ST72561 datasheet(148/262 Pages) STMICROELECTRONICS

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ST72561

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LIN

SCI

 SERIAL COMMUNICATION INTERFACE (LIN Mode) (Cont’d)

10.7.9.9 Error due to LIN Synch measurement

The LIN Synch Field is measured over eight bit

times.

This measurement is performed using a counter

clocked by the CPU clock. The edge detections

are performed using the CPU clock cycle.

This leads to a precision of 2 CPU clock cycles for

the measurement which lasts 16*8*LDIV clock cy-

cles.

Consequently, this error (DMEAS) is equal to:

2 / (128*LDIVMIN).

LDIVMIN corresponds to the minimum LIN prescal-

er content, leading to the maximum baud rate, tak-

ing into account the maximum deviation of +/-15%.

10.7.9.10 Error due to Baud Rate Quantisation

The baud rate can be adjusted in steps of 1 / (16 *

LDIV). The worst case occurs when the “real”

baud rate is in the middle of the step.

This leads to a quantization error (DQUANT) equal

to 1 / (2*16*LDIVMIN).

10.7.9.11

Impact

Clock

Deviation

Maximum Baud Rate

The choice of the nominal baud rate (LDIVNOM)

will influence both the quantisation error (DQUANT)

and the measurement error (DMEAS). The worst

case occurs for LDIVMIN.

Consequently, at a given CPU frequency, the

maximum possible nominal baud rate (LPRMIN)

should be chosen with respect to the maximum tol-

erated deviation given by the equation:

DTRA + 2 / (128*LDIVMIN) + 1 / (2*16*LDIVMIN)

+ DREC + DTCL < 3.75%

Example:

A nominal baud rate of 20Kbits/s at TCPU = 125ns

(8MHz) leads to LDIVNOM = 25d.

LDIVMIN = 25 - 0.15*25 = 21.25

DMEAS = 2 / (128*LDIVMIN) * 100 = 0.00073%

DQUANT = 1 / (2*16*LDIVMIN) * 100 = 0.0015%

LIN Slave systems

For LIN Slave systems (the LINE and LSLV bits

are set), receivers wake up by LIN Synch Break or

LIN Identifier detection (depending on the LHDM

bit).

Hot Plugging Feature for LIN Slave Nodes

In LIN Slave Mute Mode (the LINE, LSLV and

RWU bits are set) it is possible to hot plug to a net-

work during an ongoing communication flow. In

this case the SCI monitors the bus on the RDI line

until 11 consecutive dominant bits have been de-

tected and discards all the other bits received.

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