Study on S7-200 PPI Protocol Catching and its Communication Components

The S7 -200 series PLC of SIEMENS Company has been applied extensively, and the communication is the focus of the engineer concerned in the application. The PPI protocol, a communication protocol developed by SIEMENS Company especially for S7-200, is an un-opened inner protocol. However, the engineer wants to understand this protocol in order to develop and integrate control system independently. With the un-opened characteristic of the SIEMENS PPI protocol content, a new method to succeed in catching and testing the PPI protocol is proposed based on the technique of serial communications. A class of the PPI communication components is developed in the C++ Builder environment. It can be successfully applied to the practical control systems.