Function 07h    Scroll Page Down - scroll down or clear a display "window" 
entry   AH      07h 
	AL      number of lines to be blanked at top of page 
		0 = blank entire window 
	BH      attributes to be used on blank line 
	CH      row    (Y) of upper left corner or window 
	CL      column (X) of upper left corner of window 
	DH      row    (Y) of lower right corner of window 
	DL      column (X) of lower right corner of window 
return  none 
note 1) Push BP before scrolling, pop after 
     2) If in CGA text mode, affects current page only 
 
Sample Code:
\Asm\Lib\BIOS.INC -@BIOSVidScroll MACRO dist,atrib,upcol,uprow,downcol,downrow