-) speaker outputs circuits measure approximately 2-7V AC or 7-8V DC at the speaker connector when testing a normal working system. If a plus or minus for any speaker output is shorted to ground or voltage, the amplifier circuitry will turn OFF the front outputs or rear outputs for component protection. In addition, the GMLAN amplifier sets a DTC for the affected speaker output circuit.
Remote Radio Audio Signal Inputs (UE1 only)
Audio output from the OnStar(R) communications module connects to the remote audio signal inputs of the radio. When the cellular telephone mute signal goes to 0 volts, the radio over-rides any other audio signal and uses these inputs as the source for the output to the speakers.
Cellular Telephone Mute (UE1 only)
The OnStar(R) communications module uses the cellular telephone mute signal circuit to over-ride the radio for OnStar(R) communication. When cellular telephone mute is not active, this circuit is held at 1-volt by the radio. When the cellular telephone mute signal is pulled to ground, the radio over-rides any other audio signal and uses the remote audio signals as the source for output to the speakers. If the radio was OFF when this circuit is pulled low, the radio will turn ON. Additionally, the radio fades the speakers to full front, adjusts the volume to an initial audible level, and sets an Auto Tone designed for optimal use with OnStar(R). When the mute signal is no longer pulled to ground, the radio returns to the mode it was in previously.
AM/FM Reception
Radio Signal
The radio signal is sent from a broadcast station and is then received by an antenna. The strength of the signal received depends on the following:
* The power output (wattage) of the broadcasting station
* The location of the vehicle (or receiver) relative to the broadcast tower.
* Obstacles between the tower and the receiver
* Atmospheric conditions
* What band (AM or FM) the station is broadcasting
* Type of antenna and the ground plane
AM Reception
The AM band has a lower frequency range than the FM band. These longer wavelengths:
* Bend around Obstacles
* Follow the curvature of the earth
* May reflect off the ionosphere (skip)
The AM frequencies have longer range due to the ground wave. The ground wave follows the curvature of the earth and is effected by its conductivity. Greater conductivity equates to less signal loss thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 miles).
FM Reception
The shorter wavelengths of the higher frequency FM band:
* Reflect off obstacles
* Are absorbed by the ground
* Penetrate the ionosphere
Broadcasts in the FM band are limited to line of sight reception which is typically 40 km (25 miles). Even when out of a direct line of sight, the signal may be reflected into areas that would be in a shadow otherwise. Factors which affect the line of sight include:
* Height of the broadcast antenna
* Height of the receiving antenna
* Terrain and buildings in the broadcast path
XM Reception
XM satellite radio provides digital radio reception. The XM signal is broadcast from two satellites and, where necessary, terrestrial repeaters. The high power satellites allow the antenna to receive the XM signal even when foliage and other partial obstructions block the antennas view of the satellite. Terrestrial repeaters are used in dense urban areas. These repeaters will receive the satellite signal and re-broadcast them at much higher power levels in order to ensure reception in areas with densely packed tall buildings.
On-Board Diagnostic Mode
Follow the instructions below to enter and utilize the on-board diagnostic. These multiple button presses are different depending on the faceplate option content level.
1. Key On, engine Off, radio in AM/FM mode.
2. The CD/CDX option, press and hold preset button 1 (far left push-button), preset 6 button (far right pushbutton), and band button (AM/FM button). The HDD option, press and hold preset button 1 (far left pushbutton), preset 6 button (far right pushbutton), and Setup button (Config button). The NAV option, press and hold Navigation button, Destination button, and Audio button.
The following labels appear on the display.
* SW PN
* SIGNAL
* SP TES (Speaker Test)
* EXIT
Press the pushbutton positioned under the label to select.
The SW PN label displays the hardware number and the seven software module part numbers.
The SIGNAL label displays the AM/FM antenna signal strength and XM satellite 1 and 2 signal strength and terrestrial repeater signal strength.
