STM32F405 IWDG doesn't reset

[Elijah Brown]

I am having a problem where the IWDG seems to not reset the processor. I have setup a very simple project that enables the IWDG and then doesn't pet it - it should reset, but it doesn't. Running under the debugger or running standalone, it doesn't reset in either case. I can see that the IWDG RSTF is set in the RCC_CSR register. If I reset those bits using RMVF bit, the IWDG RSTF bit again gets set after the expected time. This makes me think that the independent watchdog is indeed going off, but for some reason the chip is just not resetting. This is such a simple thing it seems like, why doesn't it work?

[waclawek.jan]

NRST pin pulled up hard?

JW

[Elijah Brown]

Yes, it is connected to an external reset control chip which probably keeps that pin held high - would that keep it from resetting? I didn't think a watchdog reset would actually try and pull down that pin.

[Elijah Brown]

You are right, the reset circuit diagram does suggest that holding that pin high would prevent a reset. Thanks for the suggestion, I believe this is the problem.

[waclawek.jan · Accepted solution]

Yes, it's a recurring theme here, although maybe more in the "software reset does not work" form.

JW

[Tesla DeLorean]

Driving it high with a push-pull is a problem, you can have multiple reset sources, but they need to use open-drain ​