IEC 61158-4-19:2007

IEC 61158-4-19
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 4-19: Data-link layer protocol specification – Type 19 elements

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IEC 61158-4-19
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 4-19: Data-link layer protocol specification – Type 19 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 35.100.20; 25.040.40 ISBN 2-8318-9443-3

– 2 – 61158-4-19 © IEC:2007(E)

CONTENTS
FOREWORD.6

INTRODUCTION.8

1 Scope.9

1.1 General .9

1.2 Specifications.9

1.3 Procedures.9

1.4 Applicability.9

1.5 Conformance.9
2 Normative references .10
3 Terms, definitions, symbols, abbreviations and conventions .10
3.1 Reference model terms and definitions.10
3.2 Additional Type 19 terms and definitions .10
3.3 Symbols .13
3.4 Abbreviations .14
3.5 Additional conventions .15
4 DL-protocol overview.15
5 DLPDU structure .17
5.1 Overview .17
5.2 General DLPDU identification.17
5.3 General DLPDU structure.17
5.4 DLPDU header .18
5.5 MDT DLPDU .19
5.6 AT DLPDU .28
6 DL management .38
6.1 Overview .38
6.2 Enable and disable cyclic communication .38
6.3 Hot-plug procedure.43
6.4 Status procedures .44
7 Data transmission methods .44
7.1 Overview .44
7.2 SVC .45
7.3 RTC .45

8 Telegram timing and DLPDU handling .45
8.1 Usage of real-time channel with different network topologies.45
8.2 Communication mechanisms .46
8.3 Device synchronization.52
9 Error handling and monitoring .53
9.1 Failure of telegrams .53
9.2 Response to MDT and AT telegram failure .53
9.3 Service channel error messages.53
Annex A (Normative) – IDN – Identification numbers.55
A.1 IDN specification .55
A.2 Identification numbers in numerical orders .55
A.3 Detailed specification of communication-related IDNs .56
Bibliography.74

61158-4-19 © IEC:2007(E) – 3 –

Figure 1 – Valid MDT and AT telegram combinations .16

Figure 2 – Offsets within MDT payload.23

Figure 3 – Offsets within AT payload.32

Figure 4 – Communication phase transitions.39

Figure 5 – Block diagram of master and slave.46

Figure 6 – Telegram sequence.48

Figure 7 – Beginning of telegram .49

Figure 8 – Access to the medium .50

Figure 9 – Timing diagram of CP0.52
Figure 10 – Timing diagram of CP1 and CP2 .52
Figure 11 – Synchronization timing .53
Figure 12 – Synchronization signal generation.53
Figure A.1 – Lengths of MDTs (example) .61
Figure A.2 – Lengths of ATs (example) .63
Figure A.3 – Structure of MAC address.67
Figure A.4 – Structure of IP address .68
Figure A.5 – Structure of subnet mask .69
Figure A.6 – Structure of gateway address .70

Table 1 – Ethernet DLPDU identification .17
Table 2 – Data structure in a DLPDU .17
Table 3 – DLPDU payload header.18
Table 4 – DLPDU type .18
Table 5 – MDT MST header .19
Table 6 – MDT MST fields to be considered by the slave .19
Table 7 – MDT phase.19
Table 8 – MDT0 in CP0.20
Table 9 – MDT0 in CP1 and CP2 .22
Table 10 – MDT1 in CP1 and CP2 .22
Table 11 – MDT data field.23
Table 12 – MDT hot-plug field in HP0 and HP1 .24

Table 13 – MDT hot-plug field in HP2 .24
Table 14 – Device address field .24
Table 15 – HP control field (in HP0 and HP1) .25
Table 16 – MDT service channel field .26
Table 17 – MDT SVC (for each slave) .26
Table 18 – SVC control word (DLL).27
Table 19 – MDT real-time data field .28
Table 20 – MDT real-time data (for each device).28
Table 21 – Device control field.28
Table 22 – AT MST header .29
Table 23 – AT MST fields to be considered by the slave .29
Table 24 – AT0 structure in CP0 .30

– 4 – 61158-4-19 © IEC:2007(E)

