IEC 61784-3-18:2011

IEC 61784-3-18 ®
Edition 1.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Profiles
Part 3-18: Functional safety fieldbuses – Additional specifications for CPF 18

Réseaux de communication industriels – Profils
Partie 3-18: Bus de terrain de sécurité fonctionnelle – Spécifications
supplémentaires pour le CPF 18

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IEC 61784-3-18 ®
Edition 1.0 2011-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Profiles
Part 3-18: Functional safety fieldbuses – Additional specifications for CPF 18

Réseaux de communication industriels – Profils
Partie 3-18: Bus de terrain de sécurité fonctionnelle – Spécifications
supplémentaires pour le CPF 18

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XB
ICS 13.110, 25.040.40, 35.100.05 ISBN 978-2-88912-475-6

– 2 – 61784-3-18  IEC:2011
CONTENTS
FOREWORD . 5
0 Introduction . 7
0.1 General . 7
0.2 Patent declaration . 9
1 Scope . 10
2 Normative references . 10
3 Terms, definitions, symbols, abbreviated terms and conventions . 11
3.1 Terms and definitions . 11
3.1.1 Common terms and definitions . 11
3.1.2 CPF 18: Additional terms and definitions . 15
3.2 Symbols and abbreviated terms. 16
3.2.1 Common symbols and abbreviated terms . 16
3.2.2 CPF 18: Additional symbols and abbreviated terms . 17
3.3 Conventions . 17
4 Overview of FSCP 18/1 (SafetyNET p™) . 19
4.1 General . 19
4.2 FSCP 18/1 . 19
5 General . 20
5.1 External documents providing specifications for the profile . 20
5.2 Safety functional requirements . 20
5.3 Safety measures . 20
5.4 Safety communication layer structure . 21
5.5 Relationships with FAL (and DLL, PhL) . 22
5.5.1 General . 22
5.5.2 Data Types . 22
6 Safety communication layer services . 22
6.1 General elements . 22
6.1.1 General . 22
6.1.2 Safety object dictionary . 22
6.1.3 Safety process data object (SPDO) . 22
6.1.4 Safety heartbeat (SHB) . 22
6.1.5 Safety delay monitoring (SDM) . 23
6.2 Communication relation . 23
7 Safety communication layer protocol . 24
7.1 Safety PDU format . 24
7.1.1 General . 24
7.1.2 Safety process data objects (SPDO) . 24
7.1.3 Safety heartbeat (SHB) . 26
7.1.4 Safety PDUs embedded in a Type 22 PDU . 28
7.2 Safety communication layer management (SALMT) . 28
7.3 Safety process data communication . 30
7.4 Safety heartbeat . 32
7.5 Delay monitoring . 33
8 Safety communication layer management . 34
8.1 Parameter handling . 34
8.2 Safety object dictionary . 34

61784-3-18  IEC:2011 – 3 –
8.2.1 General . 34
8.2.2 Communication profile section . 35
8.2.3 Standardized device profile section . 51
9 System requirements . 51
9.1 Indicators and switches . 51
9.1.1 Indicator states and flash rates . 51
9.1.2 Indicators . 51
9.1.3 Switches . 52
9.2 Installation guidelines . 52
9.3 Safety function response time . 52
9.3.1 General . 52
9.3.2 Determination of FSCP 18/1 time expectation behavior . 53
9.3.3 Calculation of the worst case safety function response time . 53
9.4 Duration of demands . 53
9.5 Constraints for calculation of system characteristics . 53
9.5.1 Safety related constraints . 53
9.5.2 Probabilistic considerations . 55
9.6 Maintenance . 55
9.7 Safety manual . 55
10 Assessment . 55
Annex A (informative) Additional information for functional safety communication
profiles of CPF 18 . 57
Annex B (informative) Information for assessment of the functional safety
communication profiles of CPF 18 . 58
Bibliography . 59

Table 1 – Object definition . 18
Table 2 – Safety PDU element definition . 18
Table 3 – Communication errors and detection measures . 21
Table 4 – SPDO PDU structure . 25
Table 5 – SHB request PDU structure . 26
Table 6 – SHB response PDU structure . 27
Table 7 – SHB safety communication layer state encoding . 27
Table 8 – SALMT commands . 28
Table 9 – System states of SALMT state machine. 29
Table 10 – State transitions SALMT state machine . 30
Table 11 – System states of RxSPDO state machine . 31
Table 12 – State transitions RxSPDO state machine . 31
Table 13 – Timeouts . 32
Table 14 – Safety object dictionary structure . 34
Table 15 – Objects of communication section . 35
Table 16 – Device type . 36
Table 17 – Safety ID . 37
Table 18 – Safety consumer heartbeat entry . 37
Table 19 – Safety consumer heartbeat . 38

– 4 – 61784-3-18  IEC:2011
Table 20 – Safety producer heartbeat parameter . 39
Table 21 – Safety bus cycle times . 42
Table 22 – SPDO timeout tolerance . 43
Table 23 – Receive SPDO communication parameter . 43
Table 24 – Transmit SPDO communication parameter . 46
Table 25 – Mapping format . 49
Table 26 – Receive SPDO mapping parameter . 49
Table 27 – Transmit SPDO mapping parameter . 50
Table 28 – Indicator states definiton . 51
Table 29 – STATUS indicator states . 51

