一个精确的50uS软件延时函数 特别在系统设计时定时器不够用的情况下特别方便，不过要注意单片机的晶振 默认的是11.0592M 不一样时需要对初始值进行修改,An accurate delay function 50uS software systems, especially in the design of the timer used in circumstances not special facilities, but attention should be paid to SCM i