Asus P7H55-M LX USB3 User Manual page 23

9. Serial port connectors (10-1 pin COM1)
The connector is for a serial (COM) port. Connect the serial port module cable to the
connector, then install the module to a slot opening at the back of the system chassis.
The serial port bracket (COM1) is purchased separately.
COM1
PIN 1
P7H55-M LX/USB3
P7H55-M LX/USB3 Serial port (COM1) connector
ASUS P7H55-M LX/USB3 1-14