EN 62056-21:2002

Electricity metering - Data exchange for meter reading, tariff and load control - Part 21: Direct local data exchange

Describes hardware and protocol specifications for local meter data exchange. In such systems, a hand-held unit (HHU) or a unit with equivalent functions is connected to a tariff device or a group of devices.

Messung der elektrischen Energie - Zählerstandsübertragung, Tarif- und Laststeuerung - Teil 21: Datenübertragung für festen und mobilen Anschluss

Equipements de mesure de l'énergie électrique - Echange des données pour la lecture des compteurs, le contrôle des tarifs et de la charge - Partie 21: Echange des données directes en local

Décrit le matériel et les protocoles des échanges de données de compteurs effectués en local. Dans ces systèmes, un terminal de saisie portable (TSP) ou un appareil aux fonctions équivalentes est connecté à un ou plusieurs appareils de tarification.

Electricity metering - Data exchange for meter reading, tariff and load control - Part 21: Direct local data exchange (IEC 62056-21:2002)

General Information

• Status: Published
• Publication Date: 20-Jun-2002
• Withdrawal Date: 30-Apr-2005
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• ICS: 35.100 - Open systems interconnection (OSI)
• ICS: 91.140.50 - Electricity supply systems
• Technical Committee: CLC/TC 13 - Equipment for electrical energy measurement and load control
• Drafting Committee: IEC/TC 13 - IEC_TC_13
• Parallel Committee: IEC/TC 13 - IEC_TC_13
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 21-Jun-2002
• Completion Date: 21-Jun-2002
• Mandate: M/441 - Standardisation mandate to CEN, CENELEC and ETSI in the field of measuring instruments for the development of an open architecture for utility meters involving communication protocols enabling interoperability
• Ref Project: SIST EN 62056-21:2004 - Electricity metering - Data exchange for meter reading, tariff and load control -- Part 21: Direct local data exchange

Relations

• Replaces: EN 61107:1996 - Data exchange for meter reading, tariff and load control - Direct local data exchange
• Effective Date: 28-Jan-2023

Overview

EN 62056-21:2002 (IEC 62056-21) - titled Electricity metering - Data exchange for meter reading, tariff and load control - Part 21: Direct local data exchange - defines the hardware and protocol specifications for direct local data exchange between a meter (or tariff device) and a local reading device such as a hand‑held unit (HHU). The standard specifies physical interfaces, character transmission, and a set of communication protocols for on‑site meter reading, tariff management and load control. EN 62056-21 supersedes EN 61107:1996 and is part of the IEC/EN 62056 family for meter data exchange.

Key topics and technical requirements

• Physical interfaces: Defines supported local interfaces including electrical current‑loop, V.24/V.28 (serial), and optical read‑out ports and the physical construction/alignments for optical heads.
• Character transmission: Specifies character formats, coding, start/stop structures, signal quality checks and block check character methods (error detection).
• Data transmission protocols: Details multiple protocol modes (A, B, C, D, E) for readout and programming, including message types (request, identification, data, acknowledge, repeat‑request, programming commands).
• Communication behaviors: Covers entry/exit procedures for programming mode, partial block transfer (optional), and wake‑up methods for battery‑operated tariff devices.
• Security & access: Defines structured message exchange and references annexes on access levels and system security (informative normative annexes included).
• Annexes: Normative and informative annexes provide flow charts, HDLC metering protocol (Annex E), wake‑up methods, formatted codes and security guidance.

Practical applications and who uses it

• Electricity meter manufacturers implement the physical port, optical/read‑head alignment and protocol stacks to ensure interoperability with HHUs.
• HHU and field device vendors use EN 62056-21 to design readers and service tools that can reliably communicate on‑site with meters for meter reading, tariff programming and load control.
• Utilities, metering service providers and field technicians rely on standardized local exchange for secure, consistent on‑site data collection, meter configuration and firmware updates.
• Test labs and integrators use the standard to validate compliance, interoperability and conformance with meter communication requirements.

Related standards

• EN/IEC 62056 series (e.g., 62056-42, 62056-46, 62056-53) - physical layer, HDLC data link and COSEM application layer.
• Superseded: EN 61107:1996.

