Although generally speaking, modularisation is not a new topic in the software industry, industrial control and automation software systems based on industrial computers recently received greater attention from academia and industry due to the impact of modularisation on managing software complexities, particularly changeability. While there is a direct correlation between coupling and modularisation and their impact on software changeability and reusability, not all modularisation techniques could bring higher changeability unless it is performed in the direction of changeability. How to modularise in the direction of changeability is the core topic of this paper.