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Optical data bus system MOST150
History
The Audi A8 '03 saw the introduction of the first optical data bus
system, the MOST bus. To be precise, the MOST25. The data bus
system was named after a group known as the "Media Oriented
Systems Transport (MOST) Cooperation". This group is made up of
various automobile manufacturers, their components suppliers
and software companies, who joined forces to create a standard-
ised high-speed data transfer system.
The term "Media Oriented Systems Transport" refers to a network
designed for transmission of media-based data. This means that,
unlike in the CAN data bus, address-oriented messages are sent to
a specific recipient.
This technology is used in Audi vehicles to transfer data within the
infotainment system.The data transfer rate on the MOST25 bus is
approx.25Mbit/s.
MOST150
With the arrival of the Modular Infotainment System, the
MOST150 is being used on an Audi for the first time.
This developmental stage in MOST technology is six times faster
than the MOST25 bus.The development process necessitated
various modifications to MOST components. The transmitter and
receiver units had to be adapted, for example. Other components
such as the optical connectors, the fibre-optic cables or the
electrical connectors for the control units are identical to those for
the MOST25.
System and diagnostics manager
With the Modular Infotainment System, a maximum of five
control units are connected to the MOST bus:
• Electronic information systems control unit 1, J794
• Digital sound package control unit J525
• TV tuner R78
• DVD changer R161
• Instrument panel control unit J285
With the advent of the MOST150, the video signal from the TV
tuner R78 or the DVD changer R161 is transmitted directly via the
optical data bus for the first time. A separate FBAS connection on
the J794 as with the MOST25 is no longer fitted.
With the MIB, the electronic information systems control unit 1,
J794, performs the function of the system manager for the MOST
bus as well as being the diagnostics manager. That was previously
the job of the data bus diagnostic interface J533.
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