Technical Reference: Undocumented Opcodes for 65XX/85XX Series CPUs
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embedding-shape
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Summary
This document provides a comprehensive technical reference for undocumented or unofficial opcodes in the 65XX/85XX series CPUs, specifically focusing on the 105 operation codes not officially recognized as part of the 6502 instruction set. The content details these extra opcodes that exist beyond the 151 legal combinations in the 6502's single-byte instruction set, serving as a technical resource for programmers and hardware enthusiasts working with these legacy processors.
Key quotes
· 4 pulledThe operation codes for the 6502 CPU fit in a single byte; out of 256 possible combinations, only 151 are 'legal.'
This text describes the other 256-151= 105 operation codes.
These opcodes are not generally recognized as part of the 6502 instruction set.
They are also referred to as undefined opcodes or undocumented opcodes or non-standard opcodes or unofficial opcodes.
Article URL: http://www.ffd2.com/fridge/docs/6502-NMOS.extra.opcodes
Comments URL: https://news.ycombinator.com/item?id=46169330
Points: 7
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