Local Interconnect Network

The Local Interconnect Network (LIN) is a specification for a serial communication system, also referred to as LIN bus. LIN has been specially designed for cost-effective communication of intelligent sensors and actuators in motor vehicles, based on a single-wire bus and can be assigned to the fieldbuses. Typical applications include networking within a door or seat.

The LIN standard

LIN is a de facto standard, especially for low-cost communication of intelligent sensors and actuators in motor vehicles. It is used in applications where the bandwidth and versatility of CAN is not required. The LIN specification includes the LIN protocol, a standard format for describing an entire LIN, and the interface between a LIN and the application.

LIN Topology

A LIN is composed of a master and one or more slaves. The master has the knowledge of all the time sequence of data to be transmitted. This data is then transferred from the corresponding slaves when they are prompted by the master. He does by sending a header, which is characterized by a particular message address. Subsequently, the slave provides the data bytes to the bus.

The master is typically a micro-controller. The LIN master can also work as a gateway so that LIN slaves can also be reachable via CAN via the LIN master.

Typically, the number of slaves is limited to 16.

The LIN message

The LIN message consists of the header and the data ( with a LIN message A maximum of eight payload bytes are transferred ), it is essentially any LIN slave available to be received. The assumption of a LIN message depends entirely on the decision of control units from (recipient- selective system ). This decision is performed by so-called acceptance or message filter. It is thus possible that a LIN message is taken from one, several or all control units for further processing.

At any given time only one LIN message is always transmitted. This is no mechanism for resolving bus collisions is necessary because no collisions can occur. All messages to be transmitted are transmitted once within a cycle. The temporal order of the messages is recorded in a Schedule. This can be changed as needed.

In order to reduce the bus load by query frames for rare events, it is possible that multiple slaves on an identifier respond only when they have to share new data. This potential bus collisions are detected by the master. In this case, then appropriate query frames are transmitted, must answer to the only one slave.

The LIN specification

The specification provides two network nodes before states: sleep mode and normal mode. The transition between the two modes on the one hand initiated with an explicit command from the master and the other, on a wake -up signal frame by the master or the slave.

The diagnosis is performed at LIN with the help of command messages. In order to diagnose a slave, the master transmits a certain command. Data transmission within a diagnosis between master and slave is based on the transport protocol defined by the ISO 15765-2.

LIN is a single-wire bus, using a signal line and the car chassis as a reference potential. The signal states are as mentioned in the CAN recessive and dominant. In contrast to CAN, the board supply voltage represents the recessive state and the idle state and about 0 V to the dominant state.

The highest specified gross data rate of 20,000 bits per second ( bit / s). Recommended data rates are 2400 bit / s, 9600 bit / s and 19 200 bit / s

Error Handling

The LIN protocol provides no fault signaling ago, but two mechanisms to detect transmission errors: parity and checksum. Erroneous messages are considered and rejected as not sent. Detected errors are stored in the respective control unit and can be read by the master. In a LIN is no error signaling, detected errors are therefore not signaled via the protocol. The only exception is the chapter 6 (status management ) of the LIN Spec 2.0. It describes error detection in LIN by Response Error bit by the master to detect certain errors. The error handling for faulty communications is defined mostly dependent on the system requirements and needs in the application layer.

LIN Consortium

The LIN specification was developed by the LIN Consortium and includes the LIN protocol, a standard format for describing a whole as well as the interface between a LIN LIN and the application.