For the clarification on the MAX667CPA and MAX666, I thank you. I don't really fully understand but, I think I got the general rough idea.
But, on the topic of power rails... I don't get it. What are power rails? What is 'Configure Power Rails' for? Which part of proteus is the simulation part? and... lastly. I have another question. Can you review a circuit schematics for me? I didn't really try to read into microcontroller and IC that much so, I don't really get the principles behind microcontrollers and IC so, if I accidentally connected something wrong, sometimes I can't figure out what is wrong.