IEC 61158-4-7:2007

IEC 61158-4-7
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 4-7: Data-link layer protocol specification – Type 7 elements

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IEC 61158-4-7
Edition 1.0 2007-12
INTERNATIONAL
STANDARD
Industrial communication networks – Fieldbus specifications –
Part 4-7: Data-link layer protocol specification – Type 7 elements

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XE
ICS 35.100.20; 25.040.40 ISBN 2-8318-9434-4

– 2 – 61158-4-7 © 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 and abbreviations.10
3.1 Reference model terms and definitions.10
3.2 Service convention terms and definitions.11
3.3 Other terms and definitions .12
3.4 Symbols and abbreviations.16
4 Overview of the DL-protocol .18
4.1 Overall description of medium allocation .18
4.2 Types of entities.20
4.3 Addressing .23
4.4 Flow control.29
4.5 Graphical representation .31
5 General structure and encoding of PhIDUs and DLPDUs and related elements of
procedure.32
5.1 DLPDU formats and components.32
5.2 Description of each DLPDU component .32
5.3 PhIDU structure and encoding.36
5.4 Common DLPDU structure, encoding and elements of procedure .37
5.5 Valid DLPDU types.37
5.6 DLL timers.39
6 DLPDU-specific structure, encoding and element of procedure.43
6.1 General .43
6.2 Buffer read .43
6.3 Buffer write.44
6.4 Buffer transfer .44
6.5 Specified explicit request.45
6.6 Free explicit request.50
6.7 Messaging.53
6.8 Acknowledged messaging .58
6.9 Numbering of acknowledged messages.62
6.10 Behavior with mismatched parameters .64
7 DL-service elements of procedure, interfaces and conformance .66
7.1 General .66
7.2 Producer/consumer entity.67
7.3 Protocol elements by service.70
7.4 Bus arbitrator operation.77
7.5 Bridges.85
7.6 Interfaces .92

61158-4-7 © IEC:2007(E) – 3 –
7.7 Conformance.94
Annex A (informative) Exemplary FCS implementation.97
Annex B (informative) Object modeling .99
B.1 Modeling of the IDENTIFIER object .99
B.2 Description of the IDENTIFIER object attributes .99
B.3 Modeling of the QUEUE object .103
B.4 Description of the QUEUE object attributes . 103
B.5 Modeling of the BUFFER object.104
B.6 Description of the BUFFER object attributes. 104
Annex C (informative) Topology of multi-segment DL-subnetwork . 106
C.1 Introduction .106
C.2 Global specification .106
C.3 Local specification.107
C.4 Properties .107
C.5 Methods .107
Annex D (informative) Management of transmission errors . 111
D.1 Transmission of RP_DAT_XX .111
D.2 Transmission of a free RP_RQ(1/2) .111
D.3 Transmission of the specified RP_RQ1 . 112
D.4 Transmission of RP_MSG_NOACK.113
D.5 Transmission of RP_MSG_ACK.115
Bibliography.118

Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses .13
Figure 2 – General description of medium allocation.19
Figure 3 – Internal structure of a producer/consumer entity.20
Figure 4 – Associated buffers and queues .22
Figure 5 – Internal structure of a bus arbitrator .23
Figure 6 – Polling BA Table .23
Figure 7 – Addressing scheme.24
Figure 8 – Address partitioning .26
Figure 9 – Structure of an individual physical address .27
Figure 10 – Structure of an individual logical address .27
Figure 11 – Structure of restricted physical group address.27
Figure 12 – Structure of a restricted logical group address .28
Figure 13 – Structure of a generalized group address .28
Figure 14 – Summary of address structure.29
Figure 15 – Example of an evaluation net .31
Figure 16 – Basic DLPDU structure.32
Figure 17 – DLPDU transmission / reception order.32
Figure 18 – Identifier DLPDU .38
Figure 19 – Variable response DLPDU.38
Figure 20 – Request response DLPDU.38
Figure 21 – Message response DLPDU.39
Figure 22 – Acknowledgement response DLPDU .39

