ST72361AR4-Auto datasheet(180/279 Pages) STMICROELECTRONICS

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LINSCI serial communication interface (LIN master/slave)

ST72361xx-Auto

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Doc ID 12468 Rev 3

15.9.5

LIN baud rate

Baud rate programming is done by writing a value in the LPR prescaler or performing an

automatic resynchronization as described below.

Automatic resynchronization

To automatically adjust the baud rate based on measurement of the LIN synch field:

●

Write the nominal LIN prescaler value (usually depending on the nominal baud rate) in

the LPFR / LPR registers.

●

Set the LASE bit to enable the auto synchronization unit.

When auto synchronization is enabled, after each LIN synch break, the time duration

between five falling edges on RDI is sampled on fCPU and the result of this measurement is

stored in an internal 15-bit register called SM (not user accessible) (see Figure 83). Then

the LDIV value (and its associated LPFR and LPR registers) are automatically updated at

the end of the fifth falling edge. During LIN synch field measurement, the SCI state machine

is stopped and no data is transferred to the data register.

15.9.6

LIN slave baud rate generation

In LIN mode, transmission and reception are driven by the LIN baud rate generator

Note:

LIN master mode uses the extended or conventional prescaler register to generate the baud

rate.

If LINE bit = 1 and LSLV bit = 1 then the conventional and extended baud rate generators

are disabled: the baud rate for the receiver and transmitter are both set to the same value,

depending on the LIN slave baud rate generator:

with:

LDIV is an unsigned fixed point number. The mantissa is coded on 8 bits in the LPR register

and the fraction is coded on 4 bits in the LPFR register.

If LASE bit = 1 then LDIV is automatically updated at the end of each LIN synch field.

Three registers are used internally to manage the auto-update of the LIN divider (LDIV):

●

LDIV_NOM (nominal value written by software at LPR/LPFR addresses)

●

LDIV_MEAS (results of the field synch measurement)

●

LDIV (used to generate the local baud rate)

The control and interactions of these registers is explained in Figure 84 and Figure 85. It

depends on the LDUM bit setting (LIN divider update method)

Note:

As explained in Figure 84 and Figure 85, LDIV can be updated by two concurrent actions: a

transfer from LDIV_MEAS at the end of the LIN sync field and a transfer from LDIV_NOM

due to a software write of LPR. If both operations occur at the same time, the transfer from

LDIV_NOM has priority.

Tx = Rx =

(16*LDIV)

fCPU

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