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MOST Cooperation Multiplexes Automotive Infotainment Systems

 The wiring harness for in-vehicle entertainment is becoming increasingly complex.  Only a few years ago the only electronic entertainment device in a car was the radio.  Today, an infotainment system may include an FM radio, a satellite receiver, a CD or DVD player, an amplifier, multiple speakers, a telephone, a navigation unit, an MP3 input and one or more displays.  Tomorrow, a vehicle may contain all of the above plus a wireless connection to the internet.  The wiring for an FM/AM radio with two speakers in the dash was simple.  The wiring for a modern infotainment system is not.  What to do?

The answer is a multiplexing, but older automotive multiplexing standards, such as CAN (Controller Area Network), do not have enough bandwidth for multimedia applications.  Fortunately, a standard developed specifically for multiplexing infotainment systems is readily available.  Audi, BMW, Daimler, Harman/Becker and SMSC developed the MOST (Media Oriented Systems Transport) standard and later founded the MOST Cooperation to further refine and enhance it. They are the Partners and Steering Committee of the organization.  MOST was originally developed in response to several European companies’ recognition of their need for a common infotainment multiplexing solution. Thirteen other car manufacturers and more than seventy automotive suppliers are Associated Partners.  The original standard, MOST25, is being used by car manufacturers from Europe, Japan and Korea.  The software infrastructure is also currently being used in one vehicle manufactured in the US, the Dodge Ram pickup truck. 

The complete technical details of MOST25 are beyond the scope of this article, but they are available on the MOST Cooperation Web site, (  Basically, the standard provides for synchronous cyclic continuous repetition of MOST frames on a ring network.  Each frame is divided into a control channel, one or more synchronous channels and a packet/ethernet channel.  The timing is provided by one master device.  The primary purpose is to transmit audio or video signals at a premium quality level.   In a typical application, a MOST25 network can reduce the wiring harness weight by as much as 3 ½ pounds, the total length of wires needed by as much as 90 feet and the number of contacts needed from nearly forty to less than ten.  This is a savings in weight, cost and complexity. 

An evolutionary path is available. The latest generation, MOST150, provides a bandwidth of 150Mbs.  It doubles the bandwidth of the synchronous MOST25 channels, adds isochronous channels and adds a channel for Ethernet data transmission. With connections to the Internet, it is ready for the car of tomorrow. MOST 150 uses the same API’s as MOST25 so MOST25 applications can be migrated with little change.

Semico Spin

Multiplexing the infotainment devices in a vehicle has obvious advantages.  MOST25 and MOST150 are multiplexing standards that have been designed specifically for this application.  Any automobile manufacturer moving toward infotainment multiplexing should look no further than these standards.  Semiconductor manufacturers should be aware of the standards and helping to make them a universally accepted solution.  


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