Michael Steil personal blog
How MOS 6502 illegal opcodes work
The original NMOS version of the MOS 6502, used in computers like the Commodore 64, the Apple II and the Nintendo Entertainment System (NES), is well-known for its illegal opcodes: Out of 256 possible opcodes, 151 are defined by the architecture, but many of the remaining 105 undefined opcodes do…
- Points
- 156
- HN comments
- 74
- Submissions
- 3
- Cited by
- 13 commenters
Hardware & ElectronicsSoftware Engineering2023
On Hacker News
| Submitted | Title on HN | Points | Comments |
|---|---|---|---|
| Jul 26, 2023 | How MOS 6502 illegal opcodes work by hasheddan | 156 | 40 |
| Mar 10, 2018 | How MOS 6502 Illegal Opcodes Work (2008) by ingve | 82 | 17 |
| Apr 20, 2025 | How MOS 6502 Illegal Opcodes Work (2008) by soegaard | 66 | 17 |
Cited in comments
Linked from 14 Hacker News comments by 13 different people, from Apr 2012 to Dec 2025.
Most recent:
- djmips · Dec 6, 2025
- NobodyNada · Dec 6, 2025
- kens · Dec 4, 2022
- monocasa · Feb 26, 2022
- flohofwoe · Jun 6, 2021
- Vogtinator · Aug 8, 2020
