L9300 datasheet(87/178 Pages) STMICROELECTRONICS

87 / 178 page

In this way, actuation of loads can be performed only if the WD has been started and a certain number of good

Request/Answer has been exchanged.

In any case, WD_CNT will be saturated when WD_CNT = "1111".

When the WD algorithm is not active (FSM is in IDLE) the WD_CNT = WD_th_low.

Figure 56. Driver actuation and WD_RTS versus WD_CNT value

WD_RST = ON

Driver = OFF

WD_RST = OFF

Driver = OFF

WD_RST = OFF)

Driver = ON

(Previous state was:

WD_RST = OFF

Driver = ON

WD_RST = OFF

Driver = ON

WD_RST = OFF)

Driver = OFF

(Previous state was:

WD_RST = OFF

Driver = OFF

WD_th_low

WD_th_high

GADG0408171226PS

All the status information is stored onto the WD_Status_reg, readable through SPI. This register will be cleaned

as consequence of each read operation.

In case a WD_RST is generated, the ASIC restarts the WD evolution state machine in IDLE mode waiting for the

seed request from micro through SPI. WD configuration registers are preserved but can be modified by the micro

before starting the WD mechanism.

In the same way, also the status register, WD_Status_reg, is preserved and can be read through SPI.

14.1.3

Out Of Sequence error cases

Two cases of unexpected errors have been identified:

•

If a request of a new seed arrives to the ASIC before the previous answer received, the ASIC serves the

new request, sending the old Seed decreasing the value of WD_CNT by the amount WD_cnt_bad_step.

•

If an answer arrives to the ASIC before a new request and after another answer, the ASIC ignores this

answer but it decreases the value of WD_CNT by the amount WD_cnt_bad_step.

L9300

Q&A Watchdog

DS12258 - Rev 5

page 87/178

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