IEC 61158-6-20:2014

IEC 61158-6-20 ®
Edition 3.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Fieldbus specifications –
Part 6-20: Application layer protocol specification – Type 20 elements

Réseaux de communication industriels – Spécifications des bus de terrain –
Partie 6-20: Spécification du protocole de la couche application – Eléments
de type 20
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IEC 61158-6-20 ®
Edition 3.0 2014-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Fieldbus specifications –

Part 6-20: Application layer protocol specification – Type 20 elements

Réseaux de communication industriels – Spécifications des bus de terrain –

Partie 6-20: Spécification du protocole de la couche application – Eléments

de type 20
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XC
ICS 25.040.40; 35.100.70; 35.110 ISBN 978-2-8322-1766-5

– 2 – IEC 61158-6-20:2014 © IEC 2014
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, symbols, abbreviations and conventions . 11
3.1 Terms and definitions from other ISO/IEC standards . 11
3.2 IEC 61158-1 terms . 12
3.3 Type 20 fieldbus application-layer specific definitions . 14
3.4 Abbreviations and symbols . 17
3.5 Conventions . 18
3.6 Conventions used in state machines . 18
4 Abstract syntax . 20
5 Transfer syntax . 20
5.1 Common APDU fields . 20
5.2 Common APDU structure . 22
5.3 Device application service-specific APDU structures . 24
5.4 Data coding rules . 51
6 Common procedures . 56
6.1 Delayed response . 56
6.2 Publish mode procedure . 56
7 FAL protocol state machines . 56
7.1 General . 56
7.2 AREP mapping to data link layer . 57
7.3 Client ARPM . 58
7.4 Server ARPM . 60
7.5 Functions used by FAL state machines . 61
Annex A (normative) Application process status . 63
A.1 General . 63
A.2 Device malfunction . 63
A.3 Configuration changed . 63
A.4 Cold start . 64
A.5 More status available . 64
A.6 Loop current fixed . 64
A.7 Loop current saturated . 64
A.8 Non-primary variable out of limits . 65
A.9 Primary variable out of limits . 65
Annex B (normative) Device and dynamic variable . 66
B.1 Device variable . 66
B.2 Dynamic variable . 66
B.3 Primary variable . 67
B.4 Device variable classification . 68
B.5 Device families . 68
B.6 Device variable status . 68
Annex C (normative) Common tables . 70
C.1 Overview . 70

C.1.1 General . 70
C.1.2 Enumeration . 70
C.1.3 Bit Field . 70
C.2 Table definitions . 70
C.2.1 Publish mode control codes . 70
C.2.2 Write device variable codes . 70
C.2.3 Device variable family codes . 70
C.2.4 Device variable classification codes . 70
C.2.5 Analog channel saturated codes . 70
C.2.6 Analog channel fixed codes . 70
C.2.7 Standardized status 0 codes . 71
C.2.8 Standardized status 1 codes . 71
C.2.9 Standardized status 2 codes . 71
C.2.10 Standardized status 3 codes . 71
C.2.11 Publish trigger mode codes . 71
C.2.12 Transfer function codes . 71
C.2.13 Alarm Selection Codes . 71
C.2.14 Write Protect Codes. 72
C.2.15 Physical layer signalling codes . 72
C.2.16 Flag Assignment codes . 72
C.2.17 Loop current mode codes . 73
C.2.18 Trim point codes . 73
C.2.19 Analog channel flag codes . 73
C.2.20 Device variable codes . 73
C.2.21 Device profile codes . 74
Annex D (normative) Command requirements . 75
D.1 General . 75
D.2 Stateless request and response. 75
D.3 Read command . 75
D.4 Write command . 75
D.5 Action command . 75
D.6 Indexed command . 76
D.7 Multi-transaction command . 76
Bibliography . 77

Figure 1 – Request APDU . 22
Figure 2 – Normal response APDU . 22
Figure 3 – Command error response from slave to master . 23
Figure 4 – Aggregated command APDU . 24
Figure 5 – Coding without identification. 51
Figure 6 – Coding of Integer type data . 51
Figure 7 – Coding of Integer16 type data . 52
Figure 8 – Coding of Unsigned type data . 52
Figure 9 – Coding of Unsigned16 type data . 52
Figure 10 – Coding of single precision Floating Point type data . 52
Figure 11 – Coding of double precision Floating Point type data . 53
Figure 12 – Coding of Date type data . 53