– 4 – 61158-4-7 © IEC:2007(E)
Figure 23 – End of message transaction response DLPDU .39
Figure 24 – Buffer reading service interactions .44
Figure 25 – Buffer writing service interactions.44
Figure 26 – Buffer transfer service interactions .44
Figure 27 – Buffer transfer DLPDU sequence .45
Figure 28 – Interactions within the specified explicit request for buffer transfer service
in the aperiodic window.46
Figure 29 – Interactions within the specified explicit request for buffer transfer service
in the periodic window.47
Figure 30 – DLPDU sequence for an explicit request for a transfer .48
Figure 31 – Evaluation network for a buffer transfer specified explicit request with
(RQ_INHIBITED = False) .49
Figure 32 – Evaluation network for a buffer transfer specified explicit request with
(RQ_INHIBITED = True).49
Figure 33 – Diagram of interactions within the free explicit request for buffer transfer
service .51
Figure 34 – Evaluation network for a free explicit request .52
Figure 35 – Diagram of interactions within the unacknowledged message transfer
request service for an aperiodic transfer .55
Figure 36 – Diagram of interactions within the unacknowledged message transfer
request service for a cyclical transfer .56
Figure 37 – DLPDU sequence for an aperiodic message transfer.57
Figure 38 – DLPDU sequence for a cyclical message transfer .58
Figure 39 – Diagram of interactions within the acknowledged message transfer request
service for an aperiodic transfer .59
Figure 40 – Diagram of interactions within the acknowledged message transfer request
service for a cyclical transfer.60
Figure 41 – DLPDU sequence for an aperiodic message transfer.61
Figure 42 – DLPDU sequence for a cyclical message transfer .62
Figure 43 – Evaluation network for message aperiodic transfer.65
Figure 44 – Evaluation network for message cyclic transfer .66
Figure 45 – Simplified states machine for a producer/consumer entity .67
Figure 46 – Active bus arbitrator's simplified state machine .83
Figure 47 – Typical bridge usage .85
Figure 48 – Architectural placement of bridges in OSI Basic Reference Model (ISO/IEC
7498) .85
Figure 49 – Representation of an extended link communication .86
Figure 50 – Evaluation network for reception of an RP_MSG_ACK DLPDU.91
Figure 51 – Evaluation network for reception of an RP_MSG_NOACK DLPDU.92
Figure A.1 – Example of FCS generation .97
Figure A.2 – Example of FCS syndrome checking on reception.97
Figure D.1 – Evaluation DL-subnetwork for transmission of RP_DAT_XX.111
Figure D.2 – Evaluation DL-subnetwork for transmission of a free RP_RQ(1/2). 112
Figure D.3 – Evaluation DL-subnetwork for transmission of the specified RP_RQ1 . 113
Figure D.4 – Evaluation DL-subnetwork for transmission of RP_MSG_NOACK, first
behavior.114

61158-4-7 © IEC:2007(E) – 5 –
Figure D.5 – Evaluation DL-subnetwork for transmission of RP_MSG_NOACK, second
behavior.115
Figure D.6 – Evaluation DL-subnetwork for transmission of RP_MSG_ACK, first
behavior.116
Figure D.7 – Evaluation DL-subnetwork for transmission of RP_MSG_ACK, second
behavior.117

Table 1 – Individual and group address encoding .26
Table 2 – DLPDU control-field coding .33
Table 3 – Correspondence between name and coding of 8 bits in the control field .34
Table 4 – FCS length, polynomial and expected residual .35
Table 5 – DL-Timers .41
Table 6 – Bus arbitrator state transition table.84
Table 7 – Bridge object description .87
Table 8 – Channel object description .88
Table 9 – Segment directory object description.89
Table 10 – Network directory object description .89
Table 11 – Service primitives by type.93
Table 12 – Conformance classes .96

– 6 – 61158-4-7 © IEC:2007(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-7: Data-link layer protocol specification – Type 7 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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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 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.
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 from their respective intellectual-property-right holders.
International Standard IEC 61158-4-7 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 an editorial revision.
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;

61158-4-7 © IEC:2007(E) – 7 –
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.
The contents of the corrigendum of January 2014 have been included in this copy.

– 8 – 61158-4-7 © 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.

