说明：  PIC16F877实现按键扫描和数码管显示、蜂鸣片同时DD响，当按键下时，数码管加一，蜂鸣片DD响两次。
(PIC16F877 to achieve key-scan and digital tube display, beep sound piece at the same time DD, when the button when you are not, the digital control plus one, beep piece DD ring twice.)