IEC 61139-2:2022

Industrial networks - Single-drop digital communication interface - Part 2: Functional safety extensions

IEC 61139-2:2022 specifies the extensions to SDCI in IEC 61131-9 for functional safety. This comprises:
• a standardized OSSDe interface for redundant switching signals based on IEC 61131-2,
• minor modifications/extensions to state machines of SDCI to support the safety operations,
• a lean functional safety communication protocol on top of the standard SDCI communication which is a black channel according to IEC 61784-3:2021,
• protocol management functions for configuration, parameterization, and commissioning,
• IODD extensions for functional safety,
• a Device tool interface to support Dedicated Tools according to functional safety standards.
This document does not cover:
• communication interfaces or systems including multi-point or multi-drop linkages,
• communication interfaces or systems including multi-channel or encrypted linkages,
• wireless communication interfaces or systems,
• integration of SDCI-FS into upper-level systems such as fieldbuses/FSCPs.

Réseaux industriels - Interface de communication numérique point à point - Partie 2: Extensions de sécurité fonctionnelle

L'IEC 61139-2:2022 spécifie les extensions de la SDCI de l'IEC 61131-9 pour la sécurité fonctionnelle. Elle comprend:
• une interface OSSDe normalisée pour les signaux de commutation redondants, fondée sur l'IEC 61131-2;
• des modifications/extensions mineures des diagrammes d'états de la SDCI afin de prendre en charge les opérations de sécurité;
• un protocole de communication de sécurité fonctionnelle affiné en plus de la communication SDCI normalisée, qui constitue un canal noir selon l'IEC 61784-3:2021;
• des fonctions de gestion de protocole pour la configuration, le paramétrage et la mise en service;
• des extensions de l'IODD pour la sécurité fonctionnelle;
• une interface d'outil d'Appareil pour prendre en charge les outils dédiés, conformément aux normes de sécurité fonctionnelle.
Le présent document ne couvre pas:
• les interfaces ou systèmes de communication qui incluent des liaisons multipoints;
• les interfaces ou systèmes de communication qui incluent des liaisons chiffrées ou multicanaux;
• les interfaces ou systèmes de communication sans fil;
• l'intégration de la SDCI-FS aux systèmes de niveau supérieur, tels que les bus de terrain/FSCP.

General Information

• Status: Published
• Publication Date: 18-Aug-2022
• ICS: 25.040 - Industrial automation systems
• Technical Committee: SC 65C - Industrial networks
• Drafting Committee: PT 61139-2 - TC 65/SC 65C/PT 61139-2
• Current Stage: PPUB - Publication issued
• Start Date: 19-Aug-2022
• Completion Date: 22-Jul-2022

Overview

IEC 61139-2:2022 is an international standard published by the International Electrotechnical Commission (IEC) that defines functional safety extensions for the Single-drop Digital Communication Interface (SDCI) specified in IEC 61131-9. This document focuses on enhancing SDCI to support safety-critical industrial network applications with a robust, lean communication protocol built over the standard SDCI black channel communication.

The standard specifies:

• A standardized OSSDe interface for redundant switching signals based on IEC 61131-2.
• Updates and extensions to state machines in SDCI to enable safety operations.
• Implementation of a functional safety communication protocol adhering to IEC 61784-3:2021 black channel principles.
• Protocol management features for device configuration, parameterization, and commissioning.
• Extensions for the IODD (IO device description) to cover functional safety.
• A dedicated device tool interface supporting safety-compliant dedicated tools.

IEC 61139-2:2022 excludes multi-point, multi-drop, multi-channel, encrypted, and wireless communication interfaces, as well as integration into upper-level fieldbus or functional safety communication profiles.

