Asus TS300-E7/PS4 - Manual (Page 66)

Chapter 4: Motherboard information 4-14
9. Serial port connectors (10-1 pin COM1/COM2)
Thess connectors are for the serial (COM) ports. Connect the serial port
module cable to one of these connectors, then install the module to a slot
opening at the back of the system chassis.
10. BMC header (BMC_FW1)
The BMC connector on the motherboard supports an ASUS ® Server
Management Board 5 Series (ASMB5-iKVM).