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
a) in a synchronously-starting cyclic manner, according to a pre-established schedule, and
b) in a cyclic or acyclic asynchronous manner, as requested each cycle 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.
ABANDON
IEC 61158-4-19/FRAGF ED4
30.97
End of interruption of work - split/merged
Jan 6, 2021