SYSTEM OPERATION

LIN communication system is described below:

The master ECU performs the master tasks and slave tasks, and the slave ECUs perform the slave tasks.
When the master ECU performs a master task, the header frame which stores information to call certain slave tasks (ECU) is transmitted at regular intervals.
When the master ECU and slave ECU perform a slave task, the ECU called by the header frame transmits the response frame which stores data used for control.
A header and response collectively are called as a message frame, and the communication method that uses the message frame is called as the frame communication.
Basically, the communication data is used with some blocks of 10-bit data group which includes one start bit and one stop bit (byte field) arranged in order.

VOLTAGE VARIATION OF LIN BUS LINE

When ECU sends or receives signals, LIN bus line voltage varies as follows.

The voltage variation of LIN bus line (0 and 1 combination as a theoretical value) ranging between battery voltage (recessive) and 0 V (dominant) is output (transmitted) as a control signal.
When no communication is established, the LIN bus line remains recessive (battery voltage).

MESSAGE FRAME

A message frame consists of fields that include a synchronisation start field, identifier field, data field, and checksum field. A few bits of recessive data is used to separate the frame from each field.

Frame	Field name	Description
Header	Synch Break	A field for informing the slave ECU of the starting of header transmission by sending the dominant signal for a given period of time
	Synch Field	A field for synchronising transmission cycle of each ECU connected to the LIN bus line (The transmission speed of the slave ECU is synchronised with that of the master ECU.)
	Identifier Field	A field stores an ID to call the slave ECU. The number of bytes for the data field is also defined in this field.
Response	Data Field	A field to store the control data used by ECU that is called by the header
Response	Checksum Field	A field for checking errors in data content. The sending-end ECU calculates data field value according to the specified computing equation, and the result is stored in this filed. The receiving-end ECU detects the transmission error based on the checksum filed value.

ERROR DETECTION

By introducing checksum field into the message frame and integrating various kinds of error detection functions into the master and slave ECUs, the LIN protocol has assured higher communication reliability.