User guide

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Chapter 5 - 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.
+++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>.
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, 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 45 seconds (or by the time you
specified in register S7), your modem stops transmitting its tone, hangs up, and goes back into
command mode.
On Go Back Online
n = 0, 1, or 3
Default: none
Use the O command to bring the modem out of command mode and back into online mode.
The O command reverses the result of entering the escape code. The O command brings
modem into the online mode (originate or answer) it was in prior to entering command mode.
O0 causes the modem to exit command mode and return to online data mode.
O1 causes the modem to issue a retrain before returning to online data mode.
O3 causes the modem to issue a rate renegotiation before returning to online data mode.
Modem S-Registers
S-registers are small regions of memory where modem configuration information is stored. Whereas AT
commands tell a modem what to do, S-registers tell the modem how to do it. Each S-register has a name that
consists of the letter S and a number (S0, S1, S2, etc.), hence the term S-register. Use the Sr? command to read
the value stored in an S-register and the Sr=n command to change it.
S0 Number of Rings Until Modem Answers
Unit: 1 ring
Range: 0–255
Default: 0
Defines number of rings the modem waits before answering an incoming call. Default value is
zero, which effectively disables the auto-answer function. When auto-answer is disabled, the
modem can only answer via the ATA command. Set the S0 register value to one to cause the
modem to answer the call immediately after the first ring. Maximum number of rings that can
be configured is 255.