Hi THere!
What is best way connect Due to mega? Due used 3,3 VDC and Mega used 5 VDC, so they both used difference voltage.
Can you provide just a few details of what it is you want to do ?
We can only guess at what you mean by 'connect'.
A Mega INPUT pin will be able to read a 3.3v signal from a DUE.
But a 5v signal from a Mega will damage a DUE so you need to drop the voltage for all OUTPUTs from the Mega. There are various ways to do that. A simple voltage divider using 2 resistors is one option.
You must also connect the GND of the two boards.
...R