1. 键值采用16进制编码，即16个按键分别对应显示16进制数
0~F，按键对应关系如下：最上面一行从左至右依次为0~3，
第二行从左至右依次为4~7，第三行从左至右依次为8~B，最
下面一行从左至右依次为C~F，其中b、d显示为小写，其他字
母大写；
2. 按键按下时显示当前键值并保持，直到下一按键被按下时更新
显示；
3. 只有按键被按下时蜂鸣器发出按键音，放开后蜂鸣器不发声。
4. 每个按键对应不同的按键音。(1. The key value is encoded in hexadecimal, i.e. 16 keys display hexadecimal numbers respectively

0 ~ F, the corresponding relationship of keys is as follows: the top line is 0 ~ 3 from left to right,

The second row is 4-7 from left to right, and the third row is 8-b from left to right

From left to right, the following line is C-F, where B and D are lower case, and other words

Capital letter;

2. When the key is pressed, the current key value will be displayed and maintained until the next key is pressed

Display;

3. Only when the key is pressed, the buzzer will emit a key tone, and when it is released, the buzzer will not emit a sound.

4. Each key corresponds to a different key tone.)