Reset pin goes down every 400ms for 50us

msemegen · ‎2022-10-24

Hi,

we have problem with our custom designed board. We are using STM32L011F4P6 MCUs and some of them behaves very strange. After reset, every 400ms for 50us, reset pin (which is internally pulled up), goes down. We don't known what causes that behavior. For sure it's not software - even txt uploaded on flash file causes the same behavior.

Did anyone encountered that before?

waclawek.jan · ‎2022-10-27

If FLASH->OPTR.WDG_SW = 0, it is in "Hardware watchdog" state, i.e. the watchdog

is automatically enabled at power-on.

JW

Piranha · ‎2022-10-27

So "only" 20 posts were necessary to "prove" that the first post was right on the target...

Also check if the nRST_STDBY and nRST_STOP are configured as you actually need it to be.

Piranha · ‎2022-10-27

Noticed just now...

> it's illogical because in step 5 we activate IWDG

The only illogical thing there is guessing and not reading the reference manual. ;) And the respective bit is called WDG_SW - it enables the software (started) watchdog. Also it is enabled by default from factory.

msemegen · ‎2022-10-27

But this OB is not set by us... We can disable it only by using this magic sequence I described above...

Maybe there is problem with STLINK or CubeProgrammer...

msemegen · ‎2022-10-27

Ok,

I misunderstood the checked/unchecked behavior there, but still we have about ~250mcus where that OB is checked by default and ~250mcus where is unchecked...

waclawek.jan · ‎2022-10-28

> But this OB is not set by us...

And by whom?

ST sets it consistently at manufacturing, see default values in RM.

JW

Piranha · ‎2022-10-28

> mcus where is unchecked

Maybe the tools, with which you are reading those values, modify those bits for some reason. Or could be fake parts, which is a very popular issue now.

msemegen · ‎2022-10-30

We are using CubeMXProgrammer as a flashing tool. MCUs are from trusted discribution channels.

This is first time we encountered that behavior. We used the same hw design for other L0 family MCUs (L011K4, L010RBT6) with changes related to different pinout.

Flashing procedure is the same for every mcu, we are not configuring any option byte.

The only solution we found is simply updating IWDG...