Smart Home Technology: CAN Bus Technology

CAN is an abbreviation of Controller Area Network (hereinafter referred to as CAN) and is an ISO international standard serial communication protocol. In the automotive industry, various electronic control systems have been developed for the sake of safety, comfort, convenience, low pollution, and low cost. Since the data types used for communication between these systems and the requirements for reliability are not the same, there are many cases of multiple buses and the number of harnesses also increases. In order to meet the needs of "reducing the number of harnesses" and "high-speed communication of large amounts of data through multiple LANs", in 1986 the German electric supplier Bosch developed a CAN communication protocol for automobiles. Since then, CAN has been standardized through IS0 11898 and IS0 11519, which is the standard protocol for automotive networks in Europe.

1. The advantages of CAN bus

CAN belongs to the category of fieldbus. It is a serial communication network that effectively supports distributed control or real-time control. Compared to many RS-485 distributed control systems based on R lines, the distributed control system based on CAN bus has obvious advantages in the following aspects.

1) Strong real-time data communication between nodes in the network

First of all, the CAN controller works in a variety of ways. Each node in the network can compete to send data to the bus in a bit-by-bit arbitration mode without a lossless structure according to the bus access priority (depending on the message identifier), and the CAN protocol is abolished. The station address coding, instead of encoding the communication data, can mean that different nodes receive the same data at the same time. These characteristics make the data communication between the nodes of the network constituted by the CAN bus in real time strong and easy to form. Redundant structure improves system reliability and system flexibility. The use of RS-485 can only constitute a master-slave structure system, the communication method can only be carried out by the master station polling Wan Shi, the system's real-time, poor reliability.

2) Shorten the development cycle

The CAN bus is connected to the physical bus through the two outputs CANH and CANL of the CAN transceiver interface chip 82C250, while the CANH state can only be high or suspended, and the CANL can only be low or floating. This ensures that the phenomenon will not appear in the RS-485 network, that is, when the system is in error, when multiple nodes send data to the bus at the same time, the bus is short-circuited, thereby damaging some nodes. Moreover, the CAN node has the function of automatically shutting down the output in case of serious errors, so that the operation of other nodes on the bus is not affected, so as to ensure that it will not appear in the network, and the bus is in a "deadlock" state because of problems in individual nodes. . Furthermore, the complete communication protocol that CAN has can be implemented by the CAN controller chip and its interface chip, which greatly reduces the difficulty of system development and shortens the development cycle. These are the only RS-485 protocols that cannot be compared with the electrical protocol.

3) Fieldbus that has formed an international standard

In addition, compared with other field buses, the CAN bus is a field bus that has formed an international standard with high communication speed, easy implementation, and high cost performance. These are also important reasons why the CAN bus is used in many fields and has strong market competitiveness.

4) One of the most promising fieldbuses

CAN is the controller area network and belongs to the field of industrial fieldbus. Compared with the general communication bus, the CAN bus data communication has outstanding reliability, real-time and flexibility. Due to its good performance and unique design, CAN bus has received more and more attention. Its application in the automotive field is the most extensive. Some of the world's famous automobile manufacturers such as Benz, BMW, Porsche, Rolls-Royce and Jaguar ( Jaguar etc. all use the CAN bus to realize the data communication between the vehicle's internal control system and various inspection and execution agencies. At the same time, due to the characteristics of the CAN bus itself, its application scope is no longer confined to the automotive industry, but to the automation, aerospace, navigation, process industry, machinery industry, textile machinery, agricultural machinery, robotics, CNC machine tools, medical equipment and Development of sensors and other fields. CAN has formed an international standard and has been recognized as one of the most promising fieldbuses. Typical application protocols are SAE J1939/IS0 11783. CANopen, CANaerospace, DeviceNet. NMEA 2000, etc.