Stm32G0B1 Bootloader not working after power-on. Reset required

[Nabidev]

Hello,

we have designed different boards with STM32G0B1.

With our latest board we find that bootloader is not activated at power on, even when Boot0 is high roughly 1ms before MCU power rises (I can provide oscillogram), instead of bootloader, application is started.

Of course nBOOT_SEL option is zero. 

After giving a reset, bootloader is correctly starting.

The only difference to other boards might be MCU revision. We have that problem with MCUs marked 'Z'. 

With 'A' marking every board is working.

Are there differences between MCU revisions regarding this?

Is there a minimum time Boot0 has to be high before power on?

Is reset required to activate bootloader (i.e. is it not guaranteed to start after power on? if yes, what are the differences between reset and power on, respectively where are they documented)?

I did not find answers to the above in your documentation.

Thank you in advance

[Nabidev]

I have new information.

We had slight variations in the capacitors keeping the nRST pin low after power on.

If we increase the capacitor which delays the rising edge of nRSt, bootloader is activated even after power on.

It is, however, still unclear whether this is intended behaviour or not, or documentation error.

AN2606 chapter 47.2 clearly states that bootloader activation starts with system reset.

rm0444 chapter 5.1.2 clearly states that system reset is caused by power-on.

When we connect nRST directly to Vdd (+3.3V) and Boot0 to a power that is on 1ms BEFORE MCU-Vdd, bootloader is never activated at power on. The only way to activate bootloader is by pulling nRST low again.

If nRst rising is delayed by roughly 1ms bootloader is activated at power-on also.