Keywords: EN 62056-21, IEC 62056-21, electricity metering, direct local data exchange, meter reading, tariff device, HHU, optical port, V.24, current loop, meter communication protocol.

Standards Content (Sample)

SLOVENSKI STANDARD
01-januar-2004
1DGRPHãþD
SIST EN 61107:1997
Electricity metering - Data exchange for meter reading, tariff and load control - Part
21: Direct local data exchange (IEC 62056-21:2002)
Electricity metering - Data exchange for meter reading, tariff and load control -- Part 21:
Direct local data exchange
Messung der elektrischen Energie - Zählerstandsübertragung, Tarif- und Laststeuerung -
- Teil 21: Datenübertragung für festen und mobilen Anschluss
Equipements de mesure de l'énergie électrique - Echange des données pour la lecture
des compteurs, le contrôle des tarifs et de la charge -- Partie 21: Echange des données
directes en local
Ta slovenski standard je istoveten z: EN 62056-21:2002
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
35.100.01 Medsebojno povezovanje Open systems
odprtih sistemov na splošno interconnection in general
91.140.50 Sistemi za oskrbo z elektriko Electricity supply systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 62056-21
NORME EUROPÉENNE
EUROPÄISCHE NORM June 2002
ICS 17.220.20;35.100;91.140.50 Supersedes EN 61107:1996
English version
Electricity metering -
Data exchange for meter reading, tariff and load control
Part 21: Direct local data exchange
(IEC 62056-21:2002)
Equipements de mesure Messung der elektrischen Energie -
de l'énergie électrique - Zählerstandsübertragung,
Echange des données pour la lecture Tarif- und Laststeuerung
des compteurs, le contrôle des tarifs Teil 21: Datenübertragung für festen
et de la charge und mobilen Anschluss
Partie 21: Echange des données (IEC 62056-21:2002)
directes en local
(CEI 62056-21:2002)
This European Standard was approved by CENELEC on 2002-05-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 62056-21:2002 E
Foreword
The text of document 13/1271/FDIS, future edition 1 of IEC 62056-21, prepared by IEC TC 13,
Equipment for electrical energy measurement and load control, was submitted to the IEC-CENELEC
parallel vote and was approved by CENELEC as EN 62056-21 on 2001-05-01.
This European Standard supersedes EN 61107:1996.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-05-01
The International Electrotechnical Commission (IEC) and CENELEC draw attention to the fact that it is
claimed that compliance with this International Standard / European Standard may involve the use of a
maintenance service concerning the stack of protocols on which the present standard IEC 62056-21 /
EN 62056-21 is based.
The IEC and CENELEC take no position concerning the evidence, validity and scope of this
maintenance service.
The providers of the maintenance service have assured the IEC that they are willing to provide services
under reasonable and non-discriminatory terms and conditions with applicants throughout the world. In
this respect, the statements of the providers of the maintenance service are registered with the IEC.
Information may be obtained :
Manufacturer's identification, item 12) of 6.3.2: from
The FLAG Association, UK
www.dlms.com/flag
Enhanced identification character, item 24) of 6.3.2: from
1)
DLMS User Association
Geneva / Switzerland
www.dlms.ch
Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annexes A, B, E and ZA are normative and annexes C and D are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 62056-21:2002 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 62056-61 NOTE Harmonized as EN 62056-61:2002 (not modified).
IEC 62056-62 NOTE Harmonized as EN 62056-62:2002 (not modified).
__________
1)
Device Language Message Specification

