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Get structure details using StructureLoader

Overview

StructureLoader is a function block that recursively loads information about a structure (and nested structures) whose variable name is provided via a reference string. It collects metadata such as total size, number of entries, and detailed entry descriptions in StructDetails. This can also be used to detect changes in the structure and list the exact variable that was changed.

Contract (inputs / outputs)

  • Inputs
  • Enable : BOOL — When set to TRUE, triggers a recursive load of the structure specified by StructAdr.

  • StructAdr : REFERENCE TO STRING[200] — Reference to a string containing the name (address) of the structure to load.

  • Outputs

  • Busy : BOOL — TRUE while the loader is actively working.
  • Done : BOOL — TRUE when the load completes successfully.
  • Error : BOOL — TRUE if an error occurred during loading.
  • ErrorText : STRING[200] — Human-readable text describing the error (when Error is TRUE).
  • ErrorCode : UINT — Numeric error code for programmatic checks.
  • StructSize : UDINT — Total size in bytes (or units defined by implementation) of the loaded structure.
  • StructEntries : UINT — Number of entries (variables/members) discovered.

  • StructDetails : ARRAY[0..MAX_VARIABLE_IDX] OF StructLoad_Data_TYP — Array containing detailed metadata for each discovered variable.

  • Internal

  • Internal : StructInternal_TYP — Internal state type used for the loader's operation (not intended for external use).

Constants (from StructVariables.var)

The loader relies on a small set of project-wide constants defined in StructVariables.var. Below are the constants with their default values and recommended usage.

  • MAX_STRUCT_DEPTH : UINT := 10 — Maximum recursion depth when traversing nested structures. If your structures contain deeper nesting, increase this value to avoid ERR_MAX_RECURSIONS.

  • MAX_VARIABLE_IDX : UINT := 100 — Maximum number of variable entries the loader can record (this includes expanded array indices). This value defines the upper bound for the StructDetails array: ARRAY[0..MAX_VARIABLE_IDX] OF StructLoad_Data_TYP. Increase when you expect more members than this limit.

  • MAX_VARIABLE_NAME_LEN : UINT := 200 — Maximum length allowed for a fully qualified variable name passed in StructAdr. If you have long namespaces or deep instance paths, increase this value. Note that the loader checks and reports ERR_VAR_TO_LONG when the total name length exceeds the supported limit.

  • OVERRIDE : UINT := 2 — Number of executions per cycle. Increasing this value can speed up loading for large structures but may impact cycle time. Adjust based on performance needs.

Error handling

  • Check Error after Busy clears and Done is TRUE. When Error = TRUE use ErrorText and ErrorCode to determine the cause.