说明：  此题目是通过键盘来实现密码输入是否正确，正确的时候数码管亮，否则发出报警声。 判断是按键还是干扰是非常有用的，它体现了一个系统的抗干扰能力。高低电平在瞬间的变换是很正常的，如果没有这条语句，系统很容易出错。 其中2秒是由定时器0来完成的。 在程序的定时器中断中，用switch代替了if else结构，使得程序的可读性大大增强。 TH0 = (65536-50000) / 256 TL0 = (65536-50000) 256 使得TH0 = 3CH, TL0 = B0H,由于该单片机的晶振为12MHz 因此定时时间就为0.05ms.在定时器中断服务程序中用FLASH计数，当计数达到40时正好是2秒。
(This topic is through the keyboard to realize the correct password is correct, when GuanLiang digital alarm sound, otherwise. Judgment is a key or interference is very useful, it reflects the anti-interference ability of a system. High level in the instant transformation is very normal, if not this statement, the system is very easy to make a mistake. 2 seconds is accomplished by the timer 0. In the process of the timer interrupt, switch with replaced if else structure, make the readability of the procedures enhanced greatly. TH0 = (65536-50000)/256, TL0 = (65536-50000) 256, Make TH0 3CH, TL0 = = B0H, because the MCU crystals for 12MHz, So regularly time is 0.05 ms in timer interrupt service routines, when using FLASH counting 40 count when exactly 2 seconds.)