Asus PS4 - Manual (Page 60)

4-12 Chapter 4: Motherboard information
10. BMC header (BMC_FW1)
The BMC connector on the motherboard supports an ASUS ® Server
Management Board 4 Series (ASMB4).
The serial port module is purchased separately.
9. 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.