AN4178

Implementing a LIN slave node with STM8AF board

Doc ID 23745 Rev 1

5/13

3

Implementing a LIN slave node with STM8AF board

3.1

STM8AF microcontroller LINUART features for LIN slave

LINUART supports autonomous handling of LIN headers. The software is notified of header

reception through a dedicated flag, LHDF. This means a single interrupt occurs only when

the entire header is received, including the Break, the Synch Field and the Identifier Field.

LINUART implements a mute mode, allowing the software to remain quiet without

generating any interrupts until reception of the next header. This is very useful for filtering

frames for which the STM8AF is neither publisher nor subscriber. All data bytes of the frame

response will thus be ignored by the LINUART, and will not generate any interrupts.

The automatic resynchronization feature allows a LIN slave to be built with the STM8AF

microcontroller, without the need for an external crystal, oscillator or resonator. The

LINUART can synchronize on the Synch Field of each received header, and automatically

adjusts the baudrate prescaler in order to receive and send the rest of the frame with the

right frequency tolerance, whatever the frequency deviation of the embedded internal RC

oscillator (HSI) may be.

If one of the following errors is detected during the header reception, the software is notified

through the LHE flag:

●

resynchronization error, if the deviation is more than 14%

●

identifier error (framing error or parity error)

●

break delimiter error, if the delimiter is too short

●

header timeout, if the LIN header is longer than the T_HEADER_MAX defined in the

LIN standard

In order to enhance system robustness, the LINUART can detect a Break at any time, even

while receiving a data byte, and resynchronizes upon detecting the Break.

3.2

Software algorithm

The software algorithm described below is implemented in the STM8AF slave software. For

details, refer to Section 4.3: STM8AF LIN slave software description.

3.2.1

LIN state machine

The LIN task is called regularly by the main routine. This task is a basic LIN slave driver that

implements a state machine with the following states:

●

Idle

●

Identifier

●

DataReception

●

DataTransmission