IEC 61784-3:2021

IEC 61784-3 ®
Edition 4.0 2021-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Profiles –
Part 3: Functional safety fieldbuses – General rules and profile definitions

Réseaux de communication industriels – Profils –
Partie 3: Bus de terrain de sécurité fonctionnelle – Règles générales et
définitions de profils
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IEC 61784-3 ®
Edition 4.0 2021-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Profiles –

Part 3: Functional safety fieldbuses – General rules and profile definitions

Réseaux de communication industriels – Profils –

Partie 3: Bus de terrain de sécurité fonctionnelle – Règles générales et

définitions de profils
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100.05 ISBN 978-2-8322-9268-6

– 2 – IEC 61784-3:2021 © IEC 2021
CONTENTS
FOREWORD . 7
0 Introduction . 9
0.1 General . 9
0.2 Use of extended assessment methods in Edition 4 . 11
0.3 Patent declaration . 11
1 Scope . 12
2 Normative references . 12
3 Terms, definitions, symbols, abbreviated terms and conventions . 14
3.1 Terms and definitions . 14
3.2 Symbols and abbreviated terms . 21
3.2.1 Abbreviated terms . 21
3.2.2 Symbols . 22
4 Conformance . 22
5 Basics of safety-related fieldbus systems . 23
5.1 Safety function decomposition . 23
5.2 Communication system . 23
5.2.1 General . 23
5.2.2 IEC 61158 fieldbuses . 24
5.2.3 Communication channel types . 24
5.2.4 Safety function response time . 25
5.3 Communication errors . 25
5.3.1 General . 25
5.3.2 Corruption . 25
5.3.3 Unintended repetition . 26
5.3.4 Incorrect sequence . 26
5.3.5 Loss . 26
5.3.6 Unacceptable delay . 26
5.3.7 Insertion . 26
5.3.8 Masquerade. 26
5.3.9 Addressing . 26
5.4 Deterministic remedial measures . 27
5.4.1 General . 27
5.4.2 Sequence number. 27
5.4.3 Time stamp . 27
5.4.4 Time expectation . 27
5.4.5 Connection authentication . 27
5.4.6 Feedback message . 27
5.4.7 Data integrity assurance . 27
5.4.8 Redundancy with cross checking . 28
5.4.9 Different data integrity assurance systems . 28
5.5 Typical relationships between errors and safety measures . 28
5.6 Communication phases . 29
5.7 FSCP implementation aspects . 30
5.8 Models for estimation of the total residual error rate . 30
5.8.1 Applicability . 30
5.8.2 General models for black channel communications . 31

5.8.3 Identification of generic safety properties . 31
5.8.4 Assumptions for residual error rate calculations . 32
5.8.5 Residual error rates . 33
5.8.6 Data integrity . 35
5.8.7 Authenticity. 36
5.8.8 Timeliness . 38
5.8.9 Masquerade. 41
5.8.10 Calculation of the total residual error rates . 41
5.8.11 Total residual error rate and SIL . 43
5.8.12 Configuration and parameterization for an FSCP . 43
5.9 Relationship between functional safety and security . 45
5.10 Boundary conditions and constraints . 45
5.10.1 Electrical safety . 45
5.10.2 Electromagnetic compatibility (EMC) . 46
5.11 Installation guidelines . 46
5.12 Safety manual . 46
5.13 Safety policy . 46
6 Communication Profile Family 1 (FOUNDATION™ Fieldbus) – Profiles for functional
safety . 47
7 Communication Profile Family 2 (CIP™) and Family 16 (SERCOS®) – Profiles for
functional safety . 47
8 Communication Profile Family 3 (PROFIBUS™, PROFINET™) – Profiles for
functional safety . 48
9 Communication Profile Family 6 (INTERBUS®) – Profiles for functional safety . 48
10 Communication Profile Family 8 (CC-Link™) – Profiles for functional safety . 49
10.1 Functional Safety Communication Profile 8/1 . 49
10.2 Functional Safety Communication Profile 8/2 . 49
11 Communication Profile Family 12 (EtherCAT™) – Profiles for functional safety. 49
12 Communication Profile Family 13 (Ethernet POWERLINK™) – Profiles for