The SP TES label displays the speaker test. The first speaker under test is displayed with an audible tone. The verbiage stating Multiple Press Changes Speaker is displayed. Pressing the pushbutton under SP TES selects the next speaker tested.
Pressing the pushbutton under the EXIT label exits the on-board diagnostic.
Theft Deterrent
The radio theft deterrent system is intended to disable radio functionality if incorrect vehicle information is received by the radio. The radio disables functionality if the vehicle identification number (VIN) sequence received by the radio (A VIN sequence is usually the last six digits of the VIN.) does not match the VIN information learned by the radio. The radio receives this information in a GMLAN frame form.
The radio provides the following theft operating modes as part of the radio theft deterrent system:
* No VIN Mode - A radio that has not received or learned a VIN. In this mode the radio has limited functionality.
* Normal Mode - A radio has received a VIN sequence. The radio only learns the VIN sequence if the VIN sequence contained all six digits. In this mode the radio has full functionality.
* Theft Detected Mode - A radio that had previously learned a VIN sequence and subsequently received a VIN sequence not matching the learned sequence. In this mode the radio has limited functionality.
Radio Personalization w/ Home and Away Feature
This feature allows two different drivers to store and recall specific radio settings. The settings recalled by the radio are determined by which remote keyless entry (RKE) transmitter (1 or 2) is used to enter the vehicle. The number on the back of the RKE transmitter corresponds to driver 1 or driver 2. The radio settings automatically adjust to where they were last set by the identified driver.
The radio can store home and away presets. Home and away presets allow you to use one set of preset radio settings in the area where you live, and another set when you go out of town. You do not need to reprogram your presets every time you travel.
When battery power is removed and later applied, you do not have to reset your home radio presets because the radio remembers the presets. However, you do have to reset the away radio presets.
Radio Data System (RDS)
All audio systems are equipped with technology known as the radio data system (RDS). RDS is a system that sends data along with the audio of the FM station you are currently tuned to. RDS is a standard that defines how a FM broadcast station may send digital data along with the audio program. Think of it as a one-way wireless modem, allowing the broadcaster to send information about his program to your receiver.
RDS data is carried in what is known as a "subcarrier". A subcarrier is a frequency that the FM broadcaster is authorized to use to send data or other audio programs that are not audible in the main audio program. RDS information can be used to display program information and to control the radio.
To receive the RDS signal, all that is needed is an FM receiver with an RDS circuit. A special integrated circuit capable of dealing with the RDS signal is in the RDS circuit and passes it along to the receiver's microprocessor where it is decoded and acted upon.
RDS Basic Information
RDS basic information:
* RDS functions are provided in the FM broadcast band only.
* RDS functions will only work with FM broadcast stations that are broadcasting RDS data.
* Not all FM Broadcast stations broadcast RDS data or offer all of the RDS services.
* RDS functions may not work properly when reception is weak, reception is of poor quality, or RDS is not implemented properly by the FM Broadcaster.
In some cases, a radio station broadcasting incorrect information may cause the RDS features of the radio to appear to work improperly.
Broadcast RDS information can be used in a variety of ways by the receiver and listener, but basically falls into two categories: Display and Control.
Displaying Program Information
RDS displays textual information such as:
* The name of the station.
* The type of program.
* General information such as artist and song title, call in phone numbers, etc.
XM Satellite Radio
XM is a national satellite radio service that offers up to 100 coast to coast channels including music, news, sports, talk and children's programming. XM provides digital quality audio and text information, including song title and artist name. A service fee is required in order to receive the XM service. For more information, contact XM at www.xmradio.com or call 1-800-852-9696.
Digital Radio Receiver
The digital radio receiver is now internal to the radio.
Steering Wheel Controls
Some audio functions are available using the steering wheel controls. The steering wheel controls consist of multiple momentary contact switches that connect a series of resistors. When a steering wheel control button is pressed, a specific resistance value is noted by the radio. This results in a generated voltage, unique to the particular button.