4 Way Scroll by Malcolm Bamber
[[http://www.dark-well.pwp.blueyonder.co.uk/]]

How I scrolled a 2 by 2 tiled map
I hope it is a help to some one trying to scroll the screen 

This first part here will show you what the irq is doing when called



__SCROLL UP__ 

IF YSCROLL=3	
	
    ADD ONE TO UDFLAG
    IF UDFLAG NOT 1 OR 2 THEN THEN QUIT OUT OF IRQ
    IF UDFLAG=1 THEN SO MOVE MAP POINTER UP ONE LINE IF WE CAN
    IF UDFLAG=2 THEN COPY SCREEN DOWN ONE LINE
    SET $D011 TO 3
    SET YSCROLL TO 5 FOR NEXT TIME IRQ IS CALLED

IF YSCROLL=5	
    SET $D011 TO 5
    SET YSCROLL TO 7 FOR NEXT TIME IRQ IS CALLED
    DRAW TILE AT THE TOP OF THE SCREEN
    IF UDFLAG=1 THEN DRAW BOTTOM PART OF TILE
    IF UDFLAG=2	THEN DRAW TOP PART OF TILE

IF YSCROLL=7		
    SET $D011 TO 7	
    SET YSCROLL TO 1 FOR NEXT TIME IRQ IS CALLED
    WE SCROLL EACH WAY TWO TIMES
    IF UDFLAG=1 THEN COPY EVEN COLOURS LINES TO SCREEN COLOUR MAP FROM SPARE COLOUR MAP 
    AND SWAP SCREEN
    IF UDFLAG=1 THEN COPY ODD COLOURS LINES TO SCREEN COLOUR MAP FROM SPARE COLOUR MAP 
    AND SWAP SCREEN 

IF YSCROLL=1 
    SET YSCROLL TO 3 FOR NEXT TIME IRQ IS CALLED

__SCROLL DOWN__

IF YSCROLL=4 
    ADD ONE TO UDFLAG
    IF UDFLAG NOT 1 OR 2 THEN QUIT OUT OF IRQ
    IF UDFLAG=1 THEN COPY SCREEN AND COLOUR UP ONE LINE
    IF UDFLAG=2 THEN SO MOVE MAP POINTER DOWN ONE LINE IF WE CAN
    SET $D011 TO 4
    SET YSCROLL TO 2 FOR NEXT TIME IRQ IS CALLED

IF YSCROLL=2		
    IF UDFLAG=1 THEN DRAW TOP PART OF TILE AT BOTTOM OF SCREEN
    IF UDFLAG=2 THEN DRAW BOTTOM PART OF TILE AT BOTTOM OF SCREEN
    SET $D011 TO 2
    SET YSCROLL TO 0 FOR NEXT TIME IRQ IS CALLED

IF YSCROLL=0	
    SET $D011 TO 0
    SET YSCROLL TO 6 NEXT TIME IRQ IS CALLED
    IF UDFLAG=1 THEN COPY COLOUR ODD LINE TO SCREEN COLOUR MAP AND SWAP SCREEN
    IF UDFLAG=2 THEN COPE COLOUR EVEN LINE TO SCREEN COLOUR MAP AND SWAP SCREEN

IF YSCROLL=6 
   SET YSCROLL TO 4 FOR NEXT TIME IRQ IS CALLED	

__SCROLL LEFT__ 

IF xscroll=3
    ADD ONE TO LRFLAG				
    SET XSCROLL TO 5 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 3 FOR SMOOTH SCROLL DOT POSITION
    IF LRFLAG NOT 1 OR 2 THEN THEN QUIT OUT OF IRQ
    IF LRFLAG=1 THEN SO MOVE MAP POINTER LEFT ONE POSITION IF WE CAN
    IF LRFLAG=2 THEN COPY SCREEN RIGHT ONE POSITION 

IF xscroll=5
    SET XSCROLL TO 7 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 5 FOR SMOOTH SCROLL DOT POSITION
    DRAW A SIDE OF THE TILE ON THE LEFT SIDE OF THE SCREEN

IF xscroll=7
    SET XSCROLL TO 1 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 7 FOR SMOOTH SCROLL DOT POSITION
    IF LRFLAG=1 THEN COPY COLOUR EVEN POSIION TO SCREEN COLOUR MAP AND SWAP SCREEN
    IF LRFLAG=2 THEN COPY COLOUR ODD POSITION TO SCREEN COLOUR MAP AND SWAP SCREEN

IF xscroll=1
    SET XSCROLL TO 3 FOR NEXT TIME IRQ IS CALLED

__SCROLL RIGHT__ 

IF xscroll=4
    ADD ONE TO LRFLAG
    IF LRFLAG NOT 1 OR 2 THEN QUIT OUT IRQ
    IF LRFLAG=1 THEN SO MOVE MAP POINTER RIGHT ONE POSITION IF WE CAN
    IF LRFLAG=2 THEN COPY SCREEN LEFT ONE POSITION 
    SET XSCROLL TO 0 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 0 FOR SMOOTH SCROLL DOT POSITION

IF xscroll=2
    DRAW LEFT OR RIGHT SIDE OF TILE TO RIGHT SIDE OF SCREEN
    SET XSCROLL TO 0 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 2 FOR SMOOTH SCROLL DOT POSITION

IF xscroll=0
    SET XSCROLL TO 6 FOR NEXT TIME IRQ IS CALLED
    SET $D016 TO 0 FOR SMOOTH SCROLL DOT POSITION
    IF LRFLAG=1 THEN COPY COLOUR ODD POSIION TO SCREEN COLOUR MAP AND SWAP SCREEN
    IF LRFLAG=2 THEN COPY COLOUR EVEN POSIION TO SCREEN COLOUR MAP AND SWAP SCREEN

IF xscroll=6
    SET XSCROLL TO 4 FOR NEXT TIME IRQ IS CALLED


See Part 1 & 2 For Source Code
Part1 and Part2 Needs To Be Run Together