Table 25 – AT0 in CP1 and CP2 .30

Table 26 – AT1 in CP1 and CP2 .31

Table 27 – AT data field.31

Table 28 – AT hot-plug field in HP0 and HP1 .32

Table 29 – AT hot-plug field in HP2 .32

Table 30 – HP status field (in HP0 and HP1).33

Table 31 – AT service channel field .34

Table 32 – AT SVC (for each slave).34

Table 33 – AT SVC status description (DLL) .34
Table 34 – AT real-time data field .35
Table 35 – AT MS data field.36
Table 36 – AT MS data (for each device) .36
Table 37 – Device status field .36
Table 38 – CC data field .37
Table 39 – CC data field producer .37
Table 40 – CC consumer control.37
Table 41 – Synchronization classes of master and slave.49
Table 42 – Telegram transmission in RT and NR channels .51
Table A.1 – List of relevant communication-related IDNs .55
Table A.2 – Attributes of IDN S-0-1001 .57
Table A.3 – Attributes of IDN S-0-1002 .57
Table A.4 – Attributes of IDN S-0-1005 .58
Table A.5 – Attributes of IDN S-0-1006 .58
Table A.6 – Attributes for IDN S-0-1007.59
Table A.7 – Attributes for IDN S-0-1008.59
Table A.8 – Attributes of IDN S-0-1009 .60
Table A.9 – RTC-Offset in MDT .60
Table A.10 – Attributes of IDN S-0-1010 .61
Table A.11 – Attributes of IDN S-0-1011 .61
Table A.12 – RTC Offset in AT.62
Table A.13 – Attributes of IDN S-0-1012 .62

Table A.14 – Attributes of IDN S-0-1013 .63
Table A.15 – RTC Offset in MDT.63
Table A.16 – Attributes of IDN S-0-1014 .64
Table A.17 – RTC Offset in AT.64
Table A.18 – Attributes of IDN S-0-1015 .65
Table A.19 – Attributes of IDN S-0-1016 .65
Table A.20 – Attributes of IDN S-0-1017 .66
Table A.21 – Attributes of IDN S-0-1018 .66
Table A.22 – Attributes of IDN S-0-1019 .67
Table A.23 – Attributes of IDN S-0-1020 .68
Table A.24 – Attributes of IDN S-0-1021 .68
Table A.25 – Attributes of IDN S-0-1022 .69

61158-4-19 © IEC:2007(E) – 5 –

Table A.26 – Attributes of IDN S-0-1023 .70

Table A.27 – Structure of IDN S-0-1023 data .70

Table A.28 – Attributes of IDN S-0-1024 .71

Table A.29 – Attributes of IDN S-0-1025 .71

Table A.30 – Attributes of IDN S-0-1026 .72

Table A.31 – Attributes of IDN S-0-1028 .72

Table A.32 – Attributes of IDN S-0-1029 .73

Table A.33 – Attributes of IDN S-0-1030 .73

– 6 – 61158-4-19 © IEC:2007(E)

INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 4-19: Data-link layer protocol specification – Type 19 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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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
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 from their respective intellectual-property-right holders.
IEC draws attention to the fact that it is claimed that compliance with this standard may involve the use of patents
as follows, where the [xx] notation indicates the holder of the patent right:
Type 19 and possibly other Types:
DE 102 37 097 [RI] Korrektur von Signallaufzeiten in verteilten
Kommunikationssystemen
DE 102 00 405 0416.4-42 [RI] Verfahren zur Synchronisation in einem redundanten
Kommunikationssystem
DE 102 00 502 4759.8-32 [RI] Verfahren zur Laufzeitkorrektur in einer Kommunikationsstruktur
DE 102 00 4056364.0-31 [RI] Verfahren zum Betreiben eines Netzwerks mit Ringtopologie
DE 103 12 907.3-31 [RI] Kommunikationssystem mit redundanter Kommunikation
IEC takes no position concerning the evidence, validity and scope of these patent rights.
The holders of these patent rights have assured IEC that they are willing to negotiate licences under reasonable
and non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of
the holders of these patent rights are registered with IEC. Information may be obtained from:

61158-4-19 © IEC:2007(E) – 7 –

[RI]    Rexroth Indramat GmbH

Bgm.-Dr.-Nebel-Str. 2
D - 97816 Lohr
Germany
Attention is drawn to the possibility that some of the elements of this standard may be the subject of patent rights

other than those identified above. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61158-4-19 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 61158-4 subseries cancel and replace

IEC 61158-4:2003. This edition of this part constitutes a technical addition. This part and its
companion Type 19 parts also cancel and replace IEC PAS 62410, published in 2005.
This edition of IEC 61158-4 includes the following significant changes from 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;
b) addition of new types of fieldbuses;
c) division of this part into multiple parts numbered -4-1, -4-2, …, -4-19.
The text of this standard is based on the following documents:
FDIS Report on voting
65C/474/FDIS 65C/485/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.

– 8 – 61158-4-19 © 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.

