The audio gateway control unit (N93/1) is the central audio communications interface within the Media Oriented System Transport (MOST). Depending on the equipment, the control commands are initialized by the radio (A2) or the COMAND operating, display and control unit (A40/3) and transmitted via the MOST to the audio gateway control unit (N93/1).
Scope of function:
Amplitude-modulated reception
Sound processing and amplification
Interface between MOST and Controller Area Network bus class B (interior) (CAN-B)
Diagnostic interface
Function conditions:
Circuit 15R ON
Authentication positive
No undervoltage or overvoltage
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Amplitude-modulated reception
If the user selects a particular radio program on the operating unit, a request is sent to the audio gateway control unit (N93/1) via MOST whereupon the radio tuner generates a tuned circuit to receive the respective transmission frequency. Via the radio receiver in the audio gateway control unit (N93/1) the corresponding high-frequency signals (FM, MW, LW, and SW) are filtered out and passed on to the integrated audio processing stage and audio amplifier stage.
Sound processing and amplification
The control commands coming in from the operating units for audio sound and volume control as well as all system component audio signals sent are transmitted via MOST to the audio gateway control unit (N93/1). The integral audio processing and amplification stage digitizes and processes the incoming signals and amplifies them before outputting them to the vehicle speakers.
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Microphone input
The audio gateway control unit (N93/1) is equipped with a connection for the sound amplifier microphone (B25/6) for automatic vehicle noise adaptation. The noise level in the vehicle's interior is measured with the aid of the sound amplifier microphone (B25/6). The volume of the music output signal is continuously adapted to this noise level. In order to do this, the audio gateway control unit (N93/1) must be able to detect which signals in the measured level are driving noise and which are audio signals. This takes place by means of a comparison of the output signal with the measured signal. A simple way of looking at it is to regard the difference in both signals as being the driving noise level.
Interfaces
The audio gateway control unit (N93/1) serves as an interface between the MOST and the CAN-B. Data which are read in voltage-coded by the instrument cluster (A1) and are placed on CAN-B can as a result be made available on the MOST.
Fault management of the MOST components
During operation, the system stores all occurring faults in the non-volatile memory. These faults can be read out using STAR DIAGNOSIS at the data link connector (X11/4). The audio gateway control unit (N93/1) detects the diagnosis command and converts the incoming data to a MOST-compatible message. The diagnosis of all MOST components is controlled by the audio gateway control unit (N93/1).
Each MOST component has its own diagnostic trouble code memory.