June 7, 1983: Michael D. Eaton is granted U.S. Patent 4,387,440, "Modem Control Device Code Multiplexing," covering a way for a modem to distinguish control commands from transmitted data. This area overlapped with the command/data-mode behavior popularized by the Hayes Smartmodem 300, introduced in 1981 with the Hayes "AT" command set. The Hayes command set went on to become the de facto standard for dial-up modems.

Editor's note: Yes, I know I'm one day late. Apparently my 300 bps modem was still negotiating the connection.

[https://en.wikipedia.org/wiki/Time_Independent_Escape_Sequence]

https://en.wikipedia.org/wiki/Time_Independent_Escape_Sequence