If you don't understand EVERY detail of how the MCU operates, and, of course, how it operates its I/O, perhaps it's not appropriate for you to use 'C'-language rather than ASM. 'C' is convenient in some cases, as it allows you to write fewer lines of code, but it deprives you of precise control of the work you're doing, often making the resulting binary code much larger and much slower. It is NOT appropriate for neophytes.

RE