Abstract: Bosch introduced a new type of serial bus – CAN Controller Area Network – at the SAE (Society of Automotive Engineers) conference, which was also the time when CAN was born. Today, almost every new bus in Europe is equipped with a CAN local area network. Similarly, CAN is also used for other types of transportation, from trains to ships or for industrial control. CAN has become one of the most important buses worldwide – even leading serial buses. The working principle of CAN bus: CAN bus uses serial data transmission method, which can achieve a speed of 1Mb/s and a dual speed of 40m

Bosch introduced a new type of serial bus – CAN Controller Area Network – at the SAE (Society of Automotive Engineers) conference, which was also the time when CAN was born. Today, almost every new bus in Europe is equipped with a CAN local area network. Similarly, CAN is also used for other types of transportation, from trains to ships or for industrial control. CAN has become one of the most important buses worldwide – even leading serial buses.

The working principle of CAN bus

The CAN bus uses a serial data transmission method, which can operate at a speed of 1Mb/s on a 40m twisted pair cable or be connected using optical cables. Moreover, the bus protocol supports multiple master controllers on this bus. Many details of CAN and I2C buses are similar, but there are also some obvious differences.

When a node (station) on the CAN bus sends data, it broadcasts it to all nodes in the network in the form of a message. For each node, regardless of whether the data is sent to itself, it is received. The 11 characters at the beginning of each group of messages serve as identifiers, defining the priority of the message. This message format is called a content oriented addressing scheme. In the same system, identifiers are unique, and it is impossible for two stations to send messages with the same identifier. This configuration is crucial when several stations compete for bus reads simultaneously.

When a station wants to send data to other stations, the CPU of that station transmits the data to be sent and its own identifier to the CAN chip of this station, and is in a ready state; When it receives bus allocation, it transitions to the sending message state. The CAN chip organizes data into a certain message format according to the protocol and sends it out, while other stations on the network are in a receiving state. Each station in the receiving state checks the received messages to determine whether they are being sent to itself and whether it has been received.

Due to the fact that CAN bus is a content oriented addressing scheme, it is easy to establish high-level control systems and configure them flexibly. We can easily add some new stations to the CAN bus without the need for hardware or software modifications. When the provided new station is a pure data receiving device, the data transmission protocol does not require independent parts to have a physical destination address. It allows for synchronization of distributed processes, meaning that when controllers on the bus need to measure data, it can be obtained online without the need for each controller to have its own independent sensor.

The characteristics of CAN bus

1. It has advantages such as strong real-time performance, long transmission distance, strong resistance to electromagnetic interference, and low cost;

2. Adopting a dual line serial communication method, it has strong error detection ability and can work in high noise interference environments;

3. Has priority and arbitration functions, multiple control modules are connected to the CAN bus through CAN controllers, forming a multi host local network;

4. Can decide to receive or block the message based on its ID;

5. Reliable error handling and detection mechanisms;

6. After the information sent is damaged, it can be automatically resent;

7. Nodes have the function of automatically exiting the bus in case of serious errors;

8. The message does not contain a source or destination address and only uses identifiers to indicate functional and priority information.

Application of CAN bus

The advantages of CAN bus in networking and communication functions, as well as its high cost-effectiveness, determine that it has broad application prospects and development potential in many fields. These applications have some commonalities: CAN actually serves as a computer local area network with a bus topology on site. Regardless of the situation, it is responsible for real-time communication between any node, but it has advantages such as simple structure, high speed, anti-interference, reliability, and low price. The CAN bus was originally designed for electronic control systems in cars, and its application is now very common in cars produced in Europe. Moreover, this technology has been promoted to transportation vehicles such as trains and ships.

