INT E0 - DR Multiuser DOS - "A_CONTROL" - GET/SET AUX CONTROL PARAMETERS
        CL = B1h
        DS:DX -> AUX device control block (see below)
Return: AX = status
            0000h successful
                control block updated
            FFFFh failed
                CX = error code
SeeAlso: INT E0/CL=B0h,INT E0/CL=B2h

Format of AUX device control block:
Offset  Size    Description
 00h    BYTE    function (00h get, 01h set)
 01h    BYTE    DTR state (00h low, 01h high, FFh unknown/don't change)
 02h    BYTE    RTS state (00h low, 01h high, FFh unknown/don't change)
 03h    BYTE    DSR state (00h low, 01h high, FFh unknown/don't change)
 04h    BYTE    CTS state (00h low, 01h high, FFh unknown/don't change)
 05h    BYTE    DCD state (00h low, 01h high, FFh unknown/don't change)
 06h    BYTE    RI state (00h inactive, 01h active, FFh unknown/don't change)