olemus
modemi juhtimise käsk, algab tähepaariga AT (< attention, "tähelepanu")
= a type of instructions used to control a modem

ülevaateid
https://en.wikipedia.org/wiki/Hayes_command_set
https://docs.rs-online.com/5931/0900766b80bec52c.pdf
https://www.sparkfun.com/datasheets/Cellular%20Modules/AT_Commands_Reference_Guide_r0.pdf