ST7MC1 datasheet(126/308 Pages) STMICROELECTRONICS

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ST7MC1/ST7MC2

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LINSCI

™ SERIAL COMMUNICATION INTERFACE (LIN Mode) (cont’d)

If LHE bit is set due to this error during Fields other

than LIN Synch Field or if LASE bit is reset then

the current received Header is discarded and the

SCI searches for a new Break Field.

Note on LIN Header Time-out Limit

According to the LIN specification, the maximum

length of a LIN Header which does not cause a

timeout

equal

1.4 * (34 + 1) = 49

TBIT_MASTER.

TBIT_MASTER refers to the master baud rate.

When checking this timeout, the slave node is de-

synchronized for the reception of the LIN Break

and Synch fields. Consequently, a margin must be

allowed, taking into account the worst case: This

occurs when the LIN identifier lasts exactly 10

TBIT_MASTER periods. In this case, the LIN Break

and Synch fields last 49 - 10 = 39TBIT_MASTER pe-

riods.

Assuming the slave measures these first 39 bits

with a desynchronized clock of 15.5%. This leads

to a maximum allowed Header Length of:

39 x (1/0.845) TBIT_MASTER + 10TBIT_MASTER

= 56.15 TBIT_SLAVE

A margin is provided so that the time-out occurs

when the header length is greater than 57

TBIT_SLAVE periods. If it is less than or equal to 57

TBIT_SLAVE periods, then no timeout occurs.

LIN Header Length

Even if no timeout occurs on the LIN Header, it is

possible to have access to the effective LIN head-

er Length (THEADER) through the LHL register.

This allows monitoring at software level the

TFRAME_MAX condition given by the LIN protocol.

This feature is only available when LHDM bit = 1

or when LASE bit = 1.

Mute Mode and Errors

In mute mode when LHDM bit = 1, if an LHE error

occurs during the analysis of the LIN Synch Field

or if a LIN Header Time-out occurs then the LHE

bit is set but it does not wake up from mute mode.

In this case, the current header analysis is discard-

ed. If needed, the software has to reset LSF bit.

Then the SCI searches for a new LIN header.

In mute mode, if a framing error occurs on a data

(which is not a break), it is discarded and the FE bit

is not set.

When LHDM bit = 1, any LIN header which re-

spects the following conditions causes a wake-up

from mute mode:

- A valid LIN Break Field (at least 11 dominant bits

followed by a recessive bit)

- A valid LIN Synch Field (without deviation error)

- A LIN Identifier Field without framing error. Note

that a LIN parity error on the LIN Identifier Field

does not prevent wake-up from mute mode.

- No LIN Header Time-out should occur during

Header reception.

Figure 68. LIN Synch Field Measurement

LIN Synch Break

Extra

’1’

Bit0 Bit1 Bit2 Bit3 Bit4 Bit5 Bit6 Bit7

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

tBR = 16.LP.tCPU

SM = Synch Measurement Register (15 bits)

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