Industrial communication networks - Fieldbus specifications - Part 5-18: Application layer service definition - Type 18 elements

The fieldbus application layer (FAL) provides user programs with a means to access the fieldbus communication environment. In this respect, the FAL can be viewed as a "window between corresponding application programs." This part of IEC 61158 provides common elements for basic time-critical and non-time-critical messaging communications between application programs in an automation environment and material specific to Type 18 fieldbus. The term "time-critical" is used to represent the presence of a time-window, within which one or more specified actions are required to be completed with some defined level of certainty. Failure to complete specified actions within the time window risks failure of the applications requesting the actions, with attendant risk to equipment, plant and possibly human life. This part of IEC 61158 define in an abstract way the externally visible service provided by the Type 18 fieldbus application layer in terms of a) an abstract model for defining application resources (objects) capable of being manipulated by users via the use of the FAL service, b) the primitive actions and events of the service; c) the parameters associated with each primitive action and event, and the form which they take; and d) the interrelationship between these actions and events, and their valid sequences. The purpose of this part of IEC 61158 is to define the services provided to 1) the FAL user at the boundary between the user and the Application Layer of the Fieldbus Reference Model, and 2) Systems Management at the boundary between the Application Layer and Systems Management of the Fieldbus Reference Model. This part of IEC 61158 specifies the structure and services of the Type 18 IEC fieldbus Application Layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498) and the OSI Application Layer Structure (ISO/IEC 9545). FAL services and protocols are provided by FAL application-entities (AE) contained within the application processes. The FAL AE is composed of a set of object-oriented Application Service Elements (ASEs) and a Layer Management Entity (LME) that manages the AE. The ASEs provide communication services that operate on a set of related application process object (APO) classes. One of the FAL ASEs is a management ASE that provides a common set of services for the management of the instances of FAL classes. Although these services specify, from the perspective of applications, how request and responses are issued and delivered, they do not include a specification of what the requesting and responding applications are to do with them. That is, the behavioral aspects of the applications are not specified; only a definition of what requests and responses they can send/receive is specified. This permits greater flexibility to the FAL users in standardizing such object behavior. In addition to these services, some supporting services are also defined in this standard to provide access to the FAL to contro l certain aspects of its operation.

Industrielle Kommunikationsnetze - Feldbusse - Teil 5-18: Dienstfestlegungen des Application Layer (Anwendungsschicht) - Typ 18-Elemente

Réseaux de communication industriels - Spécifications des bus de terrain - Partie 5-18: Définition des services des couches d'application - Eléments de type 18

Industrijska komunikacijska omrežja - Specifikacije za procesno vodilo - 5-18. del: Definicija opravil na aplikacijskem nivoju - Elementi tipa 18 (IEC 61158-5-18:2007)

General Information

Status
Withdrawn
Publication Date
30-Jun-2008
Withdrawal Date
26-Aug-2012
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
09-Jul-2012
Due Date
01-Aug-2012
Completion Date
27-Aug-2012

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SLOVENSKI STANDARD
SIST EN 61158-5-18:2008
01-julij-2008
1DGRPHãþD
SIST EN 61158-5:2004
Industrijska komunikacijska omrežja - Specifikacije za procesno vodilo - 5-18. del:
Definicija opravil na aplikacijskem nivoju - Elementi tipa 18 (IEC 61158-5-18:2007)
Industrial communication networks - Fieldbus specifications - Part 5-18: Application layer
service definition - Type 18 elements
Industrielle Kommunikationsnetze - Feldbusse - Teil 5-18: Dienstfestlegungen des
Application Layer (Anwendungsschicht) - Typ 18-Elemente
Réseaux de communication industriels - Spécifications des bus de terrain - Partie 5-18:
Définition des services des couches d'application - Eléments de type 18
Ta slovenski standard je istoveten z: EN 61158-5-18:2008
ICS:
25.040.40 Merjenje in krmiljenje Industrial process
industrijskih postopkov measurement and control
35.100.70 Uporabniški sloj Application layer
35.110 Omreževanje Networking
SIST EN 61158-5-18:2008 en,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

