I'm using STM32F40CCU6 and ST-Link Debugger When I try to enter debug session, IDE say that mcu refused to connect

[gbm]

A common beginner's problem, addressed dozens of times on this forum. It's easy to find the possible diagnosis and solutions - just use search function.

[Imen.D]

Hello @AMabr.2​ and welcome to the Community :)

Have a look at this article which describes the ways to fix debugger connection issues:

How to solve debugger connection issues (st.com)

I hope this helps !

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Imen