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What is LIN | Local Interconnect Network protocol basics

This page describes what is LIN and mentions basics of Local Interconnect Network protocol (LIN Protocol).

LIN Protocol was designed by a consortium of European auto manufacturers. It is basically a low cost, low speed and short distance network.

This LIN protocol is designed to communicate changes in the switch settings. It also respond to switch changes. This protocol is basically intended to communicate events which happen in hundreds of milliseconds. Following table mentions features of LIN protocol.

The LIN bus usually operates between 9V and 18V. But the parts must survive 40 Volts on the bus. As microcontroller requires 5V for operation, it should be isolated using line driver or receiver to avoid damage and proper functioning.

Feature LIN protocol support
Transfer rate 20 Kbaud
Communication Bi-directional
Bus Length (Maximum) 40 meters

LIN protocol-Byte and Message protocol

LIN system overview

LIN protocol works as per master and slave concept. The master node controls bus by polling method to all the slave nodes. This way master informs all the slave nodes to share their data with the rest of nodes on the bus. Slave nodes only transmit when commanded by the master node, which allows bi-directional communication without further arbitration. Figure-1 depicts the LIN system overview.

LIN Byte and Message Protocol

Figure-2 depicts LIN byte protocol. As shown each byte is framed by start and stop bits. Within each byte, data is transmitted Least Significant Bit(LSB) first. The start bit is the opposite of the idle state or zero and the stop bit equals the idle state.

Message transfers start with the master issuing a synch break, followed by a synch field and a message field.
Clock used for synchronization for the entire bus is set by transmitting a synch field at beginning of each message.
Each slave node must use this synch byte to adjust their baud rate. The second byte of each message is an ident byte. This ident field informs the bus about the type of data to be followed. It also indicates which node will answer and how long the answer will be.
Once the data is on the bus, any node may receive the same. Only one slave may respond to a given command. Hence communication from one Slave node to another node does not have to be directed through the Master. Hence any two slave nodes can also communicate.

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