EUROPEAN STANDARD
EN 61158-5-18

NORME EUROPÉENNE
March 2008
EUROPÄISCHE NORM

ICS 35.100.70; 25.040.40 Partially supersedes EN 61158-5:2004


English version


Industrial communication networks -
Fieldbus specifications -
Part 5-18: Application layer service definition -
Type 18 elements
(IEC 61158-5-18:2007)


Réseaux de communication industriels -  Industrielle Kommunikationsnetze -
Spécifications des bus de terrain - Feldbusse -
Partie 5-18: Définition des services Teil 5-18: Dienstfestlegungen
des couches d'application - des Application Layer
Eléments de type 18 (Anwendungsschicht) -
(CEI 61158-5-18:2007) Typ 18-Elemente
(IEC 61158-5-18:2007)




This European Standard was approved by CENELEC on 2008-02-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2008 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61158-5-18:2008 E

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EN 61158-5-18:2008 - 2 -
Foreword
The text of document 65C/475/FDIS, future edition 1 of IEC 61158-5-18, prepared by SC 65C, Industrial
networks, of IEC TC 65, Industrial-process measurement, control and automation, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 61158-5-18 on 2008-02-01.
This and the other parts of the EN 61158-5 series supersede EN 61158-5:2004.
With respect to EN 61158-5:2004 the following changes were made:
– deletion of Type 6 fieldbus for lack of market relevance;
– addition of new fieldbus types;
– partition into multiple parts numbered 5-2, 5-3, …, 5-20.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
(dop) 2008-11-01
national standard or by endorsement
– latest date by which the national standards conflicting
(dow) 2011-02-01
with the EN have to be withdrawn
NOTE  Use of some of the associated protocol types is restricted by their intellectual-property-right holders. In all cases, the
commitment to limited release of intellectual-property-rights made by the holders of those rights permits a particular data-link layer
protocol type to be used with physical layer and application layer protocols in type combinations as specified explicitly in the
EN 61784 series. Use of the various protocol types in other combinations may require permission from their respective
intellectual-property-right holders.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61158-5-18:2007 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61131-1 NOTE  Harmonized as EN 61131-1:2003 (not modified).
IEC 61131-3 NOTE  Harmonized as EN 61131-3:2003 (not modified).
IEC 61158-3-18 NOTE  Harmonized as EN 61158-3-18:2008 (not modified).
IEC 61158-4-18 NOTE  Harmonized as EN 61158-4-18:2008 (not modified).
IEC 61158-6-18 NOTE  Harmonized as EN 61158-6-18:2008 (not modified).
IEC 61784-1 NOTE  Harmonized as EN 61784-1:2008 (not modified).
IEC 61784-2 NOTE  Harmonized as EN 61784-2:2008 (not modified).
ISO 8601 NOTE  Harmonized as EN 28601:1992 (not modified).
ISO/IEC 8877 NOTE  Harmonized as EN 28877:1993 (not modified).
__________

---------------------- Page: 3 ----------------------

- 3 - EN 61158-5-18:2008
Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

1) 2)
IEC 60559 - Binary floating-point arithmetic for HD 592 S1 1991
microprocessor systems


IEC/TR 61158-1 2007 Industrial communication networks - - -
Fieldbus specifications -
Part 1: Overview and guidance for the
IEC 61158 and IEC 61784 series


1) 2)
ISO/IEC 7498-1 - Information technology - Open Systems EN ISO/IEC 7498-1 1995
Interconnection - Basic Reference Model:
The Basic Model


1)
ISO/IEC 8822 - Information technology - Open Systems - -
Interconnection - Presentation service
definition


1)
ISO/IEC 8824 - Information technology - Open Systems - -
Interconnection - Specification of Abstract
Syntax Notation One (ASN.1)


1)
ISO/IEC 9545 - Information technology - Open Systems - -
Interconnection - Application Layer structure




1)
Undated reference.
2)
Valid edition at date of issue.

