IEC 61158-5-12:2007

IEC 61158-5-12
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 5-12: Application layer service definition – Type 12 elements

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IEC 61158-5-12
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 5-12: Application layer service definition – Type 12 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XE
ICS 35.100.70; 25.040.40 ISBN 2-8318-9460-3

– 2 – 61158-5-12 © IEC:2007(E)

CONTENTS
FOREWORD.4H5

INTRODUCTION.5H7

1 Scope.6H8

1.1 Overview .7H8

1.2 Specifications .8H9

1.3 Conformance.9H9

2 Normative references.10H9

3 Terms, definitions, symbols, abbreviations and conventions .11H10
3.1 Reference model terms and definitions .12H10
3.2 Service convention terms and definitions .13H11
3.3 Application layer and data-link service terms and definitions.14H11
3.4 Common symbols and abbreviations .15H15
3.5 Conventions .16H16
4 Concepts .17H17
4.1 Common concepts.18H17
4.2 Type specific concepts .19H17
5 Data type ASE .20H25
5.1 General .21H25
5.2 Formal definition of data type objects.22H25
5.3 FAL defined data types .23H25
5.4 Data type ASE service specification .24H31
6 Communication model specification .25H32
6.1 ASEs .26H32
6.2 AR.27H105
Bibliography .28H116

Figure 1 – Producer consumer model .29H19
Figure 2 – Client server model.30H19
Figure 3 – Server triggered invocation .31H19
Figure 4 – Slave reference model.32H20
Figure 5 – Simple slave device .33H21
Figure 6 – Enhanced slave device .34H22
Figure 7 – Master functional overview.35H23
Figure 8 – Process output data sequence .36H33
Figure 9 – Process input data sequence .37H34
Figure 10 – CoE server model .38H51
Figure 11 – Successful single SDO-Download sequence .39H56
Figure 12 – Unsuccessful single SDO-Download sequence.40H57
Figure 13 – Successful segmented SDO-Download sequence.41H57
Figure 14 – Successful single SDO-Upload sequence.42H58
Figure 15 – Unsuccessful single SDO-Upload sequence .43H59
Figure 16 – Successful segmented SDO-Upload sequence.44H59
Figure 17 – SDO information sequence .45H60
Figure 18 – Emergency service .46H61

61158-5-12 © IEC:2007(E) – 3 –

Figure 19 – Command sequence .47H62

Figure 20 – PDO mapping .48H63

Figure 21 – Sync manager PDO assigment.49H64

Figure 22 – RxPDO service .50H65

Figure 23 – TxPDO service .51H66

Figure 24 – RxPDO remote transmission sequence .52H67

Figure 25 – TxPDO remote transmission sequence .53H67

Figure 26 – EoE sequence .54H87

Figure 27 – FoE read sequence with success .55H94
Figure 28 – FoE read sequence with error .56H95
Figure 29 – FoE write sequence with success.57H95
Figure 30 – FoE write sequence with error.58H96
Figure 31 – FoE write sequence with busy.59H96
Figure 32 – Successful AL control sequence .60H106
Figure 33 – Unsuccessful AL control sequence.61H107
Figure 34 – AL state changed sequence .62H108

Table 1 – Process output data.63H36
Table 2 – Process input data .64H37
Table 3 – Update process input data .65H38
Table 4 – SII read .66H46
Table 5 – SII write .67H47
Table 6 – SII reload.68H48
Table 7 – Allocation of SDO areas.69H52
Table 8 – SDO download expedited.70H71
Table 9 – SDO download normal .71H72
Table 10 – Download SDO segment .72H73
Table 11 – SDO upload expedited .73H74
Table 12 – SDO upload normal.74H75
Table 13 – Upload SDO segment .75H76
Table 14 – Abort SDO transfer .76H76

Table 15 – Get OD list.77H77
Table 16 – OD list segment .78H78
Table 17 – Get object description .79H79
Table 18 – Get entry description.80H80
Table 19 – Object entry segment.81H82
Table 20 – Emergency .82H83
Table 21 – RxPDO .83H84
Table 22 – TxPDO .84H84
Table 23 – RxPDO remote transmission .85H85
Table 24 – TxPDO remote transmission .86H85
Table 25 – Initiate EoE .87H90
Table 26 – EoE fragment.88H91

– 4 – 61158-5-12 © IEC:2007(E)

Table 27 – Set IP parameter.89H92

Table 28 – Set address filter.90H93

Table 29 – FoE read.91H98

Table 30 – FoE write .92H98

Table 31 – FoE data.93H99

Table 32 – FoE ack .94H99

Table 33 – FoE busy .95H100

Table 34 – FoE error .96H100

Table 35 – MBX read .97H102
Table 36 – MBX write .98H103
Table 37 – MBX read upd.99H104
Table 38 – AL management and ESM service primitives .100H105
Table 39 – AL control .101H114
Table 40 – AL state change.102H115

