AN2334

Local Interconnect Network (LIN) messages

11/22

Figure 5.

LIN bus message frame format diagram

Only the master node can initiate a message by sending a header field that is received by all

nodes. Each slave node analyses the header and must be ready to send or receive data

during the response field of the frame. The identifier field within the header informs all slave

nodes in the network of the appropriate action to take. Such actions include:

–

Receiving bytes transmitted in the response field

–

Transmitting bytes in the response field

–

Doing nothing

ST72F561 has a flexible microcontroller architecture that makes the implementation of LIN

bus communication much easier than on other devices.

The LIN bus transmission of a master node, as this demoboard, has three distinct phases:

–

Synchronization break field transmission: The length of this field is 13 dominant

bits and 1 recessive bit

–

Data byte transmission: The synchronization field, the identifier field, the data

fields and the checksum field are each one byte fields.

–

Data byte reception: The data fields and the checksum field are also transmitted in

a byte wise manner.

The LIN bus protocol uses a standard baud rate: 19200 baud. In case of microcontroller

debugging, when CPU frequency is divided by two, a 9600 baud protocol is also possible.

The software PC allows users to change the baud rate.

It is necessary to define a specific ID (6 bits long) for each message, which is used for

reception or transmission. The message ID is written in a hexadecimal format with the parity

bits included. According to the LIN specification, the data field can be 1 to 8 bytes long (for

LIN 1.2 and newer).

The parity bits P0 and P1 are calculated as follows:

P0=ID0

P0=ID1

Because the application is for demonstration purposes, it uses two LIN messages for

transmission with PC (2 bytes long for VNH2 diagnostic and 8 bytes long for L9950

diagnostic).