User manual

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MT5634ZBA-USB User Guide
AT Commands
AT commands are used to control the operation of your modem. They are so called
because each command must be preceded by the characters AT to get the AT tention of
the modem.
AT commands can be issued only when the modem is in command mode or online
command mode. The modem is in command mode whenever it is not connected to
another modem. The modem is in data mode whenever it is connected to another
modem and ready to exchange data. Online command mode is a temporary state in
which you can issue commands to the modem while connected to another modem. To
put the modem into online command mode from data mode, you must issue an escape
sequence (+++) followed immediately by the AT characters and the command, e.g.,
+++ATH to hang up the modem. To return to data mode from online command mode, you
must issue the command ATO.
To send AT commands to the modem you must use a communications program, such as
the HyperTerminal applet in Windows 95 and NT 4.0, or the communications program
included with your modem. You can issue commands to the modem either directly, by
typing them in the terminal window of the communications program, or indirectly, by
configuring the operating system or communications program to send the commands
automatically. Fortunately, communications programs make daily operation of modems
effortless by hiding the commands from the user. Most users, therefore, need to use AT
commands only when reconfiguring the modem, e.g., to turn autoanswer on or off.
The format for entering an AT command is AT Xn , where X is the command and n is the
specific value for the command, sometimes called the command parameter . The value is
always a number. If the value is zero, you can omit it from the command; thus, AT&W is
equivalent to AT&W0. Most commands have a default value, which is the value that is
set at the factory. The default values are shown in the “AT Command Summary,” which
begins on the next page.
You must press ENTER to send the command to the modem. Any time the modem
receives a command, it sends a response known as a result code . The most common
result codes are OK , ERROR , and the CONNECT messages that the modem sends to
the computer when it is connecting to another modem. For a table of valid result codes,
see “Result Codes” at the end of this chapter.
You can issue several commands in one line, in what is called a command string . The
command string begins with AT and ends when you press ENTER. Spaces to separate
the commands are optional; they are ignored by the command interpreter. The most
familiar command string is the initialization string , which is used to configure the modem
when it is turned on or reset, or when your communications software calls another
modem.