L9788 datasheet(50/264 Pages) STMICROELECTRONICS

50 / 264 page

Watchdog

L9788

50/264

DS12308 Rev 4

"… within the time window" means that the end of writing the last answer byte - i.e.

RESP_BYTE0 - falls into the fixed time window mentioned above (see picture below).

Except the last answer byte, the previous answer bytes may also be written earlier than the

beginning of the fixed time window.

The question sequence is deterministic. A question will be repeated until it is answered

correctly both in value and in time. Then the next question is placed in the sequence.

The ERROR COUNTER (EC) is a 3-bit counter. Various actions are activated depending on

the value of the counter.

The result of the comparison of the controller response and the calculated correct response,

as well as the next question, are available in registers REQULO after receiving the µC

response (LSB of RESP_BYTE0) and can be read by the controller.

Figure 19. Monitoring cycle diagram

4.1.2

ERR CNT (EC) and reactions, PWR COUNTER (PWR_CNT) and

generation of the monitoring module reset

Various actions are initiated for specific counter states of the ERROR COUNTER EC. The

counter reset state is 6.

For ERROR COUNTER (EC) > 4, the open drain output WDA is pulled low (active).

If the ERROR COUNTER reaches the value “7” and a further error occurs the PWR_CNT is

incremented by one during a sequencer-run.

The state "EC = 7 and a further error occurs" is also called ERROR COUNTER overflow

("EC" > 7).

start monitor cycle

CPU response

end of writing RESP_BYTE0

starts next monitor cycle

GADG2511161221PS

1.6 ms < response time window < 100.8 ms @ 64 kHz ±5%

time window = 12.8 ms @ 64 kHz ±5%

Table 19. Error counter

ERR_CNT

0 … 4

6 … 7

Overflow

ERR_CNT > 7

WDA

Hi-Z

Low

PWR_CNT 0

unchanged

Incremented by 1

Internal

PWR_CNT

signal

Low (not

active)

If PWR_CNT = 7 and

ERR_CNT increase

=> High (active)

Else unchanged

If PWR_CNT = 7

and ERR_CNT

increase => High

(active)

Else unchanged

PWR_CNT < 7 Low (inactive)

PWR_CNT 6->7 Low

(inactive)

PWR_CNT 7 -> 7 High

(active)

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