61158-4-7 © IEC:2007(E) – 9 –
INDUSTRIAL COMMUNICATION NETWORKS –
FIELDBUS SPECIFICATIONS –
Part 4-7: Data-link layer protocol specification – Type 7 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 – 61158-4-7 © 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.
IEC 61158-2 (Ed.4.0), Industrial communication networks – Fieldbus specifications – Part 2:
Physical layer specification and service definition
IEC 61158-3-7, Industrial communication networks – Fieldbus specifications – Part 3-7: Data
link service definition – Type 7 elements
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 10731, Information technology – Open Systems Interconnection – Basic Reference
Model – Conventions for the definition of OSI services
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, the following terms, definitions, symbols and abbreviations
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 DL-entities  (N=2)
correspondent Ph-entities  (N=1)
3.1.2 DL-address [7498-3]
3.1.3 DL-connection [7498-1]
3.1.4 DL-connection-end-point [7498-1]
3.1.5 DL-connection-end-point-identifier [7498-1]
3.1.6 DL-name [7498-3]
3.1.7 DL-protocol [7498-1]
3.1.8 DL-protocol-connection-identifier [7498-1]
3.1.9 DL-protocol-control-information [7498-1]
3.1.10 DL-protocol-data-unit [7498-1]
3.1.11 DL-relay [7498-1]
3.1.12 DL-service-connection-identifier [7498-1]
3.1.13 DL-service-data-unit [7498-1]

61158-4-7 © IEC:2007(E) – 11 –

3.1.14 DL-user-data [7498-1]
3.1.15 flow control [7498-1]
3.1.16 (N)-entity [7498-1]
DL-entity
Ph-entity
3.1.17 (N)-interface-data-unit [7498-1]
DL-service-data-unit  (N=2)
Ph-interface-data-unit  (N=1)
3.1.18 (N)-layer [7498-1]
DL-layer  (N=2)
Ph-layer  (N=1)
3.1.19 (N)-service [7498-1]
DL-service  (N=2)
Ph-service  (N=1)
3.1.20 (N)-service-access-point [7498-1]
DL-service-access-point  (N=2)
Ph-service-access-point  (N=1)
3.1.21 (N)-service-access-point-address [7498-1]
DL-service-access-point-address  (N=2)
Ph-service-access-point-address  (N=1)
3.1.22 peer-entities [7498-1]
3.1.23 Ph-interface-control-information [7498-1]
3.1.24 Ph-interface-data [7498-1]
3.1.25 primitive name [7498-3]
3.1.26 reset [7498-1]
3.1.27 responding-DL-address [7498-3]
3.1.28 routing [7498-1]
3.1.29 segmenting [7498-1]
3.1.30 sequencing [7498-1]
3.1.31 system management [7498-1]
systems-management
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 confirm (primitive);
requestor.deliver (primitive)
3.2.2 deliver (primitive)
3.2.3 DL-service-primitive;
primitive
3.2.4 DL-service-provider
– 12 – 61158-4-7 © IEC:2007(E)

3.2.5 DL-service-user
3.2.6 DL-user-optional-facility
3.2.7 indication (primitive)
acceptor.deliver (primitive)
3.2.8 multi-peer
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)
3.3 Other terms and definitions
NOTE  Many definitions are common to more than one protocol Type; they are not necessarily used by all protocol
Types.
For the purpose of this part of IEC 61158, the following definitions also apply:
3.3.1
acknowledgement response DLPDU
information that the recipient of an acknowledged message emits in order to signal either the
proper reception of the message or the lack of available resources to store the message,
received by the DLE on the local link that emitted the message which requested the
acknowledgement
3.3.2
basic cycle
sequence of scanning by the bus-arbitrator of:
a) a set of DLCEP-identifiers for variables, requests, and cyclical application messages,
b) plus the window provided for aperiodic exchanges,
c) plus the window provided for message services,
d) plus the window provided for synchronization
3.3.3
basic transaction
succession of DLPDUs related to a single DL-service instance
3.3.4
bus-arbitrator (BA)
DLE that controls each data producer's right to access the medium
NOTE  At any given instant one and only one bus-arbitrator is active in each DL-segment of a DL-subnetwork.
3.3.5
consumed identified variable
identified variable that corresponds to a DLCEP-identifier for which the entity in question
receives data
3.3.6
control field
portion of an emitted or received DLPDU that gives the nature of the data exchanged and the
type of exchange
61158-4-7 © IEC:2007(E) – 13 –

