The CAN bus is a serial data communication protocol developed by German company BOSCH from the early 1980s to solve the data exchange between numerous control and test instruments in modern automobiles. It is a multi-master bus, and the communication medium can be It is twisted pair, coaxial Cable or optical fiber. Communication rate up to lMbit/s.

1) Complete framing of communication data

The CAN bus communication interface integrates the physical layer and data link layer functions of the CAN protocol and can complete the framing processing of communication data, including bit stuffing, data block coding, cyclic redundancy check, and priority discrimination.

2) Make the number of nodes in the network theoretically unlimited

One of the most significant features of the CAN protocol is to abolish the traditional station address coding and instead encode the communication data block. The advantage of this method is that it can theoretically limit the number of nodes in the network. The identifier of a data block can consist of 11-bit or 29-bit binary numbers, so two or more different data blocks can be defined. This block-by-block coding also allows different nodes to receive the same data at the same time, which is very useful in distributed control systems. The length of the data segment is up to 8B, which can meet the general requirements of control commands, working conditions and test data in the general industry. At the same time, 8B will not occupy the bus for too long, thus ensuring the real-time communication. CAN protocol adopts CRC check and can provide corresponding error handling function, ensuring the reliability of data communication. The excellent features, high reliability and unique design of CAN make it particularly suitable for the interconnection of industrial process monitoring equipment. Therefore, it has received increasing attention from the industry and has been recognized as one of the most promising field buses.

3) Free communication between nodes

The CAN bus adopts a multi-master competition bus structure, which has the characteristics of multi-master operation, distributed arbitration, serial bus and broadcast communication. Any node on the CAN bus can actively send information to other nodes on the network at any time regardless of the primary and secondary, so free communication can be achieved between the nodes. The CAN bus protocol has been certified by ISO. The technology is relatively mature. The controlled chip has been commercialized and has a high cost performance. It is particularly suitable for data communication between distributed measurement and control systems. The CAN bus card can be arbitrarily inserted on a PC AT XT compatible machine to conveniently form a distributed monitoring system.

4) Simple structure

Only two wires are connected to the outside, and an error detection and management module is integrated inside.

5) Transmission distance and rate

CAN bus features: 1 There is no master/slave in data communication. Any node can initiate data communication to any other node (or nodes). The order of communication is determined by the priority of each node's information. The priority of high-priority node information is prioritized. Communication; When two or more nodes initiate the communication at the same time, if the priority with a low priority is high, it will not cause congestion on the communication line; 3 The communication distance is up to 10km (rate lower than SKbit/s), and the rate can reach 1Mbit /s (communication distance is less than 40m): 4CAN bus transmission media can be twisted pair, coaxial cable. The CAN bus is suitable for large data short-range communication or long-distance small-data-rate communication. The real-time performance is relatively high, and it is used in a multi-master multi-slave or equal-area node.