Pandowdy.CPU

A C# 6502 CPU emulator core supporting MOS 6502 (with and without illegal instructions), WDC 65C02, and Rockwell 65C02 variants.

Built for .NET 8 and later, Pandowdy.CPU models the processor at the cycle level: a micro-op pipeline reproduces true cycle-by-cycle timing and bus activity rather than just instruction-level results. It exposes a clean, instance-based API with direct state access, a custom bus interface for memory mapping and I/O, full IRQ/NMI/Reset interrupt handling, and a debugging wrapper for tracking state changes between instructions.

Accuracy is validated against Klaus Dormann’s 6502/65C02 functional tests and the Tom Harte SingleStepTests — passing cycle-by-cycle across every opcode — backed by a suite of over 2,000 unit tests and no dependencies beyond .NET itself.