Figure 1 – Relationships of IEC 61784-3 with other standards (machinery) . 7
Figure 2 – Relationships of IEC 61784-3 with other standards (process) . 8
Figure 3 – FSCP 18/1 system . 19
Figure 4 – FSCP 18/1 software architecture . 21
Figure 5 – SPDO interaction model . 23
Figure 6 – SHB interaction model . 23
Figure 7 – Safety process data object structure . 24
Figure 8 – Safety heartbeat request structure . 26
Figure 9 – Safety heartbeat response structure . 26
Figure 10 – Safety PDU for FSCP 18/1 embedded in a Type 22 CDC data section . 28
Figure 11 – SALMT state machine . 29
Figure 12 – RxSPDO state machine . 31
Figure 13 – Heartbeat procedure . 32
Figure 14 – Delay measurement principle . 33
Figure 15 – Parameter handling . 34
Figure 16 – Safety response time components . 52
Figure 17 – Considered data fields for message size calculation . 54
Figure 18 – Residual error rate . 55

61784-3-18 © IEC:2011 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
PROFILES
Part 3-18: Functional safety fieldbuses –
Additional specifications for CPF 18

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 in addition to other activities, IEC publishes International Standards, Technical Specifications,
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with the International Organization for 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
interested IEC National Committees.
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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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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
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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.
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members of its technical committees and IEC National Committees for any personal injury, property damage or
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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.
International Standard IEC 61784-3-18 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial process measurement, control and
automation.
This standard cancels and replaces IEC/PAS 61784-3-18 published in 2009. This first edition
constitutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/639/FDIS 65C/649/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 the ISO/IEC Directives, Part 2.

– 6 – 61784-3-18  IEC:2011
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 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.
61784-3-18  IEC:2011 – 7 –
0 Introduction
0.1 General
The IEC 61158 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 many fieldbus enhancements are emerging, addressing not yet standardized
areas such as real time, safety-related and security-related applications.
This standard explains the relevant principles for functional safety communications with
reference to IEC 61508 series 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 the IEC 61158 series. It does not cover electrical safety and
intrinsic safety aspects.
Figure 1 shows the relationships between this standard and relevant safety and fieldbus
standards in a machinery environment.
Product standards
ISO 12100-1 and ISO 14121
ISO 12100-1 and ISO 14121
Safety of machinery – Principles for
IEC 61496 IEC 61131-6 IEC 61800-5-2 ISO 10218-1
IEC 61496 IEC 61800-5-2 ISO 10218-1 Safety of machinery – Principles for
IEC 61131-6
design and risk assessment
Safety f. e.g. Safety functions Safety requirements
Safety f. e.g. Safety for PLC Safety functions Safety requirements design and risk assessment
Safety for PLC
(under consideration)
light curtains for drives for robots
light curtains (under consideration) for drives for robots
Design of safety-related electrical, electronic and program-
IEC 61784-4 IEC 62443
IEC 61784-4 IEC 62443
mable electronic control systems (SRECS) for machinery
Security Security
Security Security
(profile-specific) (common part)
(profile-specific) (common part)
SIL based PL based
IEC 61784-5 IEC 61918
IEC 61784-5 IEC 61918
Installation guide Installation guide
Installation guide Installation guide Design objective
(profile-specific) (common part)
(profile-specific) (common part)
Applicable standards
ISO 13849-1, -2
ISO 13849-1, -2
IEC 60204-1
IEC 60204-1
Safety-related parts
Safety-related parts
Safety of electrical
Safety of electrical
IEC 61000-1-2
IEC 61000-1-2 of machinery
of machinery
equipment
equipment
Methodology EMC & FS
Methodology EMC & FS (SRPCS)
(SRPCS)
IEC 61326-3-1
IEC 61784-3
IEC 61784-3 IEC 61326-3-1
Non-electrical
Non-electrical
Test EMC & FS
Functional safety
Functional safety Test EMC & FS
communication
communication
Electrical
Electrical
US: NFPA 79
US: NFPA 79
profiles
profiles
(2006)
(2006)
IEC 62061
IEC 62061
Functional safety
Functional safety
IEC 61158 series /
IEC 61158 series /
for machinery
for machinery
IEC 61784-1, -2 IEC 61508 series
IEC 61784-1, -2 IEC 61508 series (SRECS)
(SRECS)
Functional safety (FS)
Fieldbus for use in Functional safety (FS) (including EMC for
Fieldbus for use in
(including EMC for
(basic standard)
(basic standard) industrial environment)
industrial control systems industrial environment)
industrial control systems
Key
(yellow) safety-related standards
(blue) fieldbus-related standards
(dashed yellow) this standard
IEC  768/11
NOTE Subclauses 6.7.6.4 (high complexity) and 6.7.8.1.6 (low complexity) of IEC 62061 specify the relationship
between PL (Category) and SIL.
Figure 1 – Relationships of IEC 61784-3 with other standards (machinery)

