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ISI5634PCI/4/8 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 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 modem and ready to
exchange data. Online command mode is a temporary state where 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 directlytyping them in the
terminal window of the communications program or indirectly
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 ATXn, 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