CODESYS 3.5 - PLC Programming With Structures - Lesson 19 - Input Mapping Walkthrough

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In this lesson we explore the input mapping layer, the first stage in the project where real world signals enter the structured system. This layer is responsible for taking all physical inputs, including digital inputs, analog values and network delivered data, and placing them into the correct structures before the rest of the logic runs. By doing this at the very beginning of the scan cycle, we ensure the entire project works with clean, consistent and predictable data.

We begin by looking at the task execution order, where input mapping is always called first. This guarantees that process structures are up to date before any control logic or interlocks make decisions. From there we step through the mapping logic, starting with the simulation manager and auto feedback system. These allow you to toggle between live field data and simulated data while still using the exact same process structures downstream, which keeps testing predictable and avoids separate simulation pathways that can behave differently from the real project.

You will see how each device type has its own dedicated mapping function. Each function accepts the process structure, the simulation structure and the raw input, and decides which source should populate the process data for that scan. The benefit of this approach is that the rest of the program never needs to know whether the data came from a real input or a simulation model. Everything downstream simply reads the process data fields.

We also cover auto feedback, which is particularly useful when working with valves or other devices that require timely feedback during commissioning. This allows simulation feedback to be automatically set based on the commanded output, removing the need to manually click several inputs within a tight time window. It can be turned off when testing fault scenarios, giving you full control.

Finally, we look at how these mapped values originate from IO hardware or network layers, such as Modbus TCP in this project. The input mapping layer sits between those hardware abstractions and the main control logic, creating a clean handoff point where all inputs have been converted into their structured format.

By the end of this lesson you will understand how the input mapping layer forms the reliable entry point into the entire project. Once the structures are populated, every other part of the program can operate on consistent data, regardless of whether you are running on real hardware or in a full simulation environment.

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