The MOST network is a bus for transmitting picture and audio data. In the E65, only audio data and control commands are transmitted. Bus communication functions in one direction. The control units are connected in series in the bus. The bus has a ring structure. If the temperature exceeds 70 °C in a device in the network, the Control Display indicates that the corresponding functions are no longer available. The entire MOST bus is powered down if the temperature exceeds 85 °C. Only the Control Display recognises the current application and its parameters such as the volume setting for listening to the radio. The Audio System Controller stores information regarding which control units are installed. This list of equipment can be called up in the Service menu of the Control Display. The equipment cannot be called up if the ring is interrupted. The Audio System Controller manages the audio sources by making available internal channels for outputting and by outputting the individual channel after being prompted by the Control Display. If the optional extra TOP Hi-Fi is fitted, the audio low frequency is recalculated prior to output and the improved audio low frequency is output.
If the MOST functions cannot be executed, this may be because of the following reasons:
No function can be selected |
Fibre-optic cable interrupted |
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Voltage supply of at least one control unit interrupted |
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Serious software conflict of at least one control unit |
Chosen functions cannot be selected |
Severe software conflict of the control unit associated with the function |
No function, note on excessive temperature |
At least one function has shut down due to excessive temperature |
The function examples always relate to the optional extra TOP Hi-Fi. If this equipment is not fitted, the audio data is not prepared in the amplifier. Instead, the audio data is prepared and output by the Audio System Controller.
The MOST is in the initial state ”Bus asleep”. Pressing the rotary pushbutton ”Audio System Controller” wakes up the Audio System Controller. The Audio System Controller switches on the light on the bus. All the control units are woken in succession when the light is switched on. The Control Display recognises that the Audio System Controller has woken. In response, the Control Display requests the Audio System Controller to provide audio channels for the function ”Radio on”. At the same time, the aerial tuner is requested to provide the station list. The aerial tuner identifies the station that was received last and sets this station. The audio data of the station are made available to the Audio System Controller. With the check-back signal from the aerial tuner, the Audio System Controller makes the audio data available for output.
The volume can be adjusted using the rotary control/push button on the Audio System Controller or the volume buttons on the multifunction steering wheel.
Example: Setting via ASK: Turning the button on the ASK transmits a change in status to the amplifier. The amplifier calculates the new parameters and outputs them. Without the TOP Hi-Fi optional extra, the ASK calculates the new audio parameters and outputs the sound. In this example, the ”Radio” function is active at volume 10. There was a status change by one step. The ASK transmits a telegram to the amplifier with the volume status change. The amplifier recalculates the audio data and outputs them with minimal delay at its speakers. The amplifier simultaneously places the signals on the bus. The ASK outputs the calculated data at its speakers. When a control unit is restarted (after a crash), this may result in faults in the ASK's channel selection. If this fault occurs, a high-frequency sound is output which might be inaudible. The cause is located by searching for the fibre-optic cable communication fault. It is important to search for the fault in the right control-unit order. Beginning with the instrument cluster, the first control unit with a fault-memory entry is sought in the direction of the Control Display consecutively in accordance with the MOST connection scheme. The fault was caused by the previous control unit. Fault causes can be traced in the hardware or software of the relevant control unit or its predecessor.
Example: Adjusting via multifunction steering wheel: Pressing the button on the multifunction steering wheel sends a status message via CAN, Control Display and MOST to the ASK. The ASK checks this status and counts the volume value upwards as long as the status is active. The ASK makes each value available to the amplifier; the volume is thus increased continuously at the speakers.
Stations and tracks (search function) can be adjusted by means of the Audio System Controller auto search button, buttons on the multifunction steering wheel or menu prompting in the Control Display.
Example: Adjusting via multifunction steering wheel: The set state is ”Listen to music via CD changer”. The next track is to be played. A status change is generated by pressing the right button block on the multifunction steering wheel. This status change is forwarded via the CAN to the Control Display. The Control Display checks in its own administration and identifies the CD changer (CDC) as the current source. The Control Display issues the request for the next or previous track to the CD changer. The CD changer aligns itself to the new track and starts playing it. At the same time, the CD changer transmits the information back to the Control Display.
Composite colour picture or RGB ensures the transmission of picture information. An exception is the graphic navigation information in the instrument cluster. These graphics are vector graphics which are output as telegrams by the navigation system. Sound is always output by each control unit via the MOST and the Audio System Controller.
Up to model year 2003_09, the Japanese version of navigation is not a MOST control unit. The connection to the MOST is established via the Flexible Bus Interface (FBI). Navigation voice output is placed by the FBI on the MOST bus. The picture data is transmitted by means of RGB and separate synchronisation to the video module and converted into RGB signals. It is then output in the Control Display. There is no navigation information in the instrument cluster.