ECU Based on CAN Bus Multi-Platform Communication
Introduction
With the IC and microcontroller widely used in the car, Hyundai Motor on the number of electronic control more and more common with the engine electronic fuel injection devices, anti-lock braking system (ABS), airbag device , electric windows devices, active suspension and so on. Although the increase in electronic control system to improve the car's power, economy and comfort, but the increased complexity of the circuit also reduces the car's reliability, increased maintenance more difficult. From the perspective of wiring, most of the traditional electron gas system with a single point to point communication, little contact with each other, this will inevitably lead to large pet cabling system. Therefore, a new concept - the car electronic controller area network CAN, also emerged. Order parts from different manufacturers in coordination with a car to be standard. In accordance with the standards ISO, CAN Bus topological structure, so called CAN bus. CAN bus is designed as a vehicle environment, micro-controller communications, the electronic control devices in the car to exchange information between ECN, the electronic control devices in the car to exchange information between ECN to form automotive control network.
Controller Area Network CAN (Controller Area Network) is a multi-master mode serial communication bus, the basic design requires a high bit rate, high resistance to electromagnetic interference, but also can detect any error. CAN in automotive applications, with many industry standards or international standards, such as the International Organization for Standardization (ISO) in ISO11992, ISO11783 and the Society of Automotive Engineers (Society of Automotive Engigeers) of SAE J1939. CAN bus has a standard equipment for vehicles included in the design of the car vehicle.
ECU Based on CAN Bus Multi-Platform Communication
1 CAN Bus Features and Communication Protocol
1.1 CAN Bus Description
CAN communication protocol provides for 4 different frame format, that data frame, remote frame, error frame, and overload frame. Based on the following a few basic rules for communication coordination: the bus access, arbitration, encoding / decoding, error annotation and ultra-cut label. CAN follow OSI model. OSI reference model in accordance with only three layers: physical layer, data link layer and supplicate layer, but still need user defined application layer. CAN-bus as an effective support for real-time control of distributed control or serial communication network, from a range of applications across multiple high-speed networks to low-cost route network. Such as: CAN in automotive components in the engine control, ABS, anti-slide system applications, the bit rate up to 1Mbps. At the same time, it can be used to transport vehicles cheap electrical system, such as electric windows, lighting, spotlight, seat adjustment, etc., to replace the hardware needed to connect. The sanctions for the twisted pair transmission medium, communications rates up to 1Mbps/40m, direct transmission distances of up to 10km/5kbps, the number of attached devices up to 110. CAN multi-master work, communication and flexible, without station node address information, bus arbitration techniques using non-destructive, real-time requirements. In addition, CAN frame structure with a short transmission signal, transmission time is short, has strong anti-interference ability.
CAN bus communication protocol with the other difference between the two main aspects: Messaging does not include destination address, it is the whole Wang broadcast, based on the terminal according to packet identifier Guolv reflect the nature of the data packets It features online access the net, plug and play and multi-station receiver; Another aspect is particularly enhanced data security to meet the control system and other high data requirements for the system requirements.
1.2 J1939 communication protocol
J1939 CAN bus protocol is a communication protocol 2.0B (29 ID) on the specific implementation of the application layer, is the SAE heavy trucks and buses for the development of communication protocols; to CAN 2.0B, based on the standard physical layer is compatible with the ISO11898 standard and consistent with the specification of the CAN controller and transceiver. CAN J1939 protocol identifier will be divided into the following sections: Priority (P), the data pages (PGN), protocol data unit (PDU) format, PDU-specific domain (PS) and the source address (SA). J1939/71 application layer document defines the various parameters of vehicle control and command of the PGN.
ECU Based on CAN Bus Multi-Platform Communication
Thus, J1939 and CAN communication protocol identifier difference is 29 (ID), the same data field. J1939 to CAN in the 29 identifiers (or Distinguishing identification) for a detailed definition of the physical. Through the PDU will be the standard format package for the J1939 CAN protocol format. PDU information frame has the priority of P, retention position R, the data page DP, protocol data unit PF, expansion unit PS, the source address SA and the data field DATA of seven parts, namely, the 29 CAN identifier with the data.