functional safety . 50
13 Communication Profile Family 14 (EPA®) – Profiles for functional safety . 50
14 Communication Profile Family 17 (RAPIEnet™) – Profiles for functional safety. 50
15 Communication Profile Family 18 (SafetyNET p™ Fieldbus) – Profiles for
functional safety . 51
Annex A (informative) Example functional safety communication models . 52
A.1 General . 52
A.2 Model A (single message, channel and FAL, redundant SCLs) . 52
A.3 Model B (full redundancy) . 52
A.4 Model C (redundant messages, FALs and SCLs, single channel) . 53
A.5 Model D (redundant messages and SCLs, single channel and FAL) . 53
Annex B (normative) Safety communication channel model using CRC-based error
checking . 55
B.1 Overview. 55
B.2 Channel model for calculations . 55
B.3 Bit error probability Pe . 56
B.4 Cyclic redundancy checking . 57
B.4.1 General . 57
B.4.2 Requirements for methods to calculate R . 57
CRC
Annex C (informative) Structure of technology-specific parts. 59

– 4 – IEC 61784-3:2021 © IEC 2021
Annex D (informative) Assessment guideline . 62
D.1 Overview. 62
D.2 Channel types . 62
D.2.1 General . 62
D.2.2 Black channel . 62
D.2.3 White channel . 62
D.3 Data integrity considerations for white channel approaches . 63
D.3.1 General . 63
D.3.2 Models B and C . 63
D.3.3 Models A and D . 64
D.4 Verification of safety measures . 64
D.4.1 General . 64
D.4.2 Implementation . 65
D.4.3 Default safety action . 65
D.4.4 Safe state . 65
D.4.5 Transmission errors . 65
D.4.6 Safety reaction and response times . 65
D.4.7 Combination of measures . 65
D.4.8 Absence of interference . 66
D.4.9 Additional fault causes (white channel) . 66
D.4.10 Reference test beds and operational conditions . 66
D.4.11 Conformance tester . 66
Annex E (informative) Examples of implicit vs. explicit FSCP safety measures. 67
E.1 General . 67
E.2 Example fieldbus message with safety PDUs . 67
E.3 Model with completely explicit safety measures . 67
E.4 Model with explicit A-code and implicit T-code safety measures . 68
E.5 Model with explicit T-code and implicit A-code safety measures . 68
E.6 Model with split explicit and implicit safety measures . 69
E.7 Model with completely implicit safety measures . 70
E.8 Addition to Annex B – impact of implicit codes on properness . 70
Annex F (informative) Legacy models for estimation of the total residual error rate . 71
F.1 General . 71
F.2 Calculation of the residual error rate . 71
F.3 Total residual error rate and SIL . 73
Annex G (informative) Implicit data safety mechanisms for IEC 61784-3 functional
safety communication profiles (FSCPs) . 74
G.1 Overview. 74
G.2 Basic principles . 74
G.3 Problem statement: constant values for implicit data . 75
G.4 RP for FSCPs with random, uniformly distributed err . 78
impl
G.4.1 General . 78
i
G.4.2 Uniform distribution within the interval [0;2 -1], i ≥ r . 79
r
G.4.3 Uniform distribution in the interval [1;2 -1], i = r . 81
G.5 General case . 83
G.6 Calculation of P . 83
ID
Annex H (informative) Residual error probability for example CRC codes (tables for
verification of calculation methods) . 85
H.1 Overview. 85

H.2 Example of a 32-bit CRC. 85
H.3 Example of a 16-bit CRC. 90
H.4 Conclusion . 94
Bibliography . 96

