5x6矩阵键盘实现，基本思想：逐行扫描，列端口设置为上拉输入，先将第一行置低，检测列有没有被拉低的，没有则置低第二行，置高第一行，检测列有没有置低的，以此类推。-5x6 matrix keyboard realization, the basic idea: Progressive scan, the column is set to pull the input port, the first line of the first set low, there has not been pull