CAN is the abbreviation of Controller Area Network (hereinafter referred to as CAN), which is an ISO international standardized serial communication protocol. In the automobile industry, various electronic control systems have been developed for the requirements of safety, comfort, convenience, low pollution and low cost. Due to the different data types and reliability requirements for communication between these systems, there are many cases where multiple buses are formed, and the number of wiring harnesses increases accordingly. In order to meet the needs of "reducing the number of wiring harnesses" and "high-speed communication of large amounts of data through multiple LANs", in 1986, the German electric company Bosch developed the CAN communication protocol for automobiles. Since then, CAN has been standardized through ISO11898 and ISO11519, and has become a standard protocol for automotive networks in Europe.
CAN's high performance and reliability have been recognized and widely used in industrial automation, ships, medical equipment, industrial equipment, etc. Fieldbus is one of the hotspots of technology development in the field of automation today, and is known as the computer local area network in the field of automation. Its appearance provides a strong technical support for the distributed control system to realize real-time and reliable data communication between nodes.
The basic frame structure of CAN is as follows:
The data frame is divided into various segments,
(1) Start of frame, indicating the segment at the beginning of the data frame. 1bit 0 (the level is 1 when the bus is idle)
(2) Arbitration segment, indicating the segment of the frame priority. ID is the priority number used for arbitration, RTR: remote transmission request bit indicates that the message is a data frame or a remote frame, 0 is data, 1 is remote
(3) Control segment, which indicates the number of bytes of data and the segment of reserved bits. IDE: Identifier extension bit 0 Standard format 1 Extended format r0 1bit0 DLC[3:0] Length of data segment (in bytes)
(4) The data segment, the content of the data, can send 0 to 8 bytes of data. All data is sent in MSB first order, and other multi-bit segments such as ID and CRC are in this order (this is the opposite of USB)
(5) CRC segment, which checks the transmission error segment of the frame. 16-bit CRC sequence and delimiter: CRC calculation includes all from frame start to data field. Delimiter: 1bit 1 invisible bit
(6) ACK segment, indicating the segment that confirms normal reception. A total of 2bit response bit + response delimiter The sender sends two 1s (invisible) and the receiver sends 0 (dominant) to respond. The delimiter is an invisible bit.
(7) End of frame, indicating the segment at the end of the data frame. 7bit 1 (recessive bit)
The intermission field can be included in the frame format or can be considered as, outside the frame format, is the free time between two frames
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