Source: Jicheng Training Network (Teacher Liang Zhibin)
1.3.1 PPI Network
The PPI protocol is a communication protocol specifically developed for the S7-200. The communication ports (Port0/Port1) of the S7-200 CPU support the PPI communication protocol, and some communication modules of the S7-200 also support the PPI protocol. The PPI network communication of the S7-200 CPU is established on the hardware basis of the RS-485 network, so its connection properties and required network hardware devices are consistent with other RS-485 networks. The main features of the PPI protocol are:
• Master-slave protocol, with at least one master station in the network.
• Token ring network, with tokens passed between PPI master stations.
• The S7-200 can act as both a PPI master and a PPI slave.
• Communication rates can be set to 9.6Kbps, 19.2Kbps, and 187.5Kbps.
• Siemens internal protocol.
The PPI network has four main applications:
1. Programming and monitoring of the CPU using Micro/WIN software.
2. Data exchange between S7-200 units.
3. Communication between S7-200 and Human-Machine Interface (HMI).
4. OPC communication between S7-200 and host computers.
1.3.2 MPI Network
The MPI (Multipoint Interface) is the communication interface for SIMATIC S7 multipoint communication, suitable for communication between a small number of stations, commonly used for connecting host computers and a few PLCs for short-distance communication. The main features of MPI are:
• Master-slave protocol, with at least one master station in the network.
• Token ring network, with tokens passed between MPI master stations.
• The S7-200 can only act as an MPI slave.
• The MPI network can have a maximum of 32 stations.
• Communication rates can be set to 19.2Kbps or 187.5Kbps.
• Siemens internal protocol.
The MPI network of S7-200 has three main applications:
1. Communication between S7-200 and S7-300/400 controllers.
2. Communication between S7-200 and touch screens.
3. Programming and monitoring of S7-200 using Micro/WIN or host computer software.
1.3.3 Profibus Network
The S7-200 achieves Profibus-DP communication through the extended EM277 module. Its main features include:
• Master-slave protocol, with at least one master station in the network.
• Token ring network, with tokens passed between Profibus master stations.
• The S7-200 can only act as a Profibus network slave through the extended EM277 module.
• Communication rates range from 9.6Kbps to 12M.
The Profibus network of S7-200 has similar applications to MPI. Compared to the MPI network, its advantages are mainly reflected in four aspects:
1. Communication rate. Profibus can reach up to 12M.
2. Number of communication stations. The Profibus network can have 127 nodes.
3. Communication data volume. The MPI network is limited to 84 bytes, while the Profibus network can transmit 244 bytes of data at once (EM277 supports 64 bytes).
4. Openness. Profibus is an open protocol and is both an international and national fieldbus standard, with rich device support.
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The content of this article comes from: Jicheng paid video tutorial + accompanying internal book content “From Beginner to Expert on Siemens S7-200 PLC” Video link: http://www.jcpeixun.com/lesson/3/
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