MC68HC908QL4 Datasheet, PDF (150/226 Pages) Motorola, Inc – Microcontrollers

Slave LIN Interface Controller (SLIC) Module
14.9 Initialization/Application Information
The LIN specification defines a standard LIN “MESSAGE FRAME” as the basic format for transferring
data across a LIN network. A standard MESSAGE FRAME is composed as shown in Figure 14-14 (shown
with 8 data bytes).
LIN transmits all data, identifier, and checksum characters as standard UART characters with eight data
bits, no parity, and one stop bit. Therefore, each byte has a length of 10 bits, including the start and stop
bits. The data bits are transmitted least significant bit (LSB) first.
HEADER
DATA
SYNCH
BREAK
0x55
SYNCH IDENT
BYTE FIELD
DATA
FIELD
0
13 OR MORE BITS (LIN 1.3)
DATA
FIELD
1
DATA
FIELD
2
DATA
FIELD
3
DATA
FIELD
4
DATA
FIELD
5
Figure 14-14. Typical LIN MESSAGE FRAME
DATA
FIELD
6
DATA
FIELD
7
CHECKSUM
FIELD
14.9.1 LIN Message Frame Header
The HEADER section of all LIN messages is transmitted by the master node in the network and contains
synchronization data, as well as the identifier to define what information is to be contained in the message
frame. Formally, the header is comprised of three parts:
1. SYNCH BREAK
2. SYNCH BYTE (0x55)
3. IDENTIFIER FIELD
The first two components are present to allow the LIN slave nodes to recognize the beginning of the
message frame and derive the bit rate of the master module.
The SYNCH BREAK allows the slave to see the beginning of a message frame on the bus. The SLIC
module can receive a standard 10-bit break character for the SYNCH BREAK, or any break symbol 10 or
more bit times in length. This encompasses the LIN requirement of 13 or more bits of length for the
SYNCH BREAK character.
The SYNCH BYTE is always a 0x55 data byte, providing five falling edges for the slave to derive the bit
rate of the master node.
The identifier byte indicates to the slave what is the nature of the data in the message frame. This data
might be supplied from either the master node or the slave node, as determined at system design time.
The slave node must read this identifier, check for parity errors, and determine whether it is to send or
receive data in the data field.
More information on the HEADER is contained in 14.9.7.1 LIN Message Headers.
14.9.2 LIN Data Field
The data field is comprised of standard bytes (eight data bits, no parity, one stop bit) of data, from 0–8
bytes for normal LIN frames and greater than eight bytes for extended LIN frames. The SLIC module will
MC68HC908QL4 Data Sheet, Rev. 7
150
Freescale Semiconductor