IEC 61158-5-20:2014

IEC 61158-5-20 ®
Edition 3.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial communication networks – Fieldbus specifications –
Part 5-20: Application layer service definition – Type 20 elements

Réseaux de communication industriels – Spécifications des bus de terrain –
Partie 5-20: Définition des services de la couche application – Eléments
de type 20
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IEC 61158-5-20 ®
Edition 3.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Industrial communication networks – Fieldbus specifications –

Part 5-20: Application layer service definition – Type 20 elements

Réseaux de communication industriels – Spécifications des bus de terrain –

Partie 5-20: Définition des services de la couche application – Eléments

de type 20
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 25.040.40; 35.100.70; 35.110 ISBN 978-2-8322-1741-2

– 2 – IEC 61158-5-20:2014 © IEC 2014
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, symbols, abbreviations and conventions . 7
3.1 Terms and definitions from other ISO/IEC standards . 7
3.2 IEC 61158-1 terms . 8
3.3 Type 20 fieldbus application-layer specific definitions . 10
3.4 Abbreviations and symbols . 12
3.5 Conventions . 13
4 Concepts . 16
5 Data type ASE . 16
5.1 Overview . 16
5.2 Formal definition of data type objects . 18
5.3 FAL defined data types . 20
5.4 Data type ASE service specification . 23
5.5 Summary of data types . 24
6 Communication model specification . 24
6.1 Common parameters . 24
6.2 ASEs . 25
6.3 ARs . 52
6.4 Summary of classes . 54
6.5 Permitted services by AREP role . 55
Bibliography . 56

Figure 1 – Data type class hierarchy . 17
Figure 2 – VFD model . 25

Table 1 – Packed ASCII character set . 23
Table 2 – ISO Latin-1 characters . 23
Table 3 – Data type summary . 24
Table 4 – Response code values . 24
Table 5 – Communication status values . 25
Table 6 – Identify service parameters . 28
Table 7 – Read service parameters . 32
Table 8 – Write service parameters . 33
Table 9 – Information report parameters . 34
Table 10 – Action service parameters . 36
Table 11 – AR get attributes service parameters . 53
Table 12 – AR set attributes service parameters . 54
Table 13 – Class summary . 55
Table 14 – Confirmed services by AREP class . 55
Table 15 – Unconfirmed services by AREP class . 55

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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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.
Attention is drawn to the fact that the use of the associated protocol type is restricted by its
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 layer protocol type to
be used with other layer protocols of the same type, or in other type combinations explicitly
authorized by its intellectual-property-right holders.
NOTE Combinations of protocol types are specified in IEC 61784-1 and IEC 61784-2.
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 third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.

– 4 – IEC 61158-5-20:2014 © IEC 2014
The main change with respect to the previous edition is listed below:
– added Data types;
– added services;
– updated the Normative references, Terms, definitions, symbols, abbreviations;
– corrected the editorial errors and the text.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/763/FDIS 65C/773/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.
A list of all parts of the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.
The committee has decided that the contents of this publication will remain unchanged until
the stability 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.
INTRODUCTION
This document is one of a series produced to facilitate the interconnection of automation
system components. It is related to other documents in the set as defined by the “three-layer”
fieldbus reference model described in IEC 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 document 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 document is a conceptual architectural
service, independent of administrative and implementation divisions.

– 6 – IEC 61158-5-20:2014 © IEC 2014
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 5-20: Application layer service definition –

