The Visual 6502 Simulator
By James Grahame
The MOS Technologies 6502 microprocessor became the inexpensive heart of the Apple II, Commodore VIC-20, Atari 800 and dozens (if not hundreds) of other popular home computers.
It's been impossible to actually watch one work -- until now. Greg at Visual 6502 spent six weeks creating a working transistor-level visual simulation of this classic chip by aligning and combining over 200 microscopic photographs.
He writes, "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.
Visit Visual6502.org for more.