The LIN bus (Local Interconnect Network) was developed to further reduce the costs of automotive networks. It was designed to complement the available and proven bus systems in areas where lower data quantities must be transmitted reliably.
Thus, LIN buses are mostly used for comfort functions and, for example, actuators, switches or illumination elements. Its architecture allows the representation of the necessary bus logic in hardware. Many microcontrollers are therefore able to operate a LIN bus with a UART or SCI interface, special interface controllers are not required.
Communication on the LIN bus follows the master/slave principle. A master initiates the communication with one or several slaves. Bus communication can only take place if a master is connected. The master triggers the connected slaves to send their data consecutively. A slave cannot begin data transfer autonomously.
The weakest point of a LIN bus is thus the master. If it fails, communication on the bus stops. Apart from that, the master requires knowledge about all connected slaves to send cyclical requests or requests defined in a scheduler table.
The LIN bus is specified by a company group. The current specification can be viewed on the website. The document not only defines how the physical transfer takes place, but also provides a transport protocol and the structure of higher communication levels.