LIN

Local Interconnected Network (LIN) is a protocol created by a consortium comprising BMW, Volvo and Volkswagen in 1998 targeting the interconnection of units in the Body function domain.

LIN was designed to be used in automotive systems, however it was introduced as an alternative to CAN by providing device connectivity services at a lower cost. As a result, LIN is mainly adopted today in non-safety related systems as it employs real time handling of messages but with loose time constrains.

Protocol details

LIN employs a bus topology with the following characteristics:

• Bandwidth up to 20 Kbit/s.
• Payload (data) up to 8 byte.
• Identifiers on 6 bits (up to $2^6 = 64$ variables).
• Content based addressing like CAN.
• Producer/consumer data exchange model (consequence of the previous point).

Bus arbitration Differently from CAN, LIN uses a TDMA strategy to grant the bus to devices. One special device, the master, is the only active device on the network.

Frame structure Frames consist of:

• A header, containing the ID of the variable. Always sent by the master.
• A response part, contaiing the variable length data field.

Data exchange The master, by following an offline scheduling table, initiates transmissions:

1. The master sends a frame in broadcast specifying the variable ID whose value is required in the header.
2. The slave producing that variable will reply by filling the response with the variable's value.

Synchronization The master synchronizes slaves on his clock by sending the clock itself in the header of every frame.

LIN/CAN

In order to achieve good levels of interoperability between systems and keep good levels of robustness, different LIN subsystems are often interconnected together using CAN serving as a backbone infrastructure. LIN masters typically have the ability to act like CAN gateways so that they can interface with CAN.

In automotive, espacially in the Body function domain, CAN/LIN is a common combination. Furthermore, since different LIN subsystems can have different requirements in terms of predictability, CAN is a good choice for interconnecting them as a protocol able to guarantee a robust and reliable transmission of frames gateway-to-gateway between different LIN networks.

LIN and EPL

When compared to EPL, we can spot an important difference between these 2 protocols:

• EPL performs a polling on nodes, no clock synchronization is required as the MN will take care of coordinating the stations. LIN, on the other side, needs synchornization
• EPL Asks when node in unicast to transmit data, then that node responds in broadcast. In LIN, the master will send an header in broadcast by specifying the needed information, and a broadcast response will be sent afterwards.

Both protocols implement a producer/consumer communication model, but in a different way.

Extra functionalities

LIN offers services to put nodes to sleep and to wake them up. This functionality is extremely important from the energy consumption point of view especially in those conditions were the engine is off.