Attention (AT) commands are the means by which you control and monitor a modem. Typically, the communications application automatically issues them, and you need not know the commands and their options.
However, to custom-configure the modem for an application, or to optimize performance, you can issue commands through the communications application yourself. In most communications applications, there is a menu item, or option, for entering extended or custom AT commands. See your communications application documentation.
You can also configure the modem by issuing AT commands directly from a simple terminal-emulation application. One such application is minicom, which is present on computers that have Red Hat.
To issue an AT command from the terminal-emulation application, you must ensure that the modem is in command mode (in which it can detect and respond to commands), rather than data mode (in which it is transmitting and receiving data). To enter command mode from data mode, enter +++. You need not press the ENTER key.
When entering AT commands, the following basic rules apply:
AT commands can be entered in uppercase, lowercase, or mixed text
The characters AT begin all AT commands, except A/ and +++
The key used as the ENTER key is specified in S-Register S3
The maximum command length is 64 characters.
You can enter more than one AT command on a line, and you can chain commands using just one “AT” at the start. However, some commands must occur at the beginning or end of the command line.