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Modbus or MODBUS is a client/server data communications protocol in the application layer. [1] It was originally designed for use with programmable logic controllers (PLCs), [2] but has become a de facto standard communication protocol for communication between industrial electronic devices in a wide range of buses and networks.
A remote terminal unit (RTU) is a microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects. [1]
RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement industrial control systems, including the most common versions of Modbus and Profibus. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units.
The DNP User Group has established four levels of subsets of the protocol for RTU compliance. The DNP Users Group has published test procedures for Levels 1 and 2, the simplest implementations. The protocol is robust, efficient, and compatible with a wide range of equipment, but has become more complex and subtle over time.
Many are designed to send information only when the master station polls the RTU. Typical legacy SCADA protocols include Modbus RTU, RP-570, Profibus and Conitel. These communication protocols, with the exception of Modbus (Modbus has been made open by Schneider Electric), are all SCADA-vendor specific but are widely adopted and used.
IEC 60870-5-101 [IEC101] is a standard for power system monitoring, control & associated communications for telecontrol, teleprotection, and associated telecommunications for electric power systems.
Here we find the solutions Ethernet/IP, three versions of PROFINET IO - the classes A, B, and C - and the solutions of P-NET, [28] Vnet/IP [29] TCnet, [30] EtherCAT, Ethernet POWERLINK, Ethernet for Plant Automation (EPA), and also the MODBUS with a new Real-Time Publish-Subscribe MODBUS-RTPS and the legacy profile MODBUS-TCP.
The simplest and most commonly used conversion is protocol conversion between Modbus RTU and Modbus TCP. In this conversion, there is no change in the overall framing. Hence it is easy to take the Serial Modbus RTU frame and encapsulate it in a TCP/UDP socket and send it over Ethernet. Since both the protocol framings are the same, except for ...