由于51单片机的的I/O口才28个，有时满足不了多任务、复杂的任务，所以用74H165和74H595实现I/O口扩展。-Since the microcontroller 51 of I/O 28 eloquence, and sometimes can not meet the multi-task, complicated task, so use 74H165 and 74H595 achieve I/O port expansion.