How to know if you're flashing an external board with nRF52840DK?

[gendor]

Is there a way of visually verifying if you're programming an external board with the nRF52840DK? Sometimes I'm not sure if the pins are wired up correctly, in which case it would program the on-board nRF52840 instead.

[Einar Thorsrud]

A quite simple way is to read the DEVICEID[0] register from FICR, as this is unique for each device. When nothing is connected to the debug out port, you should read the number of the onboard nRF on the DK. When an external device is connected, you should see a different number (which is different for each external device).

You can read it like this:

nrfjprog --memrd 0x10000060

(if you are paranoid you can read DEVICEID[1] as well, which is at 0x10000064, but that is probably overkill for this purpose)

[gendor]

Thank you, that's very helpful!