BS EN 61158-4-7:2008

INTRODUCTION
1 Scope
2 Normative references
3 Terms, definitions, symbols and abbreviations
4 Overview of the DL-protocol
5 General structure and encoding of PhIDUs and
  DLPDUs and related elements of procedure
6 DLPDU-specific structure, encoding and element
  of procedure
7 DL-service elements of procedure, interfaces
  and conformance
Annex A (informative) - Exemplary FCS implementation
Annex B (informative) - Object modeling
Annex C (informative) - Topology of multi-segment
        DL-subnetwork
Annex D (informative) - Management of transmission
        errors
Bibliography
Annex ZA (normative) - Normative references to
         international publications with their
         corresponding European publications

Gives basic time-critical messaging communications between devices in an automation environment.

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 in a synchronously-starting cyclic manner, according to a pre-established schedule, and 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. 1.2 Specifications This standard specifies procedures for the timely transfer of data and control information from one data-link user entity to a peer user entity, and among the data-link entities forming the distributed data-link service provider; the structure of the fieldbus DLPDUs used for the transfer of data and control information by the protocol of this standard, and their representation as physical interface data units. 1.3 Procedures The procedures are defined in terms of the interactions between peer DL-entities (DLEs) through the exchange of fieldbus DLPDUs; the interactions between a DL-service (DLS) provider and a DLS-user in the same system through the exchange of DLS primitives; the interactions between a DLS-provider and a Ph-service provider in the same system through the exchange of Ph-service primitives. 1.4 Applicability These procedures are applicable to instances of communication between systems which support time-critical communications services within the data-link layer of the OSI or fieldbus reference models, and which require the ability to interconnect in an open systems interconnection environment. Profiles provide a simple multi-attribute means of summarizing an implementation’s capabilities, and thus its applicability to various time-critical communications needs. 1.5 Conformance This standard also specifies conformance requirements for systems implementing these procedures. This part of this standard does not contain tests to demonstrate compliance with such requirements.