L9300 datasheet(91/182 Pages) STMICROELECTRONICS

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14.1.4

Seed generation and answer check

Seeds are 8-bit wide word generated by an LSFR pseudo-random algorithm. A new seed is generated and sent

onto an SPI word, WD_Seed, each time a new Seed request, T_start_REQ, is sent to the ASIC.

Figure 57. Seed generation algorithm block diagram

Seed

clk_4µs

Good

Answer

received

GADG0408171240PS

Seed is generated by freezing the 8-bit wide free running LSFR, running at a WD_clk clock period, each

T_start_REQ event.

As described in Figure 57, seed is generated by the LSFR algorithm. At each clock period (4 µs clock) the new

seed is generated according to the LSFR algorithm. A new seed is stored onto the WD_Seed only in case of a

correct answer received. In case of an error, the same seed is available onto the WD_Seed until a correct answer

is received.

Figure 58. Seed selection and elaboration flow

Microcontroller

ASIC

ANSWER WRITE

ANSWER CHECK

SEED

SENT SEED

OLD SEED

NEW SEED

SEED

SENT SEED

SEED

NEW SEED

SEED

OLD SEED

SEED

SEED_READ

SEED_ELABORATION

SEED_READ

ANSWER OK?

GADG0408171311PS

L9300

Q&A watchdog functional description

DS12258 - Rev 4

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