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Common protocols for industrial Ethernet
1 Modbus TCP/IP
The protocol, introduced by Schneider, embedded Modbus frames into TCP frames in a very simple way, combining Modbus with Ethernet and TCP / IP as Modbus TCP / IP. This is a connectivity-oriented approach, where each call requires a response, and this call / response mechanism is consistent with the primary / slave mechanism of Modbus, but greatly improves the constraints on the one-primary and multiple-slave polling mechanism through industrial Ethernet switching technology.
2 Profinet
Profinet Developed by Siemens and supported by Profibus International, it currently has 3 versions, with the first version defining automated components based on TCP / UDP / IP. The standard TCP / IP + Ethernet is used as the connection medium, and the standard TCP / IP protocol plus the RPC / DCOM of the application layer are used to complete the communication between nodes and network addressing. It can be attached to both traditional Profibus systems and new intelligent field devices. Existing Profibus segments can be connected to the Profinet network through a proxy device (proxy), enabling the entire Profibus devices and protocols to be used intact in the Profinet system. Traditional Profibus devices can communicate with COM objects above Profinet through agents, and realize calls between COM objects through OLE automation interface. It applies Ethernet to non-time-critical communication between high-level devices and Profibus-DP field equipment technology in order to integrate the real-time control domain to a high-level level through agents.
In the second version, Profinet opens two channels on Ethernet: the standard non-real-time communication channel using TCP / IP protocol, and the real-time channel, which bypasses the third and fourth layers, to provide accurate communication capabilities. This protocol reduces the data length to reduce the throughput of the communication stack. To optimize communication functions, Profinet defines the priority of packets according to IEEE 802.p. Up to 7 levels are available.
Profinet The third edition adopts a hardware scheme to narrow the software-based channel to further shorten the processing time of the communication stack software. To connect to integrated Ethernet switches, Profinet version 3 is also starting to address motion control solutions based on IEEE 1588 synchronous data transfer.
3 Ethernet/IP
Ethernet / IP is a protocol system suitable for industrial environment applications. It is the latest member of ODVA (Open Devicenet Vendors Asso-cation) and ControlNet International. Like DeviceNet and ControlNet, they are both networks based on the CIP (Control and Information Proto-Col) protocol. It is an object-oriented protocol, which can ensure the effective transmission of real-time I / O information and explicit information (including for configuration, parameter setting, diagnosis, etc.) on the network.
Ethernet / IP adopts the same application layer protocol CIP as Devicenet and ControlNet. Therefore, they use the same object library and consistent industry specifications, with good consistency. Ethernet / IP uses standard Ethernet and TCP / IP technologies to transmit CIP communication packages, so that the universal and open application layer protocol CIP plus the widely used Ethernet and TCP / IP protocol will constitute the architecture of Ethernet / IP protocol.
4 EtherCAT
EtherCAT (Ethernet for Control Automation Technology) is developed by BIF Beckhoff of Germany and supported by EtherCAT Technology Group (EtherCAT Technology Group, ETG). It takes Ethernet frames and sends data with a specific ring topology. Each station on the network takes data related to the station from the Ethernet frame, or inserts specific input / output data from the station itself. The last module within the network sends a frame to the first module to form and create a physical and logical ring.
EtherCAT Also through an internal priority system, real-time Ethernet frames have a higher priority over other data (such as configuration or diagnostic data, etc.). The configuration data is transmitted only transmitted in the gap of the real-time data (such as the gap time is sufficient), or through a specific channel. EtherCAT Standard Ethernet functionality is also retained and is compatible with the traditional IP protocol. To implement such a device, a dedicated ASIC chip is required to integrate at least two Ethernet ports and to employ a IEEE 1588-based temporal synchronization mechanism to support real-time applications in motion control.
5 Powerlink
Powerlink Developed by B & R and supported by the Ethernet Powerlink Standardization Group (Ethernet Powerlink Standardisation Group, EPSG).
The Powerlink protocol extends the TCP (UDP) / IP stack in the third and fourth layers. It controls the data flow on the network with the slot time communication network management (Slot Communication Network Management, SCNM) middleware on the shared Ethernet network segment. SCNM adopts the master-slave dispatching mode, and each station can only send real-time data only if it receives a request from the master station. Therefore, at a particular time, only one station has access to the bus, so there is no conflict, thus ensuring the real-time nature of the communication. For this purpose, the Powerlink requires a IEEE 1588-based time synchronization. In the second version of its extension, the CANopen-based communication and device line rules are included.
