Use the standard Serial Wire Debug (SWD) Arm® CoreSight™ Debug Access Port (DAP) protocol to enter debug interface mode.

Before the external debugger can access the CPU, it must first request the device to power up and make sure that the appropriate power domains are powered up. This is handled using the built-in CxxxPWRUPREQ and CxxxPWRUPACK feature found in the DAP. As long as the debugger is requesting the debug domain or the complete system to power up, the device stays in debug interface mode.

Note: The user must request system and debug power. To enable both power domains, write CTRL/STAT.DBGPWRUPREQ and CTRL/STAT.SYSPWRUPREQ. See nRF9160 Revision 1 Errata - Debug and Trace for more information.