IEC 61158-6-4:2023

IEC 61158-6-4 ®
Edition 4.0 2023-03
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 6-4: Application layer protocol specification – Type 4 elements

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IEC 61158-6-4 ®
Edition 4.0 2023-03
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –

Part 6-4: Application layer protocol specification – Type 4 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40; 35.100.70; 35.110 ISBN 978-2-8322-6632-8

– 2 – IEC 61158-6-4:2023 © IEC 2023
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
1.1 General . 8
1.2 Specifications . 8
1.3 Conformance . 9
2 Normative references . 9
3 Terms, definitions, symbols, abbreviated terms and conventions . 10
3.1 Referenced terms and definitions . 10
3.1.1 ISO/IEC 7498-1 terms . 10
3.1.2 ISO/IEC 8822 terms . 10
3.1.3 ISO/IEC 9545 terms . 10
3.1.4 ISO/IEC 8824-1 terms . 10
3.1.5 Fieldbus data-link layer terms . 11
3.2 Abbreviations and symbols . 11
3.3 Conventions . 12
3.3.1 General concept . 12
3.3.2 Conventions for state machines for Type 4 . 12
4 FAL syntax description . 13
4.1 FAL-AR PDU abstract syntax . 13
4.1.1 General . 13
4.1.2 Abstract syntax of APDU header . 13
4.1.3 Abstract syntax of APDU body . 15
4.2 Data types . 16
5 Transfer syntaxes . 16
5.1 APDU encoding . 16
5.1.1 APDU Header encoding . 16
5.1.2 APDU body encoding . 18
5.2 Variable object encoding and packing . 20
5.2.1 Encoding of simple variables . 20
5.2.2 Encoding of constructed variables . 21
5.2.3 Alignment . 22
5.2.4 Variable object attributes . 24
5.3 Error codes . 25
6 FAL protocol state machines . 26
7 AP-context state machine . 27
8 FAL service protocol machine (FSPM) . 27
8.1 Primitives exchanged between FAL User and FSPM . 27
8.2 FSPM states . 27
8.2.1 General . 27
8.2.2 FSPM proxy object states . 27
8.2.3 FSPM real object state machine description . 32
9 Application relationship protocol machine (ARPM) . 34
9.1 Primitives exchanged between ARPM and FSPM . 34
9.2 ARPM States . 35
9.2.1 General . 35

9.2.2 Sender state transitions . 35
9.2.3 Receiver state transitions . 36
10 DLL mapping protocol machine (DMPM) . 37
10.1 Data-link Layer service selection. 37
10.1.1 General . 37
10.1.2 DL-UNITDATA request . 37
10.1.3 DL-UNITDATA indication . 37
10.1.4 DL-UNITDATA response . 37
10.1.5 DLM-Set primitive and parameters . 37
10.1.6 DLM-Get primitive and parameters . 37
10.2 Primitives exchanged between ARPM and DLPM . 37
10.3 Primitives exchanged between DLPM and data-link layer . 38
10.4 DLPM states . 38
10.4.1 States . 38
10.4.2 Sender state transitions . 38
10.4.3 Receiver state transitions . 39
11 Protocol options. 40
Bibliography . 41

Figure 1 – State transition diagram . 12
Figure 2 – APDU header structure . 16
Figure 3 – Subfields of ControlStatus for Request . 17
Figure 4 – Subfields of ControlStatus for Response with error . 17
Figure 5 – Subfields of ControlStatus for Response with no error . 18
Figure 6 – DataFieldFormat encoding . 18
Figure 7 – Structure of request APDU body . 19
Figure 8 – Structure of response APDU body . 19
Figure 9 – Variable identifier . 19
Figure 10 – Code subfield of variable identifier . 19
Figure 11 – Sequence of data in the APDU body subfield . 21
Figure 12 – MSG consists of APDU header and APDU body . 22
Figure 13 – Summary of FAL architecture . 26
Figure 14 – FSPM proxy object state machine . 28
Figure 15 – FSPM real object state machine . 33
Figure 16 – ARPM state machine . 35
Figure 17 – DLPM state machine . 38

Table 1 – State machine description elements . 12
Table 2 – APDU header . 13
Table 3 – APDU body . 15
Table 4 – Transfer syntax for Array . 23
Table 5 – Transfer syntax for Structure . 23
Table 6 – Common variable object attributes . 24
Table 7 – Variable type identifiers . 24
Table 8 – FIFO variable object attributes . 25

