Escape Sequences, Force Answer Mode | Multi-Tech Systems MT3334HD8

3 AT Commands

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 the 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.

%En Escape 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 +++.

AForce 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.

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