IEC 61158-5-20:2007

IEC 61158-5-20
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 5-20: Application layer service definition – Type 20 elements

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IEC 61158-5-20
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 5-20: Application layer service definition – Type 20 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 35.100.70; 25.040.40 ISBN 2-8318-9473-5

– 2 – 61158-5-20 © IEC:2007(E)

CONTENTS
FOREWORD.4

INTRODUCTION.6

1 Scope.7

1.1 Overview .7

1.2 Specifications .8

1.3 Conformance.8

2 Normative references .8

3 Terms, definitions, symbols, abbreviations and conventions .9
3.1 ISO/IEC 7498-1 terms .9
3.2 ISO/IEC 8822 terms .9
3.3 ISO/IEC 9545 terms .9
3.4 ISO/IEC 8824 terms .9
3.5 IEC/TR 61158-1 terms.9
3.6 Fieldbus application-layer specific definitions .12
3.7 Abbreviations and symbols .14
3.8 Conventions .14
4 Concepts .18
5 Data type ASE.18
5.1 Overview .18
5.2 Formal definition of data type objects .19
5.3 FAL defined data types.21
5.4 Data type ASE service specification .24
5.5 Summary of data types.24
6 Communication model specification .25
6.1 Common parameters .25
6.2 ASEs .26
6.3 ARs .41
6.4 Summary of classes .44
6.5 Permitted services by AREP role .44
Bibliography.46

Figure 1 – Data type class hierarchy .18

Figure 2 – VFD model .26

Table 1 – Packed ASCII character set.
Table 2 – ISO Latin-1 characters .24
Table 3 – Data type summary .24
Table 4 – Comm status values .25
Table 5 – Response code values .25
Table 6 – Device status values .26
Table 7 – Identify service parameters .29
Table 8 – Read service parameters.32
Table 9 – Write service parameters.33
Table 10 – AR get attributes service parameters.43
Table 11 – AR set attributes service parameters .44

61158-5-20 © IEC:2007(E) – 3 –

Table 12 – Class summary.44

Table 13 – Services by AREP class .45

– 4 – 61158-5-20 © IEC:2007(E)

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 5-20: Application layer service definition – Type 20 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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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6) All users should ensure that they have the latest edition of this publication.
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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.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
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 from their respective intellectual-property-right holders.
International Standard IEC 61158-5-20 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This edition and its companion parts of IEC 61158-5 cancel and replace IEC 61158-5:2003.
This edition of this part constitutes a technical addition.
This edition of IEC 61158-5 includes the following significant changes from the prior edition:
a) deletion of the former Type 6 fieldbus for lack of market relevance;
b) addition of new types of fieldbuses;

61158-5-20 © IEC:2007(E) – 5 –

c) partition of part 5 of the third edition into multiple parts numbered -5-2, -5-3, …

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.

– 6 – 61158-5-20 © IEC:2007(E)

INTRODUCTION
This standard 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.

61158-5-20 © IEC:2007(E) – 7 –

INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 5-20: Application layer service definition – Type 20 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 20 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 standard defines in an abstract way the externally visible service provided by the
different Types of the 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 standard 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 standard specifies the structure and services of the 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

– 8 – 61158-5-20 © IEC:2007(E)

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 standard 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.
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 standard 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 20 application layer services as defined in this standard.
2 Normative references
The following referenced standards 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 standard (including any amendments) applies.
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 8859-1, Information technology – 8-bit single-byte coded graphic character sets –
Part 1: Latin alphabet No. 1
ISO/IEC 9545, Information technology – Open Systems Interconnection – Application Layer
structure
ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services

61158-5-20 © IEC:2007(E) – 9 –

3 Terms, definitions, symbols, abbreviations and conventions

For the purposes of this document, the following terms as defined in these publications apply:

3.1 ISO/IEC 7498-1 terms
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
3.2 ISO/IEC 8822 terms
a) abstract syntax
b) presentation context
3.3 ISO/IEC 9545 terms
a) application-entity-invocation
b) application-entity-type
c) application-process-invocation
d) application-process-type
e) application-service-elementt
3.4 ISO/IEC 8824 terms
a) object identifier
b) type
3.5 IEC/TR 61158-1 terms
The following IEC/TR 61158-1 terms apply.
3.5.1 application
function or data structure for which data is consumed or produced
3.5.2 application layer interoperability
capability of application entities to perform coordinated and cooperative operations using the
services of the FAL
3.5.3 application object
object class that manages and provides the run time exchange of messages across the
network and within the network device
NOTE Multiple types of application object classes may be defined.

