The Fieldbus Data Link protocol specification is a Data Link Layer Standard designed to support time-critical messaging communications to and from devices in an automation environment. Specifications This Standard specifies a) procedures for a single protocol 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; and b) the structure of the Fieldbus Data Link (DL) Protocol Data Units used for the transfer of data and control information@ and their representation as Physical Interface Data Units. Procedures The procedures are defined in terms of a) the interactions between peer DL-entities (DLEs) through the exchange of Fieldbus Data Link Protocol Data Units; b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system through the exchange of DLS primitives; and c) the interactions between a DLS-provider and a Physical service provider in the same system through the exchange of Physical service primitives. 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. Clause 10 specifies profiles for this Fieldbus protocol. Conformance This Standard also specifies conformance requirements for systems implementing these procedures. This part of ISA-S50.02 does not contain tests to demonstrate compliance with such requirements. The supplier of a protocol implementation which is claimed to conform to this Standard shall complete a copy of the PICS Proforma (see Annex E)@ and shall provide the information necessary to identify both the supplier and the implementation.