– 4 – IEC 61158-6-4:2023 © IEC 2023
Table 9 – Error codes . 25
Table 10 – Primitives exchanged between FAL-User and FSPM . 27
Table 11 – REQUEST.req FSPM constraints . 28
Table 12 – REQUEST.req FSPM actions . 29
Table 13 – RESPONSE.cnf FSPM constraints . 31
Table 14 – RESPONSE.cnf FSPM actions . 31
Table 15 – AR Send.ind proxy FSPM constraints . 32
Table 16 – AR Send.ind proxy FSPM actions . 32
Table 17 – AR Send.ind real FSPM constraints . 33
Table 18 – AR Send.ind real FSPM Actions . 34
Table 19 – Primitives issued by FSPM to ARPM . 34
Table 20 – Primitives issued by ARPM to FSPM . 34
Table 21 – Primitives issued by ARPM to ARPM . 35
Table 22 – AR Send.req ARPM constraints . 35
Table 23 – AR Send.req ARPM actions . 35
Table 24 – AR Acknowledge.req ARPM constraints . 36
Table 25 – AR Acknowledge.req ARPM actions . 36
Table 26 – AR Send.ind ARPM constraints . 36
Table 27 – AR Send.req ARPM actions . 36
Table 28 – Primitives issued by ARPM to DLPM . 37
Table 29 – Primitives issued by DLPM to ARPM . 37
Table 30 – Primitives issued by DLPM to data-link layer . 38
Table 31 – Primitives issued by data-link layer to DLPM . 38
Table 32 – AR Send.req DLPM constraints . 38
Table 33 – AR Send.req DLPM actions . 39
Table 34 – AR Acknowledge.req DLPM constraints . 39
Table 35 – AR Acknowledge.req DLPM actions . 39
Table 36 – DL-UNITDATA.ind DLPM constraints . 40
Table 37 – DL-UNITDATA.ind DLPM actions . 40

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-4: Application layer protocol specification –
Type 4 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
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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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
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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
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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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
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 the IEC 61784-1 series and the IEC 61784-2 series.
IEC 61158-6-4 has been prepared by subcommittee 65C: Industrial networks, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is an International
Standard.
This fourth edition cancels and replaces the third edition published in 2019. This edition
constitutes a technical revision.

– 6 – IEC 61158-6-4:2023 © IEC 2023
This edition includes the following significant technical change with respect to the previous
edition:
a) Use of extended data size in an APDU body. This extension is restricted to nodes operating
on a P-NET IP network.
The text of this International Standard is based on the following documents:
Draft Report on voting
65C/1204/FDIS 65C/1245/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A 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.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document 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 standards in the set as defined by the “three-layer” fieldbus
reference model described in IEC 61158-1.
The application protocol provides the application service by making use of the services
available from the data-link or other immediately lower layer. The primary aim of this document
is to provide a set of rules for communication expressed in terms of the procedures to be carried
out by peer application entities (AEs) at the time of communication. These rules for
communication are intended to provide a sound basis for development in order to serve a variety
of purposes:
• as a guide for implementors and designers;
• for use in the testing and procurement of equipment;
• as part of an agreement for the admittance of systems into the open systems environment;
• as a refinement to the understanding of time-critical communications within OSI.
This document is concerned, in particular, with the communication and interworking of sensors,
effectors and other automation devices. By using this document together with other standards
positioned within the OSI or fieldbus reference models, otherwise incompatible systems can
work together in any combination.

– 8 – IEC 61158-6-4:2023 © IEC 2023
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-4: Application layer protocol specification –
Type 4 elements
1 Scope
1.1 General
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 4 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 document specifies interactions between remote applications and defines the externally
visible behavior provided by the Type 4 fieldbus application layer in terms of
• the formal abstract syntax defining the application layer protocol data units conveyed
between communicating application entities;
• the transfer syntax defining encoding rules that are applied to the application layer protocol
data units;
• the application context state machine defining the application service behavior visible
between communicating application entities;
• the application relationship state machines defining the communication behavior visible
between communicating application entities.
The purpose of this document is to define the protocol provided to
• define the wire-representation of the service primitives defined in IEC 61158-5-4, and
• define the externally visible behavior associated with their transfer.
This document specifies the protocol of the Type 4 fieldbus application layer, in conformance
with the OSI Basic Reference Model (ISO/IEC 7498-1) and the OSI application layer structure
(ISO/IEC 9545).
1.2 Specifications
The principal objective of this document is to specify the syntax and behavior of the application
layer protocol that conveys the application layer services defined in IEC 61158-5-4.
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 protocols
standardized in IEC 61158-6 series.

