CAN bus technology and application
Overview of CAN communication technology
CAN (Controller Area Network) is a controller area network. Due to its high performance, high reliability, and unique design, CAN is increasingly valued by people.
BOSCH originally designed CAN in Germany for automobile monitoring and control systems. Modern cars are increasingly controlled by electronic devices, such as engine timing, fuel injection control, acceleration and braking control (ASC) and complex anti-lock braking systems (ABS). Since these controls require the detection and exchange of large amounts of data, the use of hard-wired signal lines is not only cumbersome and expensive, but also difficult to solve the problem. The use of CAN bus solves the above problems well.
In 1993, CAN became the international standard ISO11898 (high-speed application) and ISO11519 (low-speed application):
The CAN specification has evolved from the CAN 1.2 specification (standard format) to the CAN2.0 specification compatible with the CAN 1.2 specification (CAN2.0A is the standard format, CAN2.0B is the extended format). Most of the CAN devices currently used comply with the CAN2.0 specification.
CAN bus features
CAN bus is a serial data communication protocol. Its communication interface integrates the physical layer and data link layer functions of the CAN protocol, and can complete the framing of communication data, including bit filling, data block encoding, cyclic redundancy check, priority determination and other tasks.
The features of CAN bus are as follows:
(1) It can work in multi-master mode. Any node on the network can actively send information to other nodes on the network at any time, regardless of master or slave. The communication mode is flexible.
(2) The nodes (information) on the network can be divided into different priorities to meet different real-time requirements.
(3) It adopts a non-destructive bit arbitration bus structure mechanism. When two nodes transmit information to the network at the same time, the node with a lower priority actively stops sending data, while the node with a higher priority can continue to transmit data without being affected.
(4) Data can be received in several transmission modes: point-to-point, point-to-multipoint (grouping) and global broadcast.
(5) The maximum direct communication distance can reach 10km (rate below 5Kbps)
(6) The maximum communication rate can reach 1MB/s (at this time, the maximum distance is 40m)
(7) The actual number of nodes can reach 110.
(8) The short frame structure is adopted, and the number of valid bytes in each frame is 8.
(9) Each frame of information has CRC check and other error detection measures, and the data error rate is extremely low.
(10) The communication medium can be twisted pair, coaxial cable and optical fiber. Generally, cheap twisted pair can be used, and there are no special requirements.
(11) In the case of serious errors, the node has the function of automatically shutting down the bus, cutting off its connection with the bus so that other operations on the bus are not affected.
