With 89C51, an external crystal oscillator, reset circuit, two digital tube, two...

代码说明：

用89C51，外接晶振，复位电路，二个数码管，二个按键，做一个电子秒表，具体要求为用按键起停电子表，可用按键设计倒计时时间(如10S，20S，60S),并启动倒计时功能,能用按键选择以上两功能之一-With 89C51, an external crystal oscillator, reset circuit, two digital tube, two buttons, making an electronic stopwatch, and specific requirements for the use button start-stop electronic watches, key design can be used countdown time (such as 10S, 20S, 60S), and start the countdown function, can be used for more than two buttons select one of the functions