– 10 – 61158-5-20 © IEC:2007(E)

3.5.4 application process
part of a distributed application on a network, which is located on one device and

unambiguously addressed
3.5.5 application process identifier

distinguishes multiple application processes used in a device

3.5.6 application process object

component of an application process that is identifiable and accessible through an FAL

application relationship. Application process object definitions are composed of a set of
values for the attributes of their class (see the definition for Application Process Object Class
Definition). Application process object definitions may be accessed remotely using the
services of the FAL Object Management ASE. FAL Object Management services can be used
to load or update object definitions, to read object definitions, and to dynamically create and
delete application objects and their corresponding definitions
3.5.7 application process object class
a class of application process objects defined in terms of the set of their network-accessible
attributes and services
3.5.8 application relationship
cooperative association between two or more application-entity-invocations for the purpose of
exchange of information and coordination of their joint operation. This relationship is activated
either by the exchange of application-protocol-data-units or as a result of pre-configuration
activities
3.5.9 application relationship application service element
application-service-element that provides the exclusive means for establishing and
terminating all application relationships
3.5.10 application relationship endpoint
context and behavior of an application relationship as seen and maintained by one of the
application processes involved in the application relationship. Each application process
involved in the application relationship maintains its own application relationship endpoint
3.5.11 attribute
description of an externally visible characteristic or feature of an object. The attributes of an
object contain information about variable portions of an object. Typically, they provide status
information or govern the operation of an object. Attributes may also affect the behaviour of
an object. Attributes are divided into class attributes and instance attributes
3.5.12 behaviour
indication of how the object responds to particular events. Its description includes the
relationship between attribute values and services
3.5.13 class
a set of objects, all of which represent the same kind of system component. A class is a
generalisation of the object; a template for defining variables and methods. All objects in a
class are identical in form and behaviour, but usually contain different data in their attributes

61158-5-20 © IEC:2007(E) – 11 –

3.5.14 class attributes
an attribute that is shared by all objects within the same class

3.5.15 class code
a unique identifier assigned to each object class

3.5.16 class specific service
a service defined by a particular object class to perform a required function which is not

performed by a common service. A class specific object is unique to the object class which

defines it
3.5.17 client
a) an object which uses the services of another (server) object to perform a task
b) an initiator of a message to which a server reacts, such as the role of an AR endpoint in
which it issues confirmed service request APDUs to a single AR endpoint acting as a server
3.5.18 conveyance path
unidirectional flow of APDUs across an application relationship
3.5.19 cyclic
term used to describe events which repeat in a regular and repetitive manner
3.5.20 dedicated AR
AR used directly by the FAL User. On Dedicated ARs, only the FAL Header and the user data
are transferred
3.5.21 device
a physical hardware connection to the link. A device may contain more than one node
3.5.22 device profile
a collection of device dependent information and functionality providing consistency between
similar devices of the same device type

3.5.23 endpoint
one of the communicating entities involved in a connection
3.5.24 error
a discrepancy between a computed, observed or measured value or condition and the
specified or theoretically correct value or condition
3.5.25 error code
identification of a specific type of error within an error class

– 12 – 61158-5-20 © IEC:2007(E)

3.5.26 management information
network-accessible information that supports managing the operation of the fieldbus system,

including the application layer. Managing includes functions such as controlling, monitoring,

and diagnosing
3.5.27 network
a series of nodes connected by some type of communication medium. The connection paths

between any pair of nodes can include repeaters, routers and gateways

3.5.28 pre-defined AR endpoint

AR endpoint that is defined locally within a device without use of the create service. Pre-
defined ARs that are not pre-established are established before being used
3.5.29 pre-established AR endpoint
AR endpoint that is placed in an established state during configuration of the AEs that control
its endpoints
3.5.30 server
a) role of an AREP in which it returns a confirmed service response APDU to the client that
initiated the request
b) an object which provides services to another (client) object
3.5.31 service
operation or function than an object and/or object class performs upon request from another
object and/or object class. A set of common services is defined and provisions for the
definition of object-specific services are provided. Object-specific services are those which
are defined by a particular object class to perform a required function which is not performed
by a common service
3.6 Fieldbus application-layer specific definitions
There are additional terms defined for this part.
3.6.1 analog channel
A continuously varying electrical signal connecting a field device to the remainder of the data

