利用定时器产生一个0-99s变化的秒表 并显示在数码管上 每过一秒将这个变化写到AT24C02内部储存 再次上电时 单片机直接读AT24C02里的数据-Use the timer to generate a change in 0-99s and displayed on the digital stopwatch on this change with every passing second internal storage re-write AT24C02 microcontroller