AH = 04h
        AL = break status
            0 if break
            1 if no break
        BH = parity
            0 no parity
            1 odd parity
            2 even parity
            3 stick parity odd
            4 stick parity even
        BL = number of stop bits
            0: one stop bit
            1: two stop bits (1.5 if 5 bit word length)
        CH = word length
            0: 5 bits
            1: 6 bits
            2: 7 bits
            3: 8 bits
        CL = baud rate
            0: 110
            1: 150
            2: 300
            3: 600
            4: 1200
            5: 2400
            6: 4800
            7: 9600
            8: 19200
Return: AL = modem status (see above)
        AH = line control status (see above)
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