IEC 61784-3-1:2007

IEC 61784-3-1
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Profiles –
Part 3-1: Functional safety fieldbuses – Additional specifications for CPF 1

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IEC 61784-3-1
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Profiles –
Part 3-1: Functional safety fieldbuses – Additional specifications for CPF 1

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 35.100.05 25.040.40 ISBN 2-8318-9398-4

– 2 – 61784-3-1 © IEC:2007(E)
CONTENTS
FOREWORD.6

INTRODUCTION.8

1 Scope.11

2 Normative references .11

3 Terms, definitions, symbols, abbreviated terms and conventions .12

3.1 Terms and definitions .12

3.1.1 Common terms and definitions .12

3.1.2 CPF 1: Additional terms and definitions .16
3.2 Symbols and abbreviated terms.17
3.2.1 Common symbols and abbreviated terms .17
3.2.2 CPF 1: Additional symbols and abbreviated terms .18
3.3 Conventions .18
3.3.1 State Diagrams.18
3.3.2 Use of colors in figures.19
4 Overview of FSCP 1/1 (FOUNDATION Fieldbus™ SIS) .20
4.1 General .20
4.2 Key concepts of FSCP 1/1.21
4.2.1 Black channel .21
4.2.2 Connection key.21
4.2.3 Cross-check .21
4.2.4 FSCP 1/1.21
4.2.5 Programmable electronic system .21
4.2.6 Queuing delays .21
4.2.7 Redundancy .22
4.2.8 SIL environment .22
4.3 Key components of FSCP 1/1.22
4.3.1 Overview .22
4.3.2 Black channel .22
4.4 Relationship to the ISO OSI basic reference model .23
5 General .23
5.1 External documents providing specifications for the profile.23
5.2 Safety functional requirements .23

5.2.1 Requirements for functional safety.23
5.2.2 Functional constraints.24
5.2.3 Device manufacturer requirements .24
5.3 Safety measures .25
5.3.1 Sequence number .25
5.3.2 Time stamp .25
5.3.3 Time expectation .25
5.3.4 Connection authentication .25
5.3.5 Data integrity assurance.25
5.3.6 Redundancy with cross checking .25
5.3.7 Different data integrity assurance systems .25
5.3.8 Relationships between errors and safety measures .25
5.4 Safety communication layer structure .26
5.4.1 Network topology and device connectivity.26

61784-3-1 © IEC:2007(E) – 3 –
5.4.2 Device architecture.26

5.5 Relationships with FAL (and DLL, PhL) .27

5.5.1 General .27

5.5.2 Data Types .28

6 Safety communication layer services .28

6.1 Application Process (AP).28

6.1.1 Overview .28

6.1.2 Network visible objects .29

6.1.3 Application layer interface .29

6.1.4 Object dictionary .29
6.1.5 Application program directory .29
6.2 Function block application processes .29
6.2.1 General .29
6.2.2 Function block model.29
6.2.3 Application process .32
6.3 Device to device communications.34
6.3.1 General .34
6.3.2 Client/server .34
6.3.3 Publisher/subscriber .35
6.3.4 Report distribution .35
6.3.5 FBAP operation in a linking device .35
6.3.6 System management kernel protocol (SMKP) communications .35
6.4 Profiles.35
6.4.1 General .35
6.4.2 FSCP 1/1 profile .35
6.5 Device descriptions .36
6.6 Common file formats .37
6.7 Configuration information .37
6.7.1 Overview .37
6.7.2 Level 1 configuration: manufacturer device definition.37
6.7.3 Level 2 configuration: network definition .37
6.7.4 Level 3 configuration: distributed application definition .37
6.7.5 Level 4 configuration: device configuration .37
7 Safety communication layer protocol .37
7.1 Safety PDU format .37

7.1.1 General .37
7.1.2 Safety communication layer CRC .38
7.1.3 Black channel time synchronization monitoring.38
7.1.4 Sequence number .38
7.1.5 Virtual header.39
7.1.6 Connection key.39
7.1.7 Redundancy and cross-check .40
7.2 Protocol extensions for use in safety-related systems.40
7.2.1 Overview .40
7.2.2 Publisher-subscriber interactions.40
7.2.3 Client-server interactions.46
7.2.4 Time synchronization.51
7.2.5 Device start-up .52
7.3 Communications entity .52

