Industrial communication networks - Fieldbus specifications - Part 4-1: Data-link layer protocol specification - Type 1 elements
|Publication Date:||1 December 2007|
|ICS Code (Data link layer):||35.100.20|
|ICS Code (Industrial process measurement and control):||25.040.40|
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.