FRDM-MCXN947 – Lost SWD access after flashing UART binary ("EE42: Could not connect to core") via MC

[Matii]

Hi NXP Community,

I’m working with the FRDM-MCXN947 board and encountered a blocking issue after flashing a minimal diagnostic binary using MCUXpresso IDE. The binary was designed to initialize UART for physical validation, but after flashing it, I lost SWD access entirely. The debug console now consistently shows:

EE42: Could not connect to core.

The board still shows physical activity (e.g., LED toggling), so it’s not bricked. However, I can no longer connect via SWD, and all recovery attempts (power cycle, reconnect, etc.) have failed.

I suspect the binary reconfigured UART or clock settings in a way that disabled debug access. No ISP was used—just a standard debug flash via MCUXpresso.

I’ve experienced a similar issue before with an LPC1769, where the solution was to reset or reflash the bootloader, which successfully restored SWD access. I believe the same approach might work here, but I haven’t found any documentation or procedure for safely resetting the bootloader on the FRDM-MCXN947.

I’d appreciate any guidance from the community or NXP engineers:

• Is there a known recovery method for this board?
• How can I safely reset or reflash the bootloader?
• Are there vector catch or jumper-based mechanisms available for this family?

Any help would be greatly appreciated.

Thanks

[ZhangJennie]

Hi @Matii 

To summarize your issue: after flashing your binary file, SWD is disabled. As LEDs toggle, your board is not bricked. MCXN supports ISP mode, which allows us to erase and reprogram internal Flash even SWD is unavailable.

Thus please follow below step by step guide AN14460, "How to program MCX N series internal flash through ISP"

https://www.nxp.jp/docs/en/application-note/AN14460.pdf

Key notes:

- Use the ISP button sequence to enter recovery, then erase and reflash via MCUXpresso Secure Provisioning or blhost.

- This method is officially documented and should restore SWD access if the boot ROM is intact

Hope this will help you.

Jun Zhang