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ISDN TA/V
14.5.6 DCD C
ONTROL
Data Carrier Detect is the signaling circuit used to indicate to the attached
computer/terminal that the ISDN TA/V has detected a valid carrier signal
from the TA/V at the other end of the communications link. Whenever DCD
is present on the DTE interface this is indicated by one or both of your ISDN
TA/V’s ON-LINE LEDs being alight. How this signal is treated by the ISDN
TA/V is determined by the
&C
command.
&C0
DCD is forced on at all times.
&C1
Normal RS-232 signaling where DCD is on when the remote
ISDN TA/V’s carrier signal is detected, and off when it is not
detected.
&C2
DCD is normally forced on although it turns off for
approximately one second when the carrier is disconnected.
&C3
DCD follows the state of DTR.
&C4
Simulated control carrier. The state of DCD follows the state
of the remote ISDN TA/V’s RTS. To ensure correct
operation of this facility, the remote TA/V must be
configured with its RTS signaling command set to simulated
control carrier. This option should be selected where the
DTE requires DCD to toggle on and off in a simulated half-
duplex operation.
&C5
DCD follows the state of DTR except when disconnecting a
call; in which case DCD goes off to signal the disconnection
while DTR remains on. DTR must be turned off and then
back on again before DCD will follow and turn on as well.
