Opcodes - retro CPU reference
Decades of nerd knowledge
Free · In‑App Purchases · Designed for iPad. Not verified for macOS.
Carry around decades of retro computer knowledge in your pocket and on your wrist. Instruction sets, architecture notes, programmer tools, games, and lots more.
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
Ratings & Reviews
Updated transputer instruction list.
Some more information on Z80N.
The developer, John Kennedy, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- John Kennedy
- Size
- 60.5 MB
- Category
- Education
- Compatibility
Requires iOS 18.0 or later.
- iPhone
Requires iOS 18.0 or later. - iPad
Requires iPadOS 18.0 or later. - Mac
Requires macOS 15.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 2.0 or later.
- iPhone
- Languages
- English
- Age Rating
4+
- 4+
- In-App Purchases
Yes
- Buy Me a Coffee $0.99
- Copyright
- © John Kennedy 2026