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Operation
Clock Selection
The synchronous format relies on transmit and receive clocks to maintain character timing, so it
does not need start and stop bits for each character. The modem can be configured to use one of the
following three clock sources to transmit synchronous data:
•
Internal (&X0) - transmit clock generated by the modem.
•
External (&X1) - transmit clock signal generated by the DTE is passed to the modem with data.
•
Receiver (&X2) - transmit clock derived by the local modem from the data it is receiving from
the remote modem (also called wrap timing).
The preferred clock source varies for different computer systems. Consult your computer's manual
for its particular specifications. Regardless of which transmit clock source it is using, the modem
always outputs its transmit clock signal to the DTE on Pin 15 of the EIA interface. Pin 17 always
provides the receive clock signal derived from the incoming data. When the DTE provides external
transmit clock it does so on Pin 24.
Note
The receive clock is always controlled by the remote modem that sends the data being received. It is not
recommended to have the local and remote modems both configured to derive transmit clock from re-
ceived data.
3-34
SpectraComm Dual V.34 Modem
Installation and Operation
Synchronous Operation
060R122-000
Issue 15
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