说明：   很不错的PLC学习书籍(PLC编程使用指南PDF档)，每章都用三菱、欧姆龙、西门子三种PLC进行描述。我觉得该书不注重讲某型号的PLC使用方法，而注重于PLC程序的设计方法，对初学者比较有用(我觉得)
(PLC is a good learning books (PLC Programming Guide PDF file), each chapter are Mitsubishi, Omron, Siemens PLC describe three. I think the book does not focus on a particular model which stresses the use of PLC, and PLC program focused on the design method, more useful for beginners (I think))