5902 Bell 202 Modem Hardware Manual
October 19, 2007
22
4.5.8
Duplex
The FDX switch selects full or half duplex operation.
DUPLEX
HALF DUPLEX
FULL DUPLEX
FDX switch
Open
closed
In full duplex mode, the modem continuously transmits carrier. This mode is suitable only for:
Two back-to-back modems on a four wire network.
A master modem on a multi-dropped four wire network which connects to half duplex, constant
carrier slave modems.
In full duplex mode, the modem ignores the state of the RTS signal, although the RTS/CTS delay is
still active. The carrier detect and carrier loss delays are active. Anti-streaming is ignored. The soft
carrier turn-off tone will never be transmitted, although it will be recognized if received. Radio
carrier detect is ignored.
4.5.8.1
Constant Carrier Networks
Constant carrier operation is often used with multi-point networks. A full duplex master modem
connects to multi-dropped, half duplex, slave modems. The master modem always transmits a
carrier, which is why the system is known as a constant carrier network. The main benefits are faster
operation (the slave modems do not experience any carrier detect or loss delays), and instant
detection of communication system failure by loss of carrier. This type of network requires four
wires.
The slave modems must be configured for half duplex, constant carrier reception. Otherwise they
will be unable to transmit data. See section
4.5.3
-
Carrier Loss Delay
for details on configuring a
5902 modem for constant carrier reception.
4.5.9
Test Mode Selection
The TST switch selects the test mode. Refer to section
6.2
-
Modem Test Modes
for more
information.