– 4 – IEC 61158-6-20:2014 © IEC 2014
Figure 13 – Client state machine . 58
Figure 14 – Server state machine . 60
Figure A.1 – Loop current saturation and alarm levels . 65
Figure B.1 – Device and Dynamic variables . 66
Figure B.2 – Primary variable domains . 67
Figure B.3 – Device variable status . 69

Table 1 – Conventions used for state machines . 19
Table 2 – Response code values . 20
Table 3 – Application process status values . 21
Table 4 – Extended status values . 21
Table 5 – Identify request APDU . 24
Table 6 – Identify response value field . 25
Table 7 – Identify command specific response codes . 25
Table 8 – Read primary variable response value field . 26
Table 9 – Read primary variable command specific response codes . 26
Table 10 – Read loop current and percent of range value field . 26
Table 11 – Read loop current and percent of range command specific response codes . 27
Table 12 – Read dynamic variables and loop current value field . 27
Table 13 – Read dynamic variables and loop current command specific response
codes . 27
Table 14 – Write loop configuration value field . 28
Table 15 – Write loop configuration command specific response codes . 28
Table 16 – Read loop configuration value field . 29
Table 17 – Read loop configuration command specific response codes . 29
Table 18 – Read dynamic variable families classifications value field . 29
Table 19 – Read dynamic variable families classifications command specific response
codes . 29
Table 20 – Read device variables with status request value field . 30
Table 21 – Read device variables with status value field . 30
Table 22 – Read device variables with status command specific response codes. 31
Table 23 – Read message response value field . 32
Table 24 – Read message command specific response codes . 32
Table 25 – Read tag, descriptor, date response value field . 33
Table 26 – Read tag, descriptor, date command specific response codes . 33
Table 27 – Read primary variable transducer information response value field . 33
Table 28 – Read primary variable transducer information command specific response
codes . 34
Table 29 – Read device information response value field . 34
Table 30 – Read device information command specific response codes . 35
Table 31 – Read final assembly number response value field . 35
Table 32 – Read final assembly number command specific response codes . 35
Table 33 – Write message value field . 35
Table 34 – Write message command specific response codes . 36

Table 35 – Write tag, descriptor, date value field . 36
Table 36 – Write tag, descriptor, date command specific response codes . 36
Table 37 – Write final assembly number value field . 37
Table 38 – Write final assembly number command specific response codes . 37
Table 39 – Read long tag response value field . 37
Table 40 – Read long tag command-specific response codes . 37
Table 41 – Write long tag value field . 38
Table 42 – Write long tag command specific Response codes . 38
Table 43 – Write primary variable range value field . 39
Table 44 – Write primary variable range command specific response codes . 39
Table 45 – Enter-exit fixed current mode request value field . 40
Table 46 – Enter-exit fixed current mode response value field. 40
Table 47 – Enter-exit fixed current mode command specific response codes . 40
Table 48 – Write primary variable unit value field . 41
Table 49 – Write primary variable unit command specific response codes . 41
Table 50 – Trim loop current zero request value field . 41
Table 51 – Trim loop current zero command specific response codes . 41
Table 52 – Trim loop current gain request value field . 42
Table 53 – Trim loop current gain command specific response codes . 42
Table 54 – Read dynamic variable assignment response value field . 43
Table 55 – Read dynamic variable assignment command specific response codes . 43
Table 56 – Write dynamic variable assignment value field . 44
Table 57 – Write dynamic variable assignment command specific response codes . 44
Table 58 – Write number of response preambles value field. 45
Table 59 – Write number of response preambles command specific response codes . 45
Table 60 – Read device variable trim points request value field . 45
Table 61 – Read device variable trim points response value field . 46
Table 62 – Read device variable trim points command specific response codes . 46
Table 63 – Read device variable trim guidelines request value field . 46
Table 64 – Read device variable trim guidelines response value field . 46
Table 65 – Read device variable trim points command specific response codes . 47
Table 66 – Write device variable trim point value field . 47
Table 67 – Write device variable trim point command specific response codes . 48
Table 68 – Reset device variable trim value field . 48
Table 69 – Reset device variable trim command specific response codes . 49
Table 70 – Aggregated command specific response codes . 50
Table 71 – Coding for Date type . 53
Table 72 – Coding for one octet Enumerated Type . 54
Table 73 – One octet bit field . 54
Table 74 – Packed ASCII character set . 55
Table 75 – Acceptable subset of ISO Latin-1 characters . 56
Table 76 – Client machine state transitions . 59
Table 77 – Server machine state transitions . 61

