Editing Hayes AT command set (section)

=== Commands ===
The Hayes command set includes commands for various phone-line operations such as dialing and hanging-up. It also includes various controls to set up the modem, including a set of ''[[Register (computing)|register]] commands'' which allowed the user to directly set the various memory locations in the original Hayes modem. The command set was copied largely verbatim, including the meaning of the registers, by almost all early 300 baud modem manufacturers, of which there were quite a few.

The expansion to 1200 and 2400 baud required the addition of new commands, some of them prefixed with an [[ampersand]] ({{code|&}}) to denote those dedicated to new functionality. Hayes itself was forced to quickly introduce a 2400 baud model shortly after their 1200, and the command sets were identical as a time-saving method.<ref>Frank Durda IV, [http://nemesis.lonestar.org/reference/telecom/modems/at/history.html "The AT Command Set Reference – History"] {{Webarchive|url=https://web.archive.org/web/20080415210519/http://nemesis.lonestar.org/reference/telecom/modems/at/history.html |date=2008-04-15 }}, 1993</ref> Essentially by accident, this allowed users of existing 1200 baud modems to use the new Hayes 2400 models without changing their software. This re-inforced the use of the Hayes versions of these commands. Years later, the [[Telecommunications Industry Association]] (TIA)/[[Electronic Industries Alliance]] (EIA) formally standardized the 2400-baud command set as '''Data Transmission Systems and Equipment – Serial Asynchronous Automatic Dialing and Control''', '''[[TIA/EIA-602]]'''.

However, Hayes Communications was slow to release modems supporting higher speeds or [[Modem compression|compression]], and three other companies led: [[Microcom]], [[U.S. Robotics]], and [[Telebit]]. Each of these three used its own additional command-sets. By the early-1990s, there were four major command sets in use, and a number of versions based on one of these. Things became simpler again during the widespread introduction of [[kbits/s|14.4 and {{Val|28.8|u=kbit|up=s}}]] modems in the early 1990s. Slowly, a set of commands based heavily on the original Hayes extended set using {{code|&}} commands became popular, and [[Informal standard|then universal]]. Only one other command set has remained popular, the U.S. Robotics set from their popular line of modems.