Functional Description
Functional Description
Data Transport
MOST currently offers a band-width of 22.5 Mbits/s . In the next generation, the band-width will be increased to 50 and then later to 150 Mbits/s (as of approx. 2002).
In order to meet the different requirements of the applications regarding data transport, each MOST message is divided into three parts:
- Control data
- Asynchronous data: e.g. navigation system, arrow representation
- Synchronous data: e.g. audio, video signals
Data Transport on the MOST
The control data controls the functions and devices in the network. The information can be compared to CAN bus data.
The control data has a band-width of 700 Kbit/s. That corresponds to around 2700 messages per second.
For the data transmission of synchronous and/or asynchronous data, there is a total of 60 bytes. The limit is variable: e.g.20 bytes of synchronous data and 40 bytes of asynchronous data.
Optical Bus
The MOST bus is a plastic optical waveguide. The MOST bus is coded in green in the E65/E66. The light wavelength is 650 nm (red light). The MOST bus requires the following converter components:
- Optical transmitter
- Optical receiver
Each control unit of the MOST framework contains a transmitter and a receiver. The transmitter and receiver have been developed by BMW. The low closed circuit (rest) current properties of the transmitter and receiver enable optical wake-up by the MOST bus.
Optical Transmitter
A driver is fitted in the transmitter. The driver energizes an LED (light-emitting diode).
The LED transmits light signals on the MOST bus (650 nm light, i.e. red visible light). The repeat frequency is 44.1 KHz.
The sensing frequency on a CD player and for audio is 44.1 MHz; this means than no additional buffer is required, yet another reason why this bus system is so efficient for multimedia.
Optical Receiver
The receiver receives the data from the MOST bus. The receiver consists of:
- An LED
- A pre-amplifier
- A wake-up circuit
- An interface that converts the optical signal into an electrical signal
The receiver contains a diode that converts the optical signal into an electrical signal. This signal is amplified and further processed at the MOST network interface.
Control Unit/Control Unit Connection
The MOST ring is composed of optical point-to-point connections between 2 control units. Each control unit has a network interface. The network interface consists of:
- An opto-electrical converter (optical waveguide receiver, already mentioned).
- An opto-electrical converter (optical waveguide transmitter, already mentioned).
- A MOST transceiver (interface between the optical waveguide receiver/transmitter and the electronic network driver).
- A network driver, the so-called NetServices.
The Netservices run on a microcontroller (main computer in the control unit)
On the application level, a control unit in the MOST framework contains stand-alone function units, so-called function blocks. Examples of function blocks include:
- Tuners
- Amplifiers
- CD players
A control unit can contain several function blocks at one time, e.g. the AVT contains the functions:
- Antenna
- Amplifier
- Tuner
Interfaces
The following contains a brief summary of the tasks of the connected control units in the MOST framework:
Control Display
The Control Display is the system master of all MOST bus functions and serves as the power master. It wakes up the bus and is responsible for switching it off (power down). The DIS Plus and GT1 will show a Control Display and a Control Display (Gateway).
Audio System Controller (ASK)
The audio system controller has the following controller functions:
Network Master
The ASK performs the role of network master for the MOST bus. The functions of the network master are the following:
- Wake-up, initialization, power-down
The network master wakes up the bus and has the task of achieving an orderly initialization of the network. The ASK can operate with KLR off. To turn it on, push in the volume/ON/OFF knob. Adjustments and control is carried out by using the Controller and Control Display.
Another task of the network master is to control the power-down process. Each powerdown is initiated and started by the ASK.
- Configuration control
The network master detects the exact system configuration each time that the network is started and compares it to the stored coded configuration.
- Control of the network operation
The network master controls the MOST transceiver of the slave equipment for correct operation. The equipment which is not operating properly will be released by a reset or switched to low power mode so that they do not affect bus communication.
- Fault code memory
The network master includes the fault code memory of the MOST network. It stores all the faults occurring during the network operation as well as deviations from the nominal configuration.
Audio Master
As audio master, the ASK has the task to collect and process all the audio signals of the vehicle and to distribute them to their destinations.
The ASK controls all the acoustic requests from the Control Display. The changes in the level of a signal is not sudden, but smooth, e.g. during suppression, insertion and fading out or temporary suppression of the signal at the destination: Because of this, a high-quality acoustic sound is obtained.
The ASK also assumes the generation and preparation of different acoustic signals, e.g. PDC signals and warnings. In the event of a request for a warning or caution signal from a control unit, the ASK provides a clean acoustic change of the signals.
- Audio data
All audio data from any control unit are converted by the ASK into digital audio AF format at a sampling rate of 44.1 MHz.
- Categorization of audio sources
All possible audio sources are divided into different groups according to priority. Warning signals have priority over any other audio source. Mixing of lower priority audio signals (e.g. navigation, radio) is possible.
- Generation of acoustic gongs
These are acoustic alarm signals which help the driver perceive sounds according to a system. The different sounds, requested by the different control units,(e.g. gongs, PDC etc), must be generated only in association with a visual indication. These come from the instrument cluster and the Control Display.
The following sounds can be generated in the ASK.
- Beeping for the PDC.
- Various Check Control and warning gongs.
NOTE: A maximum of three sounds can be produced at once. Sounds are produced in order of importance. Sounds requested exceeding three will be lost.
Connection Master
As connection master, the ASK must provide channels to the equipment connected to the bus and distribute the audio signals on the outputs (loudspeakers).
The connection master also controls the basic Hi-Fi or the LOGIC 7 Hi-Fi amplifiers.
CD Changer Audio (CDC)
The CD changer is a slave control unit in the MOST framework.
Navigation System (NAV 01)
The control unit of the navigation system has controller tasks and slave functions in the MOST framework.
Slave Control Units
The following control units are slave control units:
- Kombi (control unit of the instrument cluster)
- AVT
- LOGIC7
- SVS Speech processing system
- Telephone
- MMC