The CPU Core: Registers, Flags, and Basic Instructions

Tue, 05 May 2026 00:00:00 +0000

Introduction

Welcome to the foundational stage of our Game Boy emulator! In this chapter, we’re going to construct the very brain of our system: the Central Processing Unit (CPU). The Game Boy uses a custom 8-bit CPU, often referred to as the “SM83,” which is a hybrid between a Zilog Z80 and Intel 8080. Understanding and accurately emulating its behavior is paramount to running any Game Boy software.

This milestone is critical because every single action within a Game Boy game—from moving a character to calculating damage—is ultimately a sequence of CPU instructions. Building the CPU core correctly is non-negotiable for a functional emulator. By the end of this chapter, you will have a functional, albeit minimal, CPU core capable of storing its state (registers and flags) and executing a few fundamental instructions. This forms the bedrock upon which we’ll build memory access, graphics, and more complex logic.

SM83 on AI VOID

The CPU Core: Registers, Flags, and Basic Instructions

Introduction