User Manual

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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 directly—typing 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 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.
AT Commands
Command: AT Attention Code
Values: n/a
Description: The attention code precedes all command lines except A/ and the escape sequence.
Command: ENTER Key
Values: n/a
Description: Press the ENTER or RETURN key to execute most commands. This action is frequently
abbreviated <CR>.
Command: A Answer
Values: n/a
Description: Answers an incoming call before the final ring.
Command: A/ Repeat Last Command
Values: n/a
Description: Repeats the last command string. Do not precede this command with AT. Do not press
ENTER to execute.