acquisition or control system. Some field devices support multiple analog channels (input or
output). Each analog channel transmits a single dynamic variable to or from the field device.
3.6.2 broadcast address
A broadcast address is used by a master to send a command to all devices. The broadcast
address is five octet long and has all zeros as the value.
3.6.3 busy
The device is busy and cannot execute a command at the time. A device indicates busy by
returning response code 32 when allowed by the command specification. The requested
command is not executed if a busy response is returned.

61158-5-20 © IEC:2007(E) – 13 –

3.6.4 device ID
This indicates a serial number for the device. The manufacturer is required to assigned unique

value for every device that has the identical values for Manufacturer ID and Device Type.

3.6.5 device type
This indicates the manufacturer’s type of the device i.e. the product name. The value of this
attribute is assigned by the manufacturer. Its value specifies the set of commands and data

objects supported by the device. The manufacturer is required to assigned unique value to

each type of the device.
3.6.6 device variable
A uniquely defined data item within a Field Device that is always associated with cyclical
process information. A device variable's value varies in response to changes and variations in
the process to which the device is connected.
3.6.7 dynamic variable
The connection between the process and an analog channel. A device may contain primary,
secondary, tertiary, and quaternary variables. These are collectively called the dynamic
variables.
3.6.8 long tag
It is a 32 character ISO Latin-1 string used to identify a field device.
3.6.9 loop current
The value measured by a milli-ammeter in series with the field device. The loop current is a
near DC analog 4-20 mA signal used to communicate a single value between the control
system and the field device. Voltage mode devices use "Volts DC" as their engineering units
where "loop current" values are used.
3.6.10 manufacturer ID
This indicates the manufacturer that produced the device. A manufacturer is required to use
the value assigned to it and is not permitted to use the value assigned to another
manufacturer.
3.6.11 master
A device that initiates communication activity by sending request PDU to a device.
3.6.12 polling address
An integer used to identify the device. The polling address is used to construct one octet long
address.
3.6.13 slave
A device that initiates communication activity only after it receives a request PDU from a
master device and it is required to send a response to that request.
3.6.14 tag
The tag is a 8 character ASCII string used to identify the field device.

– 14 – 61158-5-20 © IEC:2007(E)

3.6.15 unique address
This is a five octet long address of a device and it uniquely identifies the device among all

other devices that support this standard. It is a concatenation of the manufacturer ID, device

type and device ID.
3.7 Abbreviations and symbols
AE Application Entity
AL Application Layer
ALP Application Layer Protocol

APO Application Object
AP Application Process
APDU Application Protocol Data Unit
API Application Process Identifier
AR Application Relationship
AREP Application Relationship End Point
ASCII American Standard Code for Information Interchange
ASE Application Service Element
Cnf Confirmation
DL- (as a prefix) Data Link-
DLC Data Link Connection
DLL Data Link Layer
DLM Data Link-management
DLSAP Data Link Service Access Point
DLSDU DL-service-data-unit
FAL Fieldbus Application Layer
ID Identifier
IEC International Electrotechnical Commission
Ind Indication
OSI Open Systems Interconnect
Req Request
Rsp Response
SAP Service Access Point
SDU Service Data Unit
VFD Virtual Field Device
3.8 Conventions
3.8.1 Overview
The FAL is defined as a set of object-oriented ASEs. Each ASE is specified in a separate
subclause. Each ASE specification is composed of two parts, its class specification, and its
service specification.
The class specification defines the attributes of the class. The service specification defines
the services that are provided by the ASE.

