设计倒计时时钟

倒计时：当程序运行时，从59秒递减，以实现倒计时。该实验使用了8253A，8259A，数码管等，以了解这些芯片结合后的硬件设计和软件编程的方法

-Design countdown clock countdown: When program runs, decreasing from 59 seconds to achieve the countdown. The experiment used the 8253A, 8259A, digital tubes, etc., to understand the combination of these chips after the hardware design and software programming methods