过8255A读取键盘电平获得输入密码，与预设密码比较，进而实现开锁、报错功能，并控制数显管和指示灯做出相应变化。还可实现密码修改功能-8255A reading level over the keyboard to enter a password to get, compared with the default password, thus achieving unlocking, error function, and control the digital display tubes and LEDs make the appropriate changes. But also to achieve the cipher modification