INT 14 - MultiDOS Plus - RECEIVE CHARACTER
        AH = 22h
        DX = port number
Return: AH = status (see also AH=21h"MultiDOS")
            00h successful
                AL = character
            3Dh framing and parity error
            3Eh overrun error
            3Fh framing error
            40h parity error
            96h ring buffer overflow
Note:   if no character is available, this function waits until a character
          arrives or an implementation-dependent timeout elapses
SeeAlso: AH=21h"MultiDOS",AH=27h