the front panel for entering commands that control the
operation and configuration of the 3800 Series modems.
This chapter discusses guidelines necessary to operate
AT commands as well as listing the modifiers for all
AT commands supported by the 3800 Series modems.
AT commands are issued from asynchronous DTEs (such
as a personal computer).

Operating Modes

The 3800 Series modem has two operating modes,

Command mode and Data mode. Before a modem goes
online (establishes a successful connection with a remote
modem), it is considered to be in Command mode; an idle
state where you can modify its operating parameters or
issue modem commands.

In Command mode, any command issued is

acknowledged with a response in either words or digits
known as a result code. Refer to Table B-1 for a listing of
result codes.

Once the modems are online, either by answering or

originating a call, they automatically switch to Data mode.
Data mode is a state where any entries made from the
DTE are considered data and are transmitted and received
between modems. The modems remain in Data mode until
the connection is broken or until they are forced into
online Command mode using the escape sequence.

Switching Between Data Mode and
Online Command Mode

Sometimes it is necessary to change operating

parameters while the modems are online. The escape
sequence allows you to toggle the modem between Data
mode and online Command mode while maintaining a
connection with the remote modem. This is accomplished
using the escape sequence (+++) to exit Data mode and
the O command to return to Data mode.

Escape Sequence and Escape Guard Time

The escape sequence is only issued when the modem is

online and in Data mode. The 3800 Series modem uses
three consecutive plus (+) characters as the escape
sequence. (To change this value, refer to S-register S2
discussed later in Table 14-2 in the S-Register Format
section.)

To prevent the modem from interpreting an embedded

+++ in data as an escape sequence, the Escape Guard
Time value determines the length of the pause before and
after the escape sequence is issued. The 3800 Series
modem uses a one second pause as the Escape Guard
Time. (To change this value, refer to S-register S12
discussed later in Table 14-2 in the S-Register Format
section.)

To enter online Command mode while in Data mode,

enter the following sequence:

TYPE:

+++