L9396 datasheet(77/109 Pages) STMICROELECTRONICS

77 / 109 page

DS12539 Rev 6

77/109

L9396

System functional safety implementations

108

Figure 19. Seed generation algorithm block diagram

Seed is generated by the LSFR algorithm in Figure above. In particular the algorithm

generates a 7-bit length word, while the seed has 8 bits including a zero as MSB. In this way

the seeds are always positive. A new seed will be stored onto the WD_Seed only in case of

a correct answer received. In case of an error, the same seed will be available into the

WD_Seed until a correct answer will be received.

Figure 20. Seed selection and elaboration flow

Figure 21. Answer check generation algorithm block diagram

The answer is a 16-bit long word checked against a 16-bit word composed by two bytes,

Answer_Low and Answer_High, generated from the sent seed. Answer_Low is the logical

2's complement of the seed, while Answer_High is a replica of the seed being sent.

Seed

GADG2401171600PS

T_start_REQ

Microcontroller

ASIC

ANSWER WRITE

ANSWER CHECK

SEED

SENT SEED

OLD SEED

NEW SEED

SEED

SENT SEED

ANSWER OK ?

SEED

NEW SEED

SEED

OLD SEED

SEED

GADG2401171606PS

SEED_READ

SEED_ELABORATION

SEED_READ

Answer Low

Answer High

Seed

! Seed

GADG2401171609PS

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