Visual Transistor-level Simulation
of the 6502 CPU and other chips!
Welcome to Visual6502.org! Here we’ll slowly but surely present our small team’s effort to preserve, study, and document historic computers. We aim to present our work in a visual, intuitive manner for education and inspiration, and to serve as a solid verifiable reference for classic computer systems. See our slides for an introduction and some fun images.
Have you ever wondered how the chips inside your computer work? How they process information and run programs? Are you maybe a bit let down by the low resolution of chip photographs on the web or by complex diagrams that reveal very little about how circuits work? Then you’ve come to the right place!
The first of our projects is aimed at the classic MOS 6502 processor. It’s similar to work carried out for the Intel 4004 35th anniversary project, though we’ve taken a different approach to modeling and studying the chip. In the summer of 2009, working from a single 6502, we exposed the silicon die, photographed its surface at high resolution and also photographed its substrate. Using these two highly detailed aligned photographs, we created vector polygon models of each of the chip’s physical components – about 20,000 of them in total for the 6502. These components form circuits in a few simple ways according to how they contact each other, so by intersecting our polygons, we were able to create a complete digital model and transistor-level simulation of the chip.
This model is very accurate and can run classic 6502 programs, including Atari games. By rendering our polygons with colors corresponding to their ‘high’ or ‘low’ logic state, we can show, visually, exactly how the chip operates: how it reads data and instructions from memory, how its registers and internal busses operate, and how toggling a single input pin (the ‘clock’) on and off drives the entire chip to step through a program and get things done.