说明：  ATmega的闹钟源码.适合初学入门者学习AVR的时钟，计计数器，中断模块，及数码管控制. 可直接使用。 已通过测试。
(The ATmega alarm source. Suitable for beginners beginners to learn the AVR clock, meter counter, interrupt module, and digital control systems. Can be used directly. Has been tested.)