61158-5-12 © IEC:2007(E) – 5 –

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 5-12: Application 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
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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 61158-5-12 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 61158-5 subseries cancel and replace
IEC 61158-5:2003. This edition of this part constitutes a technical addition. This part and its
Type 12 companion parts also cancel and replace IEC/PAS 62407, published in 2005.
This edition of IEC 61158-5 includes the following significant changes from the previous
edition:
– 6 – 61158-5-12 © IEC:2007(E)

a) deletion of the former Type 6 fieldbus for lack of market relevance;

b) addition of new types of fieldbuses;

c) partition of part 5 of the third edition into multiple parts numbered -5-2, -5-3, …

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

FDIS Report on voting
65C/475/FDIS 65C/486/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 0Hhttp://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.

61158-5-12 © IEC:2007(E) – 7 –

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.

The application service is provided by the application protocol making use of the services

available from the data-link or other immediately lower layer. This standard defines the

application service characteristics that fieldbus applications and/or system management may

exploit.
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 application layer service defined in this standard is a conceptual architectural service,
independent of administrative and implementation divisions.

– 8 – 61158-5-12 © IEC:2007(E)

INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 5-12: Application layer service definition – Type 12 elements

1 Scope
1.1 Overview
The fieldbus Application Layer (FAL) provides user programs with a means to access the
fieldbus communication environment. In this respect, the FAL can be viewed as a “window
between corresponding application programs.”
This standard provides common elements for basic time-critical and non-time-critical
messaging communications between application programs in an automation environment and
material specific to Type 12 fieldbus. 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 different
Types of the fieldbus Application Layer in terms of
a) an abstract model for defining application resources (objects) capable of being manipulated
by users via the use of the FAL service,
b) the primitive actions and events of the service;
c) the parameters associated with each primitive action and event, and the form which they
take; and
d) the interrelationship between these actions and events, and their valid sequences.
The purpose of this standard is to define the services provided to
1) the FAL user at the boundary between the user and the Application Layer of the Fieldbus
Reference Model, and
2) Systems Management at the boundary between the Application Layer and Systems
Management of the Fieldbus Reference Model.
This standard specifies the structure and services of the IEC fieldbus Application Layer, in

conformance with the OSI Basic Reference Model (ISO/IEC 7498) and the OSI Application
Layer Structure (ISO/IEC 9545).
FAL services and protocols are provided by FAL application-entities (AE) contained within the
application processes. The FAL AE is composed of a set of object-oriented Application Service
Elements (ASEs) and a Layer Management Entity (LME) that manages the AE. The ASEs
provide communication services that operate on a set of related application process object
(APO) classes. One of the FAL ASEs is a management ASE that provides a common set of
services for the management of the instances of FAL classes.
Although these services specify, from the perspective of applications, how request and
responses are issued and delivered, they do not include a specification of what the requesting
and responding applications are to do with them. That is, the behavioral aspects of the
applications are not specified; only a definition of what requests and responses they can
send/receive is specified. This permits greater flexibility to the FAL users in standardizing such
object behavior. In addition to these services, some supporting services are also defined in this
standard to provide access to the FAL to control certain aspects of its operation.

61158-5-12 © IEC:2007(E) – 9 –

1.2 Specifications
The principal objective of this standard is to specify the characteristics of conceptual

application layer services suitable for time-critical communications, and thus supplement the

OSI Basic Reference Model in guiding the development of application layer protocols for time-

critical communications.
A secondary objective is to provide migration paths from previously-existing industrial

communications protocols. It is this latter objective which gives rise to the diversity of services
standardized as the various Types of IEC 61158, and the corresponding protocols standardized

in subparts of IEC 61158-6.
This specification may be used as the basis for formal Application 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 application layer entities within industrial automation systems.
There is no conformance of equipment to this application layer service definition standard.
Instead, conformance is achieved through implementation of conforming application layer
protocols that fulfill any given Type of application layer services as defined in this standard.
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 61131-3, Programmable controllers – Part 3: Programming languages
IEC 61158-3-12, Industrial communication networks – Fieldbus specifications – Part 3-12:
Data-link layer service definition – Type 12 elements
ISO/IEC 646:1991, Information technology – ISO 7-bit coded character set for information
interchange
ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Basic Reference
Model – Basic Reference Model: The Basic Model
ISO/IEC 7498-3, Information technology – Open Systems Interconnection – Basic Reference
Model – 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 10646, Information technology – Universal Multiple-Octet Coded Character Set (UCS)
ISO/IEC 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services

