There are 2 Universal Serial ports on the lower right portion of the back panel. These are serial ports 9 and 10.
is at the of the connector
NOTE: When using serial ports 9 and 10 as RS485 full duplex ports, the transmit + and transmit - , should be on a twisted pair, and the receive + and receive – should be on another twisted pair. For half duplex, the two communication lines in this configuration should be on a twisted pair. This applies for the differential signaling found in RS485, it’s required to keep coupled noise in the lines low and is especially important in long runs (i.e. greater than 10 ft up to 4000 ft) or runs where AC power lines are run in close proximity to the RS485 Category 5 cable.