discrete 6502
MOS 6502 CPU rebuilt from 4,051 discrete transistors
The discrete6502 is a hardware project that rebuilds the MOS 6502 CPU using 4,051 individual surface-mount transistors — no integrated chips or FPGA. The entire circuit is laid out on a custom PCB that reproduces the original silicon die's floorplan, transistor by transistor, at a scale of 291×322 mm. It is not a simulation or emulation; it runs the same dynamic NMOS logic as the original 6502, executing the same instructions at a speed of roughly 10–20 kHz.
The project solves the challenge of making a classic CPU's internal operation visible and tangible. By replacing the microscopic transistors with discrete components and placing LEDs on register bits, it allows observers to watch the processor think — seeing data flow through the datapath, decode logic, and program counter in real time.
It is designed for hardware enthusiasts, retrocomputing hobbyists, educators, and anyone interested in understanding computer architecture at the transistor level. The board includes a footprint for a Raspberry Pi Pico that serves as clock source and memory emulator, making it a self-contained teaching tool.
Key Features
Faithful Dynamic NMOS Design
Preserves the original 6502's dynamic NMOS logic, where data is stored as charge on wire capacitance and must be refreshed by the clock. Not converted to modern static logic.
