Thank you for the reply. I believe so.eone tried to run the 328p on 12mhz and it didn't work. I don't mind using g several crystals to accomplish this. Pretty sure that I can isolate the individual circuits properly. The castellated option would work too. The other thing I'm a bit shady on is if I need external pullup/pull down resistors on the unused pins of the micro. Please refer to my OP schematic to see what I mean.