Key Topics

• Functional Safety Communication Protocol: A lean protocol layered on SDCI ensuring communication integrity and error detection in safety applications.
• OSSDe Interface: A standardized output switching signal device interface allowing redundant safe switching signals in compliance with IEC 61131-2.
• State Machine Extensions: Modifications to SDCI’s data link and communication layers to support safety operations and fault monitoring.
• Safety Device and Master Architectures: Defines roles and interactions for FS-Devices (safety devices) and FS-Masters (controllers), including power supply, wake-up coordination, and fast start-up procedures.
• Parameterization and Configuration: Protocol management functions are introduced for streamlined safety parameter configuration, device commissioning, and runtime management.
• IODD Functional Safety Extensions: Enhanced device descriptions support automation tools with critical safety parameters and diagnostic data.
• Safety Layer Manager (SLM): Manages safety communication states, error handling, and safety parameterization to maintain safe operating conditions.
• Process Data Exchange and Data Storage: Extensions ensure that safety-relevant process data and device states are managed securely and reliably.

Applications

IEC 61139-2:2022 applies primarily to industrial automation systems requiring high reliability and safety compliance such as:

• Safety-critical machinery control systems that use digital communication for monitoring and controlling safety functions.
• Redundant output switching systems in safety applications requiring fail-safe signal outputs.
• Functional safety device communication in manufacturing plants to meet strict safety integrity levels.
• Integration of safety-oriented dedicated tool interfaces for device diagnostics, configuration, and maintenance.
• Applications where point-to-point communication is preferred or mandated for safe operational architectures.
• Industries such as automotive manufacturing, process automation, robotics, and material handling where functional safety standards compliance is essential.

The standard is also a foundational building block for vendors and system integrators developing safety communication solutions that align with international best practices and IEC safety standards.

Related Standards

• IEC 61131-9: Single-drop digital communication interface base standard providing the core SDCI technology extended by IEC 61139-2.
• IEC 61131-2: Standard specifying digital input/output interfaces including OSSDe devices for industrial controllers.
• IEC 61784-3:2021: Defines communication profiles including black channel principles underlying the functional safety communication protocol in IEC 61139-2.
• ISO 13849 and IEC 62061: Functional safety standards for machinery control systems which can be supported using IEC 61139-2 safety communication features.
• IODD (IO device description) standards that are extended by IEC 61139-2 to include functional safety parameters.
• Other IEC functional safety standards that address safety device design and integration within industrial automation systems.

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IEC 61139-2:2022 advances single-drop digital communication with essential functional safety extensions, enabling safer, more reliable industrial network deployments. By adopting this standard, manufacturers and system integrators can ensure compliance with international safety frameworks while benefiting from streamlined communication, configuration, and management of safety devices in automated environments.

Standards Content (Sample)

IEC 61139-2 ®
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial networks – Single-drop digital communication interface –
Part 2: Functional safety extensions

Réseaux industriels – Interface de communication numérique point à point –
Partie 2: Extensions de sécurité fonctionnelle

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IEC 61139-2 ®
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Industrial networks – Single-drop digital communication interface –

Part 2: Functional safety extensions

Réseaux industriels – Interface de communication numérique point à point –

Partie 2: Extensions de sécurité fonctionnelle

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 25.040 ISBN 978-2-8322-3946-9