– 4 – 61784-3-1 © IEC:2007(E)
7.3.1 General .52

7.3.2 Network management.52

7.3.3 FMS .52

7.3.4 H1 stack .52

8 Safety communication layer management.53

8.1 Overview .53

8.2 SMK communications .53

8.3 FMS services .53

8.4 SMK services .53

8.4.1 General .53
8.4.2 Address assignment .53
8.4.3 Time synchronization.53
8.5 Safety communication layer configuration and start-up .53
8.5.1 H1 configuration and start-up .53
8.5.2 FSCP 1/1 FBAP.54
8.5.3 Testing .54
9 System requirements.54
9.1 Indicators and switches .54
9.2 Installation guidelines.54
9.3 Safety function response time .54
9.4 Duration of demands .55
9.5 Constraints for calculation of system characteristics.55
9.5.1 Message rate.55
9.5.2 SIL level .55
9.6 Maintenance.55
9.7 Safety manual .55
10 Certification.55
Annex A (informative) Additional information for functional safety communication
profiles of CPF 1 .56
A.1 Hash function calculation.56
A.2 Fault conditions arising from locations beyond the output function block.58
Bibliography.60

Table 1 – Example state transition table .19
Table 2 – Safety measures and possible communication errors .26
Table 3 – Data types used within FSCP 1/1 .28
Table 4 – Fault state behaviour.31
Table 5 – Publisher states .41
Table 6 – Publisher state table - Received transitions .42
Table 7 – Publisher state table - Internal transitions.42
Table 8 – Subscriber states .44
Table 9 – Subscriber state table - Received transitions.45
Table 10 – Subscriber state table - Internal transitions.45
Table 11 – Server states during read operations .47
Table 12 – Received transitions for a FSCP 1/1 Server during read operations.48
Table 13 – States of a FSCP 1/1 server during write operations.49

61784-3-1 © IEC:2007(E) – 5 –
Table 14 – Received transitions for a FSCP 1/1 Server during write operations .50

Table A.1 – Fault conditions arising from locations beyond the output function block .59

Figure 1 – Relationships of IEC 61784-3 with other standards (machinery) .8

Figure 2 – Relationships of IEC 61784-3 with other standards (process).9

Figure 3 – Example state diagram.19

Figure 4 – Use of colors in figures .19

Figure 5 – Scope of FSCP 1/1 .20

Figure 6 – FSCP 1/1 architecture (H1) .22
Figure 7 – Black channel .23
Figure 8 – FSCP 1/1 in system architecture .26
Figure 9 – FSCP 1/1 H1 device.27
Figure 10 – FSCP 1/1 protocol layers .27
Figure 11 – Relationship between FSCP 1/1 and the other layers of IEC 61158 Type 1 .28
Figure 12 – Key write-lock .30
Figure 13 – Password write-lock .30
Figure 14 – Example of FSCP 1/1 communication.34
Figure 15 – Example of device description.36
Figure 16 – Safety PDU showing virtual content.41
Figure 17 – Safety PDU showing duplication of data and addition of CRC.41
Figure 18 – State transition diagram for a FSCP 1/1 Publisher.42
Figure 19 – Safety PDU showing duplication of data and addition of CRC.43
Figure 20 – Safety PDU showing virtual content.43
Figure 21 – State transition diagram for a FSCP 1/1 subscriber .44
Figure 22 – Safety PDU showing virtual content.46
Figure 23 – Safety PDU showing virtual content with sub index .46
Figure 24 – Safety PDU showing duplication of data, addition of sequence number
and CRC.47
Figure 25 – State transition diagram for a FSCP 1/1 Server during read operations .47
Figure 26 – Safety PDU showing duplication of data and addition of sequence number
and CRC.48

Figure 27 – Example of FSCP 1/1 write .49
Figure 28 – Example of FSCP 1/1 write with sub index .49
Figure 29 – State transition diagram for a FSCP 1/1 Server during write operations.50
Figure 30 – Safety PDU showing duplication of data and CRC.51
Figure 31 – Example of safety function response time components.54

