IEC 61158-4-18:2007 defines the protocol that provides basic time-critical messaging communications between devices in an automation environment. This protocol provides communication opportunities to all participating data-link entities in a synchronously-starting cyclic manner, according to a pre-established schedule, and in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those data-link entities. This first edition and its companion parts of the IEC 61158-4 subseries cancel and replace IEC 61158-4:2003. This edition of IEC 61158-4 includes the following significant changes from the previous edition:
- deletion of the former Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data link layer, for lack of market relevance;
- addition of new types of fieldbuses;
- division of this part into multiple parts numbered -4-1, -4-2, , -4-19. This bilingual version (2014-12) corresponds to the monolingual English version, published in 2007-12.