– 10 – 61158-5-12 © IEC:2007(E)

IEEE 802.1D, IEEE Standard for Information technology – Telecommunications and information

exchange between systems – IEEE standard for local and metropolitan area networks –

Common specifications – Media access control (MAC) Bridges; available at

<1Hhttp://www.ieee.org>
IEEE 802.1Q, IEEE Standard for Information technology – Telecommunications and information

exchange between systems – IEEE standard for Local and metropolitan area networks – Virtual

bridged local area networks Bridges; available at <2Hhttp://www.ieee.org>

IETF RFC 791, Internet Protocol; available at <3Hhttp://www.ietf.org>

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:
3.1.1 correspondent (N)-entities [7498-1]
correspondent AL-entities  (N=7)
[7498-1]
3.1.2 (N)-entity
AL-entity  (N=7)
[7498-1]
3.1.3 (N)-layer
AL-layer  (N=7)
3.1.4 layer-management [7498-1]
[7498-1]
3.1.5 peer-entities
3.1.6 primitive name [7498-3]
[7498-1]
3.1.7 AL-protocol
3.1.8 AL-protocol-data-unit [7498-1]
[7498-1]
3.1.9 reset
3.1.10 routing [7498-1]
[7498-1]
3.1.11 segmenting
3.1.12 (N)-service [7498-1]
AL-service  (N=7)
3.1.13 AL-service-data-unit [7498-1]
3.1.14 AL-simplex-transmission [7498-1]
3.1.15 AL-subsystem [7498-1]
3.1.16 systems-management [7498-1]
3.1.17 AL-user-data [7498-1]
61158-5-12 © IEC:2007(E) – 11 –

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 AL-service-primitive;
primitive
3.2.6 AL-service-provider
3.2.7 AL-service-user
3.2.8 indication (primitive);
acceptor.deliver (primitive)
3.2.9 request (primitive);
requestor.submit (primitive)
3.2.10 requestor
3.2.11 response (primitive);
acceptor.submit (primitive)
3.2.12 submit (primitive)
3.2.13 symmetrical service
3.3 Application layer and 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
communication object
component that manage and provide a run time exchange of messages across the network

– 12 – 61158-5-12 © IEC:2007(E)

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
data
generic term used to refer to any information carried over a fieldbus

3.3.10
data consistency
means for coherent transmission and access of the input- or output-data object between and
within client and server
3.3.11
data type
relation between values and encoding for data of that type. For this specification the data type
definitions of IEC 61131-3-12 apply.
3.3.12
data type object
Entry in the object dictionary indicating a data type
3.3.13
default gateway
device with at least two interfaces in two different IP subnets acting as router for a subnet.
3.3.14
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.)
3.3.15
device profile
collection of device dependent information and functionality providing consistency between
similar devices of the same device

3.3.16
diagnosis information
all data available at the server for maintenance purposes
3.3.17
distributed clocks
method to synchronize slaves and maintain a global time base
3.3.18
error
discrepancy between a computed, observed or measured value or condition and the specified
or theoretically correct value or condition
3.3.19
error class
general grouping for related error definitions and corresponding error codes

61158-5-12 © IEC:2007(E) – 13 –

3.3.20
error code
identification of a specific type of error within an error class

3.3.21
event
instance of a change of conditions

3.3.22
fieldbus memory management unit

function that establishes one or several correspondences between logical addresses and

physical memory
3.3.23
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
3.3.24
frame
denigrated synonym for DLPDU
3.3.25
full slave
slave device that supports both physical and logical addressing of data
3.3.26
index
address of an object within an application process
3.3.27
interface
shared boundary between two functional units, defined by functional characteristics, signal
characteristics, or other characteristics as appropriate
3.3.28
little endian
Method for data representation of numbers greater 8 bit where the least significant octet is
transmitted first.
3.3.29
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
3.3.30
mapping
correspondence between two objects in that way that one object is part of the other object
3.3.31
mapping parameters
set of values defining the correspondence between application objects and process data
objects
– 14 – 61158-5-12 © IEC:2007(E)

3.3.32
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.

