对实验板上4*4矩阵键盘的16个按键S6---S21进行按键次数统计。键号06、07……21用最左边2位数码管显示，按键次数用右侧4位数码管显示。有键按下时，显示相应键号和该键累计按键次数，没键按下时，数码管不亮。（无论键号还是按键次数都用其十进制数显示。）-The experimental board 4* 4 matrix keyboard 16 keys S6--- S21 performed keystrokes statistics. No. 21 with key 06,07 ...