50.02.4
ANSI/ISA-50.02, Part 4-1997 - Fieldbus Standard for Use in Industrial Control Systems Part 4: Data Link Protocol Specification
General reference, softbound, 442pp.
$219.00

Specifies the 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 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.

Scope:
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.

This Standard specifies 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 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.

The procedures are defined in terms of the interactions between peer DL-entities (DLEs) through the exchange of Fieldbus Data Link Protocol Data Units; the interactions between a DL-service (DLS) provider and a DLS-user in the same system through the exchange of DLS primitives; and the interactions between a DLS-provider and a Physical service provider in the same system through the exchange of Physical service primitives.

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.

This Standard also specifies conformance requirements for systems implementing these procedures. This document 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.

Purpose:
The purpose of this document is to define the Fieldbus Data Link Protocol. It is most closely related to, and lies within the field of application of, the Fieldbus Data Link Service Definition.

The Data Link Protocol provides the Data Link Service by making use of the services available from the Physical Layer. The relationship between the Standards for Fieldbus Data Link Service, Fieldbus Data Link Protocol, Fieldbus Physical Service, and OSI Network or Fieldbus Application Protocol is illustrated in Figure 1.

The primary aim of this Standard is to provide a set of rules for communication expressed in terms of the procedures to be carried out by peer Data Link entities at the time of communication. These rules for communication are intended to provide a sound basis for development in order to serve a variety of purposes:

• as a guide for implementors and designers;
• for use in the testing and procurement of equipment;
• as part of an agreement for the admittance of systems into the open systems environment; and
• as a refinement to the understanding of time-critical communications within OSI.

This Standard is concerned, in particular, with the communication and interworking of sensors, effectors and other automation devices. By using this Standard, together with other standards positioned within the OSI or Fieldbus Reference Models, otherwise incompatible systems may work together in any combination.