RE: The nRF52840 proMicro is flashed, but the firmware code does not run.

vitorengcruz — Mon, 22 Dec 2025 17:09:35 GMT

Hi St-Ivoda , I've been busy here trying to solve the same problem... Unfortunately, your solution didn't work for me, so I did some more research.

I bumped in this Kconfig item in "Action-> nRF Kconfig GUI", "Board Options->Board has nRF5 bootloader", and it was enabled. So I try to disable it and flash. it worked, board started to blink LED0.

So I'm assuming this code example doesn't include the required nRF5 bootloader in "merged.hex". As far as I understand, this newer SDK should include all bootloader, softdevice and other stacks automatically, but for some reason it didn't include the bootloader for promicro board. Or we should flash the bootloader prior to flash "merged.hex"? I'll check this and come back here.

Best Regards and Happy new year!

RE: The nRF52840 proMicro is flashed, but the firmware code does not run.

St-Ivoda — Wed, 24 Sep 2025 06:52:26 GMT

I found a solution to my problem, and I'll describe it here; perhaps it'll be useful to someone.

It was enough to completely clean the SoC.

nrfjprog -f nrf52840 --eraseall

Then flash the SoftDevice S140.

nrfjprog --program /Path/to/your/s140_nrf52_7.3.0_softdevice.hex -f nrf52 --chiperase

This is a binary BLE stack that resides in the lower portion of the flash memory and hijacks some hardware resources. In the programmer, this portion of the flash memory is marked in orange and labeled "MBR". This is likely what the microcontroller is missing.
Then, after flashing the softdevice s140, flash your board via SWD.