J-Link DLL error when flashing Ezurio BL54L15 via nRF54L-DK — SWD trace shows persistent ACK FAULT

RE: J-Link DLL error when flashing Ezurio BL54L15 via nRF54L-DK — SWD trace shows persistent ACK FAULT

NandanS — Sat, 16 Aug 2025 01:38:54 GMT

After obtaining a proper J-link module from Segger, I am able to program my custom board using the Segger J-link. My guess is that the NRF54L Devkit is not suitable for programming external boards.

Another similar ticket reflects the same and suggests that cable length can be an issue:
nRF54L DK can't program external MCU via SWD – J-Link error (Unknown Error in DLL)

I tested this by purchasing and using a shorter SWD cable (2.5cm) between the external board and nRF54L15-DK (Debug Out). With this configuration, I was also able to program my custom external board.

However, given that this cable-length constraint makes the table setup very cluttered, I will instead be using the Segger J-link going forward.

RE: J-Link DLL error when flashing Ezurio BL54L15 via nRF54L-DK — SWD trace shows persistent ACK FAULT

NandanS — Thu, 07 Aug 2025 16:25:59 GMT

The external board has it's own +3.3V source and supplies it to pin 1 of it's SWD connector.

RE: J-Link DLL error when flashing Ezurio BL54L15 via nRF54L-DK — SWD trace shows persistent ACK FAULT

Bendik Heiskel — Thu, 07 Aug 2025 14:52:31 GMT

Hi,

What VDD voltage is the external board using?

The debug out connector on the nRF54L15DK is using a level shifter. The reference voltage for the level shifter is taken from pin 1 on the debug out connector(P19).

Are you supplying this pin with the VDD voltage from the external board?

Best regards,

Bendik