Convert

        Entry:
          AH = FBh
          DS:DX -> control block (see below)

        Format of control block:

        Offset  Size    Description
         00h 12 BYTEs   reserved
         0Ch    WORD    1A00h
         0Eh  6 BYTEs   0
         14h    DWORD   (high byte first) 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