61158-5-20 © IEC:2007(E) – 15 –

3.8.2 Conventions for class definitions

Class definitions are described using templates. Each template consists of a list of attributes

for the class. The general form of the template is shown below:

FAL ASE: ASE Name
CLASS: Class Name
CLASS ID: #
PARENT CLASS: Parent Class Name

ATTRIBUTES:
1 (o) Key Attribute: numeric identifier

2 (o) Key Attribute: name
3 (m) Attribute: attribute name(values)
4 (m) Attribute: attribute name(values)
4.1 (s) Attribute: attribute name(values)
4.2 (s) Attribute: attribute name(values)
4.3 (s) Attribute: attribute name(values)
5. (c) Constraint: constraint expression
5.1 (m) Attribute: attribute name(values)
5.2 (o) Attribute: attribute name(values)
6 (m) Attribute: attribute name(values)
6.1 (s) Attribute: attribute name(values)
6.2 (s) Attribute: attribute name(values)
SERVICES:
1 (o) OpsService: service name
2. (c) Constraint: constraint expression
2.1 (o) OpsService: service name
3 (m) MgtService: service name
(1) The "FAL ASE:" entry is the name of the FAL ASE that provides the services for the class
being specified.
(2) The "CLASS:" entry is the name of the class being specified. All objects defined using
this template will be an instance of this class. The class may be specified by this
standard, or by a user of this standard.
(3) The "CLASS ID:" entry is a number that identifies the class being specified. This number
is unique within the FAL ASE that will provide the services for this class. When qualified
by the identity of its FAL ASE, it unambiguously identifies the class within the scope of
the FAL. The value "NULL" indicates that the class cannot be instantiated. Class IDs
between 1 and 255 are reserved by this standard to identify standardized classes. They

have been assigned to maintain compatibility with existing national standards. CLASS IDs
between 256 and 2048 are allocated for identifying user defined classes.
(4) The "PARENT CLASS:" entry is the name of the parent class for the class being
specified. All attributes defined for the parent class and inherited by it are inherited for
the class being defined, and therefore do not have to be redefined in the template for this
class.
NOTE  The parent-class "TOP" indicates that the class being defined is an initial class definition. The parent class
TOP is used as a starting point from which all other classes are defined. The use of TOP is reserved for classes
defined by this standard.
(5) The "ATTRIBUTES" label indicate that the following entries are attributes defined for the
class.
a) Each of the attribute entries contains a line number in column 1, a mandatory (m) /
optional (o) / conditional (c) / selector (s) indicator in column 2, an attribute type label

– 16 – 61158-5-20 © IEC:2007(E)

in column 3, a name or a conditional expression in column 4, and optionally a list of

enumerated values in column 5. In the column following the list of values, the default

value for the attribute may be specified.

b) Objects are normally identified by a numeric identifier or by an object name, or by

both. In the class templates, these key attributes are defined under the key attribute.

c) The line number defines the sequence and the level of nesting of the line. Each

nesting level is identified by period. Nesting is used to specify

i) fields of a structured attribute (4.1, 4.2, 4.3),

ii) attributes conditional on a constraint statement (5). Attributes may be mandatory
(5.1) or optional (5.2) if the constraint is true. Not all optional attributes require
constraint statements as does the attribute defined in (5.2).
iii) the selection fields of a choice type attribute (6.1 and 6.2).
(6) The "SERVICES" label indicates that the following entries are services defined for the
class.
a) An (m) in column 2 indicates that the service is mandatory for the class, while an (o)
indicates that it is optional. A (c) in this column indicates that the service is
conditional. When all services defined for a class are defined as optional, at least one
has to be selected when an instance of the class is defined.
b) The label "OpsService" designates an operational service (1).
c) The label "MgtService" designates an management service (2).
d) The line number defines the sequence and the level of nesting of the line. Each
nesting level is identified by period. Nesting within the list of services is used to
specify services conditional on a constraint statement.
3.8.3 Conventions for service definitions
3.8.3.1 General
This standard uses the descriptive conventions given in ISO/IEC 10731.
The service model, service primitives, and time-sequence diagrams used are entirely abstract
descriptions; they do not represent a specification for implementation.

3.8.3.2 Service parameters
Service primitives are used to represent service user/service provider interactions (ISO/IEC
10731). They convey parameters which indicate information available in the user/provider
interaction.
NOTE 1  See the note under 3.8.3.3 relative to the non-inclusion of service parameters that are appropriate to a
protocol specification or programming interface specification or implementation specification, but not to an abstract
service definition.
This standard uses a tabular format to describe the component parameters of the service
primitives. The parameters that apply to each group of service primitives are set out in tables
throughout the remainder of this standard. Each table consists of up to six columns: a column
for the name of the service parameter, and a column each for those primitives and parameter-
transfer directions used by the service. The possible six columns are
1) the parameter name;
2) the request primitive’s input parameters;

61158-5-20 © IEC:2007(E) – 17 –

3) the request primitive’s output parameters;

NOTE 2  This is a seldom-used capability. Unless otherwise specified, request primitive parameters are input

parameters.
4) the indication primitive’s output parameters;

5) the response primitive’s input parameters; and

6) the confirm primitive’s output parameters.

