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

数值时钟pc版，内置实时模块，结合89C51单片机控制实现其时钟功能-The the numerical clock pc version, built-in real-time module, combined with the 89C51 microcontroller control the clock function

基于89C51可以实现LED全部点亮，轮流点亮，全部熄灭的功能。-89C51 can be achieved based on LED all light, turn lights, all out of function.

单片机89C51控制按键按钮，可以使用按键完成其功能-89C51 microcontroller control push buttons, you can use the button to perform its function