---------------------- Page: 4 ----------------------

IEC 61158-5-18
Edition 1.0 2007-12
INTERNATIONAL
STANDARD

Industrial communication networks – Fieldbus specifications –
Part 5-18: Application layer service definition – Type 18 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
W
ICS 35.100.70; 25.040.40 ISBN 2-8318-9471-9

---------------------- Page: 5 ----------------------

– 2 – 61158-5-18 © IEC:2007(E)
CONTENTS
FOREWORD.3
INTRODUCTION.4
1 Scope.6
1.1 Overview .6
1.2 Specifications .7
1.3 Conformance.7
2 Normative references .7
3 Terms, definitions, abbreviations, and conventions .8
3.1 Referenced terms and definitions .8
3.2 Additional terms and definitions for distributed automation .8
3.3 Abbreviations and symbols .9
3.4 Conventions .9
4 Concepts .9
4.1 Common concepts.9
4.2 Type specific concepts .9
5 Data type ASE.11
5.1 General .11
5.2 Formal definition of data type objects .11
5.3 FAL defined data types.11
5.4 Data type ASE service specification .14
6 Communication model specification .14
6.1 General .14
6.2 ASEs .14
6.3 ARs .23
Bibliography.38

Table 1 – AR types .9
Table 2 – Process data support level .10
Table 3 – Get Attributes service parameters .15
Table 4 – Set Attributes service parameters.16
Table 5 – Error indication parameters .16
Table 6 – Connect service parameters .17
Table 7 – Disconnect service parameters.17
Table 8 – Start scan service parameters .18
Table 9 – Stop scan service parameters .18
Table 10 – M1 Verify slave configuration service parameters .25
Table 11 – Stop scan service parameters .26
Table 12 – M2 Verify slave configuration service parameters .27
Table 13 – Get Attributes service parameters .30
Table 14 – Set Attributes service parameters.30
Table 15 – Error indication parameters .31

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61158-5-18 © IEC:2007(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –

Part 5-18: Application layer service definition - Type 18 elements


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
NOTE  Use of some of the associated protocol types is restricted by their intellectual-property-right holders. In all
cases, the commitment to limited release of intellectual-property-rights made by the holders of those rights permits
a particular data-link layer protocol type to be used with physical layer and application layer protocols in type
combinations as specified explicitly in the IEC 61784 series. Use of the various protocol types in other
combinations may require permission of their respective intellectual-property-right holders.
International Standard IEC 61158-5-18 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This first edition and its companion parts of the IEC 61158-5 subseries cancel and replace
IEC 61158-4:2003. This edition of this part constitutes a technical addition.
This edition of IEC 61158-5 includes the following significant changes from the previous
edition:
a) deletion of the former Type 6 fieldbus for lack of market relevance;
b) addition of new types of fieldbuses;
c) partition of part 5 of the third edition into multiple parts numbered -5-2, -5-3, …

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– 4 – 61158-5-18 © IEC:2007(E)
The text of this standard is based on the following documents:
FDIS Report on voting
65C/475/FDIS 65C/486/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under http://webstore.iec.ch in the
data related to the specific publication. At this date, the publication will be:
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
NOTE  The revision of this standard will be synchronized with the other parts of the IEC 61158 series.
The list of all the parts of the IEC 61158 series, under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.

---------------------- Page: 8 ----------------------

61158-5-18 © IEC:2007(E) – 5 –
INTRODUCTION
This part of IEC 61158 is one of a series produced to facilitate the interconnection of
automation system components. It is related to other standards in the set as defined by the
“three-layer” fieldbus reference model described in IEC/TR 61158-1.
The application service is provided by the application protocol making use of the services
available from the data-link or other immediately lower layer. This standard defines the
application service characteristics that fieldbus applications and/or system management may
exploit.
Throughout the set of fieldbus standards, the term “service” refers to the abstract capability
provided by one layer of the OSI Basic Reference Model to the layer immediately above. Thus,
the application layer service defined in this standard is a conceptual architectural service,
independent of administrative and implementation divisions.