- 3 - EN 62056-21:2002
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 60050-300 2001 International Electrotechnical --
Vocabulary - Electrical and electronic
measurements and measuring
instruments
Part 311: General terms relating to
measurements
Part 312: General terms relating to
electrical measurements
Part 313: Types of electrical measuring
instruments
Part 314: Specific terms according to
the type of instrument
IEC/TR 62051 1999 Electricity metering - Glossary of terms - -
IEC 62056-42 2002 Electricity metering - Data exchange for EN 62056-42 2002
meter reading, tariff and load control
Part 42: Physical layer services and
procedures for connection-oriented
asynchronous data exchange
IEC 62056-46 2002 Part 46: Data link layer using HDLC EN 62056-46 2002
protocol
IEC 62056-53 2002 Part 53: COSEM application layer EN 62056-53 2002
ISO/IEC 646 1991 Information technology - ISO 7-bit--
coded character set for information
interchange
ISO/IEC 1155 1978 Information processing - Use of --
longitudinal parity to detect errors in
information messages
ISO/IEC 1177 1985 Information processing - Character--
structure for start/stop and synchronous
character-oriented transmission
ISO/IEC 1745 1975 Information processing - Basic mode--
control procedures for data
communication systems
Publication Year Title EN/HD Year
ISO/IEC 7480 1991 Information technology - --
Telecommunications and information
exchange between systems - Start/stop
transmission signal quality at DTE/DCE
interfaces
ITU-T 2000 List of definitions for interchange circuits--
Recommendation between data terminal equipment (DTE)
V.24 and data circuit-terminating equipment
(DCE)
ITU-T 1993 Electrical characteristics for unbalanced--
Recommendation double-current interchange circuits
V.28
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62056-21 © IEC:2002 – 3 –
CONTENTS
FOREWORD.9
INTRODUCTION.13
1 Scope.15
2 Normative references.15
3 Terms, definitions and abbreviations .17
3.1 Terms and definitions .17
3.2 Abbreviations.19
4 Physical properties .19
4.1 Electrical current loop interface.19
4.2 Electrical interface V.24/V.28 .23
4.3 Optical interface .25
4.3.1 Construction of the reading head.25
4.3.2 Characteristic data of the magnet.25
4.3.3 Arrangement of components in the tariff device.29
4.3.4 Alignment .29
4.3.5 Optical characteristics.29
5 Character transmission .33
5.1 Type of transmission.33
5.2 Transmission speed.33
5.3 Signal quality.33
5.4 Character format .33
5.5 Character code.33
5.6 Character security .33
6 Data transmission protocol.35
6.1 General .35
6.2 Calculation of the block check character .35
6.3 Message definitions .37
6.3.1 Request message .37
6.3.2 Identification message .37
6.3.3 Acknowledgement/option select message .37
6.3.4 Data message (except in programming mode).37
6.3.5 Acknowledgement message.37
6.3.6 Repeat-request message .37
6.3.7 Programming command message .39
6.3.8 Programming command message using optional partial blocks.39
6.3.9 Data message (programming mode) .39
6.3.10 Data message (programming mode) using optional partial blocks .39
6.3.11 Error message (programming mode) .39
6.3.12 Break message (programming mode).39
6.3.13 Block message (other protocols) .39
6.3.14 Explanations of message contents .41

62056-21 © IEC:2002 – 5 –
6.4 Communication modes .47
6.4.1 Protocol mode A .47
6.4.2 Protocol mode B .49
6.4.3 Protocol mode C .53
6.4.4 Protocol mode D .61
6.4.5 Protocol mode E (other protocols) .61
6.4.6 Entering programming mode (unknown tariff device) .63
6.4.7 Partial block communication (optional, only in protocol mode C) .65
6.5 Syntax diagrams.71
6.5.1 Readout mode .73
6.5.2 Programming mode .75
6.6 Data set structure .77
Annex A (normative) Flow chart for direct local data exchange protocol, protocol mode C .81
Annex B (normative) Wake-up methods for battery-operated tariff devices.85
Annex C (informative) Formatted codes.89
Annex D (informative) Levels of access – system security . 127
Annex E (normative) METERING HDLC protocol using protocol mode E for direct local
data exchange . 129
Bibliography . 137
Index . 139
Figure 1 – Circuit diagrams .23
Figure 2 – Construction of the reading head .25
Figure 3 – Characteristic data of the magnet .27
Figure 4 – View into optical port .29
Figure 5 – Test arrangement for the transmitter.31
Figure 6 – Test arrangement for the receiver .31
Figure 7 – Setting up a block check character (example according to ISO/IEC 1155) .35
Figure 8 – Diagram protocol mode A .47
Figure 9 – Transmission protocol for protocol mode A .49
Figure 10 – Diagram protocol mode B .51
Figure 11 – Transmission protocol for protocol mode B.51
Figure 12 – Diagram protocol mode C .55
Figure 13 – Transmission protocol for protocol mode C giving data readout without
acknowledgement from the HHU .57
Figure 14 – Transmission protocol for protocol mode C giving data readout with
confirmation of the suggested baud rate .57
Figure 15 – Transmission protocol for protocol mode C giving data readout with rejection
of the suggested baud rate.59
Figure 16 – Transmission protocol for protocol mode C. Switching to programming mode
with acceptance of the suggested baud rate .59

