Modbus RTU FAQ

Unable to Read Tag Value, Error Code 3002

  • Enable DEBUG logging, check the log, inspect the data flow, and verify if the device has responded with data. If there is a response, check if the data is correct (serial devices may produce exceptions when multiple upstream masters collect data).
  • Check if the station number is correct.
  • Verify if the address is correct (Modbus address for Neuron starts from 1).
  • Some devices may not support reading a single point at a time, so all points need to be configured (Neuron automatically optimizes batch reading).
  • Serial wiring issues.
  • Incorrect serial port configuration.
  • The device supports Modbus TCP protocol instead of Modbus RTU. Try using the Modbus TCP plugin.

Tag Value Invalid, Error Code 3008

  • The device is offline, and data cannot be updated.
  • The device does not respond with data within a certain period.
  • The device supports Modbus TCP protocol instead of Modbus RTU. Try using the Modbus TCP plugin.

Tag Value Read does not Match Expectations

  • Incorrect data type.
  • Incorrect byte order.
  • Presence of multiple upstream masters collecting data results in data corruption.
  • The DTU has enabled registration or heartbeat packets, causing Neuron to consider data flow data as incorrect.
  • The device actively uploads data, but the standard Modbus only supports requesting and then responding with corresponding data.
  • The device supports Modbus TCP protocol instead of Modbus RTU. Try using the Modbus TCP plugin.