When using jlink to connect to my board in VSCode, it displays "unknown device"

RE: When using jlink to connect to my board in VSCode, it displays "unknown device"

Amanda Hsieh — Tue, 28 Apr 2026 12:46:14 GMT

You can use the nrfutil commands in the Checking protection status doc.

RE: When using jlink to connect to my board in VSCode, it displays "unknown device"

Ethan330 — Tue, 28 Apr 2026 01:19:55 GMT

[quote userid="77782" url="~/f/nordic-q-a/127931/when-using-jlink-to-connect-to-my-board-in-vscode-it-displays-unknown-device/565566"]What are your boards, the custom boards or DKs? If it's the custom board, do you connect a debugger with them?[/quote]

Those are my custom boards ,Connect to VSCode via the jlink debugger。A few months ago, I was able to connect to VSCode using this jlink debugger without any issues, using the same custom board and the same jlink debugger。

[quote userid="77782" url="~/f/nordic-q-a/127931/when-using-jlink-to-connect-to-my-board-in-vscode-it-displays-unknown-device/565566"] You can use J-Link Commander to ensure VTref is present (~3.0–3.3V),[/quote]

VTref is 3,3V.

The error prompt indicates that the reset pin needs to be connected and pulled low。

The chip on my custom board does not have the reset pin exposed。

In my previous experience, I have never connected the reset pin when using the jlink debugger, but it still successfully connected and worked

[quote userid="77782" url="~/f/nordic-q-a/127931/when-using-jlink-to-connect-to-my-board-in-vscode-it-displays-unknown-device/565566"]and also check the protection status to ensure that the SWD connection isn't disabled.[/quote]

How to check if this SWD connection is disabled？

RE: When using jlink to connect to my board in VSCode, it displays "unknown device"

Amanda Hsieh — Mon, 27 Apr 2026 19:26:17 GMT

Hi Ethan,

[quote user=""]I tried a few of my boards, but the result was always the same: "unknown device"，I have verified these boards before and found no issues[/quote]

What are your boards, the custom boards or DKs? If it's the custom board, do you connect a debugger with them?

The log usually means that either something is wrong with the power supply or the connection. You can use J-Link Commander to ensure VTref is present (~3.0–3.3V), and also check the protection status to ensure that the SWD connection isn't disabled.

Regards,
Amanda H.