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Operation
Data Mode Overview
The modem is in data mode while it has a telephone line connection to another modem or is in the
process of establishing a connection. In Data Mode the modem transmits all the data it receives
from the DTE over the phone line.
In data mode the modem can operate either asynchronously or synchronously, as specified by the
&M command. A variety of data protocols are available for each type of operation. Some protocols
provide error correction to improve reliability and/or data compression to increase throughput. The
two types of data mode operation, and their protocols, are described at length in the following pages.
Each telephone line connection (whether switched network or private line) between two modems
in data mode begins with a handshaking sequence. During that sequence the modems determine the
VF (telephone line) speed, data protocol, and related parameters for the data link. Configuration
determines the range of choices available to the modem in the negotiation process.
Most configuration options in the modem act to limit the range over which a parameter can be
negotiated, rather than making specific assignments.
The modem's DTE can cause it to enter data mode and initiate dialing (switched network) or
handshaking (private line) by asserting the Data Terminal Ready (DTR) signal at the interface or
by issuing an AT command to dial. Configuration determines whether or not the modem is
controlled by DTR. The presence of a carrier from a remote modem causes the Dual V.34 modem
to enter data mode and assert a Data Carrier Detect (DCD) signal to its DTE.
3-26
SpectraComm Dual V.34 Modem
Installation and Operation
Data Mode Overview
060R122-000
Issue 15
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