Int 14/AH=20h

AH = 20h
AL = logical port (01h COM1, 02h COM2)
DX = physical port number

Return:
AX = status
0000h successful
FFFFh failed

See Also: AH=21h"Alloy" - AH=22h"Alloy" - AH=23h"Alloy" - Category: Serial I/O - Int 14h - A