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NUCLEO-U5 locked, ST-LINK red solid + green flashing, cannot connect

630
Associate

‎2026-04-30 11:08 PM

Hi,

I am using NUCLEO-U545RE-Q with X-NUCLEO-NFC07A1.

After downloading a program via Arduino IDE, the board got locked.

Symptoms:

  1. PC cannot detect the board, no ST-LINK device, no COM port
  2. ST-LINK LED: red always on, green flashing
  3. STM32CubeProgrammer cannot connect, error: No debug probe detected
  4. Connect Under Reset does not work

What I tried:

  1. power cycling
  2. holding RESET when plugging USB
  3. Connect Under Reset in CubeProgrammer
  4. checking CN2 jumpers (they are fine)

Questions:

  1. How can I unlock or erase this board without a BOOT0 jumper? It seems not available on this NUCLEO board.
  2. Is there any software-only way to recover the SWD?

This board is for a competition. Any help is appreciated. Thanks.

0399aa12a733f4b5f426bc88ea08ebff.jpg

 

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1 REPLY 1
Mike_ST
ST Employee

‎2026-05-04 6:34 AM

Hello,

>> How can I unlock or erase this board without a BOOT0 jumper? It seems not available on this NUCLEO board.

BOOT0

BOOT0 can be set to 1 on CN7 connector by bridging pin 5 and pin 7.

BOOT0 is also dependant of the option bytes nBOOT0 and nSWBOOT0:

Mike_ST_0-1777900639454.png

>> PC cannot detect the board, no ST-LINK device, no COM port

LD3 is off meaning the ST-Link has not activated the T-PWR_EN signal.

Please, check the quality of the USB cable, and if it is not a charger only cable with no D+/D- data lines.

 

 

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