ST7MC1K2 datasheet(165/371 Pages) STMICROELECTRONICS

165 / 371 page

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On-chip peripherals

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Figure 69.

LIN synch field measurement

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 69). 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.

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. Thus, the baud rate for the receiver and transmitter are both set to the same

value, which depends on the LIN Slave baud rate generator:

Equation 9

where

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.

LIN synch break

Extra

’1’

Bit 0

Bit 1

Start

bit

Stop

bit

start

bit

LIN synch field

Measurement = 8.TBR =SM.tCPU

LPR(n)

LPR(n+1)

LPR = tBR/(16.tCPU) = rounding (SM/128)

tCPU = CPU period

tBR = Baud rate period

tBR

SM = Synch measurement register (15 bits)

tBR = 16.LP.tCPU

Bit 2

Bit 3 Bit 4

Bit 5 Bit 6 Bit 7

Tx = Rx =

(16*LDIV)

fCPU

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