User's Guide Modem 56

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Synchronous Mode 1
Your modem is capable of dialling remote systems in asynchronous mode and then automatically
switching to synchronous mode once connection has been made. If the connection is lost, your
modem will hang up and return to asynchronous local command state.
The computer required to support synchronous communication with your modem must be
capable of switching between synchronous and asynchronous modes with the same RS-232
port, as well as controlling the state of the DTR signal under software supervision.
Selecting Synchronous Mode 1
Synchronous mode 1 is selected with the &M1 command.
• Type: AT&M1 <E>
Your modem will enter synchronous mode whenever it successfully connects to a remote
modem.
You should also:
• Type: AT&D2 <E>
This allows hang up via your computer’s DTR signal.
☞☞
☞☞
☞ Your computer will not be able to hang up the modem if the DTR Option Switch is
in the DOWN position (DTR will always be asserted). DTR must be lowered to
make the modem hang up.
To return to asynchronous operation:
• Type: AT&M0 <E>
Dialling
Your computer must be in asynchronous mode before dialling commences. To begin dialling use
the D command. Response codes sent to the computer depend upon the settings of the X, V and
Q commands. As soon as a connection can be established, your modem will assert CTS and enter
synchronous on-line state. If connection cannot be made, your modem will hang up and return to
asynchronous local command state.
Character echo and response codes should not be selected when synchronous communications
are used. Use the E0 and Q1 commands to disable character echo and response codes.
As soon as your modem has completed dialling it will examine the state of the DTR signal. If
DTR is asserted your modem will go on line in synchronous mode, otherwise the modem will
hang up and return to asynchronous local command state.