1.3 Conformance
This document do not specify individual implementations or products, nor do they constrain the
implementations of application layer entities within industrial automation systems.
Conformance is achieved through implementation of this application layer protocol specification.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 All parts of the IEC 61158 series, as well as the IEC 61784-1 series and the IEC 61784-2 series 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 61158-3-4:2023, Industrial communication networks – Fieldbus specifications – Part 3-4:
Data-link layer service definition – Type 4 elements
IEC 61158-4-4:2023, Industrial communication networks – Fieldbus specifications – Part 4-4:
Data-link layer protocol specification – Type 4 elements
IEC 61158-5-4:2023, Industrial communication networks – Fieldbus specifications – Part 5-4:
Application layer service definition – Type 4 elements
IEC 61158-6-1, Industrial communication networks – Fieldbus specifications – Part 6-1:
Application layer protocol specification – Type 1 elements
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 8824-1, Information technology – Abstract Syntax Notation One (ASN.1) – Part 1:
Specification of basic notation
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
ISO/IEC 9797-1, Information technology – Security techniques – Message Authentication
Codes (MACs) – Part 1: Mechanisms using a block cipher

– 10 – IEC 61158-6-4:2023 © IEC 2023
3 Terms, definitions, symbols, abbreviated terms and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviated terms
and conventions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
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 8824-1 terms
For the purposes of this document, the following terms as defined in ISO/IEC 8824-1 apply:
a) object identifier
b) type
3.1.5 Fieldbus data-link layer terms
For the purposes of this document, the following terms as defined in IEC 61158-3-4 and
IEC 61158-4-4 apply.
a) DL-Time
b) DL-Scheduling-policy
c) DLCEP
d) DLC
e) DL-connection-oriented mode
f) DLPDU
g) DLSDU
h) DLSAP
i) network address
j) node address
k) node
3.2 Abbreviations and symbols
AE Application Entity
AL Application Layer
ALE Application Layer Entity
APDU Application Protocol Data Unit
AR Application Relationship
AREP Application Relationship End Point
ASE Application Service Element
Cnf Confirmation
DL- (as a prefix) Data-link-
DLCEP Data-link Connection End Point
DLL Data-link Layer
DLE Data-link Entity
DLM Data-link-management
DLS Data-link Service
DLSAP Data-link Service Access Point
DLSDU DL-service-data-unit
FME FAL Management Entity
Ind Indication
IP Internet Protocol
PDU Protocol Data Unit
Req Request
Rsp Response
SME System Management Entity
.cnf Confirm Primitive
.ind Indication Primitive
.req Request Primitive
.rsp Response Primitive
– 12 – IEC 61158-6-4:2023 © IEC 2023
3.3 Conventions
3.3.1 General concept
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 three parts: its class definitions, its services,
and its protocol specification. The first two are contained in IEC 61158-5-4. The protocol
specification for each of the ASEs is defined in this document.
The class definitions define the attributes of the classes supported by each ASE. The attributes
are accessible from instances of the class using the Management ASE services specified in
IEC 61158-5-4. The service specification defines the services that are provided by the ASE.
This document uses the descriptive conventions given in ISO/IEC 10731.
3.3.2 Conventions for state machines for Type 4
A state machine describes the state sequence of an entity and can be represented by a state
transition diagram and/or a state table.
In a state transition diagram (see Figure 1), the transition between two states represented by
circles is illustrated by an arrow beside which the transition events or conditions are presented.

