INT 68 - APPC/PC - CONVERT
        AH = FBh
        DS:DX -> control block (see below)
Return: control block updated

Format of control block:
Offset  Size    Description
 00h 12 BYTEs   reserved
 0Ch    WORD    1A00h (verb "CONVERT")
 0Eh  6 BYTEs   00h
 14h    DWORD   (big-endian) return code
 18h    BYTE    conversion
                00h ASCII to EBCDIC
                01h EBCDIC to ASCII
 19h    BYTE    character set
                00h AE
                01h A
                02h G
 1Ah    WORD    length of string to convert
 1Ch    DWORD   pointer to source
 20h    DWORD   pointer to target

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