IEC 61158-4-2:2007 describes the protocol that provides communication opportunities to all participating data-link entities, sequentially and in a cyclic synchronous manner. Foreground scheduled access is available for time-critical activities together with background unscheduled access for less critical activities. This protocol optimizes each access opportunity by concatenating multiple DLSDUs and associated DLPCI into a single DLPDU, thereby improving data transfer efficiency for data-link entities that actively source multiple streams of data. This first edition and its companion parts of the IEC 61158-4 subseries cancel and replace IEC 61158-4:2003. This edition of this part constitutes a minor revision. This part and its companion Type 2 parts also cancel and replace IEC/PAS 62413, published in 2005. This edition of IEC 61158-4 includes the following changes:
- 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 (2014-07) corresponds to the English version, published in 2007-12.
