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MultiModemZPX User Guide
Introduction
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 ATtention
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 mo-
dem 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 HyperTerminal or the PhoneTools 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 con-
figuring the operating system or communications program to send the commands
automatically. Fortunately, communications programs make daily operation of mo-
dems effortless by hiding the commands from the user. Most users, therefore, need
to use AT commands only when reconfiguring the modem; for example, to turn au-
toanswer on or off.
The format for entering an AT command is ATXn, where X is the command and n is
the 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 Commands"
section, which begins on the next page.
You must press the E
command to the modem. Any time the modem receives a command, it sends a re-
sponse 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 connect-
ing 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 E
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.
4 AT Commands, S-Registers, and Result Codes
key (abbreviated <CR>, for carriage return) to send the
NTER
. Spaces to separate
NTER
22
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