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Chapter 3 - AT Commands
3.1
Working with AT Commands
The MT2834MR6's modems are controlled by instructions called AT commands, so called because the
attention characters AT precede each command or command string (sequence of commands). You can send
commands to the modem from your keyboard while in terminal mode, or you can use communications
software to issue these commands automatically.
The MT2834MR6 is in command mode when it is not dialing or online. When it is in command mode, you
have access to a complete communications system that allows you to use several features, including the
basic AT command set described in this chapter. Using the basic AT command set, you can enter phone
numbers for automatic dialing, configure modem options, and monitor telephone activity. In addition, you can
command your modem to perform advanced features such as error correction, data compression, speed
conversion, and more.
This chapter explains command mode, and shows you how to use each of the MT2834MR6's AT commands.
MT2834MR6 commands and responses are compatible with all systems and with all data communications
software using the AT command set.
For easy reference, the MT2834MR6 has a help command that provides you with short, on-screen
descriptions of the modem commands. The help command is explained later in this chapter.
3.1.1 Modes of Operation
The MT2834MR6 operates in two basic functional modes: command mode and online mode. (There is also
an in-between state, wait-for-carrier, in which the modem is out of command mode but not yet online.) When
you power up the modem, it is in command mode, and is ready to accept and respond to commands from
your keyboard or software.
An MT2834MR6 modem enters online mode after it dials, connects with another modem, and detects a valid
carrier signal. If it does not detect a carrier signal within the time frame controlled by register S7, the modem
abandons the call and re-enters command mode.
You can make the modem enter online mode without dialing by typing either the D command or the A
command.
The modem exits online mode if the carrier signal is lost or intentionally dropped. When this happens, the
modem hangs up and re-enters command mode.
By sending certain "escape" characters to the modem while online, you can make it enter command mode
without losing the carrier signal.
For autoanswer-only applications, you can disable a modem's ability to recognize AT commands by using
the %DC1 command. When you do this, the MT2834MR6 ignores all commands, and functions as a non-
intelligent modem. The %DC1 command and other MT2834MR6 commands are explained later in this
chapter.
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