The S7-200 series PLC offers three communication modes: Point-to-Point (PPI) communication, used for communication with the company's PLC programmer or other HMI products (its communication protocol is not publicly available); DP communication, which allows the PLC to connect to the PROFIBUS fieldbus network via the PROFIBUS-DP communication interface, thus expanding the PLC's application range; and Freeport communication, where the user defines the communication protocol to enable communication between the PLC and peripherals. The following demonstration uses Freeport communication to establish communication between a PC and an S7-200 series PLC.
The PC uses an RS232C interface, while the S7-200 series uses an RS485 port. Therefore, the PC's RS232 interface must first be connected to the PLC's communication port via an RS232/RS485 converter. The connection medium can be twisted-pair cable or cable. Siemens provides PC/PPI cables with built-in RS232/RS485 converters, allowing direct use of the PC/PPI cable. This makes it easy to connect the PLC and PC without adding any hardware, and also enables multi-point connections.