– 2 – IEC 61139-2:2022 © IEC 2022
CONTENTS
FOREWORD . 12
INTRODUCTION . 14
1 Scope . 17
2 Normative references . 17
3 Terms, definitions, symbols, abbreviated terms, and conventions . 18
3.1 Terms and definitions . 18
3.2 Common terms and definitions . 18
3.3 Terms and definitions related to SDCI-FS . 21
3.4 Symbols and abbreviated terms . 23
3.5 Conventions . 24
3.5.1 Behavioral descriptions . 24
3.5.2 Memory and transmission octet order . 25
4 Overview of SDCI-FS . 25
4.1 Purpose of the technology and feature levels . 25
4.1.1 Base SDCI-FS technology . 25
4.1.2 From "analog" and "switching" to communication . 26
4.1.3 Minimized paradigm shift from FS-DI to FS-Master . 27
4.1.4 Following the SDCI paradigm (SIO vs. OSSDe) . 28
4.1.5 Port class B . 30
4.1.6 "USB-Master" with safety parameterization . 31
4.1.7 Interoperability matrix of safety devices . 31
4.2 Positioning within the automation hierarchy . 32
4.3 Wiring, connectors, and power supply . 33
4.4 Relationship to SDCI . 33
4.5 Communication features and interfaces . 34
4.6 Parameterization . 34
4.7 Role of FS-Master and FS-Gateway . 35
4.8 Mapping to upper-level systems . 35
4.9 Structure of the document . 35
5 Extensions to the Physical Layer (PL) . 35
5.1 Overview. 35
5.2 Extensions to PL services . 36
5.2.1 PL_SetMode . 36
5.2.2 PL_Ready . 36
5.3 Transmitter/receiver . 37
5.3.1 Assumptions for the expansion to OSSDe . 37
5.3.2 OSSDe specifics . 37
5.3.3 Start-up of an FS-Device (Ready pulse) . 40
5.3.4 Electric characteristics of a receiver in FS-Device and FS-Master . 41
5.4 Electric and dynamic characteristics of an FS-Device . 41
5.5 Electric and dynamic characteristics of an FS-Master port (OSSDe) . 44
5.6 FS-Master port FS-DI interface . 45
5.7 Wake-up coordination . 45
5.8 Fast start-up . 46
5.9 Power supply . 46
5.10 Medium . 47

5.10.1 Constraints . 47
5.10.2 Connectors . 47
5.10.3 Cable characteristics . 47
6 Extensions to SIO . 47
7 Extensions to the data link layer (DL) . 47
7.1 Overview. 47
7.2 State machine of the FS-Master DL-mode handler . 47
7.3 State machine of the FS-Device DL-mode handler . 49
8 Extensions to the Master Configuration Manager (CM) . 51
9 Extensions of the FS-Device . 52
9.1 Principle architecture and models . 52
9.1.1 FS-Device architecture . 52
9.1.2 FS-Device model . 53
9.2 Parameter Manager (PM) . 54
9.3 Process Data Exchange (PDE) . 54
9.4 Data Storage (DS) . 54
9.4.1 General considerations and extensions including safety . 54
9.4.2 Backup levels . 55
10 Extensions of the FS-Master . 55
10.1 Principle architecture . 55
10.2 SMI service extensions . 56
10.2.1 Overview . 56
10.2.2 SMI_FSMasterAccess . 58
10.2.3 SMI_SPDUIn . 60
10.2.4 SMI_SPDUOut . 60
10.2.5 SMI_FSPDInOut . 60
10.3 ArgBlock extensions . 62
10.3.1 Overview . 62
10.3.2 FSMasterAccess . 62
10.3.3 FSCPAuthenticity . 63
10.3.4 FSPortConfigList . 63
10.3.5 FSPortStatusList. 66
10.3.6 SPDUIn . 67
10.3.7 SPDUOut . 67
10.3.8 FSPDInOut . 68
10.4 Safety Layer Manager (SLM) . 69
10.4.1 Purpose . 69
10.4.2 FS_PortModes . 69
10.4.3 FSP parameter . 69
10.5 Process Data Exchange (PDE) . 73
10.6 Data Storage (DS) . 74
11 Safety communication layer (SCL) . 74
11.1 Functional requirements . 74
11.2 Communication errors and safety measures . 74
11.3 SCL services . 75
11.3.1 Positioning of safety communication layers (SCL) . 75
11.3.2 FS-Master SCL services . 76
11.3.3 FS-Device SCL services . 77

