Why is PB13 in pull-down mode after reset on STM32G0B0?

[Ebbe]

There is no firmware in the µC! I expected all I/Os to be floating. Some are floating. But PB13 seems to be pull-down is activated. I did not find the reason in data sheet or Reference Manual. What Pins are safe floating after reset?

[waclawek.jan]

PB13 should be floating, unless you enter the built-in bootloader - see AN2606 for pins affected. 'G0B0 is Pattern 11, so if FLASH is empty and option bytes are at the factory default, default bootloader is active.

Other than that, pins are pulled up/down after reset either because they are JTASG/SWD pins (see GPIO chapter in RM), or because of the USB-C Power Delivery - Dead Battery support - the latter are pulled down even while the mcu is powered down.

JW

[Ebbe]

Ok, thank you! 🙂

I think it's the bootloader. In bootloader-mode PB13 is Slave clock input with pull-down activated.

So, as I can not prevent the µC from getting in bootloader, I have to use another pin that is not used in bootloader, or at least, a pin that has no pull-down activated.