IEC 61158-3-12:2007

IEC 61158-3-12
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 3-12: Data-link layer service definition – Type 12 elements

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IEC 61158-3-12
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 3-12: Data-link layer service definition – Type 12 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 35.100.20; 25.040.40 ISBN 2-8318-9417-4

– 2 – 61158-3-12 © IEC:2007(E)

CONTENTS
FOREWORD.4

INTRODUCTION.6

1 Scope.7

1.1 Overview .7

1.2 Specifications .7

1.3 Conformance.7

2 Normative references.8

3 Terms, definitions, symbols, abbreviations and conventions .8
3.1 Reference model terms and definitions .8
3.2 Service convention terms and definitions .9
3.3 Data-link service terms and definitions.10
3.5 Symbols and abbreviations .13
3.6 Common conventions .14
4 Data-link layer services and concepts .15
4.1 Operating principle .15
4.2 Topology .16
4.3 Data-link layer overview.16
4.4 Error detection overview .17
4.5 Parameter and process data handling introduction .17
4.6 Node reference model .18
4.7 Operation overview.19
4.8 Addressing .20
4.9 Slave classification .22
4.10 Structure of the communication layer in the slave.23
5 Communication services .24
5.1 Overview .24
5.2 Read services.24
5.3 Write services .27
5.4 Combined read/write services .29
5.5 Network services .33
5.6 Mailbox.34
6 Local interactions.39
6.1 Read local .39
6.2 Write local .39
6.3 Event local.40
Bibliography .41

Figure 1 – Mapping of logical data in an Ethernet frame consisting of a single Type 12
DLPDU.17
Figure 2 – Type 12 data-link reference model .18
Figure 3 – Type 12 segments in open mode .19
Figure 4 – Type 12 segment in direct mode .19
Figure 5 – Addressing mode overview .20
Figure 6 – Fieldbus memory management unit overview .22
Figure 7 – Layering of communication .23

61158-3-12 © IEC:2007(E) – 3 –

Figure 8 – Flow of Type 12 service primitives .24

Figure 9 – Successful mailbox write sequence.35

Figure 10 – Successful mailbox read sequence .36

Table 1 – Auto-increment physical read (APRD) .25

Table 2 – Configured-addresse physical read (FPRD).25

Table 3 – Broadcast read (BRD).26

Table 4 – Logical read (LRD).27

Table 5 – Auto-increment physical write (APWR) .27

Table 6 – Configured-address physical write (FPWR) .28
Table 7 – Broadcast write (BWR) .28
Table 8 – Logical write (LWR) .29
Table 9 – Auto-increment physical read/write (APRW) .30
Table 10 – Configured-address physical read/write (FPRW).30
Table 11 – Broadcast read/write (BRW).31
Table 12 – Logical read/write (LRW).31
Table 13 – Auto-increment physical read / multiple write (ARMW).32
Table 14 – Configured-address physical read / multiple write (FRMW) .33
Table 15 – Provide network variable (PNV).33
Table 16 – Mailbox write.36
Table 17 – Mailbox read update.37
Table 18 – Mailbox read .38
Table 19 – Read local .39
Table 20 – Write local .39
Table 21 – Event local.40

– 4 – 61158-3-12 © IEC:2007(E)

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
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

NOTE  Use of some of the associated protocol types is restricted by their 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 particular data-link layer protocol type to be used with physical layer and application layer protocols in type
combinations as specified explicitly in the IEC 61784 series. Use of the various protocol types in other combinations
may require permission of their respective intellectual-property-right holders.
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 first edition and its companion parts of the IEC 61158-3 subseries cancel and replace
IEC 61158-3:2003. This edition of this part constitutes a technical addition. This part and its
Type 12 companion parts also replace IEC/PAS 62407, published in 2005.
This edition includes the following significant changes with respect to the previous edition:
a) deletion of the former Type 6 fieldbus, and the placeholder for a Type 5 fieldbus data-link
layer, for lack of market relevance;

61158-3-12 © IEC:2007(E) – 5 –

b) addition of new types of fieldbuses;

c) division of this part into multiple parts numbered 3-1, 3-2, …, 3-19.