62056-21 © IEC:2002 – 7 –
Figure 17 – Transmission protocol for protocol mode C. Switching to programming mode
with rejection of the suggested baud rate.59
Figure 18 – Diagram protocol mode D .61
Figure 19 – Transmission protocol for protocol mode D .61
Figure 20 – Diagram for entering programming mode .63
Figure 21 – Example of a partial block unformatted read.67
Figure 22 – Example of a partial block formatted write.69
Figure 23 – Example of a partial block formatted write (with errors) .71
Figure 24 – Syntax diagrams – readout mode .73
Figure 25 – Syntax diagrams – programming mode – command.75
Figure 26 – Syntax diagram – programming mode – answer .77
Figure 27 – Data set structure .77
Figure A.1 – Flow chart for direct local data exchange protocol, protocol mode C.81
Figure B.1 – The start sequence for battery-operated devices.85
Figure B.2 – Diagram for the start sequence of battery-operated devices by fast
wake-up mode .87
Figure C.1 – Example of channel types.91
Figure C.2 – Register coding diagram.97
Figure C.3 – Bit assignment for group data. 111
Figure C.4 – Vector diagrams for quadrants I to IV . 125
Figure E.1 – Entering protocol mode E (HDLC). 129
Figure E.2 – Flow chart and switchover to METERING HDLC in protocol mode E. 131
Figure E.3 – Physical layer primitives . 133
Figure E.4 – Physical layer primitives, simplified example with one mode change only . 133
Table 1 – Electrical interface .19
Table 2 – Read, Write and Execute commands .65

62056-21 © IEC:2002 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ELECTRICITY METERING –
DATA EXCHANGE FOR METER READING,
TARIFF AND LOAD CONTROL –
Part 21: Direct local data exchange
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
The International Electrotechnical Commission (IEC) draws attention to the fact that it is
claimed that compliance with this International Standard may involve the use of a maintenance
service concerning the stack of protocols on which the present standard IEC 62056-21 is
based.
The IEC takes no position concerning the evidence, validity and scope of this maintenance
service.
The provider of the maintenance service has assured the IEC that he is willing to provide
services under reasonable and non-discriminatory terms and conditions with applicants
throughout the world. In this respect, the statement of the provider of the maintenance service
is registered with the IEC. Information may be obtained:
Manufacturer's identification, item 12) of 6.3.2: from
The FLAG Association, UK
www.dlms.com/flag
Enhanced identification character, item 24) of 6.3.2: from
DLMS User Association
Geneva / Switzerland
www.dlms.ch
62056-21 © IEC:2002 – 11 –
International Standard IEC 62056-21 has been prepared by IEC Technical Committee 13:
Equipment for electrical energy measurement and load control.
This first edition IEC 62056-21 cancels and replaces the second edition of IEC 61107
published in 1996 and constitutes a technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
13/1271/FDIS 13/1277/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.
Annexes A, B and E form an integral part of this standard.
Annexes C and D are for information only.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
The committee has decided that the contents of this publication will remain unchanged until
2006. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
62056-21 © IEC:2002 – 13 –
INTRODUCTION
IEC TC 13 has the task of preparing standards for data exchange for the purposes of meter
reading, tariff and load control, and consumer information using various alternative
communication media, with reference to ISO and ITU standards.
Meter data exchange can be local or remote. This part of IEC 62056 is restricted to local data
exchange, whereas remote data exchange is covered by other standards of the IEC 62056
series.
62056-21 © IEC:2002 – 15 –
ELECTRICITY METERING –
DATA EXCHANGE FOR METER READING,
TARIFF AND LOAD CONTROL –
Part 21: Direct local data exchange
1 Scope
This part of IEC 62056 describes hardware and protocol specifications for local meter data
exchange. In such systems, a hand-held unit (HHU) or a unit with equivalent functions is
connected to a tariff device or a group of devices.
The connection can be permanent or disconnectable using an optical or electrical coupling. An
electrical interface is proposed for use with a permanent connection, or when more than one
tariff device needs to be read at one site. The optical coupler should be easily disconnectable
to enable data collection via an HHU.
The protocol permits reading and programming of tariff devices. It is designed to be particularly
suitable for the environment of electricity metering, especially as regards electrical isolation
and data security. While the protocol is well-defined, its use and application are left to the user.
This standard is based on the reference model for communication in open systems. It is
enhanced by further elements such as an optical interface, protocol controlled baud rate
switchover, data transmission without acknowledgement of receipt. The protocol offers several
modes for implementation in the tariff device. The HHU or equivalent unit acts as a master
while the tariff device acts as a slave in protocol modes A to D. In protocol mode E, the HHU
acts as a client and the tariff device acts as a server.
As several systems are in practical use already, particular care was taken to maintain
compatibility with existing systems and/or system components and their relevant protocols.
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this International Standard. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and parties to
agreements based on this International Standard are encouraged to investigate the possibility
of applying the most recent editions of the normative documents indicated below. Members of
IEC and ISO maintain registers of currently valid International Standards.
IEC 60050-300:2001, International Electrotechnical Vocabulary (IEV) – Electrical and electronic
measurements and measuring instruments – Part 311: General terms relating to measurements
– Part 312: General terms relating to electrical measurements – Part 313: Types of electrical
measuring instruments – Part 314: Specific terms according to the type of instrument

