nrf54LM20-DK fails to connect with Quickstart using USB. Debugger LED (L05) flashes quick and repeatedly.

RE: nrf54LM20-DK fails to connect with Quickstart using USB. Debugger LED (L05) flashes quick and repeatedly.

AHaug — Wed, 07 Jan 2026 12:26:42 GMT

Hi,

The fast blinking LED happens when the debugger is powered but not enumerated. There's no limitations w.r.t what type of USB the end that's not in the DK is, as long as it supplies the proper voltage and has a data wire.

I have two thoughts:

The USB-A to C cable doesn't have data transmission capacity, i.e it just supplies voltage. This happens if the cable breaks or if it doesn't have a data wire. USB-A to C doesn't always contain a data wire.
You've plugged the cable into the nrf usb port instead of the debugger port on the DK (they're very close together so this is something that can happen with ease)

Kind regards,
Andreas

RE: nrf54LM20-DK fails to connect with Quickstart using USB. Debugger LED (L05) flashes quick and repeatedly.

Turbo J — Wed, 07 Jan 2026 10:26:24 GMT

Debug LED is under the control of the J-Link stuff and might be mentioned in the J-Link documentation (Segger.com).

User experience will tell you more than any documentation could.

RE: nrf54LM20-DK fails to connect with Quickstart using USB. Debugger LED (L05) flashes quick and repeatedly.

Anders Persson — Wed, 07 Jan 2026 10:22:29 GMT

Sorry. False alarm. Tested with a USB-C cable, works like a charm.

Maybe there is somewhere in documentation, that USB-A - USB-C cable and ports cannot be used?