INT 14 - Egberto Willies COMM-DRV - EXTENDED INITIALIZATION
        AH = 81h
        BX:DI -> port control block
Return: ???

Format of port control block:
Offset  Type    Description
 00h    WORD    port IO address
 02h    WORD    port IRQ
 04h    WORD    baud rate
 06h    WORD    parity
 08h    WORD    data bits
 0Ah    WORD    stop bits
 0Ch    WORD    break status
                    0000h off
 0Eh    WORD    flow control protocol
 10h    BYTE    input block
 11h    BYTE    output block
 12h    WORD    low threshold
 14h    WORD    high threshold
 16h    WORD    segment of buffer
 18h    WORD    offset of buffer
 1Ah    WORD    input buffer length
 1Ch    WORD    output buffer length
 1Eh    BYTE    auxiliary address
 1Fh    BYTE    spare
 20h  4 WORDs   spares