Hi kui wu,
0X40C is the FSEC area, it is used to secure the JTAG and the Ezport interfaces.
FSEC also contains the key, the MEEN etc bits.
If you use the backdoor key, then you also can use your own key to unlock it.
If you enable the mass erase, then you can do the mass erase to unlock it.
But if your mass earse is disabled, and SEC is also secured, and the backdoor key is disabled, then the secure leve is to the highest, you can't unsecure it again.
If you want to change your chip mode to secure, you can modify your flash address 0x40C to 0XFC, then the SWD is secured. You can modify the 0X40C in your app code directly, take an example:
The Flashconfig code in the .s file.
So, you don't need to secure it in your app code directly, just in the .s file before you download the code is OK.
Wish it helps you!
If you still have questions about it, please kindly let me know.
Best Regards,
Kerry
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hello，
sorry
My operation is as the following
1.Set Flash issecurity.
2. update security byte in startup file as the following
3. then dowunload
4. The following prompt box will pop up , when click "Yes" it will erase FLash to unsecured.
5. as above description, how to enable MCU to secure?
