说明：  本书为PLC编程从入门到精通的经典读物，介绍了西门子S7-200的基本工作原理，基本指令，书中还包含众多行业的丰富实例。
(This book is a classic reading material for PLC programming from introduction to mastery. It introduces the basic working principle and basic instructions of Siemens S7-200. It also contains rich examples of many industries.)