IEC 61158-3-12:2019

IEC 61158-3-12 ®
Edition 4.0 2019-04
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 3-12: Data-link layer service definition – Type 12 elements

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.

need further assistance, please contact the Customer Service

Centre: sales@iec.ch.
IEC 61158-3-12 ®
Edition 4.0 2019-04
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –

Part 3-12: Data-link layer service definition – Type 12 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40; 35.100.20; 35.110 ISBN 978-2-8322-6788-2

– 2 – IEC 61158-3-12:2019 © IEC 2019
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
1.1 General . 8
1.2 Specifications . 8
1.3 Conformance . 8
2 Normative references . 9
3 Terms, definitions, symbols, abbreviations and conventions . 9
3.1 Reference model terms and definitions . 9
3.2 Service convention terms and definitions . 10
3.3 Data-link service terms and definitions . 11
3.4 Symbols and abbreviations . 14
3.5 Common conventions . 16
4 Data-link layer services and concepts . 17
4.1 Operating principle . 17
4.2 Topology . 17
4.3 Data-link layer overview . 18
4.4 Error detection overview . 19
4.5 Parameter and process data handling introduction . 19
4.6 Node reference model . 19
4.6.1 Mapping onto OSI Basic Reference Model . 19
4.6.2 Data-link layer features . 20
4.7 Operation overview . 20
4.7.1 Relation to ISO/IEC/IEEE 8802-3 . 20
4.7.2 Type 12 modes . 20
4.7.3 Logical topology . 21
4.8 Addressing . 22
4.8.1 Addressing overview . 22
4.8.2 Segment addressing . 22
4.8.3 Device addressing . 22
4.8.4 Logical addressing . 23
4.8.5 FMMU introduction . 23
4.8.6 Sync manager introduction . 24
4.9 Slave classification . 24
4.9.1 Full slave . 24
4.9.2 Basic slave . 24
4.10 Structure of the communication layer in the slave . 24
5 Communication services . 26
5.1 Overview. 26
5.2 Read services . 26
5.2.1 Overview . 26
5.2.2 Positional physical read (APRD) . 26
5.2.3 Configured-address physical read (FPRD) . 27
5.2.4 Broadcast read (BRD) . 28
5.2.5 Logical read (LRD) . 28
5.3 Write services . 29

5.3.1 Overview . 29
5.3.2 Positional physical write (APWR) . 29
5.3.3 Configured-address physical write (FPWR) . 30
5.3.4 Broadcast write (BWR) . 30
5.3.5 Logical write (LWR) . 31
5.4 Combined read/write services . 32
5.4.1 Overview . 32
5.4.2 Positional physical read/write (APRW) . 32
5.4.3 Configured-address physical read/write (FPRW) . 32
5.4.4 Broadcast read/write (BRW) . 33
5.4.5 Logical read/write (LRW) . 34
5.4.6 Positional physical read / multiple write (ARMW) . 34
5.4.7 Configured-address physical read / multiple write (FRMW) . 35
5.5 Network services . 35
5.5.1 Overview . 35
5.5.2 Publish network variables (PNV) . 36
5.6 Mailbox . 36
5.6.1 Overview . 36
5.6.2 Mailbox data transmission services . 38
6 Local interactions . 41
6.1 Read local . 41
6.2 Write local. 41
6.3 Event local . 42
Bibliography . 43

Figure 1 – Mapping of logical data in an Ethernet frame consisting of a single Type 12
DLPDU . 18
Figure 2 – Type 12 data-link reference model . 20
Figure 3 – Type 12 segments in open mode . 21
Figure 4 – Type 12 segment in direct mode . 21
Figure 5 – Addressing mode overview. 22
Figure 6 – Fieldbus memory management unit overview . 23
Figure 7 – Layering of communication . 25
Figure 8 – Flow of Type 12 service primitives . 26
Figure 9 – Successful mailbox write sequence . 37
Figure 10 – Successful mailbox read sequence . 38

