Asus RS740-E7-RS24-EG - Manual (Page 76)

Chapter 4: Motherboard information 4-12
5. Power Supply SMBus connector (5-pin PSUSMB1)
This connector allows you to connect SMBus (System Management Bus) to the power
supply unit to read PSU information. Devices communicate with an SMBus host and/or
other SMBus devices using the SMBus interface.
This connector functions only when you install the ASUS ASMB6.
6. Serial port connector (10-1 pin COM1)
This connector is for the serial COM port. 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.