1 Scope
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 International Standard 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 International Standard defines in an abstract way the externally visible service provided
by the Type 20 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 International Standard is to define the services provided to the FAL
user at the boundary between the user and the Application Layer of the Fieldbus Reference
Model.
This International Standard specifies the structure and services of the IEC fieldbus Application
Layer, in conformance with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI
Application Layer Structure (ISO/IEC 9545).
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 International Standard to provide access to the FAL to control certain aspects of its
operation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
NOTE All parts of the IEC 61158 series, as well as IEC 61784-1 and IEC 61784-2 are maintained simultaneously.
Cross-references to these documents within the text therefore refer to the editions as dated in this list of normative
references.
IEC 61158-1:2014, Industrial communication networks – Fieldbus specifications – Part 1:
Overview and guidance for the IEC 61158 and IEC 61784 series
IEC 62591:2010, Industrial communication networks – Wireless communication network and
communication profiles – WirelessHART™
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 8824-1, 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
ANSI/IEEE 754: IEEE Standard for Floating-Point Arithmetic
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, abbreviations, symbols
and conventions apply.
3.1 Terms and definitions from other ISO/IEC standards
3.1.1 ISO/IEC 7498-1 terms
a) abstract syntax
b) application entity
c) application process
d) application protocol data unit
e) application service element
3.1.2 ISO/IEC 9545 terms
a) application-entity-invocation
b) application-service-element
c) application-service-element
3.1.3 ISO/IEC 8824-1 terms
a) object identifier
b) type
c) value
d) simple type
e) structured type
f) component type
– 8 – IEC 61158-5-20:2014 © IEC 2014
g) tag
h) true
i) false
j) integer type
k) octet string type
m) null type
3.2 IEC 61158-1 terms
For the purposes of this document, the following terms and definitions apply.
3.2.1
application
function or data structure for which data is consumed or produced
3.2.2
application object
object class that manages and provides the run time exchange of messages across the
network and within the network device
Note 1 to entry: Multiple types of application object classes may be defined.
3.2.3
application process
part of a distributed application on a network, which is located on one device and
unambiguously addressed
3.2.4
application process object
component of an application process that is identifiable and accessible through an FAL
application relationship
Note 1 to entry: 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
3.2.5
application process object class
class of application process objects defined in terms of the set of their network-accessible
attributes and services
3.2.6
application relationship
cooperative association between two or more application-entity-invocations for the purpose of
exchange of information and coordination of their joint operation
Note 1 to entry: This relationship is activated either by the exchange of application-protocol-data-units or as a
result of pre-configuration activities
3.2.7
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
Note 1 to entry: Each application process involved in the application relationship maintains its own application
relationship endpoint
3.2.8
attribute
description of an externally visible characteristic or feature of an object
Note 1 to entry: 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
3.2.9
behaviour
indication of how the object responds to particular events
Note 1 to entry: Its description includes the relationship between attribute values and services.
3.2.10
class
set of objects, all of which represent the same kind of system component
Note 1 to entry: 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
3.2.11
class attributes
attribute that is shared by all objects within the same class
3.2.12
class code
unique identifier assigned to each object class
3.2.13
class specific service
service defined by a particular object class to perform a required function which is not
performed by a common service
Note 1 to entry: A class specific object is unique to the object class which defines it.
3.2.14
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
3.2.15
conveyance path
unidirectional flow of APDUs across an application relationship
3.2.16
cyclic
term used to describe events which repeat in a regular and repetitive manner
3.2.17
endpoint
one of the communicating entities involved in a connection
3.2.18
error
discrepancy between a computed, observed or measured value or condition and the specified
or theoretically correct value or condition