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

FDIS Report on voting
65C/473/FDIS 65C/484/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 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.
NOTE  The revision of this standard will be synchronized with the other parts of the IEC 61158 series.
The list of all the parts of the IEC 61158 series, under the general title Industrial
communication networks – Fieldbus specifications, can be found on the IEC web site.

– 6 – 61158-3-12 © IEC:2007(E)

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/TR 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.

61158-3-12 © IEC:2007(E) – 7 –

INDUSTRIAL COMMUNICATION NETWORKS –

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

1 Scope
1.1 Overview
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 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 standard 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 standard 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 standard 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 fulfills the Type 12 data-link layer services defined in this standard.

– 8 – 61158-3-12 © IEC:2007(E)

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.

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 8802-3, Information technology – Telecommunications and information exchange
between systems – Local and metropolitan area networks – Specific requirements – Part 3:
Carrier sense multiple access with collision detection (CSMA/CD) access method and Physical
Layer specifications
ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services
IEE 802.1D, IEEE Standard for Local and metropolitan area networks – Media Access Control
(MAC) Bridges; available at
3 Terms, definitions, symbols, abbreviations and conventions
For the purposes of this document, the following terms, definitions, symbols, abbreviations and
conventions apply.
3.1 Reference model terms and definitions
This standard 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.
[7498-3]
3.1.1 DL-address
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]
[7498-1]
3.1.5 (N)-entity
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]
61158-3-12 © IEC:2007(E) – 9 –

3.1.11 DL-protocol-data-unit [7498-1]

[7498-1]
3.1.12 DL-relay
3.1.13 reset [7498-1]
[7498-3]
3.1.14 responding-DL-address
3.1.15 routing [7498-1]
[7498-1]
3.1.16 segmenting
3.1.17 (N)-service [7498-1]
DL-service  (N=2)
Ph-service  (N=1)
[7498-1]
3.1.18 (N)-service-access-point
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 standard 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)
– 10 – 61158-3-12 © IEC:2007(E)

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. This is the smallest data unit that can be
transmitted
3.3.5
client
1) object which uses the services of another (server) object to perform a task
2) initiator of a message to which a server reacts
3.3.6
connection
logical binding between two application objects within the same or different devices
3.4
cyclic
events which repeat in a regular and repetitive manner
3.4.1
cyclic redundancy check (CRC)
residual value computed from an array of data and used as a representative signature for the
array
3.4.2
data
generic term used to refer to any information carried over a fieldbus
3.4.3
data consistency
means for coherent transmission and access of the input- or output-data object between and
within client and server
3.4.4
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.)
61158-3-12 © IEC:2007(E) – 11 –

3.4.5
distributed clocks
method to synchronize slaves and maintain a global time base

3.4.6
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
3.4.7
error
discrepancy between a computed, observed or measured value or condition and the specified
or theoretically correct value or condition
3.4.8
event
instance of a change of conditions
3.4.9
fieldbus memory management unit
function that establishes one or several correspondences between logical addresses and
physical memory
3.4.10
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
3.4.11
frame
denigrated synonym for DLPDU
3.4.12
full slave
slave device that supports both physical and logical addressing of data
3.4.13
interface
shared boundary between two functional units, defined by functional characteristics, signal

characteristics, or other characteristics as appropriate
3.4.14
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
3.4.15
mapping
correspondence between two objects in that way that one object is part of the other object
3.4.16
medium
cable, optical fibre, or other means by which communication signals are transmitted between
two or more points
NOTE  "media" is used as the plural of medium.

– 12 – 61158-3-12 © IEC:2007(E)

3.4.17
message
ordered series of octets intended to convey information

NOTE  Normally used to convey information between peers at the application layer.

