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

[Anders Persson]

Cannot find any legend for debug LED pattern in user guide.

Quickstart (v1.7.0) log says nothing of value for finding

Fullscreen 2026-01-07T10_02_48.855Z-log.txt Download

2026-01-07T10:02:49.107Z INFO Initialising the bundled nrfutil device
2026-01-07T10:02:49.145Z DEBUG Started watching devices
2026-01-07T10:02:49.842Z INFO Using the bundled core version for nrfutil device: 8.1.1
2026-01-07T10:02:49.887Z INFO Using nrfutil device version: 2.15.7
2026-01-07T10:02:49.888Z INFO Using nrf-device-lib version: 0.22.5
2026-01-07T10:02:49.888Z INFO Using nrf-probe version: 0.51.0
2026-01-07T10:02:49.888Z INFO Using SEGGER J-Link version: JLink_V8.76

[Anders Persson]

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? 

[Turbo J]

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.

[AHaug]

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:

1. 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.
2. 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