I'm making a board which I want to be compatible with both ATMega8515 and ATMega162. Those chips are mostly compatible in terms of IO pinout, but there's one difference. The 8515 has 4 pins which are marked NC, whereas those are used for power supply on the 162. I'd like to design with belt and braces and connect the extra supply pins for use with the 162. Is this safe when using an 8515 on the same footprint?
The reason I'm asking this seemingly silly question is that I've heard a rumor that Atmel is sometimes using NC pins for internal test functionality. It would be a shame if an 8515 would go into test mode because one of the NC pins is connected to gnd or Vcc.
The datasheet just gives the standard warning: "NC = Do not connect (May be used in future devices)"