; clear screen with blitter

WIDTH  equ 20 ; 320 pixels in 16 bit chunks, 320/16 = 20
HEIGTH equ 256

clear:	btst	#14,$dff002
	bne.b	clear
	move.l	#screen,$dff054
	move.w	#$0100,$dff040
	clr.w	$dff042
	clr.l	$dff044
	move.w	#0,$dff066
	move.w	#[HEIGHT*64]+WIDTH,$dff058
	rts

;...

screen:	blk.b 40*256,0