The data-link protocol provides the data-link service by making use of the services available

from the physical layer. The primary aim of this standard is to provide a set of rules for

communication expressed in terms of the procedures to be carried out by peer data-link

entities (DLEs) at the time of communication. These rules for communication are intended to

provide a sound basis for development in order to serve a variety of purposes:

a) as a guide for implementors and designers;
b) for use in the testing and procurement of equipment;
c) as part of an agreement for the admittance of systems into the open systems environment;
d) as a refinement to the understanding of time-critical communications within OSI.
This standard is concerned, in particular, with the communication and interworking of sensors,
effectors and other automation devices. By using this standard together with other standards
positioned within the OSI or fieldbus reference models, otherwise incompatible systems may
work together in any combination.

61158-4-19 © IEC:2007(E) – 9 –

INDUSTRIAL COMMUNICATION NETWORKS –

FIELDBUS SPECIFICATIONS –
Part 4-19: Data-link layer protocol specification – Type 19 elements

1 Scope
1.1 General
The data-link layer provides basic time-critical messaging communications between devices in
an automation environment.
This protocol provides communication opportunities to all participating data-link entities
a) in a synchronously-starting cyclic manner, according to a pre-established schedule, and
b) in a cyclic or acyclic asynchronous manner, as requested each cycle by each of those
data-link entities.
Thus this protocol can be characterized as one which provides cyclic and acyclic access
asynchronously but with a synchronous restart of each cycle.
1.2 Specifications
This standard specifies
a) procedures for the timely transfer of data and control information from one data-link user
entity to a peer user entity, and among the data-link entities forming the distributed data-
link service provider;
b) the structure of the fieldbus DLPDUs used for the transfer of data and control information
by the protocol of this standard, and their representation as physical interface data units.
1.3 Procedures
The procedures are defined in terms of
a) the interactions between peer DL-entities (DLEs) through the exchange of fieldbus
DLPDUs;
b) the interactions between a DL-service (DLS) provider and a DLS-user in the same system
through the exchange of DLS primitives;

c) the interactions between a DLS-provider and a Ph-service provider in the same system
through the exchange of Ph-service primitives.
1.4 Applicability
These procedures are applicable to instances of communication between systems which
support time-critical communications services within the data-link layer of the OSI or fieldbus
reference models, and which require the ability to interconnect in an open systems
interconnection environment.
Profiles provide a simple multi-attribute means of summarizing an implementation’s
capabilities, and thus its applicability to various time-critical communications needs.
1.5 Conformance
This standard also specifies conformance requirements for systems implementing these
procedures. This part of this standard does not contain tests to demonstrate compliance with
such requirements.
– 10 – 61158-4-19 © IEC:2007(E)

2 Normative references
The following referenced documents are indispensable for the application of this standard. For

dated references, only the edition cited applies. For undated references, the latest edition of

the referenced document (including any amendments) applies.

IEC 61158-4-16, Industrial communications networks – Fieldbus specifications – Part 4-16:

Data-link layer protocol specification – Type 16 elements

IEC 61800-7-20x (all subparts), Adjustable speed electrical power drive systems – Part 7-20x:

Generic interface and use of profiles for power drive systems – Profile type x specification

ISO/IEC 7498-1, Information technology – Open Systems Interconnection – Part 1: Basic
Reference Model: The Basic Model
ISO/IEC 7498-3, Information technology – Open Systems Interconnection – Part 3: 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
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:
3.2 Additional Type 19 terms and definitions
3.2.1
broadcast
transmission to all devices in a network without any acknowledgment by the receivers

3.2.2
communication cycle
fixed time period between two master synchronization telegrams in which real-time telegrams
are transmitted in the RT channel and non real-time telegrams are transmitted in the IP
channel
3.2.3
control unit
control device (e.g., a PLC as specified in the IEC 61131 standard family)
3.2.4
control word
two adjacent OCTETs inside the master data telegram containing commands for the
addressed device
At present, these subparts are IEC 61800-7-201, 7-202, 7-203 and 7-204.