– 8 – 61784-3-18  IEC:2011
Figure 2 shows the relationships between this standard and relevant safety and fieldbus
standards in a process environment.
Product standards
IEC 61496 IEC 61800-5-2 ISO 10218-1
IEC 61131-6
IEC 61496 IEC 61131-6 IEC 61800-5-2 ISO 10218-1
Safety f. e.g. Safety functions Safety requirements
Safety for PLC
Safety f. e.g. Safety for PLC Safety functions Safety requirements
light curtains (under consideration) for drives for robots
(under consideration)
light curtains for drives for robots
IEC 61784-4 IEC 62443
IEC 61784-4 IEC 62443
Security Security
Security Security
(profile-specific) (common part)
(profile-specific) (common part)
See safety standards for machinery
(Figure 1)
IEC 61784-5 IEC 61918
IEC 61784-5 IEC 61918
Installation guide Installation guide
Installation guide Installation guide
(profile-specific) (common part)
(profile-specific) (common part)
Valid also in process industries,
whenever applicable
a)
a)
IEC 61326-3-2
IEC 61326-3-2
EMC and
EMC and
functional safety
functional safety
IEC 61784-3
IEC 61784-3
Functional safety
Functional safety
communication
communication
profiles
profiles
US:
US:
ISA-84.00.01
ISA-84.00.01
b)
b)
(3 parts = modified
IEC 61511 series
IEC 61511 series (3 parts = modified
IEC 61511)
Functional safety –
IEC 61158 series / Functional safety – IEC 61511)
IEC 61158 series /
Safety instrumented
Safety instrumented
IEC 61784-1, -2 IEC 61508 series
IEC 61784-1, -2 IEC 61508 series
systems for the
systems for the
Fieldbus for use in Functional safety (FS)
Functional safety (FS)
Fieldbus for use in DE: VDI 2180
process industry sector DE: VDI 2180
process industry sector
(basic standard)
(basic standard)
industrial control systems Part 1-4
industrial control systems
Part 1-4
Key
(yellow) safety-related standards
(blue) fieldbus-related standards
(dashed yellow) this standard
IEC  769/11
a
For specified electromagnetic environments; otherwise IEC 61326-3-1.
b
EN ratified.
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 series 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 this standard 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 within this system – implementation of a functional safety
communication profile in a standard device is not sufficient to qualify it as a safety device.

61784-3-18  IEC:2011 – 9 –
This standard describes:
– basic principles for implementing the requirements of IEC 61508 series for safety-
related data communications, including possible transmission faults, remedial
measures and considerations affecting data integrity;
– individual description of functional safety profiles for several communication profile
families in IEC 61784-1 and IEC 61784-2;
– safety layer extensions to the communication service and protocols sections of the
IEC 61158 series.
0.2 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 a patent concerning the
functional safety communication profiles for family 18 as follows, where the [xx] notation
indicates the holder of the patent right:
DE 10 2008 007 672.4-31 [PI] Verfahren und Vorrichtung zum Übertragen von
Daten in einem Netzwerk
IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he/she is willing to negotiate licences
either free of charge or under reasonable and non-discriminatory terms and conditions with
applicants throughout the world. In this respect, the statement of the holder of this patent
right is registered with IEC. Information may be obtained from:
Information may be obtained from:
[PI] Pilz GmbH & Co. KG
Felix-Wankel-Str. 2
73760 Ostfildern
GERMANY
Attention is drawn to the possibility that some of the elements of this document may be the
subject of patent rights other than those identified above. IEC shall not be held responsible for
identifying any or all such patent rights.
ISO (www.iso.org/patents) and IEC (http://www.iec.ch/tctools/patent_decl.htm) maintain on-
line data bases of patents relevant to their standards. Users are encouraged to consult the
data bases for the most up to date information concerning patents.

– 10 – 61784-3-18  IEC:2011
INDUSTRIAL COMMUNICATION NETWORKS –
PROFILES
Part 3-18: Functional safety fieldbuses –
Additional specifications for CPF 18

1 Scope
This part of the IEC 61784-3 series specifies a safety communication layer (services and
protocol) based on CPF 18 of IEC 61784-2 and IEC 61158 Type 22. It identifies the principles
for functional safety communications defined in IEC 61784-3 that are relevant for this safety
communication layer.
NOTE 1 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.
This part defines mechanisms for the transmission of safety-relevant messages among
participants within a distributed network using fieldbus technology in accordance with the
requirements of IEC 61508 series for functional safety. These mechanisms may be used in
various industrial applications such as process control, manufacturing automation and
machinery.
This part provides guidelines for both developers and assessors of compliant devices and
systems.
NOTE 2 The resulting SIL claim of a system depends on the implementation of the selected functional safety
communication profile within this system – implementation of a functional safety communication profile according to
this part in a standard device is not sufficient to qualify it as a safety device.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61158-3-22, Industrial communication networks – Fieldbus specifications – Part 3-22:
Data-link layer service definition – Type 22 elements
IEC 61158-4-22, Industrial communication networks – Fieldbus specifications – Part 4-22:
Data-link layer protocol specification – Type 22 elements
IEC 61158-5-22, Industrial communication networks – Fieldbus specifications – Part 5-22:
Application layer service definition – Type 22 elements
IEC 61158-6-22, Industrial communication networks – Fieldbus specifications – Part 6-22:
Application layer protocol specification – Type 22 elements
IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic
safety-related systems
___________
In the following pages of this standard, “this part” will be used for “this part of the IEC 61784-3 series”.
In the following pages of this standard, “IEC 61508” will be used for “IEC 61508 series”.

61784-3-18  IEC:2011 – 11 –
IEC 61508-2:2010, Functional safety of electrical/electronic/programmable electronic safety-
related systems – Part 2: Requirements for electrical/electronic/programmable electronic
safety-related systems
IEC 61784-2:2010, Industrial communication networks – Profiles – Part 2: Additional fieldbus
profiles for real-time networks based on ISO/IEC 8802-3
IEC 61784-3:2010, Industrial communication networks – Profiles – Part 3: Functional safety
fieldbuses – General rules and profile definitions
IEC 61918, Industrial communication networks – Installation of communication networks in
industrial premises
ISO/IEC 10731, Information technology – Open system interconnection – Basic reference
model – Conventions for the definition of OSI services
3 Terms, definitions, symbols, abbreviated terms and conventions
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1 Common terms and definitions
3.1.1.1
availability
probability for an automated system that for a given period of time there are no unsatisfactory
system conditions such as loss of production
3.1.1.2
black channel
communication channel without available evidence of design or validation according to
IEC 61508
3.1.1.3
communication channel
logical connection between two end-points within a communication system
3.1.1.4
communication system
arrangement of hardware, software and propagation media to allow the transfer of messages
(ISO/IEC 7498 application layer) from one application to another
3.1.1.5
connection
logical binding between two application objects within the same or different devices
3.1.1.6
Cyclic Redundancy Check (CRC)
redundant data derived from, and stored or transmitted together with, a block of data
in order to detect data corruption
procedure used to calculate the redundant data
NOTE 1 Terms “CRC code” and "CRC signature", and labels such as CRC1, CRC2, may also be used in this
standard to refer to the redundant data.

