3 AT Commands
CommPlete Communications Server 39
Escape Sequences
Escape sequences are also known as escape codes. They are used to cause the modem to enter command
mode from online mode without disconnecting the call. There are two local escape sequences used by the
modem, +++AT<CR> and <BREAK>AT<CR>, and one remote escape sequence, %%%AT<CR> (see
“Remote Configuration.”).

+++AT<CR> In-Band Escape Sequence

If the modem is online with a remote modem, you can cause the modem to enter command mode, without
disconnecting the call, by typing an escape code. The default escape code used by the modem is three plus
signs (

+++)

followed by the letters
AT
, up to 10 command characters (most typically

H

, to hang up), and
ENTER. The modem then escapes to command mode, executes the command (if any), and remains in
command mode. For example, to hang up the modem at the end of a call, type +++ATH <CR>.

<BREAK>AT<CR> Out-of-Band Escape Sequence

The MT3334HD8 provides an alternate escape method that uses a break signal as t he escape code. The
break signal— ten or more zero bits issued by data communications software—allows the DTE to signal
the modem without the risk of the modem interpreting data characters as modem control characters. The
break signal is followed by the letters
AT
, up to 60 command characters, and ENTER. When this sequence is
used, the modem executes the command and immediately returns to online mode, unless the command is
to hang up and/or reset the modem (an H or Z command). In the latter case, the modem escapes to
command mode after executing the H or Z command.

%EnEscape Sequence Options

n
= 0–5
Defaults: %E1 and %E4
The default setting is for the modem to respond to the +++ escape method. Optional settings are for the
modem to respond to the <BREAK> method, for the modem to respond to either the +++ or the
<BREAK> methods, and for the modem to ignore both methods and not escape. The %E command is
used to select these options as follows:
%E0 Modem won’t escape
%E1 +++ AT<CR> escape method (factory default).
%E2 <BREAK> escape method.
%E3 Either +++ or <BREAK> escape methods.
%E4 Disables

OK

response to +++ (factory default).
%E5 Enables

OK

response to +++.
%E1 %E5 Enables +++ method and
OK
responses to +++.
%E3 %E5 Enables +++ or <BREAK> method and

OK

responses to +++.

A Force Answer Mode

You can use the A command to force the modem into answer mode. Type ATA when in command mode
to immediately bring your modem off-hook, out of command mode, and into online answer mode, and to
cause it to transmit its carrier signal over the phone line. If no responding carrier tone is received by your
modem within forty-five seconds (or by the time you have specified in register S7), your modem stops
transmitting its tone, hangs up, and goes back into command mode.