AH = 0
        AL = initializing parameters
            7 - 6 - 5      4 - 3     2    1 - 0
            -BAUD RATE-    PARITY   STOP   WORD
                                    BITS  LENGTH
            000  110 BD    00 none  0-1   10 - 7
            001  150 BD    01 odd   1-2   11 - 8
            010  300 BD    11 even
            011  600 BD
            100 1200 BD
            101 2400 BD
            110 4800 BD
            111 9600 BD (4800 ON PCjr)
        DX = port number
Return: AX port status--see below
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