I am utilizing the DTM browser to conduct Modbus polling from an RTAC. While I am successful in retrieving points in the first polling object, I am encountering difficulties retrieving data in the second polling object. Due to the limit of 125 registers per object, I am required to utilize multiple polling objects. Thank you for your assistance.
The discrepancy in Unit ID between the first and second poll (254 vs. 255) raises questions about the Modbus Slave's behavior towards Unit IDs. Is the Modbus Slave capable of ignoring the Unit ID? It is important to note that the Modbus protocol imposes a maximum limit of 125 registers or 2000 bits (equivalent to 16 bits per word multiplied by 125 words) per transfer, as a design specification.
Have you made sure all devices in the second polling object have unique slave IDs and they don't overlap with that of the first object? Also, double-check all the settings such as baud rate, parity, stop bits to make sure they are correct and consistent with your devices. Additionally, ensure your device addresses are correctly mapped in your polling objects. Interference can also be an issue, so verify if the wiring is sturdy and away from high voltage lines to prevent noise.
It sounds like you've hit a common challenge with Modbus polling limits! One thing to check is whether the second polling object is correctly configured and that its register addresses are accurately defined. Sometimes a minor typo or misalignment in the address can cause data retrieval issues. Also, ensure that the timing between requests isn’t too short, as the RTAC may not be able to process them fast enough. If all else fails, consider using a tool to monitor the communication; it can give you insight into what's going wrong during polling. Good luck!
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Answer: Answer: To conduct Modbus polling using multiple objects in the DTM browser, you can create separate polling objects for each set of registers you want to retrieve data from. This is necessary when you reach the limit of 125 registers per object.
Answer: Answer: Difficulties in retrieving data from the second polling object could be due to configuration issues, incorrect Modbus addressing, or communication errors. Ensure that the settings for the second polling object are correctly configured and aligned with the Modbus device you are communicating with.
Answer: Answer: To overcome the limit of 125 registers per Modbus polling object in the DTM browser, you can create additional polling objects to retrieve data from more registers. By dividing the registers into multiple polling objects, you can effectively retrieve the desired data from your Modbus device.
Answer: Answer: It is recommended to organize your Modbus polling objects logically based on the registers you want to access. By structuring your polling objects in a systematic manner, you can efficiently manage and retrieve
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