IEC 61158-3-12:2019 defines the services provided to the Type 12 fieldbus application layer at the boundary between the application and data-link layers of the fieldbus reference model and systems management at the boundary between the data-link layer and systems management of the fieldbus reference model. This fourth edition cancels and replaces the third edition published in 2014. It constitutes a technical revision. The main changes are: - Technical corrections in the communication services - Editorial improvements for clarification.