L9788 datasheet(47/264 Pages) STMICROELECTRONICS

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DS12308 Rev 4

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L9788

Watchdog

263

Watchdog

4.1

Basic feature

L9788 has an internal query and answer (Q&A) watchdog with the aim of monitoring the

correctness of microcontroller activity. Via MSC bus a WDA “question” shall be read from a

MSC-WDA register. A correct response shall then be written back via MSC in a well defined

timing. If response or timing is not correct, then the WDA error counter EC (or ERR_CNT) is

increased. If the error counter is increased to values greater than 4, some output functions

are shut off. If the error counter reaches values greater than 7 (overflow), then a RST reset

may be generated if this is previously configured via MSC.

The first sequence of questions and responses starts from VDD5 higher than the UV

threshold.

Other way round, with a RST event also the WDA output pin goes to low.

Note that after startup, reset or an RST_CNT overflow the initial value of the error counter is

If WDA resets are enabled via MSC (WDA_INIT CONFIG-REG 9_1 D3): the number of RST

events generated by an error counter overflow is limited by the reset counter RST_CNT. If

RST_CNT reaches the value of 7, then RST resets via WDA are no longer generated.

With each error counter overflow, the PWR_CNT counter is increased. If it reaches a value

greater than 7, then the power latch mode is terminated.

Watchdog legenda:

ERR_CNT, EC

error 3-bit counter;

RST_CNT

reset 3-bit counter;

WDA_RST

internal reset generated by Watchdog;

PWR_CNT

power off 3-bit counter;

PWR_INT

internal signal indicating PWR_CNT overflow;

WDA

WDA open drain pin (low active);

WDA_INT

WDA internal signal, when high it drives WDA = low, when low it sets



WDA= Hi-z;

Sequencer-run

current state of WDA when it is active.

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