62056-21 © IEC:2002 – 17 –
IEC 62051:1999, Electricity metering – Glossary of terms
IEC 62056-42:2002, Electricity metering – Data exchange for meter reading, tariff and load
control – Part 42: Physical layer services and procedures for connection oriented
asynchronous data exchange
IEC 62056-46:2002, Electricity metering – Data exchange for meter reading, tariff and load
control – Part 46: Data link layer using HDLC-protocol
IEC 62056-53:2002, Electricity metering – Data exchange for meter reading, tariff and load
control – Part 53: COSEM application layer
ISO/IEC 646:1991, Information technology – ISO 7-bit coded character set for information
interchange
ISO/IEC 1155:1978, Information processing – Use of longitudinal parity to detect errors in
information messages
ISO/IEC 1177:1985, Information processing – Character structure for start/stop and
synchronous character-oriented transmission
ISO/IEC 1745:1975, Information processing – Basic mode control procedures for data
communication systems
ISO/IEC 7480:1991, Information technology – Telecommunications and information exchange
between systems – Start-stop transmission signal quality at DTE/DCE interfaces
ITU-T Recommendation V.24 (2000), List of definitions for interchange circuits between data
terminal equipment (DTE) and data circuit-terminating equipment (DCE)
ITU-T Recommendation V.28 (1993), Electrical characteristics for unbalanced double-current
interchange circuits
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purpose of this part of IEC 62056 the terms and definitions given in IEC 60050-300 and
IEC 62051, as well as the following apply:
3.1.1
tariff device
fixed data collection unit, normally linked or combined with an electricity meter, acting
as a server
3.1.2
master
central station. Station which takes the initiative and controls the data flow

