Up- and downloading of controller programs as well as status monitoring are handled with the Siemens S7-200 using the PPI interface. Connection to the PC used as a programming device is frequently implemented using the RS232/PPI Multi-Master cable. To extend this connection to a physically remote computer or to access from different work stations, a special serial cable with line drivers and if necessary a manual switcher generally needs to be installed. Alternative use of an Ethernet CP would necessitate modifying the S7 project/programm file. In addition, each individual PLC would needs its own CP.
Use of a Com-Server on the other hand provides a simple solution that works without any modifications to the controller program and usually eliminates any cabling expense. The RS232/PPI Multi-Master Cable is coinnected to the Com-Server instead of the PC. You install the COM Port Redirector on the PC and then simply tell Step7/Microwin on which virtual COM port it should look for the controller components - that’s it. The serial data are tunneled to the Com-Server and the controllers connected to it via TCP/IP or even over the Internet if needed.
The three essential steps are as follows:
The Com-Server is connected to the RS232/PPI Multi-Master Cable and the network.
The COM Port Redirector is used to create a virtual COM port on the STEP7 PCs, ...
...and the COM port is defined in STEP7/Microwin as a port for communicating with the S7.
Hard-/software versions used in the test: - Step7 Version 22.214.171.124 - RS232/PPI Multi-Master Cable - S7-200 CPU 222 Rel. 02.00 - Com-Server 58631, FW 1.46 - COM Port Redirector 2.52