The design concept and implementation method of communication between master and slave stations are introduced taking the small PLC system of Siemens S7-200 series as an example. Undisturbed switching of control of the master and slave stations was achieved according to practical needs.%以西门子公司S7-200系列小型PLC系统为例，介绍了主从站通讯的设计思路及实现方法。根据实际使用的要求，解决了主从站控制权无扰动切换的问题。
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