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.