微机原理实验四 并行I/O接口的拓展 了解并行接口的拓展方法，及8255A的工作原理、编程方法和使用方法
Microcomputer Principle Experiment 4 parallel I/O interfaces to expand the understanding of the parallel interface expansion method, and 8255A works, programming and use (2017-04-14, DOS, 4KB, 下载1次)