Asus RS500A-S6/PS4 - Manual (Page 59)

ASUS RS500A-S6/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 function only when you install an ASUS PIKE SAS RAID
card.
8. Serial port connector (10-1 pin COM1, COM2)
These connectors are for the serial (COM) ports. Connect the serial port
module cables to these connectors, then install the modules to the slots
opening at the back of the system chassis.
The serial port module is purchased separately.