ST7LITE35 datasheet(164/167 Pages) STMICROELECTRONICS

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IMPORTANT NOTES (Cont’d)

break. This can be ensured by temporarily disa-

bling 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

have a longer duration than expected:

- 24 bits instead of 13 bits

Occurrence

The occurrence of the problem is random and pro-

portional to the baudrate. With a transmit frequen-

19200

baud

(fCPU=8MHz

and

SCI-

BRR=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)x1.4=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 be-

comes ((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, i.e. 208us 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 se-

quence as it is.

16.2.2 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 (i.e. header length > 57 bits), the

LIN Header Error bit (LHE) is set, an interrupt oc-

curs 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 107), 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 register and

reading the SCIDR register in the LINSCI interrupt

routine), the LINSCI will generate another LINSCI

interrupt (due to the RDRF flag setting).

Figure 107. Header Reception Event Sequence

LIN Synch

Identifier

Field

Break

THEADER

Active mode is set

RDRF flag is set

Critical

Window

ID field STOP bit

(RWU is cleared)

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