Sub-index does not exist (Register 0007)

What does 03 mean?

An attempt was made to access a sub-index of an array parameter through Holding Register 0007 that does not exist. This indicates an incorrect index number was provided when referencing an element within an array-type parameter, leading to an invalid memory access.

• The Modbus request to Holding Register 0007 specified an invalid sub-index for an array parameter (e.g., requesting Parameter 15-05[5] when only 0-3 exist).
• Typographical error in the Modbus master's program attempting to access an element beyond the array bounds.
• Attempting to use a sub-index on a parameter that is a single value, not an array.
• Firmware version differences: A parameter might have been an array in an older version but is now a single value, or vice versa, or the array size changed.
• Misunderstanding of how array parameters are addressed via Modbus; some systems require specific register offsets for sub-indices.

Click steps to track your progress.

1. 1

   Consult the drive's communication manual to confirm if the parameter is an array and what its valid sub-index range is (e.g., 0-3, 1-N).

2. 2

   Review the Modbus master's program (e.g., PLC code) to ensure the correct sub-index is being used for the target parameter in Holding Register 0007.

3. 3

   If the parameter is a single value, remove any sub-index notation from the Modbus request.

4. 4

   Verify the drive's firmware version (e.g., Parameter 15-05) and compare it to the parameter mapping documentation to ensure compatibility of array structures.

5. 5

   Test reading/writing different sub-indices (e.g., 0, 1) using a Modbus scanner tool to pinpoint the valid range of the array.