– 12 – 61784-3-18  IEC:2011
NOTE 2 See also [35], [36] .
3.1.1.7
error
discrepancy between a computed, observed or measured value or condition and the true,
specified or theoretically correct value or condition
[IEC 61508-4:2010], [IEC 61158]
NOTE 1 Errors may be due to design mistakes within hardware/software and/or corrupted information due to
electromagnetic interference and/or other effects.
NOTE 2 Errors do not necessarily result in a failure or a fault.
3.1.1.8
failure
termination of the ability of a functional unit to perform a required function or operation of a
functional unit in any way other than as required
NOTE 1 The definition in IEC 61508-4 is the same, with additional notes.
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.11, modified]
NOTE 2 Failure may be due to an error (for example, problem with hardware/software design or message
disruption).
3.1.1.9
fault
abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit
to perform a required function
NOTE IEV 191-05-01 defines “fault” as a state characterized by the inability to perform a required function,
excluding the inability during preventive maintenance or other planned actions, or due to lack of external
resources.
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.10, modified]
3.1.1.10
fieldbus
communication system based on serial data transfer and used in industrial automation or
process control applications
3.1.1.11
frame
denigrated synonym for DLPDU
3.1.1.12
Frame Check Sequence (FCS)
redundant data derived from a block of data within a DLPDU (frame), using a hash function,
and stored or transmitted together with the block of data, in order to detect data corruption
NOTE 1 An FCS can be derived using for example a CRC or other hash function.
NOTE 2 See also [35], [36].
3.1.1.13
hash function
(mathematical) function that maps values from a (possibly very) large set of values into a
(usually) smaller range of values
___________
Figures in square brackets refer to the Bibliography.

61784-3-18  IEC:2011 – 13 –
NOTE 1 Hash functions can be used to detect data corruption.
NOTE 2 Common hash functions include parity, checksum or CRC.
[IEC/TR 62210, modified]
3.1.1.14
hazard
state or set of conditions of a system that, together with other related conditions will inevitably
lead to harm to persons, property or environment
3.1.1.15
message
ordered series of octets intended to convey information
[ISO/IEC 2382-16.02.01, modified]
3.1.1.16
message sink
part of a communication system in which messages are considered to be received
[ISO/IEC 2382-16.02.03]
3.1.1.17
message source
part of a communication system from which messages are considered to originate
[ISO/IEC 2382-16.02.02]
3.1.1.18
nuisance trip
spurious trip with no harmful effect
NOTE Internal abnormal errors can be caused in communication systems such as wireless transmission, for
example by too many retries in the presence of interferences.
3.1.1.19
performance level (PL)
discrete level used to specify the ability of safety-related parts of control systems to perform a
safety function under foreseeable conditions
[ISO 13849-1]
3.1.1.20
redundancy
existence of means, in addition to the means which would be sufficient for a functional unit to
perform a required function or for data to represent information
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.12, modified]
3.1.1.21
risk
combination of the probability of occurrence of harm and the severity of that harm
NOTE For more discussion on this concept see Annex A of IEC 61508-5:2010.
[IEC 61508-4:2010], [ISO/IEC Guide 51:1999, definition 3.2]
3.1.1.22
safety communication layer (SCL)
communication layer that includes all the necessary measures to ensure safe transmission of
data in accordance with the requirements of IEC 61508

– 14 – 61784-3-18  IEC:2011
3.1.1.23
safety data
data transmitted across a safety network using a safety protocol
NOTE The Safety Communication Layer does not ensure safety of the data itself, only that the data is transmitted
safely.
3.1.1.24
safety device
device designed in accordance with IEC 61508 and which implements the functional safety
communication profile
3.1.1.25
safety function
function to be implemented by an E/E/PE safety-related system or other risk reduction
measures, that is intended to achieve or maintain a safe state for the EUC, in respect of a
specific hazardous event
NOTE The definition in IEC 61508-4 is the same, with an additional example and reference.
[IEC 61508-4:2010, modified]
3.1.1.26
safety function response time
worst case elapsed time following an actuation of a safety sensor connected to a fieldbus,
before the corresponding safe state of its safety actuator(s) is achieved in the presence of
errors or failures in the safety function channel
NOTE This concept is introduced in IEC 61784-3:2010, 5.2.4 and addressed by the functional safety
communication profiles defined in this part.
3.1.1.27
safety integrity level (SIL)
discrete level (one out of a possible four), corresponding to a range of safety integrity values,
where safety integrity level 4 has the highest level of safety integrity and safety integrity level
1 has the lowest
NOTE 1 The target failure measures (see IEC 61508-4:2010, 3.5.17) for the four safety integrity levels are
specified in Tables 2 and 3 of IEC 61508-1:2010.
NOTE 2 Safety integrity levels are used for specifying the safety integrity requirements of the safety functions to
be allocated to the E/E/PE safety-related systems.
NOTE 3 A safety integrity level (SIL) is not a property of a system, subsystem, element or component. The correct
interpretation of the phrase “SILn safety-related system” (where n is 1, 2, 3 or 4) is that the system is potentially
capable of supporting safety functions with a safety integrity level up to n.
[IEC 61508-4:2010]
3.1.1.28
safety measure
measure to control possible communication errors that is designed and
implemented in compliance with the requirements of IEC 61508
NOTE 1 In practice, several safety measures are combined to achieve the required safety integrity level.
NOTE 2 Communication errors and related safety measures are detailed in IEC 61784-3:2010, 5.3 and 5.4.
3.1.1.29
safety-related application
programs designed in accordance with IEC 61508 to meet the SIL requirements of the
application
61784-3-18  IEC:2011 – 15 –
3.1.1.30
safety-related system
sy
...

