The 6502 microprocessor was an 8-bit microprocessor that was incredibly popular for 8-bit home computers (e.g Apple II) and consoles (e.g NES) due to its low cost.
Released by MOS Technology in 1975, the 6502 was designed by Chuck Peddle as an affordable alternative to the more expensive microprocessors of its time (such as the $300 Motorola 6800 that he also worked on) 1.
The Apple Wiki provides a technical and historical profile of the MOS Technology 6502, the 8-bit microprocessor that powered the Apple I, Apple II, and Apple III. The entry details the chip’s architecture, including its registers and instruction set, and explains how its low price point enabled the mass market success of Apple’s early hardware.
The 6502 family shaped early commercial game development through its low cost, simple bus architecture, and efficient instruction set.
Its derivatives powered many influential consoles and computers, enabling designers to allocate more silicon to graphics and audio subsystems while retaining sufficient compute for real time game logic:
The Nintendo Entertainment System (known as the Famicom in Japan) is an 8-bit console that revolutionized home gaming, powered by a 6502-based Ricoh 2A03 CPU. Our page serves as a comprehensive hub for reverse engineering the hardware, detailing the unique architecture of the Picture Processing Unit (PPU), the Audio Processing Unit (APU), and the system’s memory map. It also collects essential resources, tutorials, and tools for emulator developers and homebrew enthusiasts.
In this detailed technical presentation from the 27th Chaos Communication Congress, Michael Steil explores the inner workings of the MOS 6502 processor, the chip powering iconic systems like the Apple II, NES, and Commodore 64.
The talk breaks down the reverse engineering process into three distinct approaches: top-down (analyzing the instruction set and quirks), bottom-up (using acid decapping and high-resolution die shots to vectorize the transistor netlist), and inside-out (simulating the logic to understand undocumented behaviors and illegal opcodes). This work culminated in the Visual 6502 project, a transistor-perfect simulation of the hardware.
Dotnet6502 is a C# library designed to emulate the MOS 6502 microprocessor within the .NET ecosystem. Developed by KallDrexx, this project provides a managed-code implementation of the CPU architecture, suitable for serving as the core component in custom emulator projects or retro-computing tools. It leverages .NET Core to offer cross-platform compatibility for developers building 6502-based systems.
IEEE Spectrum investigates the famous Futurama easter egg that identifies Bender’s CPU as a MOS Technology 6502 microprocessor. The article features an interview with head writer David X. Cohen, who explains that the choice was a deliberate homage to his own teenage years spent coding 6502 assembly language for the Apple II.
The 65C816 represented a significant leap forward in the 6502 lineage. It was designed and produced by Western Design Center (WDC) as an extended version of the original 6502.
This new microprocessor retained compatibility with existing 6502 software while introducing several key improvements:
The 65C816 found its way into various gaming platforms and computers, where its improved capabilities became instrumental in delivering richer gaming experiences:
SnesLab provides a technical overview of the 65c816, the 16-bit microprocessor developed by WDC that serves as the core of the Super Nintendo’s Ricoh 5A22 CPU. The page details the processor’s relationship to the 8-bit 6502, explaining its “emulation mode” for backward compatibility and its role in executing the code for SNES games like Super Mario World.
The Apple Wiki entry profiles the WDC 65C816 (also known as the 65816), the 16-bit microprocessor developed by Western Design Center that powers the Apple IIGS. It explains how the chip maintains backward compatibility with the MOS 6502 via an “emulation mode” while offering a “native mode” with 24-bit addressing and 16-bit registers, effectively bridging the gap between 8-bit and 16-bit computing eras.
Mike’s Software Blog details the design and assembly of a custom 4-layer PCB test board for the WDC 65C816 microprocessor. The project moves away from unreliable breadboard prototypes to a stable platform featuring extensive test points, a MIC2775 reset controller, and PLD-based address decoding. The post documents the transition to KiCad 6, various assembly challenges like clock signal routing errors, and the successful validation of the hardware.
