Before you try clever tricks with connecting port pins of two processors i suggest that you try to get a better understanding of the fundamental operation of things like I/o ports.
When the port is set as an input it acts essencally like the input of any logic gate,so I suggest that the first thing you need to do is study the behaviour of as many different logic families as you can and see how the inputs behave and then you will see why you dont need to use a resistor