利用定时器产生一个0~59秒的时钟并显示在数码管上，每过一秒将这个变化的数写入AT24C02。关闭电源，再次打开电源时，单片机先从AT24C02中将原来写入的数读出来，并继续变化显示在数码管上-Timer generates a 0 to 59-second clock and display digital tube, every second will change the number of write AT24C02. Turn off the power when the power is turned on again, the microcontroller will start with the AT24C02 originally written number is read out, and continue to change the display on the digital control