AVR is almost always 1.8V to 5V range. AVR Dx has multi-viltage IO, though it's closer to dual power supply. One port (PortC IIRC) is on a 2nd voltage rail. S

AVR is almost always 1.8V to 5V range. AVR Dx has multi-viltage IO, though it's closer to dual power supply. One port (PortC IIRC) is on a 2nd voltage rail. So you can have one voltage (probably 1.8V) where most of your logic runs, but some I/O can be truly 5V in/out and push/pull.