对独立键盘S2 键的按键次数进行统计，并在与P1 口相连的八个发光二极管上以二进制形式显示出来。（判断是否按下键盘，当单片机上电时所有IO 口为高电平，S2 键一端接地另一端接P3.4，所以当键被按下时P3.4 口直接接地，此时检测P3.4 肯定为低电平。）-S2 of independent keyboard keystrokes key statistics, and in the eight light-emitting diodes are connected with the P1 p