+---+---------+ | p1.1 ------ ) --+---------+ | | 74hc08b + ----- a16 +---+---------+ | p1.2 ------ ) --+---------+ | | 74hc08c + ----- a17 +---+---------+ | p1.3 ------ ) --+---------+ | | 74hc08d + ----- a18 +---+---------+当p2.7=0, page 0 p2.7=1, page n , 由 p1.0..3 定