ST7MC1K2-Auto datasheet(364/371 Pages) STMICROELECTRONICS

364 / 371 page

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Known limitations

ST7MC1K2-Auto, ST7MC1K6-Auto, ST7MC2S4-Auto, ST7MC2S6-Auto

364/371

Occurrence

The occurrence of the problem is random and proportional to the baudrate. With a transmit

frequency of 19200 baud (fCPU = 8 MHz and SCIBRR = 0xC9), the wrong break duration

occurrence is around 1%.

Analysis

The LIN protocol specifies a minimum of 13 bits for the break duration, but there is no

maximum value. Nevertheless, the maximum length of the header is specified as

(14 + 10 + 10 + 1) x 1.4 = 49 bits. This is composed of:

●

The synch break field (14 bits).

●

The synch field (10 bits).

●

the identifier field (10 bits).

Every LIN frame starts with a break character. Adding an idle character increases the length

of each header by 10 bits. When the problem occurs, the header length is increased by 11

bits and becomes ((14 + 11) + 10 + 10 + 1) = 45 bits.

To conclude, the problem is not always critical for LIN communication if the software keeps

the time between the sync field and the ID smaller than 4 bits, that is, 208µs at 19200 baud.

Workaround

The workaround is the same as for SCI mode but considering the low probability of

occurrence (1%), it may be preferable to keep the break generation sequence as it is.

15.4.2

Header time-out does not prevent wake-up from mute mode

Normally, when LINSCI is configured in LIN slave mode, if a header time-out occurs during a

LIN header reception (that is, header length > 57 bits), the LIN Header Error bit (LHE) is set,

an interrupt occurs to inform the application but the LINSCI should stay in mute mode,

waiting for the next header reception.

Problem description

The LINSCI sampling period is Tbit/16. If a LIN Header time-out occurs between the 9th and

the 15th sample of the Identifier Field Stop Bit (refer to Figure 165), the LINSCI wakes up

from mute mode. Nevertheless, LHE is set and LIN header detection flag (LHDF) is kept

cleared.

In addition, if LHE is reset by software before this 15th sample (by accessing the SCISR

generates another LINSCI interrupt (due to the RDRF flag setting).

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