_twM4( nC, nD )
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     Set the mouse cursor position in terms of virtual screen
     coordinates. ( 640 x 200 )

       Arguments:

     nC - 'N' X coordinate to set.

     nD - 'N' Y coordinate to set.

       Return:

     Nothing.

       Example:

     To set the mouse cursor at Row 3, Column 13:

        _twM4( 13 * 8, 3 * 8 )