– 6 – IEC 61158-6-20:2014 © IEC 2014
Table 78 – Function FormReqApdu . 61
Table 79 – Function Command . 61
Table 80 – Function CommErr. 61
Table 81 – Function RespCode . 62
Table 82 – Function Commcode . 62
Table 83 – Function ApStatus . 62
Table 84 – Function Value . 62
Table A.1 – Commands that cause configuration change . 63
Table C.1 – Transfer function codes . 71
Table C.2 – Alarm Selection codes . 72
Table C.3 – Write Protect codes . 72
Table C.4 – Physical layer signalling codes . 72
Table C.5 – Flag Assignment codes . 73
Table C.6 – Loop current mode codes . 73
Table C.7 – Trim point codes . 73
Table C.8 – Analog channel flag codes . 73
Table C.9 – Device variable codes . 74

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-20: Application layer protocol specification –
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
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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 IEC 61784-1 and IEC 61784-2.
International Standard IEC 61158-6-20 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.

– 8 – IEC 61158-6-20:2014 © IEC 2014
The main changes with respect to the previous edition are listed below:
a) added protocol for new services that are added to IEC 61158-5-20;
b) added normative annexes;
c) updated then references, terms, definitions, symbols, abbreviations;
d) corrected the editorial errors and the text.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/764/FDIS 65C/774/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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
INTRODUCTION
This part of IEC 61158 is one of a series produced to facilitate the interconnection of
automation system components. It is related to other standards in the set as defined by the
“three-layer” fieldbus reference model described in IEC 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 standard
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 standard is concerned, in particular, with the communication and interworking of sensors,
effectors and other automation devices. By using this standard together with other standards
positioned within the OSI or fieldbus reference models, otherwise incompatible systems may
work together in any combination.

– 10 – IEC 61158-6-20:2014 © IEC 2014
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 6-20: Application layer protocol specification –
Type 20 elements
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 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 standard defines in an abstract way the externally visible behavior provided by the Type
20 of the fieldbus Application Layer in terms of
a) the abstract syntax defining the application layer protocol data units conveyed between
communicating application entities,
b) the transfer syntax defining the application layer protocol data units conveyed between
communicating application entities,
c) the application context state machine defining the application service behavior visible
between communicating application entities; and
d) the application relationship state machines defining the communication behavior visible
between communicating application entities; and.
The purpose of this standard is to define the protocol provided to define
a) the wire-representation of the service primitives defined in IEC 61158-5-20, and
b) the externally visible behavior associated with their transfer.
This standard specifies the protocol of the Type 20 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).
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 61158-5-20:2014, Industrial communication networks – Fieldbus specifications –
Part 5-20: Application layer service definition – Type 20 elements
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/IEEE 60559, Information technology – Microprocessor Systems – Floating-Point
arithmetic
IEEE 802.15.4: IEEE Standard for Local and metropolitan area networks –
Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs)
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviations
and conventions apply.
3.1 Terms and definitions from other ISO/IEC standards
3.1.1 Terms and definitions from ISO/IEC 7498-1
a) abstract syntax
b) application entity
c) application process
d) application protocol data unit
e) application service element
f) application entity invocation
g) application process invocation
h) transfer syntax
3.1.2 Terms and definitions from ISO/IEC 9545
a) application-entity-invocation
b) application-process-invocation
c) application-service-element
3.1.3 Terms and definitions from ISO/IEC 8824-1
a) object identifier
b) type
c) value
d) simple type
– 12 – IEC 61158-6-20:2014 © IEC 2014
e) structured type
f) component type
g) tag
h) true
i) false
j) integer type
k) octet string type
m) null type
3.1.4 Terms and definitions from ISO/IEC 8825-1
a) encoding (of a data value)
b) data value
c) identifier octets (the singular form is used in this standard)
d) length octet(s) (both singular and plural forms are used in this standard)
e) contents octets
3.2 IEC 61158-1 terms
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
...