nRF52840 Dongle not connecting to J-Link

[faskrobo]

I have an nRF52840 dongle I got from someone else that doesn't have the nrf bootloader on it. When I plug it into a USB port, the red light flashes quickly while a green light flashes slowly. It didn't show up on Device Manager or the nrf Programmer utility in Windows, so I soldered an SWD 10-pin header to the P1 interface on the back and connected it to a J-Link EDU Mini. I made sure to check that current was able to flow from each used pin on the header to another pin on the dongle, e.g. pin 1 (VCC) to OUT, SWDIO pin to the SWDIO notch next to the usb connector, reset pin to the reset button, and so on; and I checked for bridging as well. The only 3 pins not checked were the ones not used by the dongle according to the schematic: KEY, SWO, and NC.

When I connected the J-Link to a computer, the dongle did not light up, and it wasn't detected. I also tried connecting both the J-Link and the USB interface on the dongle to the computer, but the red and green lights started flashing as before and the application still didn't see it. Holding down reset didn't help. Is there something I'm misunderstanding or is it possible something isn't connected properly? What else can I try?

[Einar Thorsrud]

Hi,

What is the VDD voltage of the dongle? If the firmware has been replaced, it could be that the voltage out of REG0 is lower than expected (the default value of the nRF52840 IC is 1.8 V, while the firmware the dongle ships with sets it to 3.0 V). If it is 1.8 V, then I suspect the J-Link EDU Mini will not be able to communicate with it as it assumes 3.3 V (3.0 should be close enough, but not 1.8 V). If this is the problem then you either need to use a level shifter or a more high end debugger which has it included, or modify the dongle HW to increase the voltage. See Recover after an accidental UICR erase in the last part of nRF52840 Dongle Programming Tutorial for details.

[faskrobo]

As a point of clarification, does the J-Link require the dongle to output 3.3V on VDD while the dongle is powered by a PC via USB? And is the voltage set in the hex file provided in the tutorial above? I tried to measure the VDD voltage using a multimeter, but somehow as a result of me touching probes to pins something broke and the device won't power on anymore. There's a second dongle that I tried however and it does connect fine. Is there anything to be especially careful about when measuring voltage on an nRF dongle, and is there a way to bring back the first one or is it probably fried?

[Einar Thorsrud]

Hi,

More hi end J-Link devices has a level shifter and will adjust the signal voltage to the measured VDD voltage. The J-Link EDU Mini however only supports about 3.3 V. So if this is what has happened (UICR has been erased and the device reset before re-writing REGOUT0 to configure for 3.0V), then this makes sense.

faskrobo said:

And is the voltage set in the hex file provided in the tutorial above? 

Which specific file are you referring to? Generally though, all projects in the SDK that is built for the nRF52840 Dongle as target will set the VDD voltage correctly.

faskrobo said:

Is there anything to be especially careful about when measuring voltage on an nRF dongle, and is there a way to bring back the first one or is it probably fried?

It should be quite robust, but I cannot say how you would fix this (or if it is possible) without knowing what has happened and what has been damaged. I suggest just obtaining a new one instead of spending time troubleshooting if you believe you have damaged it, as this is a low-cost device.

[faskrobo]

In the "Revert to production bootloader" section in nRF52840 Dongle Programming Tutorial, there's a zipped hex file. So would that set the voltage?

[Einar Thorsrud]

Yes, that hex file will set the voltage to 3.0 V.