INT 14 - Digiboard DigiCHANNEL PC/X* - CHANGE PROTOCOL
        AH = 05h
        AL = protocol
            bits 7-4 unused
            bit 3: RTS/CTS
            bit 2: DSR
            bits 1,0: XON/XOFF
        BH = new XOFF character (00h = current)
        BL = new XON character (00h = current)
        DX = port number (00h-03h) (04h-43h for XAPCM232.SYS)
Return: AH = status
            00h successful
            FFh error
SeeAlso: AH=04h"Digiboard"

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