CAR AUTOMATION USING CAN

CAR AUTOMATION USING CAN

PROJECT BY

1. Sandeep T.M

2. Sachin.P

3. Vinod Kumar.J

4. Varun Kumar.SAbstractBased on requirements of modern vehicle, in-vehicle Controller Area Network (CAN) architecture has been implemented. In order to reduce point to point wiring harness in vehicle automation, CAN is suggested as a means for data communication within the vehicle environment. The benefits of CAN bus based network over traditional point to point schemes will offer increased flexibility and expandability for future technology insertions. The ARM7 based design and implementation of CAN Bus prototype for vehicle automation. It focus on hardware and software design of intelligent node. The software design for CAN bus network are mainly the design of CAN bus data communication between nodes, and data processing for analog signals. The design of software communication module includes system initialization and CAN controller initialization unit, message sending unit, message receiving unit and the interrupt service unit.I. INTRODUCTION

In todays world, automation is needed in many systems which provide better performance. Large numbers of systems are fully automated. Vehicle system is composed of automotive electrical architectures consist of a large number of electronic control units (ECU) carrying out a variety of control functions. In vehicle system we generally want greater safety, more comfort, convenience, pollution control and less fuel consumption. A modern vehicle may have many electronic control units (ECU) for various subsystems. Different such subsystems are airbags, antilock braking, engine control, audio systems, windows, doors, mirror adjustment etc. Some of these subsystems form independent or dependent subsystems. Communications among dependent sub systems is essential.

Traditional electronic control system can improve a vehicle dynamics, economy and comfort. But some problems also have come up, such as the body wiring complexity, space constraints and some reliability issues.

In order to solve these problems, the vehicle network technology has been created. In-vehicle networking protocols must satisfy requirements which include, significant reduction of wiring harness, reducing body weight and costs, improving the efficiency of fault diagnosis, low latency times and configuration flexibility and enhancing the level of intelligent control [4]. Sub-systems (ECU) require the exchange of particular performance and position information within defined communication latency. Therefore the requirement for each ECU is to communicate via some kind of network technology such as CAN (Controller Area Network) bus. At present, some vehicle buses have been already put into use, such as CAN bus, LIN (Local Interconnect Network) bus, Flex ray bus etc. In the proposed work CAN bus protocol is used for vehicle automation.II. OVER VIEW OF CAN PROTOCOL

Controller area network (CAN) provide high reliability and good real-time performance with very low cost. Due to this, CAN is widely used in a wide range of applications, such as in-vehicle communication, automated manufacturing and distributed process control environments. CAN bus is a serial data communication protocol invented by German BOSCH Corporation in 1983. CAN is a network protocol which is designed for the car industry. Since data communication in car often have many sensors transmitting small data packets, CAN supports data frames with sizes only up to 8 bytes. Meanwhile, the 8 bytes will not take the bus for a long time, so it ensures real-time communication. CAN use a large amount of overhead, which combined with a 15-bit CRC makes CAN very secure and reliable.

CAN protocol use non-destructive bitwise arbitration process to access shared resource. CAN protocol define a logic bit 0 as a dominant bit and a logic bit 1 as a recessive bit, each transmitting node monitors the bus state and compares the received bit with the transmitted bit. If a dominant bit is received when a recessive bit is transmitted then the node stops transmitting (i.e. it lost arbitration). Arbitration is performed during the transmission of the identifier field. There are two message formats: Base frame format with 11 identifier bits and Extended frame format with 29 identifier .

Figure 1. CAN Data FrameA. Hierarchical structure of CAN BUS Architecture of CAN protocol based on OSI reference model is as shown in figure 2.2. CAN protocol contain only three layers, physical layer, data link layer and application layer. Application layer has different protocols such as SAE J1939, CAN open, Device Net, etc.