3.4.18
network
set of nodes connected by some type of communication medium, including any intervening

repeaters, bridges, routers and lower-layer gateways

3.4.19
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 [derived from IEC
61158-2]
3.4.20
object
abstract representation of a particular component within a device
NOTE  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.
3.4.21
process data
data object containing application objects designated to be transferred cyclically or acyclically
for the purpose of processing
3.4.22
receiving DLS-user
DL-service user that acts as a recipient of DL-user-data
NOTE  A DL-service user can be concurrently both a sending and receiving DLS-user.
3.4.23
sending DLS-user
DL-service user that acts as a source of DL-user-data

3.4.24
server
object which provides services to another (client) object
3.4.25
service
operation or function than an object and/or object class performs upon request from another
object and/or object class
3.4.26
slave
DL-entity accessing the medium only after being initiated by the preceding slave or

61158-3-12 © IEC:2007(E) – 13 –

3.4.27
Sync manager
collection of control elements to coordinate access to concurrently used objects.

3.4.28
Sync manager channel
single control elements to coordinate access to concurrently used objects.

3.4.29
switch
MAC bridge as defined in IEEE 802.1D

3.5 Symbols and abbreviations
Auto-increment physical read
3.5.1 APRD
Auto-increment physical read/write
3.5.2 APRW
3.5.3 APWR Auto-increment physical write
3.5.4 ARMW Auto-increment physical read / multiple write
3.5.5 BRD Broadcast read
3.5.6 BRW Broadcast read/write
3.5.7 BWR Broadcast write
3.5.8 CAN Controller area network
3.5.9 CoE CANopen over Type 12 services
3.5.10 CSMA/CD Carrier sense multiple access with collision detection
3.5.11 DC Distributed clocks
Data-link layer (as a prefix)
3.5.12 DL-
DL-connection
3.5.13 DLC
DL-connection-end-point
3.5.14 DLCEP
DL-entity (the local active instance of the data-link layer)
3.5.15 DLE
3.5.16 DLL DL-layer
3.5.17 DLPCI DL-protocol-control-information
3.5.18 DLPDU DL-protocol-data-unit
3.5.19 DLM DL-management
3.5.20 DLME DL-management entity (the local active instance of DL-management)

3.5.21 DLMS DL-management service
3.5.22 DLS DL-service
3.5.23 DLSAP DL-service-access-point
DL-service-data-unit
3.5.24 DLSDU
Electrically erasable programmable read only memory
3.5.25 E²PROM
Ethernet tunneled over Type 12 services
3.5.26 EoE
Type 12 slave controller
3.5.27 ESC
Frame check sequence
3.5.28 FCS
3.5.29 FIFO First-in first-out (queuing method)
3.5.30 FMMU Fieldbus memory management unit
3.5.31 FoE File access with Type 12 services
3.5.32 FPRD Configured address physical read

– 14 – 61158-3-12 © IEC:2007(E)

3.5.33 FPRW Configured address physical read/write

3.5.34 FPWR Configured address physical write

3.5.35 FRMW Configured address physical read/multiple write

3.5.36 HDR Header
3.5.37 ID Identifier
Internet protocol
3.5.38 IP
Local area network
3.5.39 LAN
Logical memory read
3.5.40 LRD
Logical memory read/write
3.5.41 LRW
Logical memory write
3.5.42 LWR
3.5.43 MAC Medium access control
3.5.44 MDI Media-dependent interface (specified in ISO/IEC 8802-3)
3.5.45 MDX Mailbox data exchange
3.5.46 MII Media-independent interface (specified in ISO/IEC 8802-3)
3.5.47 PDI Physical device interface (a set of elements that allows access to
DL-services from the DL-user)
3.5.48 PDO Process data object
3.5.49 Ph- Physical layer (as a prefix)
Ph-entity (the local active instance of the physical layer)
3.5.50 PhE
Ph-layer
3.5.51 PhL
Physical layer device (specified in ISO/IEC 8802-3)
3.5.52 PHY
Publish network variable
3.5.53 PNV
Open systems interconnection
3.5.54 OSI
3.5.55 QoS Quality of service
3.5.56 RAM Random access memory
3.5.57 Rx Receive
3.5.58 SDO Service data object
3.5.59 SII Slave information interface
3.5.60 SyncM Synchronization manager
3.5.61 TCP Transmission control protocol

3.5.62 Tx Transmit
User datagram protocol
3.5.63 UDP
Working counter
3.5.64 WKC
3.6 Common conventions
This standard 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.

