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Operation
Synchronous Operation
Synchronous Operating Modes
The &Mn (Operating Mode) command selects between asynchronous and synchronous Data Mode
operation. Its synchronous mode setting, &M1, supports asynchronous dialing with synchronous
transmission. The \Mn command also selects the protocol that the modem will follow while it is in
synchronous Data Mode. The modem can be configured for synchronous operation by selecting one
of the above synchronous operating modes from the front panel.
Asynchronous Dialing with Synchronous Transmission
The &M1 mode, Asynchronous Dialing with Synchronous Transmission, supports DTE that are
capable of communicating synchronously or asynchronously over the same RS-232 port.
Your call is placed using the asynchronous command set. Once the call connection is established,
the modem will automatically switch to synchronous operation.
The &M1 mode also permits you to use an asynchronous DTE to dial and then switch to a
synchronous-only DTE once the call is connected. If the &D setting is other than &D0, the S25
register will determine the length of time permitted to switch DTE before the call is disconnected.
Direct Dialing in Synchronous Mode
Direct dialing in synchronous data mode can be accomplished in either of two ways:
•
DTR dialing, selected by %Zn
•
V.25 bis commands
When DTR dialing is enabled (%Z1), the modem will automatically dial the previously stored
number (stored using the &Zn=nnn command) when it detects an OFF to ON transition on DTR.
If you wish to save this profile, issue the &W command. The modem will then come up in this mode
any time power is applied.
Once DTR dialing has been selected, you may find that the modem goes off-hook and begins dialing
the stored number the moment you connect your DTE. To prevent this, turn off your modem before
you connect the DTE to the modem. When the connection is complete, turn the modem back on.
Note
The V.25 bis command set is described in detail in Chapter 5, V.25 bis Command Set Operation .
Normal Synchronous Mode
The \M0 command selects the Synchronous Protocol for normal synchronous operation. The
modem employs a constant carrier on the VF line. The DTE-to-VF speed relationship is direct, that
is the two speeds must match. The following DTE data rates are available (\Tn command) when
the modem operates in normal synchronous mode:
28,800 bps
16,800 bps
4800 bps
3-32
26,400 bps
24,000 bps
14,400 bps
12,000 bps
2400 bps
1200 bps
SpectraComm Dual V.34 Modem
Installation and Operation
Synchronous Operation
21,600 bps
19,200 bps
9600 bps
7200 bps
060R122-000
Issue 15
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