Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

PjGlasso — Mon, 23 Mar 2026 20:49:48 GMT

Hi there,

You are gonna Kick yourself if it is what I think...:grin:

The Cable is WAY TOO long. the errors are from the Jlink,

I have been through this also. Took a while to figure it out. also Don't use the Jlink to power the Board at ALL, only provide the same VDD as your board to the vRef.. be sure the Board config is correct in Nrf for Desktops.

Try it use a 3 inch cable. and check out the pics I have on here of How I connected up SWD to nRF52 & nRF54 and get it to work.

HTH

GL:-) PJ :v:

I have some videos too, of it over on the Seeed Studio support forum.

https://forum.seeedstudio.com/latest

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

Simonr — Tue, 24 Feb 2026 08:14:20 GMT

Hi Lonnie

If the custom board has VDDH floating, it's in an unspecified state. I'm sorry I didn't spot that until now, but when the device operates in normal VDD mode, VDDH definitely needs to be shorted to the VDD net.

Best regards,

Simon

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

LonnieB — Fri, 20 Feb 2026 19:39:58 GMT

Simon,

First, thank you for your expert advise and guidance. I would like to ask once more for your help as I think I uncovered something significant, and I believe a Nordic expert is needed to answer my question.

Bottom line - I believe my custom board is pulling down the output voltage of the SWDIO and SWCLK lines of the DK or J-Link)

In order to confirm the signaling is correct between the DK (or J-Link) and my custom board I connected only the necessary signal lines (SWDIO, SWCLK, GND and SWO_SEL) using breakout boards and jumpers. The DK and the J-Link both continued to give the same errors (they cannot connect to the custom board). I then attached my oscilloscope and logic analyzer to the lines. The O-scope showed data and clock on the respective lines, but the voltage shown was only 2.23V. My logic analyzer was able to decode the data and clock even with this reduced voltage and I have attached a couple of screen shots of that data (I looked for SWD protocol info for Nordic and J-Link to understand what was sent but I have not been able to locate that info yet - perhaps you can analyze the signals and tell if there is comms between the custom board and DK - or if the data is only that which the DK sends out - with no response. This is my hunch). I then removed the SWDIO and SWCLK signals from the custom board and connected them only to the o-scope. I then tried to connect the JLink probe to the custom board. The o-scope showed SWDIO data at 3.1V. So it appears that the custom board is pulling the signal lines low enough (2.3V vs 3.1V) that they are below the voltage threshold for a "1".

Going back to my previous note, could the fact that VDDH is floating, and not tied to VDD cause this? If not what else could cause this phenomenon? On my PCB, SWDIO and SWCLK are point to point from the RAYTAC module to the connector (and a test point) - so nothing else could be pulling them low.

Thanks for your help,

Lonnie

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

Simonr — Thu, 19 Feb 2026 13:11:39 GMT

The behavior here definitely sounds like a hardware issue since neither the DK or the J-Link is able to connect to it.

I asked one of my colleagues with more HW expertise than me. There is nothing obviously wrong, but for possible future revisions, you can improve the grounding in general on your board.

One thing to note though is that you run the J-Link on full speed. During connection issues like this you can try to lower the J-Link speed to see if that lets you connect and program the boards.

You can also, just to try connect the 10 pin cable 180 degrees the other way in case that is the issue (a common one if the header isn't supported with plastic to show which way it should be connected).

Best regards,

Simon

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

LonnieB — Wed, 18 Feb 2026 18:33:07 GMT

Simon,

I've not installed the nrfutil package yet - but I did try the "recover board" command from within the connected devices menu in nrf connect for VS Code. I get the same results. Here is what I have done since our last communication:

1) I rang out the SWD connector signals (that I could reach) from my custom board to the DK to ensure they were as I conceived. They are as shown in the schematic.

2) I powered the custom board at the VCC rail to 3.0V. I noted that the board consumed 5 mA vs 1 mA when I powered it through the regulator. So either back feeding the regulator consumed 4mA or the regulator wasn't working correctly and it couldn't supply 5 mA. So I connected a 270 ohm resistor to VCC and GND and powered the board through the regulator; it provided 13 mA as expected - so the regulator works well and it consumes 4 mA when back-fed - so I'm not entirely sure I want to power the board this way unless I have to.

