Local interconnect network
The Local Interconnect Network ( LIN ), also known as LIN bus , is a serial communication system for networking sensors and actuators , a field bus . LIN is used where the bandwidth and versatility of CAN is not required. Typical application examples are networking within the door or seat of a motor vehicle.
The LIN specification was developed as an industry standard by the LIN consortium until 2010. It comprises the physical layer, the bus protocol, the interface to the application and a uniform format for describing an entire LIN. The achieved level 2.2A of the specification was transferred to ISO and published as ISO standard 17987-1, Road vehicles - Local interconnect network (LIN) - Part 1–8 .
CAN in Automation has been acting on behalf of the Technical Management Board of ISO (TMB) as the registration office for the LIN Supplier ID in accordance with the ISO 17987 series of standards since 2017.
LIN topology
A LIN consists of a master and one or more slaves. The number of slaves is usually limited to 16. The master is typically a microcontroller which, as a bridge, connects the LIN to a CAN bus. On the LIN, the master determines the (usually fixed) chronological order of all messages by sending out the beginning, the so-called header . This contains an identifier that addresses a line in the configuration table . The table specifies which subscriber should send the data part of the message, which is up to eight bytes long, what kind of data it is and which subscriber or subscribers are to read the message. Each slave only needs to save the part of the table that is relevant to it. A dynamic change of the configuration during operation ( plug 'n play ) is not intended. Design tools for the configuration table ensure that no collisions occur during operation .
The LIN specification
The specification provides for two network node states: sleep mode and normal mode. The transition between the two modes is initiated on the one hand with an explicit command from the master and on the other hand via a wake-up signal frame by the master or one of the slaves.
With LIN, diagnosis is carried out with the help of command messages. In order to be able to diagnose a slave, the master transmits a specific command. The data transmission within a diagnosis between master and slave is based on the transport protocol defined by ISO 15765-2.
LIN works with a signal line that connects the network nodes wired-AND , implemented through open collector outputs and pull-up resistors on the vehicle electrical system. The high level (logical 1) represents the recessive state as well as the idle state and approx. 0 V represents the dominant state. The edge steepness is limited to about 2 V / μs in favor of acceptable radiated interference . The baud rate is accordingly limited to a maximum of 20 kBd, 2400, 9600 and 19,200 baud are common. The bus transceivers are controlled via a UART - usually called SCI (Serial Communication Interface) in the LIN context .
Error handling
Error handling is prescribed in Chapter 6 of the specification:
- Each sender must read back bit by bit what it is sending and, in the event of an error, cancel the transmission. If the master detects that it cannot send, it must report a physical bus error to its application layer .
- A checksum protects the data against transmission errors.
- The header byte encodes the maximum of 64 messages with six bits and contains two parity bits , so that all single and many double-bit errors in the header are recognized.
- A no-response error must be detected on the master for missing responses .
- Slaves must ensure that the edges in the synchronization field are within the defined tolerance.
Messages recognized as faulty are discarded. Error events are registered locally. Error signaling is not part of the protocol, but must be defined in the application layer if required.
literature
- Werner Zimmermann, Ralf Schmidgall: Bus systems in vehicle technology - protocols, standards and software architecture. 5th edition, Springer Vieweg, Wiesbaden 2014, ISBN 978-3-658-02418-5 .
- Andreas Grzemba, Hans-Christian von der Wense: LIN bus, systems, protocols, tests of LIN systems, tools, hardware, applications . Franzis, Poing 2005, ISBN 3-7723-4009-1 .
Web links
- LIN consortium: LIN Specification Package Revision 2.2A . December 2010.
- LIN Supplier ID Registration office for the LIN Supplier ID, standardized in the ISO 17987 series of standards
- E-learning learning module LIN on the Vector website