– 4 – IEC 61139-2:2022 © IEC 2022
11.4 SCL protocol . 79
11.4.1 Protocol phases to consider . 79
11.4.2 FS-Device faults . 80
11.4.3 Safety PDU (SPDU) . 80
11.4.4 FS-Input and FS-Output data . 81
11.4.5 Port number . 81
11.4.6 Status and control . 81
11.4.7 CRC signature . 82
11.4.8 TADI safety considerations (informative) . 83
11.4.9 Data types for SDCI-FS . 84
11.5 SCL behavior . 85
11.5.1 General . 85
11.5.2 SCL state machine of the FS-Master . 85
11.5.3 SCL state machine of the FS-Device . 88
11.5.4 Sequence charts for several use cases . 91
11.5.5 Monitoring of safety times . 98
11.5.6 Reaction in the event of a malfunction . 99
11.5.7 Start-up (communication) . 101
11.6 SCL management . 101
11.6.1 Parameter overview (FSP and FST) . 101
11.6.2 Parameterization approaches . 103
11.7 Integrity measures . 104
11.7.1 IODD integrity . 104
11.7.2 Tool integrity . 104
11.7.3 Transmission integrity . 104
11.7.4 Verification record . 104
11.7.5 Authentication. 105
11.7.6 Storage integrity . 105
11.7.7 FS I/O data structure integrity . 106
11.7.8 Technology parameter (FST) based on IODD . 106
11.7.9 Technology parameter (FST) based on existing Dedicated Tool (IOPD) . 107
11.8 Creation of FSP and FST parameters . 108
11.9 Integration of Dedicated Tools (IOPD) . 109
11.9.1 IOPD interface . 109
11.9.2 Standard interfaces . 109
11.9.3 Backward channel . 110
11.10 Validation . 111
11.11 Passivation . 111
11.11.1 Motivation and means . 111
11.11.2 Port selective (FS-Master) . 111
11.11.3 Signal selective (FS-Terminal) . 112
11.11.4 Qualifier settings in case of communication . 112
11.11.5 Qualifier handling in case of OSSDe . 112
11.12 SCL diagnosis . 113
12 Functional safe processing (FS-P) . 114
12.1 Recommendations for efficient I/O mappings . 114
12.2 Embedded FS controller. 114
Annex A (normative) Extensions to parameters . 115
A.1 Indices and parameters for SDCI-FS . 115

A.2 Parameters in detail . 116
A.2.1 FSP_Authenticity . 116
A.2.2 FSP_Port . 116
A.2.3 FSP_AuthentCRC . 117
A.2.4 FSP_ProtVersion . 117
A.2.5 FSP_ProtMode . 117
A.2.6 FSP_Watchdog . 117
A.2.7 FSP_IO_StructCRC . 118
A.2.8 FSP_TechParCRC . 119
A.2.9 FSP_ProtParCRC . 119
A.2.10 FSP_VerifyRecord . 119
A.2.11 FSP_TimeToReady . 119
A.2.12 FSP_MinShutDownTime . 120
A.2.13 FSP_WCDT . 120
A.2.14 FSP_OFDT . 120
A.2.15 FSP_ParamDescCRC . 120
Annex B (normative) Extensions to EventCodes . 121
B.1 Additional FS-Device EventCodes . 121
B.2 Additional Port EventCodes . 121
Annex C (normative) Extensions to Data Types . 123
C.1 Data types for SDCI-FS . 123
C.2 BooleanT (bit) . 123
C.3 IntegerT (16) . 124
C.4 IntegerT (32) . 124
C.5 Safety Code . 125
Annex D (normative) CRC generator polynomials . 126
D.1 Overview of CRC generator polynomials . 126
D.2 Residual error probabilities . 126
D.3 Implementation considerations . 128
D.3.1 Overview . 128
D.3.2 Bit shift algorithm (16 bit) . 128
D.3.3 Lookup table (16 bit) . 128
D.3.4 Bit shift algorithm (32 bit) . 130
D.3.5 Lookup table (32 bit) . 130
D.3.6 Seed values . 131
D.3.7 Octet order for CRC calculation . 132
Annex E (normative) IODD extensions . 133
E.1 General . 133
E.2 Schema . 133
E.3 IODD constraints . 133
E.3.1 General rules . 133
E.3.2 Description of the IODD structure . 133
E.3.3 Behavior of "Reset" SystemCommands in SDCI-FS . 140
E.3.4 Profile Characteristic . 141
E.3.5 ProcessDataInput and ProcessDataOutput . 141
E.4 IODD conventions . 141
E.4.1 Naming . 141
E.4.2 Process Data (PD) . 141