IEC 61784-3-18 ®
Edition 1.2 2021-04
CONSOLIDATED VERSION
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Industrial communication networks – Profiles –
Part 3-18: Functional safety fieldbuses – Additional specifications for CPF 18

Réseaux de communication industriels – Profils –
Partie 3-18: Bus de terrain de sécurité fonctionnelle – Spécifications
supplémentaires pour CPF 18
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IEC 61784-3-18 ®
Edition 1.2 2021-04
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial communication networks – Profiles –

Part 3-18: Functional safety fieldbuses – Additional specifications for CPF 18

Réseaux de communication industriels – Profils –

Partie 3-18: Bus de terrain de sécurité fonctionnelle – Spécifications

supplémentaires pour CPF 18
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040.40; 35.100.05 ISBN 978-2-8322-9767-4

IEC 61784-3-18 ®
Edition 1.2 2021-04
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Industrial communication networks – Profiles –
Part 3-18: Functional safety fieldbuses – Additional specifications for CPF 18

Réseaux de communication industriels – Profils –
Partie 3-18: Bus de terrain de sécurité fonctionnelle – Spécifications
supplémentaires pour CPF 18
– 2 – IEC 61784-3-18:2011+AMD1:2016

+AMD2:2021 CSV  IEC 2021
CONTENTS
FOREWORD . 5

0 Introduction . 7

0.1 General . 7

0.2 Patent declaration . 11

INTRODUCTION to Amendment 2 . 11

1 Scope . 12

2 Normative references . 12

3 Terms, definitions, symbols, abbreviated terms and conventions . 13
3.1 Terms and definitions . 13
3.1.1 Common terms and definitions . 13
3.1.2 CPF 18: Additional terms and definitions . 17
3.2 Symbols and abbreviated terms. 18
3.2.1 Common symbols and abbreviated terms . 18
3.2.2 CPF 18: Additional symbols and abbreviated terms . 19
3.3 Conventions . 19
4 Overview of FSCP 18/1 (SafetyNET p™) . 21
4.1 General . 21
4.2 FSCP 18/1 . 21
5 General . 22
5.1 External documents providing specifications for the profile . 22
5.2 Safety functional requirements . 22
5.3 Safety measures . 23
5.4 Safety communication layer structure . 23
5.5 Relationships with FAL (and DLL, PhL) . 24
5.5.1 General . 24
5.5.2 Data Types . 24
6 Safety communication layer services . 24
6.1 General elements . 24
6.1.1 General . 24
6.1.2 Safety object dictionary . 25
6.1.3 Safety process data object (SPDO) . 25
6.1.4 Safety heartbeat (SHB) . 25
6.1.5 Safety delay monitoring (SDM) . 25
6.2 Communication relation . 25
7 Safety communication layer protocol . 27
7.1 Safety PDU format . 27
7.1.1 General . 27
7.1.2 Safety process data objects (SPDO) . 27
7.1.3 Safety heartbeat (SHB) . 29
7.1.4 Safety PDUs embedded in a Type 22 PDU . 31
7.2 Safety communication layer management (SALMT) . 32
7.3 Safety process data communication . 34
7.4 Safety heartbeat . 36
7.5 Delay monitoring . 37
8 Safety communication layer management . 38

+AMD2:2021 CSV  IEC 2021
8.1 Parameter handling . 38

8.2 Safety object dictionary . 38

8.2.1 General . 38

8.2.2 Communication profile section . 39

8.2.3 Standardized device profile section . 55

9 System requirements . 55

9.1 Indicators and switches . 55

9.1.1 Indicator states and flash rates . 55

9.1.2 Indicators . 56

9.1.3 Switches . 56
9.2 Installation guidelines . 56
9.3 Safety function response time . 56
9.3.1 General . 56
9.3.2 Determination of FSCP 18/1 time expectation behavior . 57
9.3.3 Calculation of the worst case safety function response time . 58
9.4 Duration of demands . 58
9.5 Constraints for calculation of system characteristics . 58
9.5.1 Safety related constraints . 58
9.5.2 Probabilistic considerations .
9.6 Maintenance . 60
9.7 Safety manual . 60
10 Assessment . 61
Annex A (informative) Additional information for functional safety communication
profiles of CPF 18 . 62
A.1 Hash function calculation . 62
A.2 Void . 65
Annex B (informative) Information for assessment of the functional safety
communication profiles of CPF 18 . 66
Bibliography . 67

Figure 1 – Relationships of IEC 61784-3 with other standards (machinery) . 8
Figure 2 – Relationships of IEC 61784-3 with other standards (process) . 10
Figure 3 – FSCP 18/1 system . 21
Figure 4 – FSCP 18/1 software architecture . 24

