Intel H110 Technical Manual page 20

(2) COM1 (9-pin Block): RS232/422/485 Port
COM1 port can function as RS232/422/485 port. In normal settings COM1 functions
as RS232 port. With compatible COM cable COM1 can function as RS422 or RS 485
port. User also needs to go to BIOS to set 'Transmission Mode Select' for COM1
at first, before using specialized cable to connect different pins of this port.
Pin1
For RS485 Mode
RS232 Mode
For RS422 Mode
(3) COM2/COM3 (9-pin Block): RS232 Port
Pin1
RS232 Mode
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