ST72561 datasheet(145/262 Pages) STMICROELECTRONICS

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ST72561

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LIN

SCI

 SERIAL COMMUNICATION INTERFACE (LIN Mode) (Cont’d)

10.7.9.5 LIN Baudrate

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 Synchroni-

zation Unit.

When Auto Synchronization is enabled, after each

LIN Synch Break, the time duration between 5 fall-

ing edges on RDI is sampled on fCPU and the re-

sult 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 as-

sociated LPFR and LPR registers) are automati-

cally updated at the end of the fifth falling edge.

During LIN Synch field measurement, the SCI

state machine is stopped and no data is trans-

ferred to the data register.

10.7.9.6 LIN Slave Baud Rate Generation

In LIN mode, transmission and reception are driv-

en 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 Conven-

tional and Extended Baud Rate Generators are

disabled: the baud rate for the receiver and trans-

mitter are both set to the same value, depending

on the LIN Slave baud rate generator:

with:

LDIV is an unsigned fixed point number. The man-

tissa 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 meas-

urement)

- 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 Meth-

od)

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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