Figure 5 – SPDO interaction model . 26
Figure 6 – SHB interaction model . 26
Figure 7 – Safety process data object structure . 27
Figure 8 – Safety heartbeat request structure . 29
Figure 9 – Safety heartbeat response structure . 30
Figure 10 – Safety PDU for FSCP 18/1 embedded in a Type 22 CDC data section . 32
Figure 11 – SALMT state machine . 33
Figure 12 – RxSPDO state machine . 35
Figure 13 – Heartbeat procedure . 36
Figure 14 – Delay measurement principle . 37
Figure 15 – Parameter handling . 38
Figure 16 – Safety response time components . 57

– 4 – IEC 61784-3-18:2011+AMD1:2016

+AMD2:2021 CSV  IEC 2021
Figure 17 – Considered data fields for message size calculation . 59

Figure 18 – Residual error rate .

Table 1 – Object definition . 20

Table 2 – Safety PDU element definition . 20

Table 3 – Communication errors and detection measures . 23

Table 4 – SPDO PDU structure . 28

Table 5 – SHB request PDU structure . 29

Table 6 – SHB response PDU structure . 30
Table 7 – SHB safety communication layer state encoding . 31
Table 8 – SALMT commands . 32
Table 9 – System states of SALMT state machine. 33
Table 10 – State transitions SALMT state machine . 34
Table 11 – System states of RxSPDO state machine . 35
Table 12 – State transitions RxSPDO state machine . 35
Table 13 – Timeouts . 36
Table 14 – Safety object dictionary structure . 38
Table 15 – Objects of communication section . 39
Table 16 – Device type . 40
Table 17 – Safety ID . 41
Table 18 – Safety consumer heartbeat entry . 42
Table 19 – Safety consumer heartbeat . 43
Table 20 – Safety producer heartbeat parameter . 44
Table 21 – Safety bus cycle times . 47
Table 22 – SPDO timeout tolerance . 48
Table 23 – Receive SPDO communication parameter . 48
Table 24 – Transmit SPDO communication parameter . 51
Table 25 – Mapping format . 54
Table 26 – Receive SPDO mapping parameter . 54
Table 27 – Transmit SPDO mapping parameter . 55
Table 28 – Indicator states definiton . 56

Table 29 – STATUS indicator states . 56

+AMD2:2021 CSV  IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

PROFILES
Part 3-18: Functional safety fieldbuses –

Additional specifications for CPF 18

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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with the International Organization for 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
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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.

This consolidated version of the official IEC Standard and its amendments has been
prepared for user convenience.
IEC 61784-3-18 edition 1.2 contains the first edition (2011-04) [documents 65C/639/FDIS
and 65C/649/RVD], its amendment 1 (2016-07) [documents 65C/851/FDIS and
65C/854/RVD] and its amendment 2 (2021-04) [documents 65C/1083/FDIS and
65C/1087/RVD].
In this Redline version, a vertical line in the margin shows where the technical content
is modified by amendments 1 and 2. Additions are in green text, deletions are in
strikethrough red text. A separate Final version with all changes accepted is available
in this publication.
– 6 – IEC 61784-3-18:2011+AMD1:2016

+AMD2:2021 CSV  IEC 2021
International Standard IEC 61784-3-18 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial process measurement, control and

automation.
This publication 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 the base publication and its amendments 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.
+AMD2:2021 CSV  IEC 2021
0 Introduction
0.1 General
The IEC 61158 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 many fieldbus enhancements are emerging, addressing not yet standardized
areas such as real time, safety-related and security-related applications.

This standard explains the relevant principles for functional safety communications with
reference to IEC 61508 series 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 the IEC 61158 series. It does not cover electrical safety and
intrinsic safety aspects.
Figure 1 shows the relationships between this standard and relevant safety and fieldbus
standards in a machinery environment.
Product standards
ISO 12100-1 and ISO 14121
ISO 12100-1 and ISO 14121
Safety of machinery – Principles for
IEC 61496 IEC 61131-6 IEC 61800-5-2 ISO 10218-1
IEC 61496 IEC 61800-5-2 ISO 10218-1 Safety of machinery – Principles for
IEC 61131-6
design and risk assessment
Safety f. e.g. Safety functions Safety requirements
Safety f. e.g. Safety for PLC Safety functions Safety requirements design and risk assessment
Safety for PLC
(under consideration)
light curtains for drives for robots
light curtains (under consideration) for drives for robots
Design of safety-related electrical, electronic and program-
IEC 61784-4 IEC 62443
IEC 61784-4 IEC 62443
mable electronic control systems (SRECS) for machinery
Security Security
Security Security
(profile-specific) (common part)
(profile-specific) (common part)
SIL based PL based
IEC 61784-5 IEC 61918
IEC 61784-5 IEC 61918
Installation guide Installation guide
Installation guide Installation guide Design objective
(profile-specific) (common part)
(profile-specific) (common part)
Applicable standards
ISO 13849-1, -2
ISO 13849-1, -2
IEC 60204-1
IEC 60204-1
Safety-related parts
Safety-related parts
Safety of electrical
Safety of electrical
IEC 61000-1-2
IEC 61000-1-2 of machinery
of machinery
equipment
equipment
Methodology EMC & FS
Methodology EMC & FS (SRPCS)
(SRPCS)
IEC 61326-3-1
IEC 61784-3
IEC 61784-3 IEC 61326-3-1
Non-electrical
Non-electrical
Test EMC & FS
Functional safety
Functional safety Test EMC & FS
communication
communication
Electrical
Electrical
US: NFPA 79
US: NFPA 79
profiles
profiles
(2006)
(2006)
IEC 62061
IEC 62061
Functional safety
Functional safety
IEC 61158 series /
IEC 61158 series /
for machinery
for machinery
IEC 61784-1, -2 IEC 61508 series
IEC 61784-1, -2 IEC 61508 series (SRECS)
(SRECS)
Functional safety (FS)
Fieldbus for use in Functional safety (FS) (including EMC for
Fieldbus for use in
(including EMC for
(basic standard)
(basic standard) industrial environment)
industrial control systems industrial environment)
industrial control systems
Key
(yellow) safety-related standards
(blue) fieldbus-related standards
(dashed yellow) this standard
IEC  768/11
– 8 – IEC 61784-3-18:2011+AMD1:2016