2 Design
2.1 Automotive electronic control network
Vehicle ECU data transmission between the characteristics of the main difference is the data transmission frequency, such as high-speed run-time engine, for the high frequency data transmission, the transmission every few ms 1; in low speed, for the low frequency data transmission, every tens and even hundreds of ms 1 ms before transmission. However, in order to meet the real-time requirements, it required the control unit as much as possible of each vehicle of public data sharing, but since each control unit of the real-time requirement is because the data update rate and the control period in different and different. This requires the data exchange network is based on the priority of competing models, and its high communication speed. CAN bus is designed to meet these requirements the. CAN has been the international standard ISO11898 and the occasion for high-speed low-speed situations of ISO11519-3.
Usually used car network bus, a number of different rates in different types of nodes are connected, and use the gateway servers to achieve the vehicle's information sharing and network management. If according to the U.S. Society of Automotive Engineers (SAE) standards for vehicles Network Committee SAE J2057, the vehicle data transmission network is divided into three categories. Figure 1 is available here briefly. One gateway is the core of internal communications vehicles, which can be achieved through the CAN bus in the sharing of information and the realization of the internal car network management and fault diagnosis; to all feedback on the data bus to display on the dashboard assembly , the driver information through the dashboard can be aware of the various electronic control devices are working properly.
2.2 Hardware Design Communication Platform
In the design, the main chip microcontroller CPU used 51. CAN CAN communication controller to perform a complete agreement, complete communications capabilities, including information buffer and receive filter, so use Philips CAN controller, the SJA1000. Chosen as the CAN bus PCA82C250 transceiver, PCA82C250 is CAN protocol controller and the physical bus interface between the operating environment in the transient resistant, anti-RF and anti-electromagnetic interference performance, internal limiting circuit when a short circuit transmit output level for protection. Shielded electricity transmission medium, between the control node and the media joined the optocoupler circuit in order to improve anti-interference ability of bus interface. Figure 2 for the communications platform hardware block diagram, Figure 3 for the controller and transceiver connection interfaces.
To further improve system reliability, the system need to be considered redundant design. As the harsh automotive environment, and more disturbances in the CAN_H and CAN_L signal line and ground, respectively, between the two capacitors in parallel to filter the noise, so that a smooth signal transmission. Electricity can be installed two sets of double-shielded, two media simultaneously in the transmission of information. Only one media receiver, the redundant and non-redundant section of the bus switch to connect the critical points.
2.3 Software Design
In short, the communications platform to realize the function is so that each node (ECU) through the CAN bus communication with each other, sending and receiving commands, information, and sharing of data, thereby enhancing their control performance and operating efficiency. Vehicle CAN data bus to each node (ECU) has its own address and name of the corresponding. ECU address that the data transmission destination, and its name will identify the basic functions of the ECN. Node continuously monitors the bus sent the data. When the data received address values coincide with its own address, the node will be token. In the communication protocol, the only access to the right token of the node to send data, in order to prevent two or more nodes transmit data simultaneously to cause confusion. Each node also has the opportunity to get the token to complete the data transfer.
The software design is based on the Keil C language. Process mainly by the main module, interrupt handling module and data communication module etc., shown in Figure 4.
ECU Based on CAN Bus Multi-Platform Communication
The main module to complete the hardware initialization, register configuration, SJA1000 initialization, etc.; interrupt interrupt processing module includes data to send, receive, error handling, and alarm processing; data communication module for data request, sending, receiving, and so on.
When a node A sends data request packets (remote frame), the request to another node B message (answer frame), the Node B receives a request, through identification, then send the data (answer frame). As the data request no data field, so the data frame length is relatively much smaller. After verification by the analysis of the data and node B received the same request data procedures be verified.
Conclusion
In the design of modern cars 中, CAN Zongxianyijing Cheng Wei build a kind of auto network of trend; Er vehicle network Zuoweizhijie and car Neibugege ECU Lian Jie Bing Fuzemingling the transmission of data to send and Gong Xiang, their reliability and Wendingxingyu whole closely related to the performance of vehicles. Design and development of this paper is built based on experimental conditions, the simulation platform, communication between nodes is through communication nodes such as the CAN's. Tests showed that its operating performance is stable, but the practical needs further research and improvement, and process communications processing, error correction and fault tolerance to be further improved.