NOTE 3  The request, indication, response and confirm primitives are also known as requestor.submit,

acceptor.deliver, acceptor.submit, and requestor.deliver primitives, respectively (see ISO/IEC 10731).

One parameter (or component of it) is listed in each row of each table. Under the appropriate

service primitive columns, a code is used to specify the type of usage of the parameter on the

primitive specified in the column:
M parameter is mandatory for the primitive
U parameter is a User option, and may or may not be provided depending on dynamic
usage of the service user. When not provided, a default value for the parameter is
assumed.
C parameter is conditional upon other parameters or upon the environment of the service
user.
— (blank) parameter is never present.
S parameter is a selected item.
Some entries are further qualified by items in brackets. These may be
a) a parameter-specific constraint:
“(=)” indicates that the parameter is semantically equivalent to the parameter in the
service primitive to its immediate left in the table.
b) an indication that some note applies to the entry:
“(n)” indicates that the following note "n" contains additional information pertaining to
the parameter and its use.
3.8.3.3 Service procedures
The procedures are defined in terms of
• the interactions between application entities through the exchange of fieldbus Application
Protocol Data Units, and
• the interactions between an application layer service provider and an application layer
service user in the same system through the invocation of application layer service
primitives.
These procedures are applicable to instances of communication between systems which

support time-constrained communications services within the fieldbus Application Layer.
NOTE  The IEC 61158-5 subseries of standards define sets of abstract services. They are neither protocol
specifications nor implementation specifications nor concrete programming interface specifications. Therefore there
are restrictions on the extent to which service procedures can be mandated in the parts of IEC 61158-5 subseries.
Protocol aspects that can vary among different protocol specifications or different implementations that instantiate
the same abstract services are unsuitable for inclusion in these service definitions, except at the level of
abstraction that is necessarily common to all such expressions.
For example, the means by which service providers pair request and reply PDUs is appropriate for specification in
an IEC 61158-6 subseries protocol specification standard but not in an IEC 61158-5 subseries abstract service
definition standard. Similarly, local implementation methods by which a service provider or service user pairs
request and confirm(ation) primitives, or indication and response primitives, is appropriate for an implementation
specification or for a programming interface specification, but not for an abstract service standard or for a protocol
standard, except at a level of abstraction that is necessarily common to all embodiments of the specifying standard.
In all cases, the abstract definition is not permitted to over-specify the more concrete instantiating realization.
Further information on the conceptual service procedures of an implementation of a protocol that realizes the
services of one of the IEC 61158-5 subseries abstract service definitions can be found in IEC/TR 61158-1:2007,
9.6.
– 18 – 61158-5-20 © IEC:2007(E)

4 Concepts
The common concepts and templates used to describe the application layer service in this

standard are detailed in IEC/TR 61158-1, Clause 9.

5 Data type ASE
5.1 Overview
Fieldbus data types specify the machine independent syntax for application data conveyed by

FAL services. The Fieldbus application layer supports the definition and transfer of both basic

and constructed data types. Encoding rules for the data types specified in this clause are
provided in IEC 61158-6 subseries.
Basic types are atomic types that cannot be decomposed into more elemental types.
Constructed types are types composed of basic types and other constructed types. Their
complexity and depth of nesting is not constrained by this standard.
Data types are defined as instances of the data type class, as shown in Figure 1.
Data type
Fixed Length String
Integer8 Packed ASCII
Integer16
Integer24
ISO Latin-1
Integer32
Unsigned8
Unsigned 16
Unsigned 24
Unsigned 32
Float32
Float64
Date
Enumeration
Bit Field
Figure 1 – Data type class hierarchy
The data type definitions are represented as a class/format/instance structure beginning with
data type class entitled "Data type". The formats for data types are defined by the data type
class.
The basic data classes are used to define fixed length data types. Standard types taken from
ISO/IEC 8824 are referred to as simple data types. Other standard basic data types are
defined specifically for Fieldbus applications and a
...