W65C02S

W65C02S is an 8-bit microprocessor from Western Design Center (WDC) that extends the venerable 6502 family. It is designed to be broadly software-compatible with the classic 6502 instruction set and addressing modes, allowing existing 6502 software to run with minimal modification while enabling newer designs to benefit from updated features.

Architecturally, the W65C02S uses a 16-bit address space and an 8-bit data bus, with the standard A, X, and Y registers, a stack pointer, a program counter, and a status register. It supports the interrupt model common to the 6502 family, including IRQ, NMI, and RESET signals. The device aims to preserve the familiar timing and behavior expected by tools and ROMs written for the 6502 family, while offering some enhancements for modern design contexts.

Compared with the original 6502 and early derivatives, the W65C02S includes enhancements such as additional instructions and addressing modes intended to improve code density and performance in embedded applications. While remaining compatible at the binary level for much of the existing code, the W65C02S provides modern features that simplify certain programming tasks and make it a practical drop-in or near-drop-in replacement for aging designs.

Availability and use: The W65C02S is offered in several packages, including DIP and surface-mount variants, and is designed for standard 5V environments as well as newer, lower-voltage designs. It has found use in retrocomputing projects, educational kits, and embedded systems requiring a small, well-supported 8-bit CPU with broad software compatibility.

See also: 6502, 65C02, Western Design Center.