7.2.4.1 Supply Order

VDDIO and VDDANA must have the same supply sequence, and must be connected together.

Note that VDDIO supplies the XOSCn, so VDDIO must be present before the applicaion uses the XOSC feature. This is also applicable to all digital features present on pins supplied by VDDIO. VDDIOB must be present before the application uses features present on pins supplied by VDDIOB.