Table 1 – Auto-increment physical read (APRD) . 27
Table 2 – Configured-address physical read (FPRD) . 27
Table 3 – Broadcast read (BRD) . 28
Table 4 – Logical read (LRD) . 29
Table 5 – Auto-increment physical write (APWR) . 29
Table 6 – Configured-address physical write (FPWR) . 30
Table 7 – Broadcast write (BWR) . 31
Table 8 – Logical write (LWR) . 31
Table 9 – Auto-increment physical read/write (APRW) . 32

– 4 – IEC 61158-3-12:2019 © IEC 2019
Table 10 – Configured-address physical read/write (FPRW) . 33
Table 11 – Broadcast read/write (BRW) . 33
Table 12 – Logical read/write (LRW) . 34
Table 13 – Auto-increment physical read / multiple write (ARMW) . 34
Table 14 – Configured-address physical read / multiple write (FRMW) . 35
Table 15 – Publisher network variable (PNV) . 36
Table 16 – Mailbox write . 38
Table 17 – Mailbox read update . 39
Table 18 – Mailbox read . 40
Table 19 – Read local . 41
Table 20 – Write local . 41
Table 21 – Event local . 42

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 3-12: Data-link layer service definition –
Type 12 elements
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
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
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
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
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
Attention is drawn to the fact that the use of the associated protocol type is restricted by its
intellectual-property-right holders. In all cases, the commitment to limited release of
intellectual-property-rights made by the holders of those rights permits a layer protocol type to
be used with other layer protocols of the same type, or in other type combinations explicitly
authorized by its intellectual-property-right holders.
NOTE Combinations of protocol types are specified in IEC 61784-1 and IEC 61784-2.
International Standard IEC 61158-3-12 has been prepared by subcommittee 65C: Industrial
networks, of IEC technical committee 65: Industrial-process measurement, control and
automation.
This fourth edition cancels and replaces the third edition published in 2014. This edition
constitutes a technical revision.

– 6 – IEC 61158-3-12:2019 © IEC 2019
This edition includes the following significant technical changes with respect to the previous
edition:
– technical corrections in the communication services;
– editorial improvements for clarification.
The text of this International standard is based on the following documents:
FDIS Report on voting
65C/945/FDIS 65C/954/RVD
Full information on the voting for the approval of this International standard can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61158 series, published under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

INTRODUCTION
This part of IEC 61158 is one of a series produced to facilitate the interconnection of
automation system components. It is related to other standards in the set as defined by the
“three-layer” fieldbus reference model described in IEC 61158-1.
Throughout the set of fieldbus standards, the term “service” refers to the abstract capability
provided by one layer of the OSI Basic Reference Model to the layer immediately above.
Thus, the data-link layer service defined in this standard is a conceptual architectural service,
independent of administrative and implementation divisions.

– 8 – IEC 61158-3-12:2019 © IEC 2019
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 3-12: Data-link layer service definition –
Type 12 elements
1 Scope
1.1 General
This part of IEC 61158 provides common elements for basic time-critical messaging
communications between devices in an automation environment. The term “time-critical” is
used to represent the presence of a time-window, within which one or more specified actions
are required to be completed with some defined level of certainty. Failure to complete
specified actions within the time window risks failure of the applications requesting the
actions, with attendant risk to equipment, plant and possibly human life.
This International standard defines in an abstract way the externally visible service provided
by the Type 12 fieldbus data-link layer in terms of
a) the primitive actions and events of the service;
b) the parameters associated with each primitive action and event, and the form which they
take;
c) the interrelationship between these actions and events, and their valid sequences.
The purpose of this document is to define the services provided to
• the Type 12 fieldbus application layer at the boundary between the application and data-
link layers of the fieldbus reference model;
• systems management at the boundary between the data-link layer and systems
management of the fieldbus reference model.
1.2 Specifications
The principal objective of this document is to specify the characteristics of conceptual data-
link layer services suitable for time-critical communications, and thus supplement the OSI
Basic Reference Model in guiding the development of data-link protocols for time-critical
communications. A secondary objective is to provide migration paths from previously-existing
industrial communications protocols.
This specification may be used as the basis for formal DL-Programming-Interfaces.
Nevertheless, it is not a formal programming interface, and any such interface will need to
address implementation issues not covered by this specification, including
a) the sizes and octet ordering of various multi-octet service parameters, and
b) the correlation of paired request and confirm, or indication and response, primitives.
1.3 Conformance
This document does not specify individual implementations or products, nor does it constrain
the implementations of data-link entities within industrial automation systems.
There is no conformance of equipment to this data-link layer service definition standard.
Instead, conformance is achieved through implementation of the corresponding data-link
protocol that fulfils the Type 12 data-link layer services defined in this document.

