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Define modbus server5/19/2023 The storage size of the characteristic (bytes). PARAM_TYPE_ASCII - ASCII string or binary data PARAM_TYPE_FLOAT - IEEE754 floating point format PARAM_TYPE_U8, PARAM_TYPE_U16, PARAM_TYPE_U32 - Unsigned integer 8/16/32 bit type It is optional field and can be set to zero if the parameter is not used in the application. It is used to calculate the absolute address to the characteristic in the storage structure. Offset to instance of the characteristic in bytes. Relative register address of the characteristic in the register area. MB_PARAM_INPUT, MB_PARAM_HOLDING, MB_PARAM_COIL, MB_PARAM_DISCRETE - represents Input, Holding, Coil and Discrete input register area accordingly The short address of the device with correspond parameter UID. String description of the characteristic. The identifier of characteristic (must be unique). The Data Dictionary is the list in the Modbus master which shall be defined by user to link each CID to its corresponding Modbus registers representation using Register Mapping table of the Modbus slave being used.Įach element in this data dictionary is of type mb_parameter_descriptor_t and represents the description of one physical characteristic: Table 1 Modbus master Data Dictionary description This approach allows the upper layer (e.g., MESH or MQTT) to be isolated from Modbus specifics thus simplify Modbus integration with other protocols/networks. The CID is linked to a corresponding Modbus registers through the table called Data Dictionary and represents device physical parameter (such as temperature, humidity, etc.) in specific Modbus slave device. The additional layer is called Modbus controller and its goal is to add an abstraction such as CID - characteristic identifier. The architectural approach of ESP_Modbus includes one level above standard Modbus IO driver. Refer to the Modbus Organization’s with protocol specifications for specifics. The following document (and included code snippets) requires some familiarity with the Modbus protocol. It does not require a checksum calculation, as lower layers already provide checksum protection. Modbus TCP/IP or Modbus TCP - This is a Modbus variant used for communications over TCP/IP networks, connecting over port 502. Modbus ASCII messages are framed by leading colon (“:”) and trailing newline (CR/LF). The ASCII format uses a longitudinal redundancy check checksum. Modbus ASCII - This is used in serial communication and makes use of ASCII characters for protocol communication. The RS-485 interface communication is usually used for this type. Modbus messages are framed (separated) by idle (silent) periods. A Modbus RTU message must be transmitted continuously without inter-character hesitations. Modbus RTU is the most common implementation available for Modbus. The RTU format follows the commands/data with a cyclic redundancy check checksum as an error check mechanism to ensure the reliability of data. Modbus RTU - This is used in serial communication and makes use of a compact, binary representation of the data for protocol communication.
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