同步减法
........\bcd7.v
........\debounce.v
........\sub2.bit
........\sub2.ucf
........\sub2.v
........\sub2_tb.v
同步加法
........\bcd7.v
........\counter.bit
........\counter.ucf
........\counter.v
........\counter_tb.v
........\debounce.v
异步减法
........\bcd7.v
........\debounce.v
........\sub.bit
........\sub.ucf
........\sub.v
........\sub_tb.v
异步加法
........\bcd7.v
........\counter2.bit
........\counter2.ucf
........\counter2.v
........\counter2_tb.v
........\debounce.v