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Multiplex Communication System

System Diagram:




SYSTEM DIAGRAM

SYSTEM DESCRIPTION

- The PRIUS primarily uses the 3 types of multiplex communication systems.

- The Controller Area Network (CAN) is a network of the vehicle control systems (engine electrical, chassis electrical, and hybrid system) and maintains communication between the ECUs.
- The Body Electronics Area Network (BEAN) is a network of the ECUs of the body electric system control and maintains communication between the ECUs.
- The Audio Visual Communication Local Area Network (AVC-LAN) is a network of the ECUs of the audio visual system and the audio visual devices and maintains communication between the devices and the ECUs.




- These 3 types of multiplex communication systems are connected to the gateway ECU. The gateway ECU, which has communication circuits that support the 3 types of multiplex communication systems, enables communication among the multiplex communication systems.
For example, to activate air conditioning control, the A/C ECU receives the engine coolant temperature signal that is input into the ECM via the CAN, gateway ECU and BEAN.

CAN System Diagram:




- The CAN in the PRIUS is established between the hybrid vehicle control ECU, battery ECU, EPS ECU, ECM, skid control ECU, steering angle sensor*, yaw rate & deceleration sensor*, gateway ECU and DLC3.

BEAN System Diagram:




- The BEAN in the PRIUS is established between the body ECU, meter ECU, A/C ECU, transponder key ECU, power source control ECU, transmission control ECU, smart ECU* and gateway ECU.

AVC-LAN System Diagram:




- The AVC-LAN is established between the multi-display, audio head unit, navigation ECU* and gateway ECU.

BASIC OF MPX (Multiplex Communication)

1. GENERAL




The PRIUS multiplex communication system 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 the basic unit that represents the amount of information. A bit is represented by binary values "0" or "1". A frame is a body of data that is transmitted together. A frame contains a "header" that indicates the beginning of the data and an "end message" that indicates the end of the data.

2. NETWORK STYLE




Through serial communication, various ECUs are connected on a network to exchange various pieces of information. Such a system is called a multiplex communication system.

- The CAN communication on the PRIUS uses the multi star style bus connection. In this style of network, groups of ECUs are connected in star shapes. The ECU in the center of each star is known as a master ECU. The ECUs cannot communicate with each other without first using a sub bus line to communicate with its respective master ECU. The master ECUs are able to connect to each other through a main bus line. The PRIUS has 2 junction connectors serving as master ECUs.




- The BEAN on the PRIUS uses a daisy chain style bus connection. In this style of network, each ECU is connected to a ring shape (which can also be called a common communication wire). Each ECU uses the wire for signal inputs and outputs. A transmitting ECU could send an output signal to the wire, and the signal would circle the wire and return to the same ECU. Communication through the wire can be maintained even if wire is an open circuit.




- The AVC-LAN in the PRIUS uses a star style bus connection. In this style of network, the ECUs are connected in a star shape. The ECUs in the center of the star is known as the master ECU. The ECUs cannot establish communication with each other without first passing through the master ECU. The PRIUS multi-display or audio head unit both serve as master ECUs.

3. DIFFERENCE OF CAN, BEAN AND AVC-LAN




It is not possible to exchange data between the CAN, BEAN and AVC-LAN because the data specifications for each protocol are quite different. Before a data exchange can be made, the gateway ECU must perform a gateway function (conversion) on the data.

HINT:
The acronym "bps" stands for bit per second.
The CAN communication speed is much higher than the BEAN and AVC-LAN's communication speed. The vehicle control system uses the CAN because of its speed (to avoid system control delays), and its ability to send and receive large volumes of data at a time.

4. COMMUNICATION WIRE




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