Chapter 10 - Modem Mode At Commands, S-Registers, Result Codes; Escape Code Sequence; Command Organization - Multitech MultiConnect MTS2SA-T User Manual

Chapter 10 – Modem Mode AT
Commands, S-Registers, Result Codes
This chapter covers the V.22bis, V.32, V.34, and V.92 commands, S-Registers, and Result Codes. The
AT commands are used to control the operation of your modem. They are called AT commands because
the characters AT must precede each command 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 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., +++ 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, or some other available terminal program. 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 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&B is equivalent to AT&B0. Most commands have a
default value, which is the value that is set at the factory.
You must press ENTER (depending on the terminal program it could be some other key) 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; the
command interpreter ignores them. 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.

Escape Code Sequence +++

When the modem has established a connection and has entered online data mode, it is possible to break
into the data transmission in order to issue further commands to the modem in an online command mode.
This is achieved by the DTE sending to the modem a sequence of three ASCII characters specified by S-
Register S2. The default character is '+'. The maximum time allowed between receipt of the last character
of the three-escape character sequence (+++) from the DTE and sending of the OK result code to the
DTE is controlled by the S12 register.

Command Organization

The commands in this chapter are listed in the following order:
•
First, the commands that begin with letters are listed in alphabetical order
•
Then the commands that begin with symbols are listed in this order &, \, –, %, +, #, +++
•
Fast Connect Commands
•
V.92 Commands
Multi-Tech Systems, Inc. MultiConnect Serial-to-Serial Adapter User Guide (S000354A)
Chapter 10 − Modem Mode AT Commands, S-Registers, and Result Codes
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