Chapter 4 - AT Commands, S-Registers, and Result Codes
Introduction
One of the ways you can communicate with and configure your MTA128ST-USB is to use AT commands. AT commands are so-called because, with only a few exceptions, each command string begins with the characters AT. Using AT commands, you can read and set parameters, and perform actions such as dialing.
Note: For purposes of brevity, the MTA128ST-USB is referred to as the TA (terminal adapter) throughout this chapter.
Entering AT Commands
If your MTA128ST-USB (TA) is connected to a computer terminal, you can send AT commands to it by entering them on the keyboard. If the TA is connected to a computer, you can send AT commands to it by typing them in the terminal window of a data communications program such as HyperTerminal. You can also send some AT commands indirectly by configuring your data communications program.
To enter AT commands, use the following format: AT <command string> <cr>. The characters AT cause the TA to interpret the following string as a command. The command string consists of one or more commands. The carriage return character, <cr>, sends the command string to the TA. If you are entering a command string in your communication program’s terminal window, insert the carriage return character by pressing the ENTER key on your keyboard. If configuring a communications program, you typically must insert the carriage return character by adding ^M to the end of the command string.
The TA has three modes of operation: off-line command mode (the default state), on-line command mode, and data mode. The TA responds to AT commands only when it is in one of the command modes. After the TA establishes a connection and goes on-line in data mode, it interprets any further characters you enter as data rather than as commands and transmits them to the remote device.
When the TA is in data mode, you can switch it to on-line command mode by sending it an escape sequence. The TA responds to two types of escape sequences:
•In-bandwhere the escape sequence is part of the data stream.
The in-band escape sequence is +++AT<cr>. To change the in-band escape character (+), change the value in register S2.
•Out-of-bandwhere the escape sequence is outside the data stream. The out-of-band escape sequence is <break >AT<cr>. You can send the break signal in the out-of-band escape sequence only from software, not by pressing SHIFT+BREAK on your keyboard.
When it detects the escape sequence, the TA enters on-line command mode where it responds to commands while maintaining the connection with the remote device.
The TA’s command buffer can store 80 characters, including spaces and other characters used in telephone numbers. If you mistype a command string, before you press ENTER, edit it by using the backspace or the delete key. As you type a command string, it appears on your monitor screen, letting you verify your input as you type it.
The AT commands recognized by the TA are listed by function in this chapter first in an abbreviated list, followed by a more detailed list. For an alphabetical list of AT commands, see AT commands in the index.
