ST72361AR4-Auto datasheet(274/279 Pages) STMICROELECTRONICS

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Important notes

ST72361xx-Auto

274/279

Doc ID 12468 Rev 3

Occurrence

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

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

occurrence is around 1%.

Workaround

If this wrong duration is not compliant with the communication protocol in the application,

software can request that an Idle line be generated before the break character. In this case,

the break duration is always correct assuming the application is not doing anything between

the idle and the break. This can be ensured by temporarily disabling interrupts.

The exact sequence is:

●

Disable interrupts

●

Reset and set TE (IDLE request)

●

Set and reset SBK (Break Request)

●

Re-enable interrupts

LIN mode

If the LINE bit in the SCICR3 is set and the M bit in the SCICR1 register is reset, the LINSCI

is in LIN master mode. A single break character is sent by setting and resetting the SBK bit

in the SCICR2 register. In some cases, the break character may have a longer duration than

expected:

●

24 bits instead of 13 bits

Occurrence

The occurrence of the problem is random and proportional to the baud rate. 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.

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

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

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