Takes Japanese MITSUBISHI FX series and OMRON C series P type PLC as examples, simply analyzes the status of three PLC parts which related with outside circuit, the design of hardware circuit is given.

• 以日本三菱FX系列、欧姆龙C系列P型PLC为例 ,简要分析PLC与外部电路有联系的三部分情况 ,提出此方面的硬件电路设计