ISO transmission protocol: used for data exchange between S7 stations and communication between PC stations, S5 stations and third-party systems;
characteristic:
1. Communication between stations is based on MAC address;
2. Data transmission using data blocks is suitable for 8Kbytes of data;
3. Data transmission can be realized by using send/receive and fetch/write services;
4. Data reception is confirmed by the other party through the fourth layer of the ISO reference model;
5. Data cannot be transmitted through routers. ISO does not support routing. Therefore, this protocol is based on MAC addresses instead of IP addresses;
ISO-on-TCP protocol: used for data exchange between S7 stations and communication between PC stations, S5 stations and third-party systems;
characteristic:
1. The communication between stations is based on IP addresses;
2. Data transmission using data blocks is suitable for 8Kbytes of data;
3. Data transmission can be realized by using send/receive and fetch/write services;
4. Data reception is confirmed by the other party through the fourth layer of the ISO reference model;
5. Data can be transmitted through routers;
UDP protocol: used for data exchange between two stations;
characteristic:
1. Unreliable transmission of related data blocks between two bytes (a 2048 data block is divided into two packets);
2. Support multicast. By establishing a multicast ring, multicast allows a group of stations to receive and send data to this group together;
3. Send/receive can be applied to realize data transmission;
4. Data can be transmitted through the router;
PPI communication
It is a communication protocol specially developed by Siemens for S7-200, which is built into the CPU.
characteristic:
1. Physically based on RS485 interface;
2. Master-slave protocol, the master station sends a request to the slave station equipment, the slave station responds, and the slave station cannot actively send information;
3. The PPI protocol does not limit the number of master stations communicating with a slave station, but in a network, the master station cannot exceed 32;
MPI communication
It is the interface of SIMATIC multipoint communication.
characteristic:
1. It is suitable for communication between a small number of sites, and is mostly used for short-distance communication between the upper computer and a small number of PLCs;
2. The communication rate is 19.2K-12Mbit/s, but directly connected to the MPI network of the PLC, the highest communication rate is 187.5KBIT/S, which is mainly limited by the communication rate of S7-200CPU;
3. In the MPI network, there can be up to 32 stations, the longest communication distance of a network segment is 50M, and the longer communication distance can be extended by RS485 repeater;
4. Master-master communication and master-slave communication are allowed, and the number of connections for each CPU communication port is 4;
5. MPI cannot communicate with a CPU as a PPI master station;
6. S7-200PLC can only be used as a slave station of MPI, not as a master station. S7-200PLC can only be accessed through PPI;
PROFIBUS
Fieldbus communication has good real-time performance. It is different from the PROFINET communication medium and has no connection.
characteristic:
1. Based on RS485 serial communication;
2. The maximum bandwidth is 12Mbps;
3. The data transmission method is half-duplex;
4. One-time data transmission is 32 bytes;
5. The maximum user data is 244bytes;
6. Special interface modules are required for configuration and diagnosis;
7. Special tools need to be used for network diagnosis;
8. There is generally only one master station in the network, and a multi-master station system will cause the DP cycle period to be too long;
9. An interface can only be used as a slave station or a master station;
classification:
1. PROFIBUS-DP (decentralized periphery) is a high-speed and low-cost communication used for communication between device-level control systems and distributed IO. It is often used for communication between controllers and between controllers and modules, which can replace the transmission of half DC24V signals;
2. PROFIBUS-PA (process automation) connects the communication between sensors and control agencies, which can replace 4-20ma analog quantity transmission;
3. PROFIBUS-FMS (filed bus message specification) is used in the workshop-level monitoring network. It is a token structure, real-time multi-master network, which transmits a large amount of data between controllers, and the real-time performance is not high;
PROFINET
Fieldbus communication has good real-time performance.
characteristic:
1. Based on industrial Ethernet;
2. Applications developed based on standard Ethernet can be directly applied to PROFINET;
3. The maximum bandwidth is 100Mbps;
4. The data transmission method is full duplex;
5. One-time data transmission is 254bytes;
6. The maximum user data is 1400bytes;
7. Use standard Ethernet card for configuration and diagnosis;
8. Use standard IT tools to perform network diagnosis;
9. There is no limit to the number of master stations in a network, any controller can run in the network, and multiple controllers will not affect the response time of IO;
10. An interface can be used as both a controller and an IO device;