3.3.7
destination address
three octets specifying the DL-segment of the DLE to whom the message is sent, and the
destination DLSAP’s sub-address within the local link DL-segment
3.3.8
DLCEP-address
information that the bus-arbitrator emits to allocate the medium to a data producer for the
purpose of exchanging a variable
3.3.9
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
3.3.10
DLSAP
distinctive point at which DL-services are provided by a single DL-entity to a single higher-
layer entity.
NOTE  This definition, derived from ISO/IEC 7498-1, is repeated here to facilitate understanding of the critical
distinction between DLSAPs and their DL-addresses. (See Figure 1.)
DLS-user-entity
DLS-user-entity
DLS-users
DLSAP DLSAP DLSAP
DLSAP-
address DLSAP-
DLSAP-
group DL-
address
addresses
address
DL-layer
DL-entity
PhSA P PhSA P
Ph-layer
NOTE 1  DLSAPs and PhSAPs are depicted as ovals spanning the boundary between two adjacent layers.
NOTE 2  DL-addresses are depicted as designating small gaps (points of access) in the DLL portion of a DLSAP.
NOTE 3  A single DL-entity may have multiple DLSAP-addresses and group DL-addresses associated with a
single DLSAP.
Figure 1 – Relationships of DLSAPs, DLSAP-addresses and group DL-addresses
3.3.11
DL(SAP)-address
either an individual DLSAP-address, designating a single DLSAP of a single DLS-user, or a
group DL-address potentially designating multiple DLSAPs, each of a single DLS-user.

– 14 – 61158-4-7 © IEC:2007(E)

NOTE  This terminology is chosen because ISO/IEC 7498-3 does not permit the use of the term DLSAP-address to
designate more than a single DLSAP at a single DLS-user
3.3.12
(individual) DLSAP-address
DL-address that designates only one DLSAP within the extended link
NOTE  A single DL-entity may have multiple DLSAP-addresses associated with a single DLSAP.
3.3.13
end of message transaction indication DLPDU
information that the source entity of a message emits in order to return link access control to
the bus-arbitrator at the end of a message transaction
3.3.14
extended link
DL-subnetwork, consisting of the maximal set of links interconnected by DL-relays, sharing a
single DL-name (DL-address) space, in which any of the connected DL-entities may
communicate, one with another, either directly or with the assistance of one or more of those
intervening DL-relay entities
NOTE  An extended link may be composed of just a single link.
3.3.15
frame
denigrated synonym for DLPDU
3.3.16
group DL-address
DL-address that potentially designates more than one DLSAP within the extended link. A
single DL-entity may have multiple group DL-addresses associated with a single DLSAP. A
single DL-entity also may have a single group DL-address associated with more than one
DLSAP
3.3.17
identified variable (or simply "variable")
DLL variable (buffer) for which an associated DLCEP-identifier has been defined
3.3.18
identifier
16-bit word associated with a system variable. A DLCEP-identifier uniquely designates a
single variable within the DL-subnetwork
3.3.19
invalid DLCEP-identifier
identifier not recognized locally
3.3.20
local link
set of devices that respect the DL-protocol and that are interconnected through a medium .
Only one bus-arbitrator is active on a single local link
3.3.21
macrocycle
set of basic cycles needed for all cyclical DLCEP-identifiers to be scanned
3.3.22
message DL-address
information that the bus-arbitrator emits to allocate the medium to a source entity for a
message transfer
61158-4-7 © IEC:2007(E) – 15 –

