Hayes Command Set

Long before the days of widespread DSL most home computers connected to the outside world via a modem. A defacto standard, the Hayes “AT” commands were a way to control and configure the modem.

During a connection (e.g., to a Telegard BBS for access to Bitnet or Fidonet) entering +++ would place the user in Command mode. Commands were prefixed with AT, e.g., ATDT9501986? would cause the modem to dial (via touch tone) the number 9501986. The ATH commands would control the modem's switch hook.

A long stream of AT commands could be sent to the modem before connecting to set a default configuration. Through the ATS series of commands one could, among other things, dramatically speed up the touchtone dial rate (e.g. ATS11?=50 for 50ms tone duration).

NOTE: Programmers dealing with baseband (cell phone modems) still have to know AT commands, now in a very, very larger set than originally…

> Definitely NOT an obsolete skill - a large number of embedded OS platforms & business hardware still use the AT commands due to the unnecessary overhead of a GUI.