DNP3 (Distributed Network Protocol 3) is a communication protocol used between automation components. The protocol is formulated with reference to IEC 870-5. The purpose is to unify the communication method of SCADA, enabling it to use the DNP3 protocol for communication with master stations, remote terminal units (RTUs), intelligent electronic devices (IEDs), etc., It is mainly used in utilities such as electric and water companies. The DNP3 protocol is reliable and is designed to enable stable communication in the adverse environments encountered by electric utility automation systems. It is specifically built to handle issues such as distortion caused by electromagnetic interference (EMI), aging components, and poor transmission media. The protocol employs a large number of CRC check codes to ensure the accuracy of data, making it suitable for data communication fields that require high security, moderate speed and medium data volume.
     Modbus TCP is a variant of the Modbus family, a simple and vendor-neutral communication protocol designed for supervising and controlling automation equipment. It specifically facilitates the use of Modbus messaging in both “Intranet” and “Internet” environment through TCP/IP protocols. The most common application of this protocols is connecting PLCs, I/O modules, and gateways to other simple field buses or I/O networks via Ethernet.
     The DNP-211-S is a gateway device that supports the protocol conversion between DNP3 Outstation and Modbus TCP Master. It can integrate multiple Modbus TCP I/O devices into a single DNP3 I/O device, allowing the DNP3 master station in the system to control the underlying Modbus TCP I/O devices through the DNP-211-S. On the Modbus side, the DNP-211-S supports common function codes such as 1, 2, 3, 4, 5, 6, 15, and 16. On the DNP3 side, it provides corresponding data groups such as 1, 10, 11, 30, 40, and 41. All Modbus TCP I/O data and DNP3 address mappings can be configured through the DNP-211-S utility software.