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– 6 – 61158-5-18 © IEC:2007(E)
DIGITAL DATA COMMUNICATIONS FOR MEASUREMENT AND CONTROL –
FIELDBUS SPECIFICATIONS –

Part 5-18: Application layer service definition - Type 18 elements


1 Scope
1.1 Overview
The fieldbus application layer (FAL) provides user programs with a means to access the
fieldbus communication environment. In this respect, the FAL can be viewed as a “window
between corresponding application programs.”
This part of IEC 61158 provides common elements for basic time-critical and non-time-critical
messaging communications between application programs in an automation environment and
material specific to Type 18 fieldbus. The term “time-critical” is used to represent the
presence of a time-window, within which one or more specified actions are required to be
completed with some defined level of certainty. Failure to complete specified actions within
the time window risks failure of the applications requesting the actions, with attendant risk to
equipment, plant and possibly human life.
This part of IEC 61158 define in an abstract way the externally visible service provided by the
Type 18 fieldbus application layer in terms of
a) an abstract model for defining application resources (objects) capable of being
manipulated by users via the use of the FAL service,
b) the primitive actions and events of the service;
c) the parameters associated with each primitive action and event, and the form which they
take; and
d) the interrelationship between these actions and events, and their valid sequences.
The purpose of this part of IEC 61158 is to define the services provided to
1) the FAL user at the boundary between the user and the Application Layer of the Fieldbus
Reference Model, and
2) Systems Management at the boundary between the Application Layer and Systems
Management of the Fieldbus Reference Model.
This part of IEC 61158 specifies the structure and services of the Type 18 IEC fieldbus
Application Layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498) and
the OSI Application Layer Structure (ISO/IEC 9545).
FAL services and protocols are provided by FAL application-entities (AE) contained within the
application processes. The FAL AE is composed of a set of object-oriented Application
Service Elements (ASEs) and a Layer Management Entity (LME) that manages the AE. The
ASEs provide communication services that operate on a set of related application process
object (APO) classes. One of the FAL ASEs is a management ASE that provides a common
set of services for the management of the instances of FAL classes.
Although these services specify, from the perspective of applications, how request and
responses are issued and delivered, they do not include a specification of what the requesting
and responding applications are to do with them. That is, the behavioral aspects of the
applications are not specified; only a definition of what requests and responses they can
send/receive is specified. This permits greater flexibility to the FAL users in standardizing

---------------------- Page: 10 ----------------------

61158-5-18 © IEC:2007(E) – 7 –
such object behavior. In addition to these services, some supporting services are also defined
in this standard to provide access to the FAL to control certain aspects of its operation.
1.2 Specifications
The principal objective of this part of IEC 61158 is to specify the characteristics of conceptual
application layer services suitable for time-critical communications, and thus supplement the
OSI Basic Reference Model in guiding the development of application layer protocols for time-
critical communications.
A secondary objective is to provide migration paths from previously-existing industrial
communications protocols. It is this latter objective which gives rise to the diversity of services
standardized as the various Types of IEC 61158, and the corresponding protocols
standardized in subparts of IEC 61158-6.
This specification may be used as the basis for formal Application Programming-Interfaces.
Nevertheless, it is not a formal programming interface, and any such interface will need to
address implementation issues not covered by this specification, including
a) the sizes and octet ordering of various multi-octet service parameters, and
b) the correlation of paired request and confirm, or indication and response, primitives.
1.3 Conformance
This part of IEC 61158 does not specify individual implementations or products, nor do they
constrain the implementations of application layer entities within industrial automation
systems.
There is no conformance of equipment to this application layer service definition standard.
Instead, conformance is achieved through implementation of conforming application layer
protocols that fulfill the Type 18 application layer services as defined in this part of IEC 61158.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60559, Binary floating-point arithmetic for microprocessor systems
IEC/TR 61158-1 (Ed.2.0), Industrial communication networks – Fieldbus specifications –
Part  1: Overview and guidance for the IEC 61158 and IEC 61784 series
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model – Part 1: The Basic Model
ISO/IEC 8822, Information technology – Open Systems Interconnection – Presentation service
definition
ISO/IEC 8824, Information Technology – Abstract Syntax notation One (ASN-1): Specification
of basic notation
ISO/IEC 9545, Information technology – Open Systems Interconnection – Application Layer
structure

