How to disable nRF52 on the board when using nRF52840DK as a debugger

[DX_HK]

I am attaching an adapter board to the nRF52840DK to debug a custom board.

However, if there is any contact failure on the adapter board, the nRF52 on the DK will be the debug target, not the custom board.

This is correct behavior, but it often causes great confusion when debugging.

I have multiple nRF52840DKs, and I don't have a need for the nRF52 that I use as a debugger.

Is there a way to prevent the debug target from becoming the onboard nRF52?

Of course, this can be achieved by destroying the on-board nRF52, but I would like to solve it with jumper settings if possible.

[Simonr]

Hi

By shorting solder bridge SB47 on the nRF52840 DK (top left of the DK), you can supply power to the external board through the Debug out connector P19. While SB47 is shorted, it is not possible to program the onboard nRF52840 SoC even if the external board is unplugged. This is stated on page 28 of the nRF52840 DK user guide.

Best regards,

Simon

[DX_HK]

Thank you.
I tried it right away and it worked fine.

However, with the old model of nRF52833DK (ver 1.1.0, Atmel SAM series J-Link), it doesn't seem to work well even if I close J47.
There seem to be some differences, so the jumper specifications may be different.
However, I could not read from the documentation that the jumpers behave differently depending on the DK version.

Do you know anything?

[PaKa]

The nRF5340 OBD equipped boards uses one pin pulled to VDD to select between internal and external targets, the ATSAM3U OBD equipped boards uses another pin pulled to GND to select between internal and external targets. You can see which pins are used in the nRF52 DK user guide for the nRF5340 OBD and in the nRF52840 DK user guide for the ATSAM3U OBD.

If you have connected all lines like in the user guide this should not be an issue but if you have selectively only connected active pins then this will be visible.