How the Hayes AT Command Set Became the Universal Language of Dial-Up Modems
The Hayes AT command set, introduced in 1981 with the Smartmodem, revolutionized modem control by using existing data pins and an in-band escape sequence (+++) to switch between data and command modes. This allowed software to dial numbers automatically, a crucial step for BBSs and the emerging microcomputer era. Despite initial fragmentation with proprietary extensions from vendors like USRobotics and Microcom, the Hayes-compatible standard, formalized as TIA/EIA-602, became universal by the early 1990s. The article details the command syntax, register commands, and the security flaw in TIES (Time Independent Escape Sequence) that could disconnect a modem via a ping of death.
By essentially accident, this allowed users of existing 1200 baud modems to use the new Hayes 2400 models without changing their software.
- _the_inflator
Hayes modems were pretty much the crème de la crème back then.
I never heard of them since the CompuServe and AOL times.
- cbdevidal
That's funny. I clicked on the HN article on the home page about the AT Protocol[1] expecting an article on the Hayse set. And then I scrolled down and saw this article.
- nomel
> This had a major denial of service security implication in that it would lead to the modem hanging up the connection should the computer ever try to transmit the byte sequence +++ATH0 in data mode.
Does this mean you couldn't send the documentation for the modem using the modem?