Figure 1 – Relationships of IEC 61784-3 with other standards (machinery) . 9
Figure 2 – Relationships of IEC 61784-3 with other standards (process) . 10
Figure 3 – Transitions from Ed. 2 to Ed. 4 and future Ed. 5 assessment methods . 11
Figure 4 – Safety communication as a part of a safety function . 23
Figure 5 – Example model of a functional safety communication system . 24
Figure 6 – Example of safety function response time components . 25
Figure 7 – Conceptual FSCP protocol model . 30
Figure 8 – FSCP implementation aspects. 30
Figure 9 – Black channel from an FSCP perspective . 31
Figure 10 – Model for authentication considerations . 36
Figure 11 – Fieldbus and internal address errors . 37
Figure 12 – Example of slowly increasing message latency . 39
Figure 13 – Example of an active network element failure . 40
Figure 14 – Example application 1 (m = 4) . 42
Figure 15 – Example application 2 (m = 2) . 42
Figure 16 – Example of configuration and parameterization procedures for FSCP . 44
Figure A.1 – Model A . 52
Figure A.2 – Model B . 53
Figure A.3 – Model C . 53
Figure A.4 – Model D . 54
Figure B.1 – Binary symmetric channel (BSC) . 55
Figure B.2 – Block codes for error detection . 56
Figure B.3 – Example of a block with a message part and a CRC signature . 57
Figure B.4 – Proper and improper CRC polynomials . 58
Figure D.1 – Basic Markov model . 64
Figure E.1 – Example safety PDUs embedded in a fieldbus message . 67
Figure E.2 – Model with completely explicit safety measures . 67
Figure E.3 – Model with explicit A-code and implicit T-code safety measures . 68
Figure E.4 – Model with explicit T-code and implicit A-code safety measures . 69
Figure E.5 – Model with split explicit and implicit safety measures . 69
Figure E.6 – Model with completely implicit safety measures . 70
Figure F.1 – Example application 1 (m = 4) . 72
Figure F.2 – Example application 2 (m = 2) . 73
Figure G.1 – FSCP with implicit transmission of authenticity and/or timeliness codes . 75
Figure G.2 – Example of an incorrect transmission with multiple error causes . 76
Figure G.3 – Impact of errors in implicit data on the residual error probability . 77
Figure H.1 – Residual error probabilities (example of a 32-bit CRC – result 1) . 87
Figure H.2 – Residual error probabilities (example of a 32-bit CRC – result 2) . 87

– 6 – IEC 61784-3:2021 © IEC 2021
Figure H.3 – Residual error probabilities (example of a 32-bit CRC – result 3) . 88
Figure H.4 – Residual error probabilities (example of a 32-bit CRC – result 4) . 88
Figure H.5 – Residual error probabilities (example of a 32-bit CRC – result 5) . 89
Figure H.6 – Residual error probabilities (example of a 32-bit CRC – result 6) . 89
Figure H.7 – Residual error probabilities (example of a 16-bit CRC – result 1) . 92
Figure H.8 – Residual error probabilities (example of a 16-bit CRC – result 2) . 92
Figure H.9 – Residual error probabilities (example of a 16-bit CRC – result 3) . 93
Figure H.10 – Residual error probabilities (example of a 16-bit CRC – result 4) . 93
Figure H.11 – Residual error probabilities (example of a 16-bit CRC – result 5) . 94
Figure H.12 – Example 1 of improper polynomial . 94
Figure H.13 – Example 2 of improper polynomial . 95

Table 1 – Overview of the effectiveness of the various measures on the possible errors . 29
Table 2 – Typical relationship of residual error rate to SIL . 43
Table 3 – Typical relationship of residual error on demand to SIL . 43
Table 4 – Overview of profile identifier usable for FSCP 6/7 . 48
Table B.1 – Example dependency d and block bit length n . 56
min
Table C.1 – Common subclause structure for technology-specific parts . 59
Table F.1 – Definition of items used for calculation of the residual error rates . 72
Table F.2 – Typical relationship of residual error rate to SIL . 73
Table F.3 – Typical relationship of residual error on demand to SIL . 73
Table H.1 – Residual error probabilities (R ) for example CRC32 polynomial . 86
CRC1
Table H.2 – Residual error probabilities (R ) for example CRC16 polynomial . 91
CRC2
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
PROFILES –
Part 3: Functional safety fieldbuses –
General rules and profile definitions

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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.
International Standard IEC 61784-3 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This fourth edition cancels and replaces the third edition, published in 2016 and its
Amendment 1, published in 2017. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• Contents of previous Annex F were corrected based on feedback from peer review and
subsequent analysis (in particular deletion of RP for data integrity, reduction of the
U
Equation for RR , and clarifications on the values of RP and R ).
A I T
• Additional assumptions for residual error rate calculations, clarification of assumption a).

