PORTA	equ	0
PORTB	equ	1
DDRA	equ	2
DDRB	equ	3

	org	0800h
	movb	#$ff,DDRA
	movb	#$00,DDRB
	clr	PORTA
wait_1:	ldab	PORTB
	andb	#3
	beq	wait_1
	decb
	beq	more
less:	dec	PORTA
	bra	wait_2
more:	inc	PORTA

wait_2:	ldab	PORTB
	andb	#3
	bne	wait_2
	bra	wait_1