nRF54L DK can't program external MCU via SWD – J-Link error (Unknown Error in DLL)

[Doris.chen]

Hello Nordic Team,

I’m trying to use the nRF54L DK to program an external MCU via SWD, but I’m encountering an error during connection. I’ve already followed this guide:

https://docs.nordicsemi.com/bundle/ug_nrf54l15_dk/page/UG/nRF54L15_DK/program_debug/program_ext_board.html

However, I’m still unable to connect to the external target via nRF Connect for Desktop – Programmer.

Here is the error log I get:

18:14:44.589	Error: Failed with exit code 1. Failed to device info one or more devices:
  * 1057763412: [Probe] Device error: Failed to write DebugPort register 2: Unknown Error in J-Link DLL (error code = -1)
  Message: Operation device-info failed
18:14:44.590	Using nrfutil device to communicate with target via JLink
18:14:45.728	Reading readback protection status for Application core
18:14:45.729	Failed "reading readback protection status for application core". 
  Error: code: 1, description: Generic, message: Batch task protection-get failed
18:14:45.892	Error: Failed with exit code 1. One or more batch tasks failed
  - [Probe] Device error: Failed to write DebugPort register 2: Unknown Error in J-Link DLL (error code = -1)

Interestingly, with the same external target, I’m able to successfully program it using an nRF54L PDK (another board), so I don’t think the issue is with the target itself.

1. Are there any extra jumpers, settings required on the nRF54L DK to enable external MCU programming?

2. Is there a known limitation when using nRF Connect Programmer with the nRF54L DK’s onboard debugger?

3. Do I need to use nrfjprog or nrfutil manually instead of the GUI?

Any help or suggestions would be appreciated.

Thank you very much!

Best regards,
Doris