61158-3-12 © IEC:2007(E) – 15 –

This standard 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 standard. 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:
parameter is mandatory for the primitive.
M
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 standard 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 standard ISO/IEC 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.

– 16 – 61158-3-12 © IEC:2007(E)

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.
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 often is
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 thence 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
standard 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 blocked 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.

This blocking 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.

61158-3-12 © IEC:2007(E) – 17 –

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 the master, so that the process data can be
transferred directly to one or more different control tasks. Each task can create its own process
image and exchange it within its own timeframe. The physical order of the nodes is completely
arbitrary and is only relevant during the first initialization phase.
The logical address space is 2 octets (= 4 GB). Thus a Type 12 fieldbus can be considered to
be a serial backplane for automation systems that enables connection to distributed process
data for both large and very small automation devices. Using a standard Ethernet controller
and standard Ethernet cables, a very large number of I/O channels can be connected to
automation devices so that they can be accessed with high bandwidth, minimum delay and a
near-optimum effective usable data rate. At the same time, devices such as fieldbus scanners
can be connected as well, thus preserving existing technologies and standards.
4.4 Error detection overview
Type 12 master and slave nodes (DLEs) check the Ethernet frame check sequence (FCS) to
determine whether a frame is received correctly. Since one or several slaves may modify the
frame during the transfer, the FCS is checked by each node on reception and recalculated
during retransmission. If a slave detects a checksum error, the slave does not repair the FCS
but flags the master by incrementing an error counter, so that the source of a single fault can
be located precisely within the open-loop topology.

When reading data from or writing data to a Type 12 DLPDU, the addressed slave increments
a working counter (WKC) positioned at the end of the DLPDU. Slaves which are merely
forwarding the DLPDU, but not extracting information from it or inserting information within it,
do not modify the counter. By comparing the working counter with the expected number of
accessing slave nodes, a master can check whether the expected number of nodes have
processed the corresponding DLPDU.
4.5 Parameter and process data handling introduction
Industrial communication systems need to meet different requirements in terms of their data
transmission characteristics. Parameter data can be transferred acyclically and in large
quantities, usually in situations where the timing requirements are relatively non-critical and the
transmission is triggered by the control system. Diagnostic data is also transferred acyclically
in an event-driven mode, but the timing requirements are more demanding and the
transmission is usually triggered by a peripheral device.

– 18 – 61158-3-12 © IEC:2007(E)

Process data, on the other hand, is typically transferred cyclically with different cycle times.

The timing requirements are most stringent for process data communication. This international

standard supports a variety of services and protocols to meet these differing requirements.

4.6 Node reference model
4.6.1 Mapping onto OSI Basic Reference Model

Type 12 services are described using the principles, methodology and model of
ISO/IEC 7498-1 (OSI). The OSI model provides a layered approach to communications

standards, whereby the layers can be developed and modified independently. The Type 12

specification defines functionality from top to bottom of a full OSI communications stack.

Functions of the intermediate OSI layers, layers 3–6, are consolidated into either the Type 12
data-link layer or the DL-user of the Type 12 data-link layer. The Type 12 data-link reference
model is shown in Figure 2.
HTTP,
Files
FTP, …
Application
DLS-user
CANopen over EtherCAT
TCP UDP
File
Object Dictionary
Access
IP
over
EtherCAT
Ethernet
SDO PDO Mapping
over EtherCAT
control/ Sync
Mailbox Process data
status settings
FMMU
SyncM FMMU
DLL
FMMU
FMMU n
SyncM SyncM
DLL Slave Layer
SyncM
info address Management
DL control/
DL status
Data-link layer
Physical layer
Figure 2 – Type 12 data-link reference model

4.6.2 Data-link layer features
The data-link layer provides basic time-critical support for data communications among devices
connected. The term “time-critical” is used to describe applications having a time window,
within which one or more specified actions are required to be completed with some defined
level of
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