Local Interconnect Network (LIN) messages

AN2334

10/22

3

Local Interconnect Network (LIN) messages

Created by the LIN Consortium (a collection of automotive, software and semiconductor

manufacturers), LIN is a low speed bus with a maximum speed of 20kbaud. The most

significant advantage offered by LIN bus is the low cost of implementation. Implementing a

LIN node costs approximately half of an equivalent CAN bus node.

The LIN bus protocol is based on the common UART byte interface. Any microcontroller with

a UART interface can be used as a node on the LIN bus since the basic transmission uses

the UART format. The LIN bus protocol specification 1.2 defines three standard baud rates:

2400 baud, 9600 baud and 19200 baud. Communication is based on a master/slave

mechanism.

The bus is composed of one master node (Driver door) and five slave nodes (All Doors,

Front Right Door, Dashboard, PC VNH2 Diagnostic and PC UH22/L9950 Diagnostic). All

arbitration and collision management takes place in the master node to further simplify and

lower the cost of the slave nodes.

Figure 4.

Master/slave diagram

–

All Doors is used for locking/unlocking all doors

–

Front Right Door is the slave node in the front right door that receives all

messages for mirror positioning (X-Y and fold) and for front right window lift

–

Dashboard is questioned from the master node each 250 ms in order to give

information for turning on/off turn indicator and defroster

–

PC-VNH2 is used for demonstration purposes to send VNH2 diagnostic

information to PC

–

PC-UH22/L9950 is also used for demonstration purposes to send L9950

diagnostic information to PC

All communications on the bus take the form of messages, which have a defined format

known as the message frame. A diagram showing the format of the message is shown in

Figure 5. The message frame is composed of a header and a response. The header is

further broken down into three fields:

–

The synchronization break field, composed of 13 dominant bits (0) and at least

one recessive bit (1), which indicates the beginning of a frame.

–

The synchronization field, which allows a slave to be synchronized on the current

master baud rate.

–

The identifier field, which identifies the requested message and the length of the

response field.

MASTER

Driver Door

SLAVE

All Doors

SLAVE

Front Right Door

SLAVE

Dashboard

SLAVE

PC-VNH2 Diag

SLAVE

PC-UH22/L9950 Diag

LIN Bus

CAN Bus