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CODESYS 3.5

  • CODESYS PLC Course – Structured Programming With DUTs

    CODESYS PLC Course – Structured Programming With DUTs

    Liam (Site Owner) Liam (Site Owner)

    Estimated Time: 4 Hours

    Difficulty: 🔴🔴⭕⭕⭕

    Number of lessons: 29

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Expert Consulting | Liam Bee

PLC Automation Consulting

With 20+ years of real-world automation experience, I can help ensure you're project gets started in the best way possible.
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In this lesson we explore organization blocks, which are essential entry points that allow a PLC program to execute. Without at least one OB present, the CPU cannot run any user logic, even if the project contains many function blocks. OB1, the main cyclic program block, is the core routine that the CPU executes repeatedly, and it is where calls to other blocks are typically placed.

You see how to add OB1, how to choose the programming language, and how the declaration area allows constants and temporary variables. OB1 itself contains no retained memory, so it is not the place for complex logic or data storage. Instead, it serves as the program structure through which other blocks are executed, such as the ladder function block example shown in the lesson.

The startup OB is introduced next. Whenever the CPU transitions from stop to run, this OB executes a single time before OB1 begins scanning. Its presence alone changes CPU behavior because the PLC will always run it at startup if it exists, even if the block contains no logic.

Cyclic interrupt OBs are also covered. These blocks run at precise time intervals and interrupt the main program according to their configured priority. Each OB has attributes such as priority, event queuing, and timing settings, which influence how it behaves relative to other execution tasks. The lesson compares these priorities with OB1 and the startup OB to show how execution order is managed.

Additional OB types are outlined, including time delay interrupts, hardware interrupts, time error OBs for cycle time violations, diagnostic error OBs, and module related interrupts such as plug and pull events. The hardware interrupt OB is demonstrated in more detail, showing the data passed into the block such as hardware identifiers, event types, and pointers to diagnostic data.

Programming error OB is highlighted as useful during development to prevent the CPU from stopping on runtime errors. However, the lesson cautions strongly against leaving it in a finished project because it can hide serious faults like invalid memory access or divide by zero conditions.

Other OB categories such as time of day interrupts, motion control interrupts, and synchronous cycle tasks are briefly listed, noting that their use is more specialized.

The lesson concludes by reinforcing that OBs exist to organize and control program execution flow. They are not intended to contain large sections of logic but to structure how and when other blocks run within the PLC scan cycle.

#AlwaysLearning #Siemens #TIAPortal #Automation #PLC #HMI #TIA #DoAndGrow
The Complete Guide To TIA Portal V20 - Programming Basics - Organisation Blocks
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Latest Tip

Technology objects share the same Task Pane as sta Technology objects share the same Task Pane as standard instructions, but their visibility is conditional. Firmware version, installed licenses, and device capabilities all influence what appears.

This explains why two projects can show different instruction sets even on the same PC. The pane reflects what the target hardware can actually execute.

Engineers often misinterpret missing folders as software issues. In most cases, the project configuration or CPU selection is the limiting factor.

By tying instructions to real device capability, TIA Portal reduces configuration errors before deployment.

Watch more about this in The Complete Guide To TIA Portal V20 on YouTube: https://www.youtube.com/watch?v=pXX8jD81m_U

#AlwaysLearning #Siemens #TIAPortal #Automation #PLC #HMI #DoAndGrow

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PLC Automation Consultancy & Training | Liam Bee

Learn PLC automation properly, through structured courses, deep technical guides, and industrial consultancy.

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