– 10 – IEC 61158-5-20:2014 © IEC 2014
3.2.19
error code
identification of a specific type of error within an error class
3.2.20
management information
network-accessible information that supports managing the operation of the fieldbus system,
including the application layer
Note 1 to entry: Managing includes functions such as controlling, monitoring, and diagnosing.
3.2.21
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
3.2.22
service
operation or function than an object and/or object class performs upon request from another
object and/or object class
Note 1 to entry: 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.
3.3 Type 20 fieldbus application-layer specific definitions
For the purposes of this document, the following terms and definitions apply.
3.3.1
analog channel
continuously varying electrical signal connecting a field device to the remainder of the data
acquisition or control system
Note 1 to entry: Some field devices support multiple analog channels (input or output). Each analog channel
transmits a single dynamic variable to or from the field device.
3.3.2
broadcast
process of sending a PDU to all devices that are connected to the network and are able to
receive the transmission
3.3.3
broadcast address
address used by a master to send a command to all devices
3.3.4
burst mode
initiation of communication activity by a slave device at cyclic interval without request from a
master
3.3.5
comm error
detectable error in receiving a PhPDU or DLPDU, also ‘Communication error code’ octet of
APDU
3.3.6
device
any entity containing an implementation of Type 20 fieldbus
3.3.7
device ID
serial number for a device that is unique among all instances of one type of device
Note 1 to entry: The manufacturer is required to assigned unique value for every device that has the identical
values for Manufacturer ID and Device Type.
3.3.8
device type
manufacturer’s type of a device, e.g. its product name
Note 1 to entry: The value of this attribute is unique among all manufacturers and all type of devices. Its value
specifies the set of commands and data objects supported by the device.
3.3.9
device variable
uniquely defined data item within a Field Device that is always associated with the process-
related information
Note 1 to entry: A device variable's value varies in response to changes and variations in the process to which the
device is connected.
3.3.10
dynamic variable
device variable that is assigned as the dynamic variable and possibly associated with an
analog channel
Note 1 to entry: A device may contain up to four variables – primary, secondary, tertiary, and quaternary
variables. These are collectively called the dynamic variables.
3.3.11
expanded device type
manufacturer’s type of the device
Note 1 to entry: The value of this attribute is unique among all manufacturers and all type of devices. Its value
specifies the set of commands and data objects supported by the device.
3.3.12
field device
physical entity that is connected to the process or to plant equipment and has at least one
signalling element that communicates with other signalling element(s) via the network
Note 1 to entry: It directly connects to the sensor or actuator or performs process control function and it is directly
connected to the physical layer specified in this standard. It may generate or receive an analog signal in addition to
a digital signal.
3.3.13
long tag
32 character restricted ISO Latin-1 string used to identify a field device
3.3.14
loop current
value measured by a milli-ammeter in series with the field device
Note 1 to entry: 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.

– 12 – IEC 61158-5-20:2014 © IEC 2014
3.3.15
manufacturer ID
string identifying the manufacturer that produced the device
Note 1 to entry: A manufacturer is required to use the value assigned to it and is not permitted to use the value
assigned to another manufacturer.
3.3.16
master
device that initiates communication activity by sending request PDU to a another device and
expecting a response frame from that device
3.3.17
network
single pair of cable, connectors, associated signaling elements by which a given set of
signaling devices are interconnected and non-signaling elements that are attached to the
same pair of cable
Note 1 to entry: An installation using multiple-pair wire and a common network power supply is considered as
multiple networks.
3.3.18
polling address
identifier assigned to a device such that it is unique within the network to which the device is
connected
3.3.19
slave
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
3.3.20
tag
8 character ASCII string used to identify the field device
3.3.21
unique ID
identifier assigned to a device which is unique among all instances of the devices compliant to
this standard
3.4 Abbreviations and symbols
AE Application Entity
AL Application Layer
AP Application Process
APDU Application Protocol Data Unit
APO Application Process Object
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
VFD Virtual Field Device
3.5 Conventions
3.5.1 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.
3.5.2 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.
– 14 – IEC 61158-5-20:2014 © IEC 2014
(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. The CLASS ID
is not used in this document.
(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 document.
(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
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.
c) The label "MgtService" designates an management service.
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.
3.5.3 Conventions for service definitions
3.5.3.1 General
This document 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.

3.5.3.2 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.
This document 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 document. 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;
3) the request primitive’s output parameters;
NOTE 1 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 2 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.
3.5.3.3 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.

– 16 – IEC 61158-5-20:2014 © IEC 2014
NOTE The IEC 61158-5 subseries 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 document but not in an IEC 61158-5 subseries abstract service
definition document. 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 document or for a protocol
document, except at a level of abstraction that is necessarily common to all embodiments of the specifying
document. 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 61158-1, 9.6.
4 Concepts
The common concepts and templates used to describe the application layer service in this
document are detailed in IEC 61158-1, Clause 9.
5 Data type ASE
5.1 Overview
5.1.1 General
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 docu
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