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– 8 – 61158-5-18 © IEC:2007(E)
3 Terms, definitions, abbreviations, and conventions
3.1 Referenced terms and definitions
3.1.1 ISO/IEC 7498-1 terms
For the purposes of this document, the following terms as defined in ISO/IEC 7498-1 apply:
a) application entity
b) application process
c) application protocol data unit
d) application service element
e) application entity invocation
f) application process invocation
g) application transaction
h) real open system
i) transfer syntax
3.1.2 ISO/IEC 8822 terms
For the purposes of this document, the following terms as defined in ISO/IEC 8822 apply:
a) abstract syntax
b) presentation context
3.1.3 ISO/IEC 9545 terms
For the purposes of this document, the following terms as defined in ISO/IEC 9545 apply:
a) application-association
b) application-context
c) application context name
d) application-entity-invocation
e) application-entity-type
f) application-process-invocation
g) application-process-type
h) application-service-element
i) application control service element
3.1.4 ISO/IEC 8824 terms
For the purposes of this document, the following terms as defined in ISO/IEC 8824 apply:
a) object identifier
b) type
3.2 Additional terms and definitions for distributed automation
For the purposes of this document, the following terms and definitions apply.
3.3
Register X
register containing bit-oriented cyclic data of type input data that is transmitted from a slave to
a master

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61158-5-18 © IEC:2007(E) – 9 –
3.4
Register Y
register containing bit-oriented cyclic data of type output data that is transmitted from a
master to a slave
3.5
Register Wr
register containing word-oriented cyclic data of type input data that is transmitted from a slave
to a master
3.6
Register Ww
register containing word-oriented cyclic data of type output data that is transmitted from a
master to a slave
3.7 Abbreviations and symbols
RX Register X
RY Register Y
RWr Register Wr
RWw Register Ww
3.8 Conventions
There are no conventions defined specific to Type 18 FAL.
4 Concepts
4.1 Common concepts
IEC/TR 61158, Clause 9 describes the concepts of the application layer service descriptions
and the templates used in this document, except as specifically overridden in 4.2.
4.2 Type specific concepts
4.2.1 Overview
Described in this communication model specification are the Application Service Elements
(ASE) and the Application Process (AP) object class models. The syntax and related encoding
of attributes is described by the Type 18 Application layer protocol specification.
The Type 18 AL identifies two types of FAL user, master and slave. For each FAL user type
there are two classes of Data Link Entity (DLE), Class 1 and Class 2, corresponding to the
Polled and Packed class of the DLE, respectively. See appropriate definitions and
specifications in the Type 18 Data link for more information about the Polled and Packed class
of DLE. Therefore, there are 4 types of Application Relationship (AR) as shown in Table 1.
AR classes and device types share the same naming conventions.
Table 1 – AR types
AR class Symbol FAL user type DLE class
Master Class 1 M1 Master Polled
Master Class 2 M2 Master Packed
Slave Class 1 S1 Slave Polled
Slave Class 2 S2 Slave Packed

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– 10 – 61158-5-18 © IEC:2007(E)
An Application Process (AP) object model consists of
• one Device Manager object,
• one Connection Manager object, and
• one or more Process Data objects.
The specific classes of objects included depend upon the type of device and are identified by
prefixes that match the symbol of the related AR class (or device type).
4.2.2 Stations and slots
Each device and its corresponding FAL is identified by a number. This identifying number is
named the Station number. The station number is the address used to identify the device and
the AR End Point (AREP) associated with the transmission and reception of its process data.
Cyclic process data is further addressed by slot number. One slot is the granularity of the
position dependent mapping of the cyclic data fields. A station may occupy more than one
slot. The slots belonging to an AREP are identified by the range of slots beginning with the
station number and with a length equal to the number of occupied slots as configured by the
FAL user.
4.2.3 Transmission methods
The Type 18 AL implements a master/slave type architecture. Only a master is able to initiate
transmissions. Slave devices respond to transmissions from the master. The access method
employed is scanning. A scan cycle is one where the master device transmits data to, and
recei
...

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