Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

RE: Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

Arshad Khan — Tue, 09 Dec 2025 00:09:22 GMT

Hello,

thank you for your suggestion. I ended up getting a programmer instead of using the NRF52840-DK board, mainly because my BMD-840 ublox was set to HV mode (1.8V) and I was unsure if different voltages could power the target as well as provide SWD Data/Clock at 1.8V without level shift (I'd assume that if UICR register is set to 1.8V for onchip NRF52840 on the DK board and it is getting powered from the USB, it should be able to do it. But that was not working).

Anyhow, the programmer (JLink) works great. Thank you.

RE: Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

Kazi Afroza Sultana — Fri, 05 Dec 2025 10:41:11 GMT

Hello,

The error is related to the debug probe. It seems that debug probe can not communicate correctly to the target; still it's not powered properly. It would be helpful to watch the setup and your connection.

''Initially it was not. The SWDIO and VDD on the DK board were 3 and 3.1V respectively (for case 1, where custom PCB is powered externally) and the board is at 1.8V. ''

This will not work as you know the target and the DK board must have same power level.

Also, can you try to use debug out pin P19 to program the external board? source: Debug output

RE: Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

Arshad Khan — Wed, 03 Dec 2025 14:41:53 GMT

Hi Kazi,

Initially it was not. The SWDIO and VDD on the DK board were 3 and 3.1V respectively (for case 1, where custom PCB is powered externally) and the board is at 1.8V.

After reading a few more post on this forum, one suggested that either to connect SWD_SEL to VDD on the custom board i.e., at 1.8V and it will shift the SWDIO and CLK to 1.8V. I tried that but that did not work, the SWDIO pin remains at 3V.

Then another post suggested to power the DK board with J3 and move the power switch on USB (https://devzone.nordicsemi.com/f/nordic-q-a/92524/unable-to-program-a-blank-nrf52840/396680) and doing that made all SWDIO and VDD and everything on 1.8V (that is same as custom board VDD). After that I connected my custom PCB board which already is powered externally and is at 1.8V. This did not work as well.

Please let me know if you need any more information before you can suggest what could be wrong.

Thank you.

RE: Custom PCB with BMD380 SWD with NRF52840 DK v3.0.2

Kazi Afroza Sultana — Wed, 03 Dec 2025 14:28:04 GMT

Hello,

Have you checked the voltage level of your custom board as if it as same as DK?