So I wanted to make the RESET button on my ATmega4809 Xplained Pro actually reset the CPU (not the default, apparently), and went into the Device Programming Panel of AS7, to set the appropriate fuse bit (RSTPINCFG)
It's giving me a warning:
Changing the RSTPINCFG can disable the UPDI pin. Only debuggers with 12V activation functionality can restore UPDI functionality if UPDI is disabled.
So: I can't find anything in the datasheet about RSTPINCFG having any effect on the UPDI pin, or about UPDI ever getting disabled on a permanent basis (the pin is described as "dedicated"), or about anything 12V-ish ever being involved with UPDI. WTF?
I would rather not brick my board... Is it safe to enable external RESET functionality?