How the LIN bus works
A LIN bus consists of a master node and one or more slave nodes. All nodes contain a slave communication task that is decomposed into send and receive tasks, while the host node also contains an additional host send task. In real-time LIN, communication is always initiated by the host task.
Nodes in a LIN network do not use any information about system settings other than the naming of the host node. We can add nodes to the LIN without requiring other slave nodes to change hardware and software.
The host node sends a message header containing the sync interrupt, sync byte and message identifier. The slave task is activated after receiving and filtering the identification code and starts the transmission of the message response. The response contains two, four or eight data bytes and a checksum byte. The header and response parts make up a message frame. All communications on the LIN bus are initiated by the host task in the host node. The host task determines the current communication content according to the schedule, sends the corresponding frame header, and allocates frame channels for message frames. After the slave node on the bus receives the frame header, it interprets the identifier to determine whether and what kind of response it should respond to the current communication. Based on this message filtering method, LIN can implement multiple data transmission modes, and a message frame can be received and utilized by multiple nodes at the same time. The physical layer of the LIN bus adopts a single-wire connection, and the maximum transmission distance between the two electronic control units is 40m. Specifications for its bus drivers and receivers follow the modified ISO 9141 single-wire standard. Based on SCI/UART (Universal Asynchronous Receiver/Receiver Interface Single Bus Serial Communication) protocol; SCI/UART interface is present on almost all microcontroller chips. Low transmission rate, less than 20kb/s, using NRZ encoding.