2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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.
NOTE All parts of the IEC 61158 series, as well as IEC 61784-1 and IEC 61784-2 are maintained simultaneously.
Cross-references to these documents within the text therefore refer to the editions as dated in this list of normative
references.
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model: The Basic Model
ISO/IEC 7498-3, Information technology – Open Systems Interconnection – Basic Reference
Model: Naming and addressing
ISO/IEC/IEEE 8802-3, Information technology – Telecommunications and information
exchange between systems – Local and metropolitan area networks – Specific requirements –
Part 3: Standard for Ethernet
ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services
IEEE Std 802.1D, IEEE Standard for Local and metropolitan area networks – Media Access
Control (MAC) Bridges; available at http://www.ieee.org [viewed 2018-09-11]
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviations
and conventions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Reference model terms and definitions
This document is based in part on the concepts developed in ISO/IEC 7498-1 and
ISO/IEC 7498-3 and makes use of the following terms defined therein.

– 10 – IEC 61158-3-12:2019 © IEC 2019
3.1.1 DL-address [7498-3]
3.1.2 DL-connectionless-mode transmission
[7498-1]
3.1.3 correspondent (N)-entities [7498-1]
correspondent DL-entities  (N=2)
correspondent Ph-entities  (N=1)
3.1.4 DL-duplex-transmission
[7498-1]
3.1.5 (N)-entity [7498-1]
DL-entity  (N=2)
Ph-entity  (N=1)
3.1.6 (N)-layer
[7498-1]
DL-layer  (N=2)
Ph-layer  (N=1)
3.1.7 layer-management [7498-1]
3.1.8 peer-entities
[7498-1]
3.1.9 primitive name [7498-3]
3.1.10 DL-protocol
[7498-1]
3.1.11 DL-protocol-data-unit [7498-1]
3.1.12 DL-relay [7498-1]
3.1.13 reset [7498-1]
3.1.14 responding-DL-address
[7498-3]
3.1.15 routing [7498-1]
3.1.16 segmenting
[7498-1]
3.1.17 (N)-service [7498-1]
DL-service  (N=2)
Ph-service  (N=1)
3.1.18 (N)-service-access-point [7498-1]
DL-service-access-point  (N=2)
Ph-service-access-point  (N=1)
3.1.19 DL-service-data-unit [7498-1]
3.1.20 DL-simplex-transmission
[7498-1]
3.1.21 DL-subsystem [7498-1]
3.1.22 systems-management
[7498-1]
3.1.23 DLS-user [7498-1]
3.1.24 DLS-user-data [7498-1]
3.2 Service convention terms and definitions
This document also makes use of the following terms defined in ISO/IEC 10731 as they apply
to the data-link layer:
3.2.1 acceptor
3.2.2 asymmetrical service
3.2.3 confirm (primitive);
requestor.deliver (primitive)
3.2.4 deliver (primitive)
3.2.5 DL-service-primitive;
primitive
3.2.6 DL-service-provider
3.2.7 DL-service-user
3.2.8 DL-user-optional-facility
3.2.9 indication (primitive);
acceptor.deliver (primitive)
3.2.10 request (primitive);
requestor.submit (primitive)
3.2.11 requestor
3.2.12 response (primitive);
acceptor.submit (primitive)
3.2.13 submit (primitive)
3.2.14 symmetrical service
3.3 Data-link service terms and definitions
3.3.1
application
function or data structure for which data is consumed or produced
3.3.2
application objects
multiple object classes that manage and provide a run time exchange of messages across the
network and within the network device
3.3.3
basic slave
slave device that supports only physical addressing of data
3.3.4
bit
unit of information consisting of a 1 or a 0
Note 1 to entry: This is the smallest data unit that can be transmitted.
3.3.5
client
object which uses the services of another (server) object to perform a task
3.3.6
client
initiator of a message to which a server reacts

