Opcodes - retro CPU reference
Opcodes - retro CPU reference has 6 ratings, averaging 4.8 stars, #28,544 of 73,199 in Education.
Description
Opcodes – The Retro CPU Reference
The definitive opcode reference for the legendary processors that launched the personal computer revolution.
Whether you're a retrocomputing enthusiast, a student of computer history, writing code for classic hardware, or just a big old nerd - the Opcodes app gives you everything you need.
Eighteen iconic processors covered: Intel 4004 · Intel 8008 · Intel 8080 · Intel 8085 · Intel 8088 · Zilog Z80 · Motorola 6800 · Intel 8085 · Motorola 6809 · MOS 6502 · Signetics 2650 · RCA 1802 - SC/MP · Motorola 68000 · Intel 8086 · WDC 65816 · Texas Instruments TMS9900 · INMOS Transputer · ARM2
For every opcode:
• Full description of what the instruction does.
• Hex, octal, and decimal values.
• Flags affected.
• Addressing modes and cycle counts.
• Assembly code examples - including loops, conditionals, and common patterns.
More than just opcodes:
• CPU history and historical context.
• IC pinout diagrams.
• Notable systems that used each CPU, with memory maps and other background information.
• Chip variants and successors.
• A silly card game(!)
• Simple assembler / disassembler for many CPUs.
Built for exploration:
• Search for opcodes by name or category.
• Sort by mnemonic, opcode byte, or category.
• Filter by category, Quick Find with a colorful map.
• Undocumented instructions clearly marked and optionally displayed.
More than microprocessors:
• Information on key support chips: video, sound, memory and more.
Cool design:
• Clean, readable layout optimised for quick reference.
• Multiple colour themes.
• Full "dark mode" support.
Everything is included with absolutely no in-app purchase required.
Recent additions:
• Quiz game - test your CPU knowledge!
• Share CPU cards - beautiful shareable images showing specs and history for any processor
• External references - curated links to community resources for all 18 CPUs
• "Opcodes display first" setting - choose whether selecting a CPU shows opcodes or info first
• Chip-maker colour themes - Zilog, MOS Tech, and Motorola replace the old themes
• Enhanced 6502 docs - JMP page boundary bug, BRK behaviour, and Read-Modify-Write quirks
• Fixed Scratchpad hang when switching tabs
Growth change in ratings
| Per | Growth | Growth % | Actual change | Measured over |
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| day | Not enough history yet | |||
| week | 0 | — | 0 | 14 days |
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How these figures are measured
Change in ratings, scaled to each window from the real gap between crawls. A window needs a full period of history before it reports anything.
Tracking since 09/05/2026. History accumulates as changes are observed — check back soon.
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