STM32U585 GPIO in RESET

[RocketTomek]

Problem : GPIO PB7,8 is pull up in reset state.

Reproduction: After Clearing Reset  (Reset Goes low)  the voltage on PB7 and PB8 goes high. uc is erased. We have external pull down connected to those pins (100k), but the signal stays at 2.5V

Could you confirm that pull-up in reset mode on those pins is correct behavior?

I suspected that GPIO should go to input mode and pull down pull up should be disabled.

[TDK]

PB7 and PB8 are in analog mode with no pullups during reset and should be pulled down if an external resistor is present. Perhaps measure resistance between them and ground with the chip unpowered and ensure you see 100 kOhm.

Don't see anything in the RM suggesting these pins are special.

[RocketTomek]

I have 100KOhm between each pin and 100kOhm while board is powered off.

We took second board and we performed following procedure:

• Erase both cores, uA and uB
• Clear Reset signal (J0link commander - "clrreset")
• Measure Votlage on PB7 and PB8. 0V measured.
• Set Reset Signal
• Measure Voltage on PB7 and PB8. 2.42V measured

We will do more tests tomorrow.

[TDK · Accepted solution]

Sounds like the chip is inside the bootloader. Those pins have pullups in the bootloader.

Is BOOT0 pulled low? Are option bytes set up to run the bootloader? Is this a custom board?

Perhaps program something on the boards to blink an LED, run that code so you know it's running and not in the bootloader.

See AN2606 for information on when the bootloader is ran and how it initializes pins:

cd00167594-stm32-microcontroller-system-memory-boot-mode-stmicroelectronics.pdf