Format of ABLOCKMFI parameter block:
Offset	Size	Description	)
 00h	WORD	0009h (length of following data)
 02h	WORD	top-left coordinate of character block
 04h	WORD	width of block
 06h	DWORD	-> block of DWORDs describing characters (see #03881)
 0Ah	BYTE	length of block in characters
SeeAlso: #03878