TwinCAT Variable Naming Guide

General Rules

• Use PascalCase for all public-facing symbols (e.g., I/O, HMI mappings, FB names, methods, properties).
• Use _camelCase for local/internal variables that are not mapped to I/O or HMI.
• Keep physical I/O and HMI commands/status clearly separated.
• Avoid using global variable lists (GVLs) or internal variables for HMI mapping.

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Physical I/O

• Declare in VAR_INPUT / VAR_OUTPUT sections of MAIN or in dedicated function blocks.
• Use PascalCase nouns or noun phrases.
• Examples:

StartButton
SystemPressure
PumpMotorCurrent

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HMI Mappings

• Declare in VAR_INPUT / VAR_OUTPUT of MAIN or FBs.
• Use PascalCase nouns or noun phrases.
• To help differentiate from Physical I/O:
  • Commands: Always use the Command suffix (e.g., StartCommand, StopCommand)
  • Statuses / Feedback: Use suffixes such as Status, Feedback, or Text as appropriate.

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Function Blocks

• Prefix with fb, followed by PascalCase name:

fbSumpPump
fbBurnerControl

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Methods

• Use PascalCase with a Verb or Verb–Noun pattern:

UpdateSetpoint
Reset
StartPump
StopPump

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Properties

• Use PascalCase nouns or noun phrases:

TargetTemperature
PumpRunHours
AlarmText

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VAR_INPUT

• Use PascalCase, nouns or noun phrases (e.g., StartButton, SetpointLevel, RecipeNumber). Use Command or Cmd suffix for commands (e.g., StartCommand).

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VAR_OUTPUT Names

• Use PascalCase, nouns or noun phrases (e.g., PumpStatus, LevelFeedback, AlarmText). Use Status, Feedback, or Text suffixes where applicable.

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Local Variables

• Use a leading underscore and camelCase:

_lastSetpoint
_alarmState
_previousPumpSpeed

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Mapping Notes

• Avoid exposing internal variables directly to HMI.
• Keep physical IO → FB → HMI mapping clear and traceable.

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Quick Reference Summary

- Public I/O & HMI: PascalCase
- FB instances: fbPascalCase
- Methods: VerbNoun PascalCase
- Locals: _camelCase
- Commands: Always use `Command` suffix
- Status/Feedback/Text suffixes for clarity