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AT&C Controlling Data Carrier Detect
The &C command enables you to control how DCD will operate. DCD is a RS-232 interface
signal from the modem to a remote device, such as a terminal or a computer, indicating that the
modem is receiving a carrier signal from a remote modem. This signal is switched on (asserted)
when your modem is receiving a valid carrier signal from a remote modem. The &C3 option
allows a connection that was commenced as a voice call to switch to fax or data mode without an
interruption to the DCD signal (which might cause the application to think that the line has been
lost).
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The &C command will only have effect when the DCD option switch is in the UP
position and %T0 is selected. (Refer to the Dumb Mode Section for details.)
Options
AT&C0 DCD signal is always asserted
AT&C1 ■ DCD signal responds to remote modem
AT&C2 DCD signal always on, pulses low on disconnect
AT&C3 DCD asserted during voice session
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We recommend &C2 for UNIX computers which require DCD to be asserted when
issuing commands to the modem.
Range
0-3
See Also
S Register 9 Carrier Detect Response Time
S Register 10 Lost Carrier/Hang Up Delay
%T DCD Control
Dumb Mode Switches
%P Connect Message Timing