– 6 – 61784-3-1 © IEC:2007(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS – PROFILES

Part 3-1: Functional safety fieldbuses – Additional specifications

for CPF 1
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
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
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
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 the functional safety communication profiles for

family 1 as follows, where the [xx] notation indicates the holder of the patent right:
US 6,999,824 [FF] System and method for implementing safety
instrumented systems in a fieldbus architecture
IEC takes no position concerning the evidence, validity and scope of these patent rights.
The holders of these patents rights have assured the 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
statement of the holders of these patent rights are registered with IEC.
Information may be obtained from:
[FF] Fieldbus Foundation
9005 Mountain Ridge Drive
Bowie Bldg. - Suite 190
Austin, TX  78759-5316
Tel: +1 512 794 8890
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.

61784-3-1 © IEC:2007(E) – 7 –
International Standard IEC 61784-3-1 has been prepared by subcommittee 65C: Industrial

networks, of IEC technical committee 65: Industrial process measurement, control and

automation.
The text of this standard is based on the following documents:

FDIS Report on voting
65C/470/FDIS 65C/481/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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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.
The list of all parts of the IEC 61784-3 series, under the general title Industrial communication
networks – Profiles – Functional safety fieldbuses, can be found on the IEC website.

– 8 – 61784-3-1 © IEC:2007(E)
INTRODUCTION
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
IEC 61496 IEC 61131-6 IEC 61800-5-2 Safety of machinery – Principles for
Safety of machinery – Principles for
IEC 61496 IEC 61131-6 IEC 61800-5-2
Safety f. e.g. Safety for Safety functions design and risk assessment
Safety for PLC design and risk assessment
Safety f. e.g. Safety for Safety functions
light curtains PLC for drives
(under consideration)
light curtains PLC for drives
Design of safety-related electrical, electronic and programmable
IEC 61784-4 IEC 62443
IEC 61784-4 IEC 62443
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
Design objective
Installation guide Installation guide
Installation guide Installation guide
(profile-specific) (common part) Applicable standards
(profile-specific) (common part)
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 61326-3-1
of machinery
IEC 61326-3-1 of machinery
equipment
equipment
EMC and (SRPCS)
EMC and (SRPCS)
functional safety
functional safety
IEC 61784-3
IEC 61784-3
Non-electrical
Non-electrical
Functional safety
Functional safety
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
Fieldbus for use in Functional safety (including EMI for
Fieldbus for use in (including EMI for
(basic standard)
(basic standard) industrial environment)
industrial control systems
industrial control systems industrial environment)
Key
(yellow) safety-related standards
(blue) fieldbus-related standards
(dashed yellow) this standard
Figure 1 – Relationships of IEC 61784-3 with other standards (machinery)

61784-3-1 © IEC:2007(E) – 9 –
Figure 2 shows the relationships between this standard and relevant safety and fieldbus

standards in a process environment.

Product standards
IEC 61496 IEC 61131-6 IEC 61800-5-2
IEC 61496 IEC 61131-6 IEC 61800-5-2

Safety f. e.g. Safety for Safety functions
Safety for PLC
Safety f. e.g. Safety for Safety functions
light curtains (under coPLnsiCderation) for drives
light curtains PLC for drives
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
Fieldbus for use in
Functional safety
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
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.

– 10 – 61784-3-1 © IEC:2007(E)

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.
61784-3-1 © IEC:2007(E) – 11 –

INDUSTRIAL COMMUNICATION NETWORKS – PROFILES

Part 3-1: Functional safety fieldbuses – Additional specifications

for CPF 1
1 Scope
This part of the IEC 61784-3 series specifies a safety communication layer (services and

protocol) based on CPF 1 of IEC 61784-1 and IEC 61158 Type 1 and 9. 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 61131-2, Programmable controllers – Part 2: Equipment requirements and tests
IEC 61158-2, Industrial communication networks – Fieldbus specifications – Part 2: Physical
layer specification and service definition

IEC 61158-3-1, Industrial communication networks – Fieldbus specifications – Part 3-1: Data-
link layer service definition – Type 1 elements
IEC 61158-4-1, Industrial communication networks – Fieldbus specifications – Part 4-1: Data-
link layer protocol specification – Type 1 elements
IEC 61158-5-5, Industrial communication networks – Fieldbus specifications – Part 5-5:
Application layer service definition – Type 5 elements
IEC 61158-5-9, Industrial communication networks – Fieldbus specifications – Part 5-9:
Application layer service definition – Type 9 elements
IEC 61158-6-5, Industrial communication networks – Fieldbus specifications – Part 6-5:
Application layer protocol specification – Type 5 elements
—————————
In the following pages of this standard, “this part” will be used for “this part of the IEC 61784-3 series”.