– 12 – IEC 61158-3-12:2019 © IEC 2019
3.3.7
connection
logical binding between two application objects within the same or different devices
3.3.8
cyclic
events which repeat in a regular and repetitive manner
3.3.9
cyclic redundancy check
CRC
residual value computed from an array of data and used as a representative signature for the
array
3.3.10
data
generic term used to refer to any information carried over a fieldbus
3.3.11
data consistency
means for coherent transmission and access of the input- or output-data object between and
within client and server
3.3.12
device
physical entity connected to the fieldbus composed of at least one communication element
(the network element) and which may have a control element and/or a final element
(transducer, actuator, etc.)
3.3.13
distributed clocks
method to synchronize slaves and maintain a global time base
3.3.14
DL-segment
link
local link
single DL-subnetwork in which any of the connected DLEs may communicate directly, without
any intervening DL-relaying, whenever all of those DLEs that are participating in an instance
of communication are simultaneously attentive to the DL-subnetwork during the period(s) of
attempted communication
3.3.15
error
discrepancy between a computed, observed or measured value or condition and the specified
or theoretically correct value or condition
3.3.16
event
instance of a change of conditions
3.3.17
fieldbus memory management unit
function that establishes one or several correspondences between logical addresses and
physical memory
3.3.18
fieldbus memory management unit entity
single element of the fieldbus memory management unit: one correspondence between a
coherent logical address space and a coherent physical memory location
3.3.19
frame
denigrated synonym for DLPDU
3.3.20
full slave
slave device that supports both physical and logical addressing of data
3.3.21
interface
shared boundary between two functional units, defined by functional characteristics, signal
characteristics, or other characteristics as appropriate
3.3.22
master
device that controls the data transfer on the network and initiates the media access of the
slaves by sending messages and that constitutes the interface to the control system
3.3.23
mapping
correspondence between two objects in the way that one object is part of the other object
3.3.24
medium
cable, optical fibre, or other means by which communication signals are transmitted between
two or more points
Note 1 to entry: "media" is used as the plural of medium.
3.3.25
message
ordered series of octets intended to convey information
Note 1 to entry: Normally used to convey information between peers at the application layer.
3.3.26
network
set of nodes connected by some type of communication medium, including any intervening
repeaters, bridges, routers and lower-layer gateways
3.3.27
node
a) single DL-entity as it appears on one local link
b) end-point of a link in a network or a point at which two or more links meet
[SOURCE: IEC 61158-2, for option b), with some wording adjustment]

– 14 – IEC 61158-3-12:2019 © IEC 2019
3.3.28
object
abstract representation of a particular component within a device
Note 1 to entry: An object can be
a) an abstract representation of the capabilities of a device, composed of any or all of the following components:
1) data (information which changes with time);
2) configuration (parameters for behavior);
3) methods (things that can be done using data and configuration); or
b) a collection of related data (in the form of variables) and methods (procedures) for operating on that data that
have a clearly defined interface and behavior.
3.3.29
process data
data object containing application objects designated to be transferred cyclically or acyclically
for the purpose of processing
3.3.30
receiving DLS-user
DL-service user that acts as a recipient of DL-user-data
Note 1 to entry: A DL-service user can be concurrently both a sending and receiving DLS-user.
3.3.31
sending DLS-user
DL-service user that acts as a source of DL-user-data
3.3.32
server
object which provides services to another (client) object
3.3.33
service
operation or function than an object and/or object class performs upon request from another
object and/or object class
3.3.34
slave
DL-entity accessing the medium only after being initiated by the preceding slave or the master
3.3.35
Sync manager
collection of control elements to coordinate access to concurrently used objects
3.3.36
Sync manager channel
single control elements to coordinate access to concurrently used objects
3.3.37
switch
MAC bridge as defined in IEEE 802.1D
3.4 Symbols and abbreviations
APRD Auto-increment physical read
APRW Auto-increment physical read/write

