Finite state machines: 3-state counter
	Input			Next		Output
	q1	q0	x	q1+	q0+	z1	z0	D1	D0
	0	0	0	0	0	0	0	0	0
	0	0	1	0	1	0	0	0	1
	0	1	0	0	1	0	1	0	1
	0	1	1	1	0	0	1	1	0
	1	0	0	1	0	1	0	1	0
	1	0	1	0	0	1	0	0	0
	1	1	0	d	d	d	d	d	d
	1	1	1	d	d	d	d	d	d