– 12 – 61784-3-1 © IEC:2007(E)

IEC 61158-6-9, Industrial communication networks – Fieldbus specifications – Part 6-9:

Application layer protocol specification – Type 9 elements

IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic

safety-related systems
IEC 61511 (all parts), Functional safety – Safety instrumented systems for the process

industry sector
IEC 61784-1, Industrial communication networks – Profiles – Part 1: Fieldbus profiles

IEC 61784-3, 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
IEC 62280-1:2002, Railway applications – Communication, signalling and processing systems
– Part 1: Safety-related communication in closed transmission systems
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
NOTE Availability depends on MTBF (mean time between failure) and MDT (mean down time):
Availability = MTBF / (MTBF + MDT).
3.1.1.2
black channel
communication channel without available evidence of design or validation according to
IEC 61508 series
3.1.1.3
bridge
abstract device that connects multiple network segments along the data link layer
3.1.1.4
communication channel
logical connection between two end-points within a communication system
3.1.1.5
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
3.1.1.6
connection
logical binding between two application objects within the same or different devices

61784-3-1 © IEC:2007(E) – 13 –

3.1.1.7
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.

NOTE 2 See also [28], [29] .
3.1.1.8
error
discrepancy between a computed, observed or measured value or condition and the true,
specified or theoretically correct value or condition
NOTE 1 An error can be caused by a faulty item, e.g. a computing error made by faulty computer equipment.
[IEV 191-05-24], [IEC 61508-4:1998], [IEC 61158]
NOTE 2 Errors may be due to design mistakes within hardware/software and/or corrupted information due to
electromagnetic interference and/or other effects.
NOTE 3 Errors do not necessarily result in a failure or a fault.
3.1.1.9
failure
termination of the ability of a functional unit to perform a required function
NOTE 1 The definition in IEV 191-04-01 is the same, with additional notes.
[IEC 61508-4:1998], [ISO/IEC 2382-14.01.11]
NOTE 2 Failure may be due to an error (for example, problem with hardware/software design or message
disruption)
3.1.1.10
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 preventative maintenance or other planned actions, or due to lack of external
resources.
[IEC 61508-4:1998], [ISO/IEC 2382-14.01.10]

3.1.1.11
fieldbus
communication system based on serial data transfer and used in industrial automation or
process control applications
3.1.1.12
frame
denigrated synonym for DLPDU
—————————
Figures in square brackets refer to the bibliography.

– 14 – 61784-3-1 © IEC:2007(E)

3.1.1.13
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 [28], [29].
3.1.1.14
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.
NOTE 2 Common hash functions include parity, checksum or CRC.
[IEC 62210, modified]
3.1.1.15
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
3.1.1.16
master
active communication entity able to initiate and schedule communication activities by other
stations which may be masters or slaves
3.1.1.17
message
ordered series of octets intended to convey information
[ISO/IEC 2382-16.02.01, modified]
3.1.1.18
message sink
part of a communication system in which messages are considered to be received
[ISO/IEC 2382-16.02.03]
3.1.1.19
message source
part of a communication system from which messages are considered to originate

[ISO/IEC 2382-16.02.02]
3.1.1.20
proof test
periodic test performed to detect failures in a safety-related system so that, if necessary, the
system can be restored to an “as new” condition or as close as practical to this condition
NOTE A proof test is intended to confirm that the safety-related system is in a condition that assures the specified
safety integrity.
[IEC 61508-4 and IEC 62061, modified]
3.1.1.21
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

61784-3-1 © IEC:2007(E) – 15 –

EXAMPLE Duplicated functional components and the addition
...