说明：  带校时和音乐报时功能时钟的设计与实现 介绍了I/O口输入与输出的应用，中断的应用，以及基于状态机思想的系统分析和系统设计
(With the school musical chime clock time and the design and implementation introduces I/O port input and output ports, interrupt the applications, and ideas based on state machine system analysis and system design)