Int 14 Fn 20  - Multidos Plus - Initialize Port                            [S]

   AH = 20h
   AL = port parameters (see #0226 at AH=00h"SERIAL")
   DX = port number (0-3)

Return: AH = status
       00h successful
       41h no such port
       64h monitor mode already active

See Also: AH=00h"SERIAL",AH=04h"MultiDOS",AH=21h"MultiDOS",AH=23h"MultiDOS"