– 8 – IEC 61784-3:2021 © IEC 2021
• After correction, contents of previous Annex F were exchanged with the contents of
previous Subclause 5.8.
• Contents of Subclause 5.9 on security replaced by a simple reference to IEC 62443 in
accordance with Guide 120.
• Changes in Annex B: Dependency of this Annex B with the BSC model has been
highlighted. First two paragraphs and figure in Clause B.2 have been deleted because of
little relevance. The approximation Equation (B.4) has been deleted due to obsolescence,
based on the observations that the CRC shall be anyway explicitly calculated in order to
prove properness, and that it may produce optimistic results. Guidance for calculation of
R in B.4.2 has been reviewed.
CRC
• Changes in Annex D: Formula D.1 was changed from an approximation to a proper
Equation, with some adjustments, and contents of D.4.3 were clarified (default safety
action).
• New informative Annex H, providing additional guidance for the calculation of RCRC.
The text of this International Standard is based on the following documents:
FDIS Report on voting
65C/1067/FDIS 65C/1072/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61784-3 series, published under the general title Industrial
communication networks – Profiles – Functional safety fieldbuses, can be found on the IEC
website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
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.
0 Introduction
0.1 General
The IEC 61158 (all parts) fieldbus standard together with its companion standards
IEC 61784-1 and IEC 61784-2 defines a set of communication protocols that enable
distributed control of automation applications. Fieldbus technology is now considered well
accepted and well proven. Thus, fieldbus enhancements continue to emerge, addressing
applications for areas such as real time and safety-related applications.
IEC 61784-3 (all parts) explains the relevant principles for functional safety communications
with reference to IEC 61508 (all parts) and specifies several safety communication layers
(profiles and corresponding protocols) based on the communication profiles and protocol
layers of IEC 61784-1, IEC 61784-2 and IEC 61158 (all parts). It does not cover electrical
safety and intrinsic safety aspects. It also does not cover security aspects, nor does it provide
any requirements for security.
Figure 1 shows the relationships between IEC 61784-3 (all parts) and relevant safety and
fieldbus standards in a machinery environment.

NOTE IEC 62061 specifies the relationship between PL (Category) and SIL.
Figure 1 – Relationships of IEC 61784-3 with other standards (machinery)

– 10 – IEC 61784-3:2021 © IEC 2021
Figure 2 shows the relationships between IEC 61784-3 (all parts) and relevant safety and
fieldbus standards in a process environment.

a
For specified electromagnetic environments; otherwise IEC 61326-3-1 or IEC 61000-6-7.
Figure 2 – Relationships of IEC 61784-3 with other standards (process)
Safety communication layers which are implemented as parts of safety-related systems
according to IEC 61508 (all parts) provide the necessary confidence in the transportation of
messages (information) between two or more participants on a fieldbus in a safety-related
system, or sufficient confidence of safe behaviour in the event of fieldbus errors or failures.
Safety communication layers specified in IEC 61784-3 (all parts) do this in such a way that a
fieldbus can be used for applications requiring functional safety up to the Safety Integrity
Level (SIL) specified by its corresponding functional safety communication profile.
The resulting SIL claim of a system depends on the implementation of the selected functional
safety communication profile (FSCP) within this system – implementation of a functional
safety communication profile in a standard device is not sufficient to qualify it as a safety
device.
IEC 61784-3 (all parts) describes:
• basic principles for implementing the requirements of IEC 61508 (all parts) for safety-
related data communications, including possible transmission faults, remedial measures
and considerations affecting data integrity;
• functional safety communication profiles for several communication profile families in
IEC 61784-1 and IEC 61784-2, including safety layer extensions to the communication
service and protocols sections of IEC 61158 (all parts).

