AT commands — the universal modem language

AT Commands — A 40-Year-Old Standard

AT commands trace back to the Hayes Smartmodem of 1981. The protocol — sending ASCII text commands beginning with "AT" (for ATtention) over a serial interface — was so successful it became the industry standard, surviving multiple generations of modem technology. ITU-T standardized the core syntax in V.250; 3GPP extended it for cellular use in TS 27.007 ("AT command set for User Equipment"). Every cellular modem implements AT commands. A typical command-response exchange: the application sends "AT+CFUN=1\r"; the modem responds with "OK\r\n". Some commands accept parameters; some return data;…