STM32F401RE - NRST held low

Semiconductor Integrated Circuits (ICs)
,
1

I started tinkering with Nucleo STM32F401RE. I was just blinking led succesfully at PA0 pin and suddenly the problem occured.

The CubeIDE gives me an error code when I’m trying to program it (Target Held under Reset).

I measured the Voltage on NRST pin (68mV). So I think something is holding the NRST pin LOW all the time.

I have tried different boot methods with Cube programmer but none of them have worked. I suspect there is something wrong with the board (maybe something shortcuts the NRST to GND)?

Does anyone have any suggestions?

2

Hello Vale Niskanen,

Thank you for your inquiry.

Per Page 22 of the datasheet for STM32F401RE

In regulator OFF mode, the following features are no more supported:
• PA0 cannot be used as a GPIO pin since it allows to reset a part of the V12 logic power
domain which is not reset by the NRST pin.
• As long as PA0 is kept low, the debug mode cannot be used under power-on reset. As
a consequence, PA0 and NRST pins must be managed separately if the debug
connection under reset or pre-reset is required

3

Thanks Kristofer for your answer.

As far as I understand the nucleo board (STM32F401RE) has LQFP64 package. So does this chip even have the Regulator OFF option(page 22)?

Also I’m quite beginner with these boards so I would appreciate little more help/instructions with the issue :slightly_smiling_face: