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COMSPHERE 3821Plus Modem
4-26 February 1998 3821-A2-GB20-30
Recovering AT Commands
Certain dialing methods, such as V.25bis and
synchronous operation, disable the use of AT commands
and place the modem into a state known as Dumb mode.
The 3821Plus is capable of normal operation when in
Dumb mode. Moreover, the SDCP normally can be used
to load the Async Dial factory default and restore the use
of AT commands. However, if an SDCP is for some
reason unavailable, the following procedure may be used.
The AT Recovery command (AT***) places the
modem into a temporary state that restores AT commands.
When in this state, the modem’s previous settings are
retained except for the following configuration options:
• The DTE Dialer Type configuration option
(&M and &Q) is set to AT
• The Async/Sync Mode configuration option
(&M and &Q) is set to Async
• The DSR Control configuration option (&S) is set
to Forced On
• The LSD Control configuration option (&C) is set
to Forced On
If these settings are not appropriate, then change them
to a setting compatible with your current application.
The procedures for an AT recovery using an
asynchronous terminal or personal computer are listed in
the following section. Read through these procedures
before performing a recovery:
" Procedure
1. Turn the modem Off and then ON. The modem
performs a power-up self-test in which all LEDs
light. While this is running, repeatedly press the
A key of your DTE’s keyboard (or keep the key
depressed if your keyboard automatically repeats
characters that way). Keep doing this until A’s (or
a’s) appear on your DTE screen. (You may use all
uppercase or all lowercase characters.)
At least three consecutive A’s must be entered
within a 2-second time interval.
If these characters are not echoed back to the DTE
screen after the power-up self-test is complete, then
the modem is still in Dumb mode and maintains its
current configuration. Turn the modem Off and
then ON again, and repeat Step 1.
2. Once the characters are echoed back to the DTE,
TYPE: T***
(The case of this character must be consistent with
the case used in Step 1. Mixed case prefixes such as
aT or At are not recognized.)
This must be entered within 10 seconds after
receiving the echoed characters.
PRESS: Enter
The screen displays OK.
The modem is now in AT Recovery mode, and
remains in this state until a Save or power reset
occurs. While in this mode, you can use AT
commands to make any necessary changes to
configuration options.
Keep in mind that the &C command is changed to
Forced On (&C0), the &M and &Q commands are
changed to Async mode with AT commands
enabled (&M0 and &Q0), and the &S command is
changed to Forced On (&S0). If these settings are
not appropriate, then reset them to a desired choice
before exiting AT Recovery mode.
3. To save changes, use the &W command:
TYPE: AT&Wn
Where: n is one of the following storage areas:
0 for Active (Saved)
1 for Customer 1
2 for Customer 2
PRESS: Enter
The modem exits AT Recovery mode and returns to
its previous application environment. Only the
Active (Saved) area affects modem operation. To
move a Customer area to Active (Saved), use the Z
command.