1 Scope
1.1 General
The data-link layer provides basic time-critical messaging communications between devices in an automation environment.
This protocol provides communication opportunities to all participating data-link entities:
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• in a synchronously-starting cyclic manner, according to a pre-established schedule, or
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• in an acyclic manner, as requested by each of those data-link entities.
Thus, this protocol can be characterized as one which provides cyclic and acyclic access asynchronously
but with a synchronous restart of each cycle.