Escape character (+++) instructs the modem to leave data state and
enter command state without breaking the connection. Note that this
command is only effective in asynchronous mode.
For the modem to distinguish escape characters from data, escape
characters must be preceded and proceeded by a guard time period.
This is called the escape sequence. To enter the escape sequence while
the modem is on line in data state:
1. Wait for one second of guard time without typing or transferring
anything.
2. Enter the three consecutive escape characters (+++). Do not press
the return key.
3. Wait for another second of guard time without typing or
transferring anything.
Upon recognition of the escape sequence, the modem sends an OK
response code and escapes to command state.
The default escape character is + (ASCII 43) and the default guard
time is one second. Both are changed by adjusting the values in
registers S2 and S12, respectively.
5.46 Call-Back Security
@A
Command @A enables or disables the call back security function.
@A0 Disables callback security.
@A1
Enables call back security.
5.47 Ring Sound Control
@B
Command @B enables or disables the ringing sound generated through
the modem speaker when an incoming ring is detected.
@B0 Disables incoming ring sound.
@B1 Enables incoming ring sound.
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