4-1
3825-A2-GB30-20
November 1996
AT Commands and S-Registers
4-1
4-1
Switching Between Data Mode and Online Command Mode
4-1
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Escape Sequence and Escape Guard Time
4-1
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4-2
4-2
4-17
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4-27
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4-27
4-27
4-27
4-28
Security Configuration Examples
4-28
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Overview
This chapter discusses guidelines necessary to operate
AT commands as well as listing all AT commands
supported by the 3825Plus modem. AT commands are
issued from asynchronous DTEs.
Operating Modes
The 3825Plus 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. (Any command issued is
acknowledged with a response in either words or digits
known as result codes. Refer to Table A-1 in Appendix A
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 3825Plus modem uses three
consecutive plus (+) characters as the escape sequence.
(To change this value, refer to S-register S2 discussed
later in Table 4-2 in the S-Register List section.)
To prevent the modem from interpreting an embedded
+ + + in data as an escape sequence, the Escape Guard
Time value determines the idle time required before and
after the escape sequence is issued. The 3825Plus uses a
1-second pause as the Escape Guard Time. (To change
this value, refer to S-register S12 discussed later in
Table 4-2 in the S-Register List section.)
4
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