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Abstract-To makeautomated driving a reality, we need more than visionary technology. We need on-the-pulse information, controversial debate and a gathering of the best minds from industry and society. The revolution of AD (Automated Driving) won’t happen overnight. Firstly, intelligent on-board technology have to support drivers more and more. Next, vehicle parts should communicate with each other and these distributed systems require protocols for communication between microcontrollers. So, CAN (Control Area Network) protocol is best used since the traffic congestion is eliminated as the messages are transmitted based on their priority and it allows the entire network to meet the timing constraints. It provides error free transmission as each node can check for errors during the transmission of the message and send the error frame.
I. INTRODUCTION
For the technology behind automated driving, firstly we need very good sensors. We must give the car an awareness of its surroundings that has to be in some respect even better than a human’s. The car needs to see, feel or hear everything that is going on around it. The car also needs a kind of inherent driving competence. Automated driving will be safe with on-board sensors alone. But with connectivity, it will become a lot more comfortable and applicable to more traffic situations.With rapidly changing in computer and information technology, much of the technology finds various ways into vehicles system for different applications. Vehicles are undergoing dramatic changes in their capabilities and how they interact with the drivers. Although some vehicles have provisions for deciding to either generate warnings for the human driver or controlling the vehicle autonomously, they usually must make these decisions in real time with only incomplete information. So, it is important that human drivers still have some control over the vehicle. Advanced in-vehicle information systems provide vehicles with different types and levels of intelligence to assist the driver. The introduction into the interior design of vehicle systems has allowed an almost symbiotic relationship between the driver and vehicle by providing a sophisticated & intelligent driver-vehicle interface through an intelligent information network.Proposed system will apply for the use of two wire system from CAN protocol to interconnect between control terminals of the system. There will be several nodes designed in the system including main controller, different HMI modules such as sensors, keypad, touchpad etc. and few others. Each node will consists of its own controller and CAN transceiver. The communication between the nodes and controller will make use of CAN bus protocol.
CAN DATA LINK LAYER
2.3.1 BUS ARBITRATION
CAN is a protocol for short messages. Each transmission can carry 0-8 bytes of data.
It uses CSMA/CD+AMP (Carrier Sense Multiple Access/Collision Detection with Arbitration on Message Priority). Thus the protocol is message oriented and each message has a specific priority according to which it gains access to the bus in case of simultaneous transmission. An ongoing transmission is never interrupted. During the bus idle state, any node can access the CAN bus. In the event of multiple accesses, the priority is decided by a method called “NonDestructive Bitwise Arbitration”. Nondestructive means that the winner of the arbitration the message with the higher priority must continue transmitting the message without having to restart the message transmission from the beginning
Arbitration is performed during the transmission of the identifier field. Each CAN message has an identifier which is of 11 bits. This identifier is the principle part of the CAN arbitration field, which is immediately after the Start bit. The identifier not only identifies the type of message but also indicates the priority of the message. During arbitration, 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 has lost arbitration. As soon as a node has lost the arbitration the node ceases to transmit, becoming a receiver of the ongoing message. At the end of transmission of the Arbitration Field, all nodes but one would have lost arbitration, and the highest priority message will get through unimpeded.
When the bus is free again the CAN Controller automatically makes a new attempt to transmit its message. Another round of arbitration is performed and the message with the highest priority gets through again leaving the messages with lower priority to content for the bus in the subsequent cycles. The CAN protocol requires that a specific identifier is sent only by one node this ensures that no two messages with the same identifier contend for bus access.