Lexus IS250 IS220d GSE20 ALE20 - MULTIPLEX COMMUNICATION
MULTIPLEX COMMUNICATION SYSTEM - SYSTEM DESCRIPTION
| MULTIPLEX COMMUNICATION SYSTEM BASICS |
The LEXUS IS250 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 various pieces of information. Such a system is called a multiplex communication system.
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.
The AVC-LAN uses a star style, which is centered on the multi-display or audio head unit.
If DTC of ECU communication stop is output, connectors may be disconnected, or communication buses may be open at 2 points. It will not become abnormal with only 1 communication bus open.
If 2 communication buses are open at the position as shown in the illustration, DTC of ECU communication stop between those 2 buses is output.
Difference of CAN, BEAN and AVC-LAN
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 (LEXUS Original) | AVC-LAN (LEXUS Original) |
| Communication Speed | 500 Kbps* (Max. 1 Mbps) | Max. 10 Kbps* | Max. 17. 8 Kbps* |
| Communication Wire | Braided-pair Wire | AV Single Wire | Braided-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:
A single, Automobile Vinyl (AV) wire is used for BEAN communication. A braided-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''. |
Braided-pair Wire for AVC-LAN Braided-pair Wire for CAN | Pair of insulated lines braided 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. |
| GATEWAY ECU |
The gateway ECU of the LEXUS IS250 has the following functions.
| Function | Outline |
| Gateway | Data for respective protocols (CAN, BEAN and AVC-LAN) are arranged differently. Therefore, it is not possible to exchange data between different protocols. For this reason, data arrangement must be converted before transferring data to communication bus (CAN, BEAN and AVC-LAN). This conversion is called gateway function, which is performed by gateway ECU. |
| Diagnosis (only for BEAN) | By connecting intelligent tester to DLC3 and operating tester, technicians can access ECUs via network gateway ECU and BEAN. In this manner, DTCs can be output from BEAN, Data List (for checking ECU data) and Active Test (to actuate desired actuator) can be performed. |
| Customize (only for BEAN) | Customized body electronics system enables control function settings of ECUs to be changed through use of intelligent tester. However, this system can only change setting of ECUs that belong to bus in which communication is centered on gateway ECU. |