0.2 Use of extended assessment methods in Edition 4
This edition of the generic part of IEC 61784-3 (all parts) includes extended models for use
when estimating the total residual error rate for an FSCP. This value can be used to
determine if the FSCP meets the requirements of functional safety applications up to a given
SIL. These extended models for qualitative and quantitative safety determination methods are
detailed in Annex E and 5.8.
Upon publication of this new edition of the generic part, FSCPs shall be assessed using the
methods from this Edition 4, based on the extended models specified in 5.8 (derived from a
modified version of Annex F of Edition 3). The informative Annex F contains the legacy
models for reference purpose only.
Figure 3 shows the transitions from original assessment methods of Edition 2 to extended
assessment methods in this Edition 4 and the future Edition 5.

Key
DI Data Integrity
TADI Timeliness, Authenticity, Data Integrity
Figure 3 – Transitions from Ed. 2 to Ed. 4 and future Ed. 5 assessment methods
0.3 Patent declaration
The International Electrotechnical Commission (IEC) draws attention to the fact that it is
claimed that compliance with this document may involve the use of patents concerning
functional safety communication profiles for families 1, 2, 3, 6, 8, 12, 13, 14, 17 and 18 given
in IEC 61784-3-1, IEC 61784-3-2, IEC 61784-3-3, IEC 61784-3-6, IEC 61784-3-8,
IEC 61784-3-12, IEC 61784-3-13, IEC 61784-3-14, IEC 61784-3-17 and IEC 61784-3-18.
IEC takes no position concerning the evidence, validity and scope of these patent rights.
The holders of these patent rights have assured IEC that they are willing to negotiate licences
under reasonable and non-discriminatory terms and conditions with applicants throughout the
world. In this respect, the statements of the holders of these patent rights are registered with
IEC. Information may be obtained from the patent database available at http://patents.iec.ch.
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those in the patent database. IEC shall not be held
responsible for identifying any or all such patent rights.

– 12 – IEC 61784-3:2021 © IEC 2021
INDUSTRIAL COMMUNICATION NETWORKS –
PROFILES –
Part 3: Functional safety fieldbuses –
General rules and profile definitions

1 Scope
This part of the IEC 61784-3 series explains some common principles that can be used in the
transmission of safety-relevant messages among participants within a distributed network
which use fieldbus technology in accordance with the requirements of IEC 61508 (all parts)
for functional safety. These principles are based on the black channel approach. They can be
used in various industrial applications such as process control, manufacturing automation and
machinery.
This part and the IEC 61784-3-x parts specify several functional safety communication
profiles based on the communication profiles and protocol layers of the fieldbus technologies
in IEC 61784-1, IEC 61784-2 and IEC 61158 (all parts). These functional safety
communication profiles use the black channel approach, as defined in IEC 61508. These
functional safety communication profiles are intended for implementation in safety devices
exclusively.
NOTE 1 Other safety-related communication systems meeting the requirements of IEC 61508 (all parts) can exist
that are not included in IEC 61784-3 (all parts).
NOTE 2 It does not cover electrical safety and intrinsic safety aspects. Electrical safety relates to hazards such
as electrical shock. Intrinsic safety relates to hazards associated with potentially explosive atmospheres.
All systems are exposed to unauthorized access at some point of their life cycle. Additional
measures need to be considered in any safety-related application to protect fieldbus systems
against unauthorized access. IEC 62443 (all parts) will address many of these issues; the
relationship with IEC 62443 (all parts) is detailed in a dedicated subclause of this document.
NOTE 3 Implementation of a functional safety communication profile according to this document in a device is not
sufficient to qualify it as a safety device, as defined in IEC 61508 (all parts).
NOTE 4 The resulting SIL claim of a system depends on the implementation of the selected functional safety
communication profile within this system.
NOTE 5 Annex C explains the numbering scheme used for the technology-specific parts (IEC 61784-3-x) as well
as their common general structure.
NOTE 6 Annex D provides a guideline for the assessment and test of safety communication profiles as well as
safety-related device
...