参考两个链接：
http://www.ad.siemens.com.cn/service/answer/solution.aspx?Q_ID=74626&cid=1029
https://support.industry.siemens.com/cs/document/80925383/plcsim%E4%BB%BF%E7%9C%9Fs7-400%E4%B9%8B%E9%97%B4%E7%9A%84s7%E9%80%9A%E8%AE%AF?dti=0&lc=zh-CN
