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Feature Reference DART 300 Modem
Page 28 2110212 Rev 1.0
4.4.3.6. Data Carrier Detect (DCD)
Since CDPD modems do not use traditional wireline carrier, DCD is used to indicate the on-line
state of the modem. If there is an open UDP or TCP PAD mode session (either client or server)
then DCD is asserted. When using SLIP or PPP modes the signal is asserted when the modem is
placed in on-line state to the network with the ATO or ATD command.
DART 200
The DART 200 allowed the DCD control signal to be configured to track connection,
RF coverage, or registration state. The DART 300 does not support configuration of
DCD.
Using UDP or TCP mode and enabling auto-answer, the modem can open a server session without
asserting DCD if the host has de-asserted RTS. The modem will not assert DCD until it is able to
send the RING and CONNECT result codes to indicate the transition from command state to data
state. De-assertion of RTS indicates the host cannot receive these messages. As soon as RTS is
asserted, the modem will send the result codes and assert DCD.
CAUTION
Due to multi-processing in the modem, the DCD signal may be asserted slightly before
the modem has completed the transition to data state. The host device should allow a
delay of 500ms after receiving the CONNECT message and DCD signal before
beginning transmission or there may be some data lost.