– 6 – IEC 61139-2:2022 © IEC 2022
E.4.3 IODD conventions for user interface . 142
E.4.4 Master Tool features . 142
E.5 Securing . 142
E.5.1 General . 142
E.5.2 DefaultValues for FSP . 143
E.5.3 FSP_Authenticity . 143
E.5.4 FSP_Protocol . 143
E.5.5 FSP_IO_Description . 144
E.5.6 Sample serialization for FSP_ParamDescCRC . 144
E.5.7 FST and FSP parameters and Data Storage . 145
E.5.8 Sample IODD of an FS-Device . 145
Annex F (normative) Device Tool Interface (DTI) for SDCI . 156
F.1 Purpose of DTI . 156
F.2 Base model . 156
F.3 Invocation interface . 157
F.3.1 Overview . 157
F.3.2 Detection of Device Tool . 158
F.3.3 Program Interface Description – PID . 161
F.3.4 Temporary Parameter File – TPF . 164
F.3.5 Temporary Backchannel File – TBF . 169
F.3.6 Temporary Acknowledgment File – TAF . 171
F.3.7 Invocation behavior . 171
F.4 Device data objects (DDO) . 172
F.4.1 General . 172
F.4.2 Structure of DDO package . 173
F.5 Communication Interface . 173
F.5.1 General . 173
F.5.2 Principle of DTI communications . 174
F.5.3 Gateways . 175
F.5.4 Configuration of the Communication Server . 175
F.5.5 Definition of the Communication Interface . 176
F.5.6 Sequence for establishing a communication relation . 176
F.5.7 Usage of the Communication Server in stand-alone mode . 177
F.5.8 SDCI specifics . 178
F.5.9 Changing communication settings . 178
F.6 Reaction on incorrect Tool behavior . 179
F.7 Compatibility . 179
F.7.1 Schema validation . 179
F.7.2 Version policy . 180
F.8 Scalability . 180
F.8.1 Scalability of a Device Tool . 180
F.8.2 Scalability of a Master Tool . 181
F.8.3 Interactions at conformance class combinations . 181
F.9 Schema definitions. 181
F.9.1 General . 181
F.9.2 Schema of the PID . 181
F.9.3 Schema of the TPF . 183
F.9.4 Schema of the TBF . 185
F.9.5 Schema of the TAF . 186

F.9.6 Schema of DTI primitives . 187
Annex G (normative) Main scenarios of SDCI-FS . 189
G.1 Overview. 189
G.2 Sequence chart of commissioning . 190
G.3 Sequence chart of replacement . 191
G.4 Sequence chart of misconnection. 192
Annex H (normative) System requirements . 193
H.1 Indicators . 193
H.1.1 General . 193
H.1.2 OSSDe . 193
H.1.3 Safety communication. 193
H.1.4 Acknowledgment request . 193
H.2 Installation guidelines, electrical safety, and security . 193
H.3 Safety function response time . 194
H.4 Duration of demands . 194
H.5 Maintenance and repair . 194
H.6 Safety manual . 194
Annex I (informative) Information for test and assessment of SDCI-FS components . 195
Bibliography . 196

