实现一个中断处理程序，要求在主程序运行过程中，每隔20秒响铃一次，同时在屏幕上显示信息“The bell is ring!”,按键后恢复原状。-Achieve an interrupt handling procedures, the requirements at the main program is running every 20 seconds ringing once, at the same time information on the screen " The bell is ring!" , After the keys restitution.