I plan on using a voltage divider to read 12v input with my 5v microcontroller. I was going to use a 5.1v zener to protect the pins, but I was wondering if the voltage did go over 5.1, what would the pin read? Would it still be pulled high, or would the zener pull it low?

Thanks

 

Your input will read high.

You do not need a 5.1V zener. You can clamp the input by putting a Schottky diode between the input and the +5V supply (anode at the input, cathode at the +5V supply).