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AT&M Synchronous/Asynchronous Mode
The &M command enables you to select either asynchronous or synchronous operation.
During asynchronous transmissions, the time between characters being sent may vary, and the
characters are delimited by start and stop bits to co-ordinate data transfer.
During synchronous transmissions, the interval between the transmission of each character is of
equal length, controlled by clock signals.
Synchronous transmission is most commonly used in communications involving mainframe
computers.
Options
AT&M0 ■ Asynchronous mode
The modem will dial and answer in the asynchronous mode and then enter
asynchronous on-line state when a connection is established.
AT&M1 Synchronous mode with asynchronous dialling The modem remains in
asynchronous mode while it is on-hook, dialling or answering. When a
connection is established, the modem automatically switches to synchronous
operation.
AT&M2 Synchronous mode with dialling invoked by the DTR signal
The modem remains in asynchronous mode while it is on-hook, dialling or
answering.
You must issue the AT&D2 command prior to using this synchronous mode.
When your local computer asserts the DTR (Data Terminal Ready) signal,
the modem will dial stored phone number zero (see the &Zn command).
When an incoming call is detected, the modem will attempt to answer it as
soon as the DTR signal is asserted and the number of rings specified in S
Register 0 is reached.
As soon as a connection is established, the modem automatically switches to
synchronous operation.
If DTR is lowered at any time, the modem will hang up.
AT&M4 Asynchronous mode with dialling invoked by the DTR signal
When your computer asserts the DTR signal, the modem will dial stored
phone number zero (see &Zn command).
You must issue the AT&D2 command prior to using this synchronous mode.
When an incoming call is detected, the modem will attempt to answer it as
soon as the DTR signal is asserted and the number of rings specified in S
Register 0 is reached.
If DTR is lowered at any time, the modem will hang up.