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13-13980-A2-GB30-20 November 1996
AT Command Set and
S-Registers
Overview 13-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating Modes 13-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Switching Between Data Mode and Online Command Mode 13-1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Command Guidelines 13-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AT Command List 13-2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
AT Command Format 13-5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
S-Register List 13-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
S-Register Format 13-14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overview
The
A
T command set provides an alternative method to
the front panel for entering commands that control the
operation and configuration of the 3800Plus
modems.
AT commands are issued from an asynchronous DTE
(such as a personal computer). This chapter explains how
to use A
T commands and lists the modifiers for all
AT commands supported by the 3800Plus
modems.
Operating Modes
The 3800Plus
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 Appendix B for a list of
result codes.
Once the modems go 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 3800Plus
modem uses three
consecutive plus (+) characters as the escape sequence.
(To change this value, refer to S-register S2 discussed
later in Table 13-2 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
Plus modem
uses a one second pause as the Escape Guard T
ime. (To
change this value, refer to S-Register S12 discussed later
in Table 13-2 in the S-Register Format
section.)
To enter online Command mode while in Data mode,
enter the following sequence:
TYPE: +++
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