--- title: "Halt and Catch Fire" url: https://daily.dev/posts/halt-and-catch-fire-ulfnfmbyi source_url: https://unstack.io/halt-and-catch-fire type: article source: "Hacker News" published: 2026-05-17T02:03:35.363Z updated: 2026-05-17T02:03:58.461Z tags: ["hardware", "assembly", "computer-history"] reading_time: 6 upvotes: 0 comments: 0 language: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Halt and Catch Fire **[Hacker News](https://daily.dev/sources/hn)** · 6 min read · 0 upvotes · 0 comments ## Summary The 'Halt and Catch Fire' (HCF) phrase originated as engineering humor using the three-letter assembly mnemonic convention, but became real on the Motorola 6800 processor. Two undocumented opcodes ($9D and $DD) caused the CPU to enter a runaway state where the program counter incremented endlessly, reading all memory sequentially at high speed, with no way to recover except a reset or power cycle. Gerry Wheeler named and documented this behavior in BYTE magazine in December 1977. Motorola engineers later discovered the behavior was intentionally preserved as a fast RAM-scanning tool during hardware bring-up. The post also covers similar phenomena on other processors including the 6502, the Pentium F00F bug, and modern x86 fuzzing research that still uncovers invalid processor states. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [6502 Emulation - The Jump Indirect Bug](https://daily.dev/posts/6502-emulation---the-jump-indirect-bug-wn0qipigx) · Two Stop Bits · 0 upvotes · 0 comments - [Hackaday Europe 2026: The 1-Bit CPU That Ran Factories](https://daily.dev/posts/hackaday-europe-2026-the-1-bit-cpu-that-ran-factories-ks7azuz3f) · Hackaday · 0 upvotes · 0 comments --- Tags: [#hardware](https://daily.dev/tags/hardware), [#assembly](https://daily.dev/tags/assembly), [#computer-history](https://daily.dev/tags/computer-history) [View this post on daily.dev](https://daily.dev/posts/halt-and-catch-fire-ulfnfmbyi)