Figure 1 – State transition diagram
Table 1 – State machine description elements
Events or conditions that trigger this state
transaction
Current
# Next state
state =>
action
Name of The current Events or conditions that trigger this state The next state after the
this state to transaction. actions in this transition is
transition which this taken
=>
state
transition
The actions that are taken when the above events
applies
or
conditions are met. The actions are always indented
below events or conditions
The conventions used in the state transition table (Table 1) are as follows.
:= Value of an item on the left is replaced by value of an item on the right. If an item on the
right is a parameter, it comes from the primitive shown as an input event.
xxx A parameter name.
Example:
Identifier:= reason
means value of a 'reason' parameter is assigned to a parameter called 'Identifier.'
"xxx" Indicates fixed value.
Example:
Identifier:= "abc"
means value "abc" is assigned to a parameter named 'Identifier.'
= A logical condition to indicate an item on the left is equal to an item on the right.
< A logical condition to indicate an item on the left is less than the item on the right.
> A logical condition to indicate an item on the left is greater than the item on the
right.
<> A logical condition to indicate an item on the left is not equal to an item on the
right.
&& Logical "AND"
|| Logical "OR"
Service.req represents a Request Primitive; Service.req{} indicates that a request primitive
is sent;
Service.ind represents an Indication Primitive; Service.ind{} indicates that an Indication
Primitive is received;
Service.rsp represents a Response Primitive; Service.rsp{} indicates that a Response
Primitive is sent;
Service.cnf represents a Confirm Primitive; Service.cnf{} indicates that a Confirm Primitive
is received.
4 FAL syntax description
4.1 FAL-AR PDU abstract syntax
4.1.1 General
The information stored in an APDU depends on whether the APDU holds a request or a
response. The role of the state machine that encodes the APDU (the FSPM) determines how
the APDU is encoded.
APDUs always consist of an APDU header and an APDU body. In response APDUs the APDU
body can be empty.
4.1.2 Abstract syntax of APDU header
Table 2 defines the contents of the APDU header.
Table 2 – APDU header
Field name Subfield name Possible values Constraint (present if) Comment
ControlStatus Instruction Errorcode
Method
Store
Load
And
Or
Test-And-Set
Segmented Load
Segmented Store
ControlStatus Errorcode Described in ControlStatus.Instruction
Figure 3 to = Errorcode
Figure 5
ControlStatus Addressing method Variable Object ControlStatus.Instruction
<> Errorcode
Flat
– 14 – IEC 61158-6-4:2023 © IEC 2023
Field name Subfield name Possible values Constraint (present if) Comment
ControlStatus Addressing method Variable Object ControlStatus.Instruction Variable object means 2
=Method octet MethodID
Flat
Flat means 4 octet
MethodID
ControlStatus SourceID NoSourceIDInData Used by the requesting
application to indicate to
SourceIDInData
the responding
application that the
performed instruction can
be related to a specific
SourceID
ControlStatus SecureDataExchange NoSecureData APDU is a request APDU Read type instruction:
Used by the requesting
SecureData
application to ensure an
authenticated response.
Write type instruction:
Used by the requesting
application to ensure an
authenticated write type
instruction in the
responder.
ControlStatus ActualDataError NoActualError ControlStatus.Instruction Used by the responding
<> Errorcode user application to
ActualError
indicate, that an actual
error can affect the
accessed Variable
Object
ControlStatus SystemResult NoSystemResult ControlStatus.Instruction Used by the responding
= Method user application to
SystemResult
indicate that additional 2
octet data are inserted in
the APDU data before
the result data for the
accessed Variable
identifier
Hence, DataLength is 2
higher than the method
result length.
ControlStatus HistoricalDataError NoHistoricalError ControlStatus.Instruction Used by the responding
<> Errorcode user application to
HistoricalError
indicate that an error can
have affected the
accessed Variable
Object
DataFieldFormat Offset/Attribute No Offset/Attribute Indicates, whether the
APDU Body holds an
Offset/Attribute
Offset/Attribute field
DataFieldFormat Variable Identifier Simple APDU is a request APDU Indicates the format of
Format the Variable Identifier in
Complex
a request APDU
DataFieldFormat Offset/Attribute size Integer16 APDU is a response Indicates the size of the
APDU AND Offset/Attribute field of
Integer32
DataFieldFormat.Offset/A the APDU Body
ttribute = Offset/Attribute
DataLength min. 2 Indicates the total length
of the APDU Body.
MaxDataSize indicates
the max length of the
data part of the APDU
Body.
4.1.3 Abstract syntax of APDU body
The APDU header indicates the interpretation of the contents of the APDU body.
Table 3 defines the contents of the APDU body.
Table 3 – APDU body
Field name Subfield name Possible values Constraint (present if) Comment
VariableIdentifier Code.Bitaddressing No BitAddressing APDU is a request If this field indicates
APDU AND APDU BitAddressing, the
BitAddressing
Header indicates VariableIdentifier also
Complex holds a Bit-no
VariableIdentifier
VariableIdentifier Code.Bit-no 0 to 7 APDU is a request Bit-no selects a bit
APDU AND APDU within one octet. Bit-no
Header indicates = 0 selects bit 1 etc.
Complex The octet is selected by
VariableIdentifier AND Offset/Attribute.
VariableIdentifier
indicates BitAddressing
VariableIdentifier Code.Offset/Attribute Integer16 APDU is a request
size APDU AND
Integer32
DataFieldFormat.Variabl
e Identifier Format =
Complex AND
DataFieldFormat.Offset/
Attribute =
Offset/Attribute
VariableIdentifier ID −32 768 to APDU is a request
APDU AND
+32 767
DataFieldFormat.Variabl
e Identifier Format =
Simple
VariableIdentifier ID −8 388 608 to APDU is a request
APDU AND
+8 388 607
DataFieldFormat.Variabl
e Identifier Format =
Complex
Offset/Attribute −32 768  APDU is a request Negative values select
APDU AND attribute, positive
+32 767
DataFieldFormat.Offset/ values select part of
Attribute = constructed variable
Offset/Attribute AND
VariableIdentifier.Code.
Offset/Attribute size =
Integer16
Offset/Attribute −2 147 483 648 to APDU is a request Negative values select
+2 147 483 647 APDU AND attribute, positive
DataFieldFormat.Offset/ values select part of
Attribute = constructed variable
Offset/Attribute AND
VariableIdentifier.Code.
Offset/Attribute size =
Integer32
Offset/Attribute −32 768 to APDU is a response Negative values select
APDU AND attribute, positive
+32 767
DataFieldFormat.Offset/ values select part of
Attribute = constructed variable
Offset/Attribute AND
DataFieldFormat.Offset/
Attribute size= Integer16
– 16 – IEC 61158-6-4:2023 © IEC 2023
Field name Subfield name Possible values Constraint (present if) Comment
Offset/Attribute −2 147 483 648 to APDU is a response Negative values select
+2 147 483 647 APDU AND attribute, positive
DataFieldFormat.Offset/ values select part of
Attribute = constructed variable
Offset/Attribute AND
DataFieldFormat.Offset/
Attribute size= Integer32
Data Any
RequestedLength 0 to 65 535 APDU is a request Indicates the length of
APDU AND data to Read, as the
ControlStatus.Instruction number of octets
indicates Load OR
Segmented Load
Sequence 0 to 2 APDU is a request Indicates whether this
APDU AND request is the first, one
ControlStatus.Instruction in the middle, or the last
indicates Segmented of a segmented
Load OR Segmented transfer.
Store
4.2 Data types
The notation for data types is the same as IEC 61158-6-1 Type 1 elements, for the following
types:
• Integer, Integer8, Integer16, Integer32
• Unsigned, Unsigned8, Unsigned16
• Floating32, Floating64
5 Transfer syntaxes
5.1 APDU encoding
5.1.1 APDU Header encoding
5.1.1.1 APDU header structure
The abstract syntax of the APDU header is defined in 4.1.2. Subclause 5.1 describes the
encoding of the header. The APDU header consists of three fields, as shown in Figure 2.

