PCI-946-1 and P3S440BX Technical Reference manual
2-10
2.5.2.3. RS-422 - Full Duplex Operation
The RS-422 protocol uses both RX and TX lines during a communication session. Upon
power-up or reset, the Serial Port 2 interface circuits are automatically configured for full
duplex operation. Pins 3 and 4 of J8 act as the receiver lines and pins 5 and 6 act as the
transmitter lines.
In RS-422 mode, the software should not use the handshake signals (e.g., DSR, DTR),
since they are not connected. However, software handshaking can be used (e.g., XON-
XOFF).
2.5.2.4. RS-485 - Party Line Operation
The RS-485 offers to multiple station the ability to transmit and receive over the same
pair of wires (RX outputs: pins 3 and 4 of J8), and share the same communication line
with multiple stations.
The RS-485 protocol offers advantages such as increased speed over long distances,
improved reliability over similar RS-232 setups, the ability to share transmission line,
and simpler cabling requirements than the RS-422 protocol.
In this configuration, only one system takes control of the communication at a time.
Upon power-up or reset, the transceiver is by default in "receiver mode" to avoid line
perturbation.
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