A beginner-focused tutorial covering the fundamentals of CPU organization in microcontrollers, including register types (data, address, stack pointer, link register, program counter), the fetch-execute cycle, and the main instruction categories: arithmetic, logic, shifting, unconditional jumps, conditional branches, and subroutine call/return mechanics. It also explains how C maps to these low-level CPU operations and compares stack-based vs. link-register approaches for subroutine calls.
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