Figure II. Hierarchical structure of CAN BUSB. FEATURES OF CAN CONTROLLER

1. Message transmission

2. Prioritization of message

3. Arbitration

4. Multimaster (CSMA/CD+AMD method)5. System flexibility

6. Communication speed

7. Error detection, error notification and error recovery function.

8. Fault confiment.

9. Multicast.

10. Data consistency.

Use of the CAN network in vehicles

There are four main applications for serial communication in vehicles, each having different requirements and objectives.

Networking controllers for engine timing, transmission, chassis and brakes. The data rates are in the range - typical of real-time systems of 200 kbit/s to 1 Mbit/s.

Networking components of chassis electronics and electronics which make the vehicle more comfortable. Examples of such multiplex applications are lighting control, air-conditioning, and central locking and seat and mirror adjustment. Particular importance has to be attached here to the cost of the components and wiring requirements. Typical data rates are around 50 kbit/s.

In the near future, serial communication will also be used in the field of mobile communication in order to link components such as car radios, car telephones, navigation aids etc. to a central, ergonomically designed control panel. The functions defined in the Prometheus project, such as vehicle-to-vehicle and vehicle-to-infrastructure communication will depend to a large extent on serial communication.

At present, CAN is used for the first three applications, but for diagnosis the preferred solution is an interface according to ISO 9141.

How the CAN network functions

Principles of data exchange.

When data are transmitted by CAN, no stations are addressed, but instead, the content of the message (e.g. rpm or engine temperature) is designated by an identifier that is unique throughout the network. The identifier defines not only the content but also the priority of the message. This is important for bus allocation when several stations are competing for bus access.

If the CPU of a given station wishes to send a message to one or more stations, it passes the data to be transmitted and their identifiers to the assigned CAN chip (Make ready). This is all the CPU has to do to initiate data exchange. The message is constructed and transmitted by the CAN chip. As soon as the CAN chip receives the bus allocation (Send Message) all other stations on the CAN network become receivers of this message (Receive Message). Each station in the CAN network, having received the message correctly, performs an acceptance test to determine whether the data received are relevant for that station (Select). If the data are of significance for the station concerned they are processed (Accept), otherwise they are ignored.

A high degree of system and configuration flexibility is achieved as a result of the content-oriented addressing scheme. It is very easy to add stations to the existing CAN network without making any hardware or software modifications to the existing stations, provided that the new stations are purely receivers. Because the data transmission protocol does not require physical destination addresses for the individual components, it supports the concept of modular electronics and also permits multiple reception (broadcast, multicast) and the synchronization of distributed processes: measurements needed as information by several controllers can be transmitted via the network, in such a way that it is unnecessary for each controller to have its own sensor.

1. Broadcast transmission and acceptance filtering by CAN nodes

2. Principle of non-destructive bitwise arbitrationNon-destructive bitwise arbitration:

For the data to be processed in real time they must be transmitted rapidly. This not only requires a physical data transfer path with up to 1 Mbit/s but also calls for rapid bus allocation when several stations wish to send messages simultaneously.

In real-time processing the urgency of messages to be exchanged over the network can differ greatly: a rapidly changing dimension (e.g. engine load) has to be transmitted more frequently and therefore with fewer delays than other dimensions (e.g. engine temperature) which change relatively slowly. The priority at which a message is transmitted compared with another less urgent message is specified by the identifier of the message concerned. The priorities are laid down during system design in the form of corresponding binary values and cannot be changed dynamically. The identifier with the lowest binary number has the highest priority.

Bus access conflicts are resolved by bitwise arbitration on the identifiers involved by each station observing the bus level bit for bit. In accordance with the wired and mechanism, by which the dominant state (logical 0) overwrites the recessive state (logical 1), the competition for bus allocation is lost by all those stations with recessive transmission and dominant observation. All "losers automatically become receivers of the message with the highest priority and do not reattempt transmission until the bus is available again.CONCLUSIONReal-time, reliability and flexibility, all these characteristics make CAN BUS an indispensable network communication technology applied in automobile network communication field. In this project, the CAN-bus based communication system for vehicle automation is designed. Software system and hardware system are easily to be expanded and upgraded.