61158-4-1-2007 Industrial communication networks - Fieldbus specifications - Part 4-1: Data-link layer protocol specification - Type 1 elements (Edition 1.0)
Réseaux de communication industriels - Spécification des bus de terrain - Partie 4-1: Spécification du protocole de la couche liaison de données - ?léments de Type 1 (Edition 1.0)
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General The data-link layer provides basic time-critical messaging communications between devices in an automation environment. This protocol provides the data-link service by making use of the services available from the physical layer. The relationship between the International Standards for fieldbus data-link service@ fieldbus data-link protocol@ fieldbus physical service and systems management is described in IEC/TR 61158-1. This protocol provides communication opportunities to all participating data-link entities a) in a cyclic asynchronous manner@ sequentially to each of those data-link entities@ and b) in a synchronous manner@ either cyclically or acyclically@ according to a pre-established schedule. The specified protocol also provides means of changing the set of participating data-link entities and of modifying the set of scheduled communications opportunities. When the set of scheduled communications opportunities is null@ the distribution of communication opportunities to the participating data-link entities is completely asynchronous. Thus this protocol can be characterized as one which provides access asynchronously but with a synchronous overlay.