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 port is displayed in binary form. (Press the keyboard to determine whether, when all the power the microcontroller IO port is high, S2 key grounded at one end and the other end P3.4, so when the key is pressed P3.4 port directly to ground, then the detection P3. 4 is definitely low.)