Asus RS500A-E6/PS4 - Manual (Page 59)

ASUS RS500A-E6/PS4 4-11
7. Serial General Purpose Input/Output connectors (8-1 pin SGPIO1/2)
These connectors are used for the SAS chip SGPIO interface that controls
the LED pattern generation, device information and general purpose data.
These connectors functions only when you install an ASUS PIKE SAS RAID
card.
The serial port module is purchased separately.
8. Serial port connector (10-1 pin COM2)
This connector is for a serial (COM) port. Connect the serial port module
cable to this connector, then install the module to a slot opening at the back
of the system chassis.