Figure 1 – Positioning of SDCI-FS in functional safety automation . 14
Figure 2 – Relationship of this document to standards . 16
Figure 3 – Memory and transmission octet order . 25
Figure 4 – SDCI-FS communication layer model . 25
Figure 5 – Port interface extensions for SDCI-FS . 26
Figure 6 – Migration to SDCI-FS . 27
Figure 7 – Minimized paradigm shift from FS-DI to FS-Master. 28
Figure 8 – FS-Master types and feature levels . 28
Figure 9 – Original pin layout of SDCI (port class A) . 29
Figure 10 – Optimized OSSDe commissioning with FS-Master . 30
Figure 11 – Level "d" of an FS-Master (Class B) . 31
Figure 12 – Off-site configuration and parameterization . 31
Figure 13 – SDCI-FS within the automation hierarchy . 33
Figure 14 – The SDCI physical layer of an FS-Master (class A) . 36
Figure 15 – The physical layer of an FS-Device (class A) . 36
Figure 16 – Cross compatibility OSSD and OSSDe . 37
Figure 17 – Principle OSSDe function . 38
Figure 18 – Test pulses to detect cross connection faults . 39
Figure 19 – OSSD timings. 40
Figure 20 – Typical start-up of an OSSD sensor . 40
Figure 21 – Start-up of an FS-Device . 40
Figure 22 – Switching thresholds for FS-Device and FS-Master receivers . 41
Figure 23 – Reference schematics (one OSSDe channel) . 42
Figure 24 – Voltage level definitions . 42
Figure 25 – Charge capability at power-up . 45

– 8 – IEC 61139-2:2022 © IEC 2022
Figure 26 – OSSDe input filter conflict resolution . 45
Figure 27 – Start-up of an FS-Device . 46
Figure 28 – Required fast start-up timings . 46
Figure 29 – State machine of the FS-Master DL-mode handler . 48
Figure 30 – State machine of the FS-Device DL-mode handler . 50
Figure 31 – Extension to the Configuration Manager (VerifyRecord) . 51
Figure 32 – Principle architecture of the FS-Device . 53
Figure 33 – The FS-Device model . 54
Figure 34 – Principle architecture of the FS-Master . 56
Figure 35 – SMI service extensions . 58
Figure 36 – FSP parameter use cases . 70
Figure 37 – PDE Splitter . 73
Figure 38 – PDE Composer . 74
Figure 39 – Positioning of the SDCI-FS Safety Communication Layer (SCL) . 76
Figure 40 – FS-Master Safety Communication Layer services . 76
Figure 41 – FS-Device Safety Communication Layer services . 78
Figure 42 – Protocol phases to consider . 79
Figure 43 – Safety PDUs of FS-Master and FS-Device . 80
Figure 44 – The 1 % share rule of IEC 61784-3:2021 . 83
Figure 45 – SCL state machine of the FS-Master . 86
Figure 46 – SCL state machine of the FS-Device . 89
Figure 47 – FS-Master and FS-Device both with power ON . 92
Figure 48 – FS-Master power OFF  ON . 93
Figure 49 – FS-Device with delayed SCL start . 94
Figure 50 – FS-Device with power OFF and ON . 95
Figure 51 – FS-Master detects CRC signature error . 96
Figure 52 – FS-Device detects CRC signature error . 97
Figure 53 – Monitoring of the SCL cycle time . 98
Figure 54 – Parameter types and assignments . 102
Figure 55 – FSCP-Host-centric system . 103
Figure 56 – Structure of the FSP_VerifyRecord . 105
Figure 57 – Start-up of SDCI-FS . 106
Figure 58 – Securing of FST parameters via dedicated tool . 107
Figure 59 – Modification of FST parameters via Device Tool . 108
Figure 60 – Creation of FSP and FST parameters . 109
Figure 61 – Example of a communication hierarchy . 110
Figure 62 – Motivation for Port selective passivation . 111
Figure 63 – Qualifier handler (communication) . 112
Figure 64 – Qualifier handler (OSSDe) . 112
Figure 65 – Qualifier behavior per FS-Master port. 113
Figure 66 – Mapping efficiency issues . 114
Figure A.1 – Instance of an FS I/O data description . 118
Figure A.2 – Example FS I/O data st
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