3.3.23
message response DLPDU
information that a data producer emits in response to a message DLCEP-identifier DLPDU
NOTE  The desired destination entity or entities pick up this information.
3.3.24
node
single DL-entity as it appears on one local link
3.3.25
periodic scanning of variables
action by the bus-arbitrator that guarantees the cyclical exchange of variables
NOTE  This is the basic principle of the Type 7 DL-service and protocol.
3.3.26
produced identified variable
identified variable that corresponds to a DLCEP-identifier for which the DLE emits data
3.3.27
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.
3.3.28
request DLCEP-address
information that the bus-arbitrator emits to allocate the medium to the initiator of an explicit
request for a variable exchange
3.3.29
request response DLPDU
information that the initiator of an explicit request for a variable exchange emits in response to
a request DLCEP-identifier DLPDU, and to whose transmittal the bus-arbitrator also responds
3.3.30
sending DLS-user
DL-service user that acts as a source of DL-user-data
3.3.31
source address
24-bit word including the DL-segment number of the entity sending the message, and the
entity's sub-address within the DL-segment
3.3.32
timers
5. 6
see
3.3.33
triggered message scanning
function of a bus-arbitrator that makes it possible to transfer messages
3.3.34
triggered scanning of variables
function of a bus-arbitrator that makes possible the non-cyclical exchange of variables

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3.3.35
triggered periodic scanning of messages
function of a bus-arbitrator that makes it possible to request triggered message exchanges
cyclically
3.3.36
triggered periodic scanning of variables
function of a bus-arbitrator that makes it possible to request triggered variable transfers
cyclically
3.3.37
turnaround time
time interval between reception or emission of the last MAC symbol of a DLPDU, signaled by
a SILENCE indication from the PhL, and the reception or emission of the first MAC symbol of
the subsequent DLPDU, signaled by an ACTIVITY indication from the PhL, both as measured
in a given station
3.3.38
variable response DLPDU
information that a data producer emits in response to a DLCEP-identifier DLPDU, which also
alerts data consumers to the relevance of the immediately time-proximate DLPDU
3.4 Symbols and abbreviations
3.4.1 BA bus-arbitrator
3.4.2 B_Dat_Cons buffer which contains the value of the data consumed
3.4.3 B_Dat_Prod buffer which contains the value of the data produced
3.4.4 B_Req1/2 buffer containing the list of DLCEP-identifiers that are the objet
of a specified explicit request for a transfer at the priority 1
(urgent) or 2 (normal)
3.4.5 ID_DAT DLPDU used to allocate the medium to a buffer transfer
3.4.6 ID_MSG DLPDU used to allocate the medium to a message exchange
3.4.7 ID_RQ1/2 DLPDU used to allocate the medium to a request for a buffer
transfer
3.4.8 PRT physical reaction time
3.4.9 Q_IDMSG queue of requested DLCEP-identifiers received by the BA for
message transfer
3.4.10 Q_IDRQ1/2 queue of requested DLCEP-identifiers received by the BA at
the priority 1 (urgent) or 2 (normal)
3.4.11 Q_Msg_Cyc queue which contains messages to be emitted that are
associated with cyclical exchanges
3.4.12 Q_Msg_Aper queue which contains messages to be emitted that are
associated with aperiodic exchanges
3.4.13 Q_Req1/2 queue containing the list of DLCEP-identifiers that are the
objet of a free explicit request for a transfer at the priority 1
(urgent) or 2 (normal)
3.4.14 Q_RPRQ queue for aperiodic transfers in progress
3.4.15 RQ_Inhibit Indicator used to manage explicit request for variable

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exchanges
3.4.16 RP_ACK DLPDU used to transfer an acknowledgement of message
exchange, Transfer OK
3.4.17 RP_DAT DLPDU used to carry the value of the identified variable
previously requested.
3.4.18 RP_DAT_MSG DLPDU used to carry the value of the identified variable
previously requested with a request for a message exchange.
3.4.19 RP_DAT_RQ1/2 DLPDU used to carry the value of the identified variable
previously requested with a request for an explicit transfer of
variables.
3.4.20 RP_DAT_RQ1/2_MSG DLPDU used to carry the value of the identified variable
previously requested with a request for an explicit transfer
of variables and a request for a message transfer.
3.4.21 RP_MSG_ACK DLPDU used to carry the message to be exchanged with a
request of acknowledgement of this exchange.
3.4.22 RP_MSG_NOACK DLPDU used to carry the message to be exchanged without a
request of acknowledgement of this exchange.
3.4.23 RP_NAK DLPDU used to transfer an acknowledgement of message
exchange, that the message was received correctly, but was
not stored by the DLE.
3.4.24 RP_END DLPDU used to terminate a message exchange.
3.4.25 STT station turnaround time
3.4.26 Tl latency time
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