Ответ: Unused pins.. Из slau049:
Pin Potential Comment AVCC DVCC AVSS DVSS VREF+ Open VeREF+ DVSS VREF–/VeREF– DVSS XIN DVSS XOUT Open XT2IN DVSS 13x, 14x, 15x and 16x devices XT2OUT Open 13x, 14x, 15x and 16x devices Px.0 to Px.7 Open Switched to port function, output RST/NMI DVCC or VCC Pullup resistor 100 k. Test/VPP DVSS P11x devices Test DVSS 11xx and 12xx devices TDO Open TDI Open TMS Open TCK Open