Format of user buffer ptr info area:
Offset	Size	Description	)
 00h	WORD	flags
		0000h don't read interface's data buffer
		0001h read data buffer
 02h	DWORD	pointer to ring buffer
 06h	WORD	length of ring buffer
 08h	WORD	ring buffer offset to last byte read by caller
 0Ah	DWORD	pointer to WORD containing offset of last byte
		  in ring buffer filled
 0Eh	DWORD	pointer to screen buffer
 12h	DWORD	pointer to field containing cursor position
 16h	DWORD	pointer to terminal status area (see #03372)