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Gpio status during bootmode

abhijith_raj
Associate III

‎2025-08-01 12:38 AM

Hi, 

I am working in STM32G491, currently working on MCU firmware upgrade part. I have a doubt regarding the output pins. Currently we have SET 2 GPIOs to high. That is power enable for another device say A. From another external device B, it is controlling bootpin and nrst pin. 

My doubt is if I make mcu to bootmode does that GPIO output value changes?

The situatuion is during device running, I make 2 gpio high. From another device mcu got entered to bootmode. Does the output pin change the high value?

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waclawek.jan
Super User

‎2025-08-01 12:46 AM - edited ‎2025-08-01 12:48 AM

By "bootmode", you mean the default bootloder  in System ROM? And you enter it through reset?

If yes, reset itself sets all pins to their defaults as given by reset values of the GPIO registers; and the bootloader sets those pins which it uses, see AN2606, usually to pulled-up input state, unless given interface gets activated. This is unfortunately poorly documented.

In some STM32 the dead-battery USB-C mechamism also causes surprising pin states.

JW

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