Figure 2 – APDU header structure
5.1.1.2 ControlStatus
ControlStatus is coded into one octet. If the APDU is a request APDU, the ControlStatus holds
the subfields instruction, addressing method, SourceID and SecureDataExchange. The
interpretation of this octet is shown in Figure 3.

Figure 3 – Subfields of ControlStatus for Request
If the instruction is = 000 ( = Errorcode), the remaining five bits of ControlStatus holds the error
code. The possible values are shown in Figure 4.

Figure 4 – Subfields of ControlStatus for Response with error
If the instruction is <> 000 (<> Errorcode), the remaining five bits of ControlStatus holds the
subfields Statuscode and HistoricalDataError. The coding of these fields is shown in Figure 5.

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Figure 5 – Subfields of ControlStatus for Response with no error
5.1.1.3 DataFieldFormat
DataFieldFormat is coded into one octet. The coding of this octet is shown in Figure 6.

Figure 6 – DataFieldFormat encoding
5.1.1.4 DataLength
DataLength is an Integer32, indicating the total length of the APDU body.
5.1.2 APDU body encoding
5.1.2.1 APDU body structure
The abstract syntax for the APDU Body is described in 4.1.3. Subclause 5.1.2 describes the
encoding. The interpretation of the APDU Body is indicated by the APDU header.
A request APDU body can consist of up to four of five possible fields, as shown in Figure 7.

Figure 7 – Structure of request APDU body
A response APDU body can consist of up to two fields, as shown in Figure 8.

Figure 8 – Structure of response APDU body
5.1.2.2 Variable identifier
The Variable Identifier can be either simple or complex. If it is simple, it consists of only one
subfield, ID, which is of type Integer16. If it is complex, it consists of two subfields, code (1 octet)
and ID (3 octets) as shown in Figure 9.

Figure 9 – Variable identifier
The coding of the Code subfield of the variable identifier is shown in Figure 10.

Figure 10 – Code subfield of variable identifier

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