ST Link error (DEV_TARGET_UNDER_RESET)

Vanshika1 · ‎2025-07-09

I have a customized pcb with stm32l476 as the mcu and stm32f103 as a debugger. Since my debugger is not flashed i am using an external st-link from the nucleo-l476. When i try to connect it in the normal mode and reset mode, STM32 Cube Programmer gives me an error that DEV_TARGET_HELD_UNDER_RESET and when i try to connect it in hot plug mode, it connects but gives an error that NO DATA READ. What should i do?

Aziz BRIGUI · ‎2025-08-12

Hello @Vanshika1

I suspect the reset pin on the MCU is held low. Could you double check please ?

Aziz

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Tesla DeLorean · ‎2025-08-12

If your MCU share a common NRST pin this may occur.

Would need to see a schematic.

Make sure analogue VDDA \ VSSA are connected to a supply (power, ground respectively), otherwise circuit will clamp in reset state.

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