* = $1000

		
start		lda	$d011		;loads raster register 
		bpl	start		;is bit 7 set? if not, wait
					;now we are on a non visible area
					;so we can change background colour
					;with no flicker 


		ldx	#$00		;starting background colour black
		stx	$d021
		
		
loop1		jsr	pause


		
		inx

loop2		lda	$d011		;loads raster register 
		bpl	loop2		;is bit 7 set? if not, wait

					
		stx 	$d021		;sets colour
		
		bne	loop1		;x register is 0? if not, go to loop1

		jmp	start		;start again from the beginning

		
pause		ldy	#$00
		sty	delay
loop		iny
		bne	loop
		inc	delay
		lda	delay
		cmp	#150
		bne	loop		;note that the branch goes directly to the "iny"
					;instruction. no need to clear the y register as
					;it has already wrapped around to 0 (the first 
					;"loop" is exited when y register  = 0).
		rts

delay		byte	0