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 is the default crystal 11.0592M not the same as the initial value when the need to modify