Multiplex Communication System System Description

The LEXUS GS430/300 Multiplex Communication System (MPX) uses serial communication, which converts multiple pieces of information into serial communication data. As a result, they can be transmitted through a single communication wire.

Serial communication data consists of bits and frames. A bit is a basic unit of information represented by the binary values ''0'' and ''1''. The amount of information is represented by the number of bits. A frame is a group of bits. A frame contains a ''header'' that indicates the beginning of the frame and an ''end message'' that indicates the end of the frame.

Based on serial communication, various ECUs are connected on a network to exchange multiple pieces of information. Such a system is called a Multiplex Communication System (MPX).

1. The BEAN uses a ring and bus style of network to connect ECUs. This style of communication method is called a daisy chain. In a daisy chain, communication can be maintained even if the network has an open circuit.
   

   
   
   
   




2. CAN communication uses the bus style network to connect ECUs. This network consists of a main bus line (comprising junction connectors) and a sub bus line (comprising ECUs that are connected to the main bus line). This style enables communication among all the connected ECUs.
   

   
   
   
   

3. The AVC-LAN uses a star style, which is centered on the multi-display or audio head unit as a master ECU.
   

Difference of CAN, BEAN and AVC-LAN

1. The CAN, BEAN and AVC-LAN protocols have set guidelines for data. The guidelines include communication speed, type of communication wire, drive type and data length. These guidelines are established to facilitate ECU data communication.
   
   

   Control	Driving Control System	Body Electrical Control System	Body Electrical Control System
   Protocol	CAN (ISO Standard)	BEAN (TOYOTA Original)	AVC-LAN (TOYOTA Original)
   Communication Speed	500 Kbps* (Max. 1 Mbps)	Max. 10 Kbps*	Max. 17. 8 Kbps*
   Communication Wire	Twisted-pair Wire	AV Single Wire	Twisted-pair Wire
   Drive Type	Differential Voltage Drive	Single Wire Voltage Drive	Differential Voltage Drive
   Data Length	1 to 8 Bytes (Variable)	1 to 11 Bytes (Variable)	0 to 32 Bytes (Variable)

   HINT:

   1. *: The abbreviation ''bps'' stands for ''bits per second''.
      
   2. The CAN is comprised of 2 junction connectors that are connected to the main bus line. The junction connectors are also connected to sub bus lines.
      

2. A single, Automobile Vinyl (AV) wire is used for BEAN communication. A twisted-pair wire is used for CAN and AVC-LAN communication.
   
   

   Communication Wire	Outline
   AV Single Wire for BEAN	Lightweight single communication wire that consists of insulated single core line surrounded by insulation. Voltage is applied to this line in order to drive communication. This system is called ''Single Wire Voltage Drive''.
   Twisted-pair Wire for AVC-LAN Twisted-pair Wire for CAN	Pair of insulated lines twisted together. Communication is driven by applying positive (+) and negative (-) voltage to 2 lines in order to send single signal. This system, which is called ''Differential Voltage Drive'', can reduce noise.