Local Interconnect Network (LIN)

Local Interconnect Network (LIN)

History

The first version of the LIN standard was adopted by Audi, BMW, Daimler-Benz, Motorola, Volvo and Volkswagen in 1999. Just two years later, the LIN consortium celebrated the first series launch of a LIN bus subsystem (SLK).

Its main characteristics are as follows:
- Simple concept
- LIN applications are always easy to develop and maintain
- LIN is also designated as a subbus (supplement to CAN)
- LIN is based on cost-effective standard components







The system facilitates the exchange of data between a LIN master control unit and up to 16 LIN slave control units.







- Single-wire bus
- No shielding required
- Data transfer rate: 19.2 kbit/sec

Tasks







- Monitors the transfer of data and the data transfer speed
- Sends out the message header
- Specifies the cycle, when and how often which message is placed on the LIN data bus
- Performs the translation function/acts as gateway
- The only control unit connected to the CAN data bus in the LIN bus system
- Diagnosis of the LIN slave control units is performed via the LIN master control unit

LIN Slave Control Unit

Tasks

- Individual control units, or even sensors and actuators, can be deployed as LIN slave control units within a LIN data bus system. Electronics that evaluate the measured values are integrated into the sensors. The values are then transferred as a digital signal via the LIN bus. Only one pin is required on the LIN master's socket for multiple sensors and actuators.
- The LIN actuators are intelligent electronic or electromechanical assemblies, which receive their tasks from the LIN master control unit via the LIN data signal. The LIN master uses the integrated sensors to query the actual status of the actuators and thus perform a required/actual comparison.

Data Signal







Data transfer:
- The sensors and actuators only respond if a header has been sent out by the LIN master control unit. The data transfer rate ranges from 1 to 20 kbit/sec.

Signal:
- Recessive level - If no message or a recessive bit is sent via the LIN data bus, close to battery voltage is present on the data bus line.
Dominant level - To transmit a dominant bit via the LIN data bus, the data bus line is switched to ground by a transceiver in the sender control unit.

Transmission Reliability

Data transfer stability is ensured by the specification of tolerances during transmission and reception in the recessive and dominant level range.










LIN Messages










The header is sent by the LIN master control unit on a cyclical basis It can be divided into four sections:
- Synch break
- Synch delimiter
- Synch field
- Identifier field

The synch break is at least 13 bit times in length. It is sent at a dominant level. A length of 13 bits is required in order to communicate the start of a message to all LIN slave control units. A maximum of 9 dominant bits are transferred consecutively in the subsequent message parts. The synch delimiter is at least 1 bit long and recessive (UBat).







All LIN slave control units can adjust to (synchronize with) the system clock rate of the LIN master control unit via this bit sequence. All control units must be synchronized to ensure a seamless exchange of data. If the synchronization is lost, the bit values would be positioned incorrectly in the message upon reception. This would lead to errors in the data transfer.

The identifier field is 8 bit times in length. The first 6 bits contain the message ID and the number of data fields in the response. The number of data fields in the response can range from 0 to 8. The last 2 bits contain the checksum of the first 6 bits. The checksum is used to detect transfer errors and is necessary to avoid allocation to the wrong message in the event of transfer errors in the identifier.







Response message header:
The response consists of 1 to 8 data fields. One data field consists of 10 bits. Each data field comprises a dominant start bit, a data byte (which contains the information) and a recessive stop bit. The start and stop bits are used for synchronization and to avoid transfer errors.

LIN Usage at Porsche

Previous LIN applications: Rain sensor, TPM & Weight sensors

Panamera: Shown in the chart below.