+AMD2:2021 CSV  IEC 2021
NOTE Subclauses 6.7.6.4 (high complexity) and 6.7.8.1.6 (low complexity) of IEC 62061 specify the relationship
between PL (Category) and SIL. IEC 62061 specifies the relationship between PL (Category) and SIL.
Figure 1 – Relationships of IEC 61784-3 with other standards (machinery)
Figure 2 shows the relationships between this standard and relevant safety and fieldbus
standards in a process environment.

+AMD2:2021 CSV  IEC 2021
Product standards
IEC 61496 IEC 61800-5-2 ISO 10218-1
IEC 61131-6
IEC 61496 IEC 61131-6 IEC 61800-5-2 ISO 10218-1

Safety f. e.g. Safety functions Safety requirements
Safety for PLC
Safety f. e.g. Safety functions Safety requirements
Safety for PLC
light curtains (under consideration) for drives for robots
(under consideration)
light curtains for drives for robots

IEC 61784-4 IEC 62443
IEC 61784-4 IEC 62443
Security Security
Security Security
(profile-specific) (common part)
(profile-specific) (common part)
See safety standards for machinery

(Figure 1)
IEC 61784-5 IEC 61918
IEC 61784-5 IEC 61918
Installation guide Installation guide
Installation guide Installation guide

(profile-specific) (common part)
(profile-specific) (common part)
Valid also in process industries,
whenever applicable
a)
a)
IEC 61326-3-2
IEC 61326-3-2
EMC and
EMC and
functional safety
functional safety
IEC 61784-3
IEC 61784-3
Functional safety
Functional safety
communication
communication
profiles
profiles
US:
US:
ISA-84.00.01
ISA-84.00.01
b)
b)
IEC 61511 series (3 parts = modified
IEC 61511 series (3 parts = modified
Functional safety – IEC 61511)
IEC 61158 series / Functional safety – IEC 61511)
IEC 61158 series /
Safety instrumented
Safety instrumented
IEC 61784-1, -2 IEC 61508 series
IEC 61784-1, -2 IEC 61508 series
systems for the
systems for the
Functional safety (FS)
Fieldbus for use in Functional safety (FS)
Fieldbus for use in DE: VDI 2180
DE: VDI 2180
process industry sector
process industry sector
(basic standard)
(basic standard)
industrial control systems Part 1-4
industrial control systems
Part 1-4
Key
(yellow) safety-related standards
(blue) fieldbus-related standards
(dashed yellow) this standard
– 10 – IEC 61784-3-18:2011+AMD1:2016

+AMD2:2021 CSV  IEC 2021
IEC  769/11
a
For specified electromagnetic environments; otherwise IEC 61326-3-1 or IEC 61000-6-7.
b
EN ratified.
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 series 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 this standard 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 within this system – implementation of a functional safety
communication profile in a standard device is not sufficient to qualify it as a safety device.

+AMD2:2021 CSV  IEC 2021
This standard describes:
– basic principles for implementing the requirements of IEC 61508 series for safety-

related data communications, including possible transmission faults, remedial

measures and considerations affecting data integrity;

– individual description of functional safety profiles for several communication profile

families in IEC 61784-1 and IEC 61784-2;

– safety layer extensions to the communication service and protocols sections of the
IEC 61158 series.
0.2 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 a patent concerning the
functional safety communication profiles for family 18 as follows, where the [xx] notation
indicates the holder of the patent right:
Verfahren und Vorrichtung zum Übertragen von
DE 10 2008 007 672.4-31 [PI]
Daten in einem Netzwerk
IEC takes no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured the IEC that he/she is willing to negotiate licences
either free of charge or under reasonable and non-discriminatory terms and conditions with
applicants throughout the world. In this respect, the statement of the holder of this patent
right is registered with IEC. Information may be obtained from:
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INTRODUCTION to Amendment 2
This Amendment 2 introduces several editorial and informational corrections in the context of
Edition 4 of IEC 61784-3.
– 12 – IEC 61784-3-18:2011+AMD1:2016

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INDUSTRIAL COMMUNICATION NETWORKS –

PROFILES
Part 3-18: Functional safety fieldbuses –

Additional specifications for CPF 18

1 Scope
This part of the IEC 61784-3 series specifies a safety communication layer (services and
protocol) based on CPF 18 of IEC 61784-2 and IEC 61158 Type 22. It identifies the principles
for functional safety communications defined in IEC 61784-3 that are relevant for this safety
communication layer.
NOTE 1 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.
This part defines mechanisms for the transmission of safety-relevant messages among
participants within a distributed network using fieldbus technology in accordance with the
requirements of IEC 61508 series for functional safety. These mechanisms may be used in
various industrial applications such as process control, manufacturing automation and
machinery.
This part provides guidelines for both developers and assessors of compliant devices and
systems.
NOTE 2 The resulting SIL claim of a system depends on the implementation of the selected functional safety
communication profile within this system – implementation of a functional safety communication profile according to
this part in a standard device is not sufficient to qualify it as a safety device.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61158-3-22, Industrial communication networks – Fieldbus specifications – Part 3-22:
Data-link layer service definition – Type 22 elements

