I have drop voltage to 3.3V in TX3 PORT ( use resistance)
it can run on mega2560 to mega2560 ,but can't run on mega2560 to due .
what should I do.
MEGA is a 5V logic device; whereas DUE is a 3.3V logic device. They are incompatible; therefore, the solution is to install 5/3.3V level sifters (Fig-1, 2).
Figure-1: Level sifter using discrete components.
Figure-2: Integrated package
Then the logic stands as:
(5/3)*2 = 3.3V. Try and see if it works! Theoretically, it is working; practically, it may work or not!
That should work. Measure signals with a DMM, setup serial connection on the 5V device, do not send anything and measure the voltage over R2.
There is some confusion, you're talking about Mega and Due but the image shows Uno and ESP12E.