APWR Auto-increment physical write
ARMW Auto-increment physical read / multiple write
BRD Broadcast read
BRW Broadcast read/write
BWR Broadcast write
CAN Controller area network
CoE CAN application protocol over Type 12 services
CSMA/CD Carrier sense multiple access with collision detection
DC Distributed clocks
DL- Data-link layer (as a prefix)
DLC DL-connection
DLCEP DL-connection-end-point
DLE DL-entity (the local active instance of the data-link layer)
DLL DL-layer
DLPCI DL-protocol-control-information
DLPDU DL-protocol-data-unit
DLM DL-management
DLME DL-management entity (the local active instance of DL-management)
DLMS DL-management service
DLS DL-service
DLSAP DL-service-access-point
DLSDU DL-service-data-unit
E²PROM Electrically erasable programmable read only memory
EoE Ethernet tunneled over Type 12 services
ESC Type 12 slave controller
FCS Frame check sequence
FIFO First-in first-out (queuing method)
FMMU Fieldbus memory management unit
FoE File access with Type 12 services
FPRD Configured address physical read
FPRW Configured address physical read/write
FPWR Configured address physical write
FRMW Configured address physical read/multiple write
HDR Header
ID Identifier
IP Internet protocol
LAN Local area network
LRD Logical memory read
LRW Logical memory read/write
LWR Logical memory write
MAC Medium access control
MDI Media-dependent interface (specified in ISO/IEC/IEEE 8802-3)
MDX Mailbox data exchange
MII Media-independent interface (specified in ISO/IEC/IEEE 8802-3)
PDI Physical device interface (a set of elements that allows access to DL-services from the
PDO Process data object
– 16 – IEC 61158-3-12:2019 © IEC 2019
Ph- Physical layer (as a prefix)
PhE Ph-entity (the local active instance of the physical layer)
PhL Ph-layer
PHY Physical layer device (specified in ISO/IEC/IEEE 8802-3)
PNV Publish network variable
OSI Open systems interconnection
QoS Quality of service
RAM Random access memory
Rx Receive
SDO Service data object
SII Slave information interface
SyncM Synchronization manager
TCP Transmission control protocol
Tx Transmit
UDP User datagram protocol
WKC Working counter
3.5 Common conventions
This document uses the descriptive conventions given in ISO/IEC 10731.
The service model, service primitives, and time-sequence diagrams used are entirely abstract
descriptions; they do not represent a specification for implementation.
Service primitives, used to represent service user/service provider interactions (see
ISO/IEC 10731), convey parameters that indicate information available in the user/provider
interaction.
This document uses a tabular format to describe the component parameters of the DLS
primitives. The parameters that apply to each group of DLS primitives are set out in tables
throughout the remainder of this document. Each table consists of up to six columns,
containing the name of the service parameter, and a column each for those primitives and
parameter-transfer directions used by the DLS:
– the request primitive’s input parameters;
– the indication primitive’s output parameters;
– the response primitive’s input parameters; and
– the confirm primitive’s output parameters.
NOTE The request, indication, response and confirm primitives are also known as requestor.submit,
acceptor.deliver, acceptor.submit, and requestor.deliver primitives, respectively (see ISO/IEC 10731).
One parameter (or part of it) is listed in each row of each table. Under the appropriate service
primitive columns, a code is used to specify the type of usage of the parameter on the
primitive and parameter direction specified in the column:

