Chip archaeology: Visual 6502

If there’s one chip that shaped the computer industry more than the infamous Intel 4004, it’s the MOS 6502.  This 8-bit 1MHz CPU, designed by Chuck Peddle in the early 70s was the one that powered famous computer systems such as the Apple I and II, the Commodore PET and the Atari 2600 and the Nintendo Entertainment System (NES) game consoles.

Chuck Peddle, together with Bill Mensch who did the layout of the chip mostly by hand (!) were true pioneers in the field of computer electronics and it is hence only fitting that their CPU is the subject of a study that is making headway on ‘imaging’ for posterity this hugely-influential piece of electronics.

According to the chip archaeologists at (Greg James, Barry Silverman, and Brian Silverman) emulators of the chip only provide an approximation of the internal workings of the chip and the only real way to glean in-depth understanding of the chip is to strip away the polysilicon layers of the chip using acid, photographing the results in high-resolution.
This then reveals the inner structure of the chip in great detail and allows a three-dimensional understanding of the chip’s 20000 interior components that can be used to build a working model of its operation.
They further state: “While a multitude of people understand the instruction set for the 6502, almost no one, apart from the original designers, understands how the physical chip achieves this instruction set.”

To top it off, they have turned their discovered knowledge of the chip into a Javascript html 5 simulation that steps through the 6502’s inner digital workings (make sure you have an HTML5 browser though and lots of RAM!)

Another “chip archaeologist” is Michael Steil (see also my other article on Michael), who did a superb presentation at last month’s C3, talking about reverse engineering the 6502 and going in-depth into the assembly code.

It just goes to show that this almost 40 year old chip still has some secrets!

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  1. Pingback: Commodore, it’s not just BASIC | MOS 6502

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