61158-4-19 © IEC:2007(E) – 11 –

3.2.5
cross communication
direct data transfer between slave devices (without active involvement of master)

3.2.6
cycle time
duration of a communication cycle

3.2.7
cyclic communication
periodic exchange of telegrams

3.2.8
cyclic data
part of a telegram, which does not change its meaning during cyclic operation of the network
3.2.9
cyclic operation
operation in which devices in the communication network are addressed and queried one after
the other at fixed, constant time intervals
3.2.10
device
a slave in the communication network, (e.g., a power drive system as defined in the IEC
61800 standard family, I/O stations as defined in the IEC 61131 standard family)
3.2.11
device address field
address field (eight bits) containing the address of the device
3.2.12
device control
four adjacent OCTETs inside the master data telegram containing commands for each device
3.2.13
device status
four adjacent OCTETs inside the acknowledge telegram containing status information for each
device
3.2.14
DLE station identifier
network address assigned to a DLE
3.2.15
DLE station slot
unit (granularity of one) of position dependent mapping (for cyclic data field) of which a DLE
may occupy one or more, delineated by the range beginning at the DLE station identifier with
a length equal to the configured number of occupied slots
3.2.16
element
part of IDNs – each IDN has 7 elements, whereas each one has a specific meaning (e.g.,
number, name, data)
3.2.17
EtherType
part of the Type 19 specific telegram header

– 12 – 61158-4-19 © IEC:2007(E)

3.2.18
forwarding
mode by which a device passes on a received telegram to the other port, either changed or

unchanged
3.2.19
identification number (IDN)
designation of operating data under which a data block is preserved with its attribute, name,

unit, minimum and maximum input values, and the data

3.2.20
line, line structure
network topology, in which the transmission medium is routed from station to station in the
form of a line; the information is transmitted in one direction from the master down to the last
slave in the line, and then flows back to the master via all the slaves in the reverse order
(CP16/3)
3.2.21
loopback
mode by which a device passes on a received telegram to the same port and to the other port,
either changed or unchanged
3.2.22
master
node, which assigns the other nodes (i.e., slaves) the right to transmit
3.2.23
master data telegram (MDT)
telegram, in which the master inserts its data
3.2.24
master DLE
DLE that performs the functions of network master
3.2.25
master synchronization telegram (MST)
telegram, or part of a telegram, in which the master inserts a time synchronization signal
3.2.26
MDT0 telegram
telegram, in which the master transmits its synchronization data, as well as parts or all of its
real-time data, to the slaves
3.2.27
participant
node
3.2.28
physical layer
first layer of the ISO-OSI reference model
3.2.29
protocol
convention about the data formats, time sequences, and error correction in the data exchange
of communication systems
61158-4-19 © IEC:2007(E) – 13 –

3.2.30
real-time data
part of the telegram that does not change its meaning during cyclic operation of the interface

3.2.31
RT channel
defined time slot within the communication cycle, which passes the CPF16 real-time

telegrams
3.2.32
service channel (SVC)
non real-time transmission of information upon master request during RT channel
3.2.33
slave
node, which is assigned the right to transmit by the master
3.2.34
slave DLE
DLE that performs the functions of network slave
3.2.35
station
node
3.2.36
status word
two adjacent OCTETs inside the acknowledge telegram containing status information of a
device
3.2.37
S-0-nnnn
designation of IDNs
3.2.38
telegram
DLPDU
3.2.39
topology
physical network architecture with respect to the connection between the stations of the

communication system
3.3 Symbols
3.3.1 ADR
device address (1 ≤ ADR ≤ 254) adjusted directly on the device e.g., using
a selector switch
3.3.2 AT MST header in AT
3.3.3 AT0.3 acknowledge telegrams
3.3.4 INFO service channel information
3.3.5 J jitter in t
tscyc Scyc
3.3.6 MDT0 master data telegram with synchronization data that the slaves evaluates
3.3.7 MDT1.3
master data telegrams without synchronization data
3.3.8 P1 port 1
3.3.9 P2
port 2
– 14 – 61158-4-19 © IEC:2007(E)

3.3.10 RxD received data
3.3.11 SLKN slave identification parameter, slave arrangement

3.3.12 SVC service channel
3.3.13 t AT transmission starting time
3.3.14 t shortest AT transmission starting time

1min
3.3.15 t command value valid time
3.3.16 t feedback acquisition capture point
3.3.17 t minimum feedback processing time
3.3.18 t transmit to transmit recovery time in a slave with several slaves
ATAT
3.3.19 t time, by which the transmitted signal is delayed by the cable, for each unit
cable
of length (approx., 5 ns/m)
3.3.20 t control unit cycle time
Ncyc
3.3.21 t time, by which the received signal is delayed by a forwarding slave (input-
rep
output)
3.3.22 t time, which a master telegram needs, until it has passed through the
ring
network and reached the master again
3.3.23 t communication cycle time
Scyc
3.3.24 TxD transmitted data
3.4 Abbreviations
3.4.1 AHS service transport handshake of the device (acknowledge HS)
3.4.2 AT acknowledge telegram
3.4.3 C1D class 1 diagnostic
3.4.4 CC cross communication between participants
3.4.5 CP communication phase
3.4.6 CPS communication phase switching
3.4.7 CRC cyclic redundancy check
3.4.8 FCS DLPDU check sequence
3.4.9 HS service channel handshake (see AHS and MHS)
3.4.10 IDN identification number
3.4.11 MDT master data telegram
3.4.12 MDT MST header in MDT
3.4.13 MHS service transport handshake of the master
3.4.14 MS communication from slave to master
3.4.15 MST master synchronization telegram
3.4.16 NRC non real-time channel
3.4.17 NRT non real-time mode
3.4.18 RT real-time
3.4.19 RTC real-time channel
3.4.20 RTD real-time data in MDT or AT
3.4.21 SERCOS serial real-time communication system interface
3.4.22 SFD start DLPDU delimiter
3.4.23 SVC service channel
61158-4-19 © IEC:2007(E) – 15 –

