You are correct I have no experience with this processor but I found this in the data sheet before I answered and I do not see the pinMode in you code.
All digital pins have optional pullup, pulldown, or keeper resistors. These are used to keep the pin at logic HIGH or logic LOW or the same logic level when it is not being actively driven by external circuity. Normally these resistors are used with pushbuttons & switches. The pinMode function with INPUT_PULLUP or INPUT_PULLDOWN must be used to configure these pins to input mode with the built-in resistor.