This sample of a direct write video page scroll routine for standard text
mode screens was taken from ANSI.SYS
; DATA
Attribute          db 7
VideoMemSeg	   dw b800
VideoPageSegOff    db 0
; SET UP FOR BLANKING LAST LINE
mov     bh,Attribute            ; Current Video attribute
mov	bl,20h			; ASCII space character
mov	bp,50h			; 80 words per line
; POINT TO VIDEO MEMORY AT THE CORRECT PAGE
mov     ax,VideoMemSeg          ; Segment address of video memory (B800)
add	ax,VideoPageSegOff	; Video page number * Page byte length / 16
mov     es,ax
mov     ds,ax
xor	di,di			; Move to first line
mov	si,0A0h 		;  from second line (160 bytes per line)
mov	cx,780h 		; Page word length
; DO IT
cld                       
rep	movsw			; Scroll the page
mov     ax,bx
mov     cx,bp
rep	stosw			; Blank the last line