Table of Contents
Advertisement
MT5634HD8 User Guide
Working with AT Commands
The MT5634HD8's modems are controlled by instructions called AT commands, so
called because the attention characters{xe "AT commands:attention code"}{xe "AT
commands:AT"} AT precede each command or sequence of commands (known as a
command string){xe "command string"}. You can send commands to the modem from
your keyboard while in terminal mode, or you can use communications software to
issue these commands automatically.
The modem is in command mode{xe "command mode"} when it is not dialing or
online. When it is in command mode, you have access to a complete communications
system that allows you to use several features, including the basic AT command set
described in this chapter. Using the basic AT command set, you can enter phone
numbers for automatic dialing, configure modem options, and monitor telephone ac-
tivity. In addition, you can command your modem to perform advanced features such
as error correction, data compression, speed conversion, and more.
This chapter describes the modem's operational modes, and shows you how to use
each of the modem's AT commands. These commands and responses are compatible
with all systems and with all data communications software using the AT command
set.
Modes of Operation
The MT5634HD8 operates in two basic functional modes: {xe "command
mode"}command mode and online mode{xe "online mode"} . (There is also an in-
between state, {xe "wait-for-carrier mode"}wait-for-carrier, in which the modem is
out of command mode but not yet online.) When you power up the modem, it is in
command mode, and is ready to accept and respond to commands from your keyboard
or software.
The modem enters online mode{xe "online mode"} after it dials, connects with
another modem, and detects a valid carrier signal. If it does not detect a carrier
signal within the time frame controlled by register S7{xe "S-registers:S7"}{xe
"abort timer"}, the modem abandons the call and re-enters command mode.
You can make the modem enter online mode{xe "online mode"} without dialing by
typing either the D command{xe "Dial command"}{xe "AT commands:D"} or the {xe
"AT commands:A"}A command{xe "Answer command"}.
The modem exits online mode{xe "online mode"} if the carrier signal is lost or in-
tentionally dropped. When this happens, the modem hangs up and re-enters
command mode.
By sending certain "escape" characters to the modem while online, you can make it
enter command mode without losing the carrier signal.
Command Structure
You can control a wide variety of modem operations and options when the modem is
in command mode. AT commands tell the modem to dial a number, to answer a call,
to operate at a certain speed, to use a certain compression technique, and many other
functions. AT commands consist of one or two letters, which may be preceded by an
ampersand (&), a percent character (%), or a slash character (\). The Q command,
14
CommPlete Communications Server
Advertisement
Table of Contents