(1) The application of CAN bus technology: Most well-known foreign cars have adopted CAN bus technology, such as Volvo, Lincoln, Audi, BMW, etc., while domestic car brands, such as Chery, have also applied bus technology to several models. CAN bus technology sends various driving data of a car to the “bus” through sensors distributed throughout the vehicle body. On this information sharing platform, any receiving end that needs this data can read the required information from the “bus”, so as to coordinate the operation of various systems of the car, share information, ensure safe, comfortable, and reliable driving of the vehicle. Generally speaking, the more high-end cars are equipped with CAN-BUS, the higher the price, and models such as the Touareg and Passat are equipped with multiple CAN buses.

(2) Hardware Design of Automotive CAN Bus Node ECU: The core technology of automotive CAN bus research and development is to design an ECU with a CAN interface, where the CAN bus module of the ECU is composed of a CAN controller and a CAN transceiver. The CAN controller executes the complete CAN protocol and completes communication functions, including information buffering and receiving filtering. A CAN transceiver is required as the interface between the CAN controller and the physical bus, which realizes the conversion of logical level signals between the CAN controller and the bus.

(3) The application of CAN bus in domestic independent brand cars: Due to limitations such as cost control and technological strength, CAN-BUS bus technology generally appears in high-end foreign cars. In A-level and below models, this technology mostly appears in joint venture brands such as POLO and New Bora. Among domestic brands, there are very few models that adopt CAN bus technology, and Fengyun 2 is one of the representative models. Fengyun 2 CAN bus technology can achieve communication between the engine, gearbox, ABS, body, instrument panel, and other controllers, achieving timely sharing of information across the entire vehicle. In the combination instrument panel of Fengyun 2, more than 20 information such as stage mileage, precise display of open doors, and reminder of unfastened seat belts can all be displayed, which is twice the number of products in the same class, thus increasing the safety level during driving.

(4) Future development trend of intelligent sensors: CAN bus, as a reliable automotive computer network bus, has been applied in many advanced cars. By applying CAN bus to intelligent sensors, the signals obtained by sensors can be transmitted in real-time, reliably, high-speed, and accurately through the bus. This enables various automotive computer control units to share all information and resources through the CAN bus, achieving the goal of simplifying wiring, reducing the number of sensors, avoiding duplicate control functions, improving system reliability, reducing costs, and better matching and coordinating various control systems. Meanwhile, due to the use of fully digital communication in the entire intelligent sensor network, the bus also has good anti-interference ability, which is the development trend of future intelligent sensors and intelligent control networks.

In addition, with the help of CAN bus technology, various internal sensors achieve information sharing, greatly reducing the number of interfaces between wiring harnesses and controllers in the vehicle body, avoiding hidden dangers such as interference and wear caused by excessive wiring harnesses, and reducing the occurrence rate of faults in the automotive electrical system. Open the engine hood and you will see a clear and concise layout inside the cabin. In terms of maintenance, the application of CAN bus technology also ensures the most convenient troubleshooting. The CAN bus intelligent butler system complies with European and American OBDII standards and regulations, achieving the function of online diagnosis. After a vehicle malfunction occurs, each controller stores fault codes through the CAN bus intelligent housekeeping system. Professional personnel diagnose various fault states for the vehicle through diagnostic equipment, quickly and accurately locate the fault point, and troubleshoot the problem as soon as possible. The use of CAN bus technology for system integration information transmission greatly improves the response speed of various components, reduces the occurrence of accessory wear, and correspondingly reduces maintenance costs; Moreover, the application of advanced integrated technology has significantly improved the technological content of vehicles and enhanced their product competitiveness.

The data communication of CAN bus has outstanding reliability, real-time performance, and flexibility. Due to its excellent performance and unique design, CAN bus is increasingly valued by people, and its application in the automotive field is the most extensive. Some famous car manufacturers in the world mostly use CAN bus to achieve data communication between the internal control system of the car and various detection and execution mechanisms. Meanwhile, due to the inherent characteristics of CAN bus, its application scope is no longer limited to the automotive industry, but is developing towards fields such as automatic control, aerospace, navigation, process industry, mechanical industry, textile machinery, agricultural machinery, robots, CNC machine tools, medical equipment, and sensors. CAN has formed an international standard and is recognized as one of the most promising fieldbuses.