IEC 61158-4-22, Industrial communication networks – Fieldbus specifications – Part 4-22:
Data-link layer protocol specification – Type 22 elements
IEC 61158-5-22, Industrial communication networks – Fieldbus specifications – Part 5-22:
Application layer service definition – Type 22 elements
IEC 61158-6-22, Industrial communication networks – Fieldbus specifications – Part 6-22:
Application layer protocol specification – Type 22 elements
IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic
safety-related systems
___________
In the following pages of this standard, “this part” will be used for “this part of the IEC 61784-3 series”.
In the following pages of this standard, “IEC 61508” will be used for “IEC 61508 series”.

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IEC 61508-2:2010, Functional safety of electrical/electronic/programmable electronic safety-

related systems – Part 2: Requirements for electrical/electronic/programmable electronic

safety-related systems
IEC 61784-2:2010, Industrial communication networks – Profiles – Part 2: Additional fieldbus

profiles for real-time networks based on ISO/IEC 8802-3

IEC 61784-3:2010, Industrial communication networks – Profiles – Part 3: Functional safety

fieldbuses – General rules and profile definitions

IEC 61918, Industrial communication networks – Installation of communication networks in

industrial premises
ISO/IEC 10731, Information technology – Open system interconnection – Basic reference
model – Conventions for the definition of OSI services
3 Terms, definitions, symbols, abbreviated terms and conventions
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1 Common terms and definitions
3.1.1.1
availability
probability for an automated system that for a given period of time there are no unsatisfactory
system conditions such as loss of production
3.1.1.2
black channel
communication channel without available evidence of design or validation according to
IEC 61508
3.1.1.3
communication channel
logical connection between two end-points within a communication system
3.1.1.4
communication system
arrangement of hardware, software and propagation media to allow the transfer of messages

(ISO/IEC 7498 application layer) from one application to another
3.1.1.5
connection
logical binding between two application objects within the same or different devices
3.1.1.6
Cyclic Redundancy Check (CRC)
redundant data derived from, and stored or transmitted together with, a block of data
in order to detect data corruption
procedure used to calculate the redundant data
NOTE 1 Terms “CRC code” and "CRC signature", and labels such as CRC1, CRC2, may also be used in this
standard to refer to the redundant data.

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NOTE 2 See also [35], [36] .
3.1.1.7
error
discrepancy between a computed, observed or measured value or condition and the true,

specified or theoretically correct value or condition

[IEC 61508-4:2010], [IEC 61158]

NOTE 1 Errors may be due to design mistakes within hardware/software and/or corrupted information due to

electromagnetic interference and/or other effects.

NOTE 2 Errors do not necessarily result in a failure or a fault.

3.1.1.8
failure
termination of the ability of a functional unit to perform a required function or operation of a
functional unit in any way other than as required
NOTE 1 The definition in IEC 61508-4 is the same, with additional notes.
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.11, modified]
NOTE 2 Failure may be due to an error (for example, problem with hardware/software design or message
disruption).
3.1.1.9
fault
abnormal condition that may cause a reduction in, or loss of, the capability of a functional unit
to perform a required function
NOTE IEV 191-05-01 defines “fault” as a state characterized by the inability to perform a required function,
excluding the inability during preventive maintenance or other planned actions, or due to lack of external
resources.
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.10, modified]
3.1.1.10
fieldbus
communication system based on serial data transfer and used in industrial automation or
process control applications
3.1.1.11
frame
denigrated synonym for DLPDU
3.1.1.12
Frame Check Sequence (FCS)
redundant data derived from a block of data within a DLPDU (frame), using a hash function,
and stored or transmitted together with the block of data, in order to detect data corruption
NOTE 1 An FCS can be derived using for example a CRC or other hash function.
NOTE 2 See also [35], [36].
3.1.1.13
hash function
(mathematical) function that maps values from a (possibly very) large set of values into a
(usually) smaller range of values
NOTE 1 Hash functions can be used to detect data corruption.
___________
Figures in square brackets refer to the Bibliography.

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NOTE 2 Common hash functions include parity, checksum or CRC.

[IEC/TR 62210, modified]
3.1.1.14
hazard
state or set of conditions of a system that, together with other related conditions will inevitably

lead to harm to persons, property or environment

3.1.1.15
message
ordered series of octets intended to convey information

[ISO/IEC 2382-16.02.01, modified]
3.1.1.16
message sink
part of a communication system in which messages are considered to be received
[ISO/IEC 2382-16.02.03]
3.1.1.17
message source
part of a communication system from which messages are considered to originate
[ISO/IEC 2382-16.02.02]
3.1.1.18
nuisance trip
spurious trip with no harmful effect
NOTE Internal abnormal errors can be caused in communication systems such as wireless transmission, for
example by too many retries in the presence of interferences.
3.1.1.19
performance level (PL)
discrete level used to specify the ability of safety-related parts of control systems to perform a
safety function under foreseeable conditions
[ISO 13849-1]
3.1.1.20
redundancy
existence of means, in addition to the means which would be sufficient for a functional unit to

perform a required function or for data to represent information
[IEC 61508-4:2010, modified], [ISO/IEC 2382-14.01.12, modified]
3.1.1.21
risk
combination of the probability of occurren
...