INT 14 - Digiboard DigiCHANNEL PC/X* - CHANGE BAUD RATE
        AH = 04h
        AL = initializing parameters
            bits 7-5 unused
            bits 4,3: parity (00 none, 01 odd, 11 even)
            bit 2: stop bits (0 = one, 1 = two)
            bits 1,0: data bits (00 = five, 01 = six, 10 = seven, 11 = eight)
        BX = baud rate
        DX = port number (00h-03h) (04h-43h for XAPCM232.SYS)
Return: AH = status
            00h successful
            FFh error