3.3.33
message
ordered series of octets intended to convey information

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

3.3.34
network
set of nodes connected by some type of communication medium, including any intervening
repeaters, bridges, routers and lower-layer gateways
3.3.35
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]
3.3.36
object
abstract representation of a particular component within a device
NOTE  An object can be
1) an abstract representation of the capabilities of a device. Objects can be composed of any or all of the following
components:
a) data (information which changes with time);
b) configuration (parameters for behavior);
c) methods (things that can be done using data and configuration).
2) a collection of related data (in the form of variables) and methods (procedures) for operating on that data that
have clearly defined interface and behavior.
3.3.37
object dictionary
data structure addressed by Index and Sub-index that contains descriptions of data type
objects, communication objects and application objects
3.3.38
process data
collection of application objects designated to be transferred cyclically or acyclically for the
purpose of measurement and control
3.3.39
process data object
structure described by mapping parameters containing one or several process data entities
3.3.40
segment
collection of one real master with one or more slaves
3.3.41
server
object which provides services to another (client) object

61158-5-12 © IEC:2007(E) – 15 –

3.3.42
service
operation or function that an object and/or object class performs upon request from another

object and/or object class
3.3.43
slave
DL-entity accessing the medium only after being initiated by the preceding slave or

3.3.44
sub-index
subaddress of an object within the object dictionary
3.3.45
Sync Manager
collection of control elements to coordinate access to concurrently used objects.
3.3.46
Sync Manager channel
single control elements to coordinate access to concurrently used objects.
3.3.47
switch
MAC bridge as defined in IEEE 802.1D
3.4 Common symbols and abbreviations
Application layer (as a prefix)
3.4.1 AL-
3.4.2 ALE AL-entity (the local active instance of the application layer)
3.4.3 AL AL-layer
3.4.4 APDU AL-protocol-data-unit
3.4.5 ALM AL-management
3.4.6 ALME AL-management Entity (the local active instance of AL-management)
3.4.7 ALMS AL-management service
3.4.8 ALS AL-service
3.4.9 AR Application relationship
Application service element
3.4.10 ASE
Controller Area Network
3.4.11 CAN
CAN in Automation
3.4.12 CiA
CANopen over Type 12 services
3.4.13 CoE
Carrier sense multiple access with collision detection
3.4.14 CSMA/CD
3.4.15 DC Distributed clocks
3.4.16 DL Data-link-layer
3.4.17 DNS Domain name system (server for name resolution in IP networks)
3.4.18 E²PROM Electrically erasable programmable read only memory
3.4.19 EoE Ethernet tunneled over Type 12 services
3.4.20 ESC Type 12 slave controller
3.4.21 FCS Frame check sequence

– 16 – 61158-5-12 © IEC:2007(E)

3.4.22 FIFO First-in first-out (queuing method)

3.4.23 FMMU Fieldbus memory management unit

3.4.24 FoE File access with Type 12 services

3.4.25 HDR Header
3.4.26 ID Identifier
Internet engineering task force
3.4.27 IETF
Internet protocol
3.4.28 IP
Local area network
3.4.29 LAN
Medium access control
3.4.30 MAC
Object dictionary
3.4.31 OD
3.4.32 OSI Open systems interconnection
3.4.33 PDI Physical device internal interface (a set of elements that allows
access to DL-services from the AL)
3.4.34 PDO Process data object
3.4.35 PhL Ph-layer
3.4.36 QoS Quality of service
3.4.37 RAM Random access memory
3.4.38 Rx Receive
Service data object
3.4.39 SDO
slave information interface
3.4.40 SII
Synchronization manager
3.4.41 SM
Synchronization manager
3.4.42 SyncM
Transmission control protocol
3.4.43 TCP
3.4.44 Tx Transmit
3.4.45 UDP User datagram protocol
3.4.46 WKC Working counter
3.5 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.
This standard uses a tabular format to describe the component parameters of the service
primitives. The parameters that apply to each group of service primitives are set out in tables
throughout the remainder of this standard. Each table consists of up to five columns,
containing the name of the service parameter, and a column each for those primitives and
parameter-transfer directions used by the service:
⎯ 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.

61158-5-12 © IEC:2007(E) – 17 –

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 service-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 service-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 Concepts
4.1 Common concepts
All of IEC/TR 61158-1, Clause 9 is incorporated by reference, except as specifically overridden
in 103H4.2.
4.2 Type specific concepts
4.2.1 Operating principle
This standard and its companion Type 12 standards describe 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 frames directly and
extract the relevant user data, or insert data and transfer the frame to the next slave device.
The last slave device within the segment sends the fully processed frame back, so that it is
returned by the first slave device to the master as response frame.

– 18 – 61158-5-12 © IEC:2007(E)

This procedure utilizes the full duplex capability of Ethernet: both communication directions are

operated independently. Communication without switch between a master device and a

Type 12 segment consisting of one or several slave devices may be established.

Industrial communication systems have to meet different requirements in terms of the data

transmission characteristics. Parameter data is transferred acyclically and in large quantities,

whereby the timing requirements are relatively non-critical, and the transmission is usually

triggered by the control system. Diagnostic data is also transferred acyclically and event-driven,

but the timing requirements are more demanding, and the transmission is usually triggered by
a peripheral device.
Process data, on the other hand, is typically transferred cyclica
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