Hi everyone, I'm facing issues connecting an external debugger to the NUCLEO-H7S3L8 board (STM32H7S3L8). Current Setup: Board powered via CN5 (ST-LINK USB) JP1 closed (to disable on-board ST-LINK) External debugger connected to CN1 (MIPI20 connector) SWD mode at low speed (500 kHz to 1 MHz) Correct power sequence: Power CN5 first → wait for COM LED (LD8) to stabilize → then connect external probe What I have already tried: BOOT0 = 1 (jumper on CN11[5-7]) to enter bootloader mode and halt using external debugger Internal ST-LINK works fine when JP1 is open (using STM32CubeProgrammer) Problem: The external debugger is unable to connect or halt the CPU, please guide me how to fix it. Thanks,regards,Surender.

Associate

Question

Unable to halt/connect STM32H7S3L8 using external debugger on Nucleo-H7S3L8 (JP1 closed)

Hi everyone,

I'm facing issues connecting an external debugger to the NUCLEO-H7S3L8 board (STM32H7S3L8).

Board powered via CN5 (ST-LINK USB)
JP1 closed (to disable on-board ST-LINK)
External debugger connected to CN1 (MIPI20 connector)
SWD mode at low speed (500 kHz to 1 MHz)
Correct power sequence: Power CN5 first → wait for COM LED (LD8) to stabilize → then connect external probe

BOOT0 = 1 (jumper on CN11[5-7]) to enter bootloader mode and halt using external debugger
Internal ST-LINK works fine when JP1 is open (using STM32CubeProgrammer)

Problem:

The external debugger is unable to connect or halt the CPU, please guide me how to fix it.
Thanks,
regards,
Surender.

Super User

Hi,

what is your external debugger ?

>external debugger is unable to connect or halt the CPU

Which program + debug probe ?

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Associate

Hi,
I solved my problem:
When I used APSEL=1 I was able to halt the CPU.
Debug probe was a 20-pin SWD debug probe.
External debugger was PALMICE.