利用T0实现对外部脉冲的计数，利用按键模拟产生外部脉冲。计数值为1,4,7……时，LED0亮，LED1灭；计数值为2,5,8……时，LED1亮，LED0灭；每满10次计数，蜂鸣器鸣叫。(Using T0 to achieve external pulse count, the use of key to simulate the external pulse. The count value is 1,4,7...... When LED0 is bright and LED1 is out, the counting value is 2,5,8...... When the LED1 is bright, the LED0 is out; every 10 counts, the buzzer calls.)