B&B Electronics 3PCIU4 - Manual (Page 81)

DIP Switch / Mode Settings
Manual Documentation Number 3PCIoUx-1008 Appendix A A -1
DIP Switch 1 (RS-422/485 only)
The top DIP switch (1) configures the port for RS-485 or RS-422 operation.
For RS-422 operation (which uses two wire pairs and sends point-to-point or
point-to-multipoints) the transmitter can be enabled all the time. Placing the
middle DIP switch in the TX ON position accomplishes this.
For RS-485 operation the middle DIP switch is placed in the TX SD position.
In this position the transmitter is only enabled when data is being sent. The
transmitter is tri-stated when not sending data, allowing other transmitters on
the communications line to transmit without interference.
DIP Switch 2 (RS-422/485 only)
The bottom DIP switch (2) configures the port for half-duplex (two-wire)
RS-485 operation or full-duplex (four wire) RS-422/RS-485 operation.
Placing the bottom DIP switch in the RX ON position configures the port for
four wire operation. In this mode the port’s receiver is continuously enabled,
allowing it to receive all data on the communications line. Since the port’s
transmitter sends data on the other wire pair the port does not receive its own
transmissions.
Placing the bottom DIP switch in the RX position configures the port for
two wire operation. In this mode the port’s transmitter and receiver are
connected to the same wire pair. The receiver is disabled when its transmitter
is sending, preventing the port from receiving its own data.