3) I connected the board to power and to a Segger J-Link EDU mini, just to see if it would work. I received a connection error for the J-Link as well - it is suspiciously like the nrf connect error:

SEGGER J-Link Commander V9.12 (Compiled Jan 21 2026 12:09:03)
DLL version V9.12, compiled Jan 21 2026 12:08:09

Connecting to J-Link via USB...O.K.
Firmware: J-Link EDU Mini V2 compiled Dec 10 2025 15:50:17
Hardware version: V2.00
J-Link uptime (since boot): 0d 00h 03m 04s
S/N: 802003272
License(s): FlashBP, GDB
USB speed mode: Full speed (12 MBit/s)
VTref=3.301V

Type "connect" to establish a target connection, '?' for help
J-Link>connect
Please specify device / core. <Default>: NRF52840_XXAA
Type '?' for selection dialog
Device>?
Please specify target interface:
J) JTAG (Default)
S) SWD
T) cJTAG
TIF>s
Specify target interface speed [kHz]. <Default>: 4000 kHz
Speed>1000
Device "NRF52840_XXAA" selected.

Connecting to target via SWD
InitTarget() start
InitTarget() end - Took 13.0ms
InitTarget() start
InitTarget() end - Took 6.79ms
Error occurred: Could not connect to the target device.
For troubleshooting steps visit: https://kb.segger.com/J-Link_Troubleshooting

4) I also assembled another board - in case I did something wrong on the first one (and I also wondered if I didn't give enough "soak" time in the reflow process to heat the Raytac module). The 2nd board - with more soak time - has exactly the same output on the exposed pins, and gives the same errors on nrf connect and J-link as the first board.

5) I then contacted Raytac for tech support but they are celebrating the New Year in Taiwan - so tech support will have to wait with them until next week.

6) Finally, I though I found a problem in my schematic - I did not connect VDDH to 3.3V. I changed the power scheme several times, and I must have forgotten to short it to VDD. However, in searching the Dev Zone I found a reply from you several years ago that says you don't need to short VDD and VDDH - at least to program the board - Here is an excerpt:

***************

I have checked with my colleagues, and there shouldn't be any problem of letting VDDH float while powering the chip in normal voltage mode while you program it. It is just not recommended to leave it floating over time, which is why the PS tells you to short them. Sorry for the confusion.

Best regards,

Simon

********************

So I'll try to load "nrfutil" and see if I get anything different there. So at this point I would appreciate a full HW review - I have included a zip file of the PCB gerbers.

Thanks so much for your advice and time,

Lonnie

devzone.nordicsemi.com/.../nRF52840_5F00_test_5F00_board_5F00_2025_2D00_12_2D00_08.zip

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

Simonr — Wed, 18 Feb 2026 08:36:44 GMT

Hi Lonnie

Are you able to do other nrfutil commands with the custom board connected to your DK, like nrfutil device recover for example. If that fails it might be worth a shot to test with the 3.0V, but I think it should work with 3.3V.

Other than that I don't really see what else could be wrong. If you'd like we could do a full HW review if you share your PCB layout files (preferably gerber format).

Best regards,

Simon

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

LonnieB — Mon, 16 Feb 2026 15:57:25 GMT

Simon,

Thanks for the reply. I copied much of the design from the nrf52840 feather, including the connectors and their pinouts, and I checked voltages while my board was connected to the DK - and they look correct - so I think the 10-pin cable is connected correctly. The schematic attached is the full schematic (it is a test board with access to I2C and some GPIO pins that I can use to test code and various sensors before I spin a production board) and J2 is the 10 pin header - it is center bottom of the schematic.

Powering my board from a 3.0V (vs 3V3) supply is probably doable (I'd have to connect my power supply directly to the VCC rail of the board without going through the regulator, but if it is threshold levels that you are concerned about, I doubt that my board wouldn't recognize a 3V signal. I can try if you have doubts.

Thanks again,

Lonnie

RE: Unable to flash custom nRF52840 board using nRF52840dk - Device error: Setting the debug port SELECT register failed while powering up sys and debug regions (Unknown error in the J-Link DLL (error code =-1)).

Simonr — Mon, 16 Feb 2026 15:24:03 GMT

Hi Lonnie

This sounds strange. The setup looks correct here. A common mistake is that the 10-pin cable is connected the wrong way if you don't have the 10 pin header with plastic to make sure it can only be mounted one way.

If not, are you able to set the custom board voltage to 3.0V, since that is the DK's supported voltage by default. https://docs.nordicsemi.com/bundle/ug_nrf52840_dk/page/UG/dk/ext_programming_support_P19.html

Is this the full schematics of your board? Which of the headers in the schematics is the 10 pin header?

Best regards,

Simon