M parameter is mandatory for the primitive.
U parameter is a User option, and may or may not be provided depending on
the dynamic usage of the DLS-user. When not provided, a default value for
the parameter is assumed.
C parameter is conditional upon other parameters or upon the environment of
the DLS-user.
(blank) parameter is never present.
Some entries are further qualified by items in brackets. These may be a parameter-specific
constraint:
indicates that the parameter is semantically equivalent to the parameter in
(=)
the service primitive to its immediate left in the table.
In any particular interface, not all parameters need be explicitly stated. Some may be
implicitly associated with the primitive.
In the diagrams which illustrate these interfaces, dashed lines indicate cause-and-effect or
time-sequence relationships, and wavy lines indicate that events are roughly
contemporaneous.
4 Data-link layer services and concepts
4.1 Operating principle
This document describes a real-time Ethernet technology that aims to maximize the utilization
of the full duplex Ethernet bandwidth. Medium access control employs the master/slave
principle, where the master node (typically the control system) sends the Ethernet frames to
the slave nodes, which extract data from and insert data into these frames.
From an Ethernet point of view, a Type 12 segment is a single Ethernet device which receives
and sends ISO/IEC/IEEE 8802-3 Ethernet frames. However, this Ethernet device is not limited
to a single Ethernet controller with downstream microprocessor, but may consist of a large
number of Type 12 slave devices. These process the incoming Ethernet frames while they are
in transit within the device, reading data from the Ethernet frame and/or inserting their own
data into the frame before transferring the frame to the next slave device. The last slave
device within the segment sends the fully processed Ethernet frame back in the reverse
direction through the chain of devices, returning the collected information through the first
slave device to the master, which receives it as an Ethernet response frame.
This procedure utilizes the full duplex capability of Ethernet: both communication directions
are operated independently with reading and writing by the slaves on the outbound path and
only transmission-to-reception timing measurements on the inbound path as the Ethernet
frame retraverses each intermediate slave device.
Full-duplex communication between a master device and a Type 12 segment consisting of
one or several slave devices may be established without using a switch.
4.2 Topology
The topology of a communication system is one of the crucial factors for the successful
application in automation. The topology has significant influence on the cabling effort,
diagnostic features, redundancy options and hot-plug-and-play features.

– 18 – IEC 61158-3-12:2019 © IEC 2019
The star topology commonly used for Ethernet can lead to increased cabling effort and
infrastructure cost. Particularly for automation applications, a line or tree topology is often
preferable.
The slave node arrangement represents an open-loop bus. At the open end, the master
device sends frames, either directly or via Ethernet switches; it receives them at the other end
after they have been processed by each intervening device. Each Ethernet frame is relayed
from the first node to the next one, and successively to each other node in series. The last
node returns the Ethernet frame back to the master using the full duplex capabilities of
Ethernet. The resulting topology is a physical line.
Branches, which in principle are possible anywhere, can be used to enhance the line structure
into a tree structure form. A tree structure supports very simple wiring; individual branches,
for example, can branch into control cabinets or machine modules, while the main line runs
from one module to the next. Branches are possible if a device has more than two ports. This
document allows up to two branching links in addition to the basic set of two series interfaces.
An Ethernet frame received on port n (n not zero) is forwarded to port n+1. If there is no port
n+1 the Ethernet frame is forwarded to port 0. If no device is connected or the port is closed
by the master, a request to send to that port will be processed as if the same data are
received by this port (i.e. loop is closed).
4.3 Data-link layer overview
A single Ethernet frame can carry several Type 12 DLPDUs which are packed into the
Ethernet frame without gaps. Several nodes can be addressed individually by these DLPDUs.
The Ethernet frame is terminated with the last Type 12 DLPDU, except when the frame size is
less than 64 octets, in which case the Ethernet frame is padded to 64 octets.
The Type 12 DLPDU packing leads to better utilization of the Ethernet bandwidth than would
separate Ethernet frames to and from each slave node. However, for e.g. a 2-channel digital
input node with just two bits of user data, the overhead of a single Type 12 DLPDU can still
be excessive.
Therefore slave nodes may also support logical address mapping. The process data can be
inserted anywhere within a logical address space. If a Type 12 DLPDU is sent that contains
read or write services for a certain process image area located at the corresponding logical
address, instead of addressing a particular node, the nodes insert the data at or extract the
data from their appropriate place(s) within the process data, as noted in Figure 1.
Frame Type12
Ethernet HDR Process data WKC FCS
HDR HDR
Figure 1 – Mapping of logical data in an Ethernet frame
consisting of a single Type 12 DLPDU
Each node that detects an address match with the process image inserts its data, so that
many nodes can be addressed simultaneously with a single Type 12 DLPDU. The master can
assemble a completely sorted logical process image via a single Type 12 DLPDU,
independent of the physical wiring order of the slave devices.

Additional mapping is no longer required in
...