3.5 Additional conventions
3.5.1 DLPDU support level
There are two levels of cycle time support for a DLPDU:

• level B – 50 ns jitter synchronization class (master and slave);

• level C – 50 μs jitter synchronization class (master and slave).

Refer to 8.2.7 for additional information.

3.5.2 DLPDU IDN concept
All data types are assigned identification numbers (IDNs). They include real-time data
(commands and feedback values), parameters, and procedures. Most IDNs are similar to
those for Type 16 (see IEC 61158-4-16, 2.4). Several IDNs relate to the application and are
defined in their relevant standards (e.g., IEC 61800-7-20x for Power Drive Systems).
Refer to Annex A for additional information, as well as to IEC 61158-4-16, Annex A.1 for
detailed IDN specification.
4 DL-protocol overview
This protocol type provides a highly optimized means of interchanging fixed-length real-time
data and variable-length segmented messages between a single master device and a set of
slave devices, interconnected in a ring or a line topology. The ring topology provides for
redundant communication paths, and in case of a fault it automatically switches to a set of two
lines without disturbing the communication.
This protocol type also provides for direct real-time data transmission between slaves, inside
the real-time channel (RTC), within each cycle.
The exchange of real-time data is totally synchronous by configuration and is unaffected by
the messaging traffic.
The device addresses are set by the user, for example, using a selector. Additional devices
may be added whenever required, even during operation, without affecting the address
selections, which already exist. The determination of the number, identity and characteristics
of each device may be configured or may be detected automatically at start-up.
Slave interfaces shall be used to connect the slave devices to the network. At the physical

layer, a slave represents the connection of one or more devices to the network. Logically, one
slave with several devices shall act the same as several slaves with one device each.
This protocol type also provides a non real-time channel (NRC), in which any Standard
Ethernet DLPDUs can be exchanged between Type 19 devices and any other connected
Ethernet network nodes.
There are two classes of Type 19 DLE:
a) master DLE;
b) slave DLE.
Only the master DLE is able to initiate the cyclic transmission.
Type 19 telegrams are Ethernet DLPDUs according to ISO/IEC 8802-3. Type 19 real-time
telegrams shall be transmitted in the real-time part of the communication cycle time. They

– 16 – 61158-4-19 © IEC:2007(E)

transport mainly command values and actual values. Type 19 header specifies two sub types

of type 19 telegrams:
• Master data telegram (MDT), in which the master transmits real-time data to the slaves;

• Device telegram (AT), in which the slaves transmit real-time data to other devices.

Other Ethernet DLPDUs can be transmitted in the NRC channel.

Type 19 specifies 4 MDTs (MDT0 to MDT3). The MDTs shall be transmitted by the master and

received by each slave. The MDTs shall contain all information (e.g., synchronization,

command values, digital outputs) which is sent from the master to the slaves through the real-

time channel.
MDT0 shall always be transmitted. MDT1 through 3 shall be transmitted only if required
depending on the total amount of data to be transmitted to the slaves. The master shall
always send the same number of MDTs during each communication cycle.
Type 19 specifies 4 ATs (AT0 to AT3). The ATs shall be transmitted by the master with empty
data fields. Each slave shall insert its data into its allocated data field within the AT. The ATs
shall contain all information (e.g., feedback values, digital inputs) which is sent from the
slaves to the master as well as to other slaves through the real-time channel.
AT0 shall always be transmitted. AT1 through 3 shall be transmitted only if required
depending on the total amount of data to be transmitted to the master. The master shall
always send the same number of ATs during each communication cycle.
The allocations of the service channels (SVC) and the real-time data fields (RTD) in the MDT
as well as in the AT shall be configured with parameters. The RTD lengths in the MDTs and
the ATs shall depend on the configuration and may be different for each slave depending
upon configuration. The numb
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