Brainboxes CC-310 Hardware Manual page 18

Specifications
Port 1 With Full Duplex Settings.
Both jumpers left unconnected (not shorted).
Port 1 With Half Duplex Settings.
Both jumpers shorted, causing the RXD- & TXD- and the
RXD+ & TXD+ signals to short together at the 9-pin
connector. The multiplex jumpers should only be set for
RS485 Half Duplex operation, when one twisted pair is used to
interconnect both transmit and receive lines.
NOTE: Any changes to RS485 Multiplex Operation must be
accompanied with appropriate changes to the driver software; see
the Chapter 3 - "PCI Velocity RS422/485 Software Configuration"
for more details.
For further details on the RS422 and RS485 standard, pinouts, half
duplex and full duplex RS485 systems, wiring diagrams and
optional grounding diagrams refer to Chapter 4 - "Optional
RS422/485 Operation."
PCI VELOCITY / OPTO ISO RS422/485
Chapter 2 Page 12