Brown Out Reset does not work

[Andreas1]

Hello,

we have a pcb with an STM32F765VIT6 on it. Everything works nicely except that there are unfrequent bit flips in the flash after disconnect and connecting the power supply..

We tried to activate the brown out reset in software but after measuring the NRST pin, it only resets at ~1,7V and not above 2V as wanted.

We tried the code from the following website:

https://stm32f4-discovery.net/2015/08/hal-library-22-bor-for-stm32fxxx/

Is there anything we are forgetting? (Maybe for the STM32F7 there are other things to consider?)

[AvaTar]

> Everything works nicely except that there are unfrequent bit flips in the flash after disconnect and connecting the power supply..

I suppose you have a problem with your power supply. Flash bits don't use to faint.

Are these critical Flash areas programmed at runtime ?

[Andreas1]

No they are not programmed at runtime. But I have to mention that we are connecting and disconnecting the power supply using two relais. So there is enough noise. After reading out the flash and comparing it to the original one, there are differences. So is there any guide on how to activate the Brown Out Reset on the STM32F7? Thank you.

[AvaTar]

> But I have to mention that we are connecting and disconnecting the power supply using two relais. ... After reading out the flash and comparing it to the original one, there are differences

This doesn't sound good. I suspect you violate the specs somewhere, and a coordinated brown-out reaction will not help you.

I'm no hardware guy, though.

[Andreas1]

We soldered an external reset controller which generates a reset when the voltage goes under 3,08V. And up to now we did not have any problems. So I think the Brown Out Reset would help but we do not get it to work. Another option is to make a redesign and use an external reset controller but using the internal BOR would be a lot easier..

[waclawek.jan]

Have you tried to set/read the option bits using a programmer, e.g. STLink Utility?

JW

[AvaTar]

Still, under no circumstances should the Flash content change accidentally at power-off, except you interrupt an erase/program.