AT Modem Command Syntax

A command string should start with "AT" or "at", except for the commands "A/" and "+++". "At" or "aT" are invalid.
Several commands can be given in one command string.
The commands can be given in upper or lower case.
A command string should contain less than 40 characters.
When an error is made during the typing of the command, it can be corrected using the backspace key.
Commands and command strings must be terminated with an <ENTER>, except +++ and A/
A telephone number can exist of following characters:
0 1 2 3 4 5 6 7 8 9 * = , ; # + > . All other characters are ignored (space, underscore ). They help formatting the dial string.
Commands that use a numerical parameter, can be used without a numerical value. In this case the command will be issued with the value zero.
If the command string contains two consecutive commands without parameter, as discussed above, the modem will respond with an error.
After the command ATZ has been issued, a pause of two seconds should be respected before entering the next commands.
IMPORTANT: The commands below are standard Hayes AT commands. Some vendors implement their own AT commands which will only work with their brand/model of modem.