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STM32F767 - erratical Read Out Protection set, Option Bytes scrambled

Question asked by Andreas Richter on Nov 3, 2017
Latest reply on Nov 4, 2017 by Andreas Richter

Sometimes without any reproduceable reason my project with STM32F767 does not power up. If this occurs Read Out Protection is set (which I definitely do not have done) and Option Bytes are scrambled: BOOT_ADD0 and BOOT_ADD1 are set to 0xffff. In this case STM32 seems to be "dead" (does nothing). But I can access it via STLink and reanimate it with a "complete erase" following reflashing firmware and new setting of the Option Bytes. This is not reliable behaviour for releasing the project so I wonder what can be the cause for this. Vcc is 3.3V stable, coming from a LDO from 5V supply. Capacitors near to MCU Vcc pins are present. Maybe it is important that I am using RTC circuit with connected CR2032 as RTC battery. Any help is welcome - I do not have any idea where to begin investigations.

 

Best regards

DF8OE

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