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No More Secrets v0.96 - NMOS 6510 Unintended Opc No More Secrets v0.96 - NMOS 6510 Unintended Opcodes

'Back in the days' so called 'illegal' opcodes were researched independently by different parties, and detail knowledge about them was considered 'black magic' for many conventional programmers. They first appeared in the context of copy protection schemes, so keeping the knowledge secret was crucial.

When some time later some of these opcodes were documented by various book authors and magazines, a lot of misinformation was spread and a number of weird myths were born. It took another few years until some brave souls started to systematically investigate each and every opcode, and until the mid 90s that Wolfgang Lorenz came up with his test suite that finally contained elaborated test programs for them.

Still, a few opcodes were considered witchcraft for a while (the so called 'unstable' ones), until other people finally de-capped an actual CPU and solved the remaining riddles.

This document tries to present the current state of the art in a readable form, and is in large parts the result of pasting existing documents together and editing them


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