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CCC · Reverse engineeringCurated

MOS 6502: 3,510 transistors become readable again

Summary

Michael Steil shows how high-resolution chip photos were turned into a functional transistor model of the MOS 6502 and new insights into illegal opcodes. The MOS 6502 was developed in 1975. Visual6502 simulates the reconstructed mask at transistor level.

Ideas

  • An exposed chip can be documented photographically layer by layer.
  • Polygon models translate visible traces and transistors into circuits that can be simulated.
  • Transistor simulation explains processor behaviour without the original design documents.
  • Illegal opcodes arise from real circuit paths rather than mere chance.
  • Visualisation connects semiconductor physics, logic gates and the visible machine state.
  • Open reconstructions preserve historical hardware as executable knowledge.

Insights

  • Reverse engineering can explain an artefact more precisely than its surviving documentation.
  • Manageable old hardware makes modern layers of abstraction tangible again.
  • Digital archaeology gains scientific value through models that others can use.

Quotes

  • 3510 transistors in 60 minutes – subtitle of the talk

Habits

  • Steil explains every abstraction from the visible silicon to the executed opcode.

References

Critique

  • The reconstructed model explains one specific chip and not every 6502 variant.
  • Physical analogue effects are necessarily simplified in a logical simulation.

Remarks

  • The talk combines retro computing with an analysis method that is still useful today.
  • The small number of transistors is what makes a complete visual explanation practical at all.

Recommendations

  • Start chip analysis with clearly documented images and reproducible coordinates.
  • Compare simulation results with measurements of real hardware.
  • Publish extracted netlists, tools and corrections together.

Watch the talk

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