MicroMod nRF52840 Processor Hookup Guide
El Duderino, MAKIN-STUFF 
Troubleshooting
We've got some troubleshooting tips for a couple of common "gotchas" you may run into using the nRF52840 Processor.
Force Bootloader Mode
In case your board gets stuck in an unresponsive state you can force the nRF52840 into Bootloader mode by double-tapping the RESET button on your Carrier Board. This can help recover the board from an unknown state or you can use it to directly interact with the board in bootloader mode. You can also use the RESET button to start any code that hangs after upload in case the Processor is still in Bootloader mode.
MicroMod Board Installation
If you run into problems after modifying the Arduino nRF5284X core the easiest way to remedy that is to use the Boards Manager tool in Arduino to switch to an older version of the core and then revert to the current version. Alternatively, you can use the Boards Manager to uninstall and reinstall the Arduino core.
After you have reverted or reinstalled the core go through the steps outlined in the Arduino Software Setup section of this guide to install the custom MicroMod nRF52840 Processor board definition.
General Troubleshooting Help & Technical Support
If you need technical assistance or more information regarding this or another SparkFun product that is not working as you expected, we recommend heading on over to the SparkFun Technical Assistance page for some initial troubleshooting.
If you don't find what you need there, the SparkFun Forums: MicroMod are a great place to find and ask for help. If this is your first visit, you'll need to create a Forum Account to search product forums and post questions.