62056-21 © IEC:2002 – 19 –
3.1.3
slave
station responding to requests of a master station. The tariff device is normally a slave station
3.1.4
client
a station, asking for services, normally the master station
3.1.5
server
a station, delivering services. The tariff device (e.g. the meter) is normally the server,
delivering the requested values or executing the requested tasks
3.2 Abbreviations
HHU hand-held unit
4 Physical properties
4.1 Electrical current loop interface
a) Type of signal
20 mA current loop
Absolute limits:
Open-circuit voltage: max. 30 V d.c.
Loop current: max. 30 mA
Table 1 – Electrical interface
Current Send (TX) Receive (RX)
Zero, no loop current, SPACE ≤2,5 mA ≤3 mA
One, 20 mA loop current, MARK
≥11 mA ≥9 mA
Voltage drop Send (TX) Receive (RX)
One, 20 mA loop current, MARK
≤2 V ≤3 V
Maximum open-circuit voltage during operation 30 V d.c.
b) Power supply
On the tariff device side the interface is passive. The HHU supplies the necessary power.
c) Connections
Via terminals or suitable connectors. Polarity errors can prevent communication, but shall
not harm the devices.
62056-21 © IEC:2002 – 21 –
d) Circuit arrangements in two-wire configuration (one slave station)
IEC  722/02
Figure 1a – Circuit diagram of a two-wire single slave configuration
e) Circuit arrangements in two-wire configuration (multiple slave stations)
IEC  723/02
Figure 1b – Circuit diagram of a two-wire multiple slave configuration
f) Circuit arrangements in four-wire configuration (one slave station)
IEC  724/02
Figure 1c – Circuit diagram of a four-wire single slave configuration

62056-21 © IEC:2002 – 23 –
g) Circuit arrangements in four-wire configuration (multiple slave stations)
IEC  725/02
Figure 1d – Circuit diagram of a four-wire multiple slave configuration
Figure 1 – Circuit diagrams
If a nominal voltage of the master station (HHU) of 26 V is assumed, eight slave stations (tariff
devices) can be connected in series.
4.2 Electrical interface V.24/V.28
Relevant ITU-T recommendations apply:
ITU-T Recommendation V.24: only circuits No. 102 (Signal ground), 103 (Transmitted data)
and 104 (Received data) are used.
ITU-T Recommendation V.28: The electrical characteristics of the interchange circuits shall be
according to the ITU-T V.28 Recommendation. These enable signalling rates up to 20 kbit/s.

62056-21 © IEC:2002 – 25 –
4.3 Optical interface
4.3.1 Construction of the reading head
Annular magnet Infrared receiver Infrared transmitter
View into reading head
Side view
IEC  726/02
Figure 2a – Arrangement of components
IEC  727/02
Figure 2b – Dimensions
Figure 2 – Construction of the reading head
4.3.2 Characteristic data of the magnet
Cohesion force
The cohesion force F is defined as the perpendicular pulling force measured when the magnet
is positioned on a bright 2 mm thick deep-drawing steel plate St 12, minus the weight of the
reading head itself.
62056-21 © IEC:2002 – 27 –
IEC  728/02
Cohesion force
F ≥ҏ5 N in contact with the steel plate; F > 1.5 N at a distance of 2 mm from the steel plate.
Figure 3a – Cohesion force
IEC  729/02
Internal diameter d = 13 mm ± ҏ1 mm; External diameter d = 28 mm minimum
i a
Magnetization: axial, north pole directed towards the tariff device.
Figure 3b – Dimensions
Figure 3 – Characteristic data of the magnet

62056-21 © IEC:2002 – 29 –
4.3.3 Arrangement of components in the tariff device
IEC  730/02
Figure 4 – View into optical port
4.3.4 Alignment
Although no mechanical alignment is specified, optimum data transfer is achieved (under test
conditions) when the reading head is in the correct position (cable downwards), the infrared
receiver in the tariff device is aligned directly opposite the infrared transmitter in the reading
head, and the infrared receiver in the reading head is directly opposite the infrared transmitter
in the tariff device.
Slight variations to this position should not affect performance significantly, but for larger
variations, degradation of the optical characteristics can occur.
4.3.5 Optical characteristics
4.3.5.1 Wavelength
The wavelength of the radiated signals in both directions is between 800 nm and 1 000 nm
(infrared).
4.3.5.2 Transmitter
The transmitter in the tariff device, as well as in the reading head, generates a signal with
a radiation strength E over a defined reference surface (optically active area) at a distance
e/T
of a = 10 mm (±1 mm) from the surface of the tariff device or the reading head.
The following limiting values apply:
ON-condition (ON = SPACE = Binary 0): 500 ≤ E ≤ 5 000 µW/cm²
e/T
OFF-condition (OFF = MARK (quiescent state) = Binary 1): E ≤ҏ10 µW/cm²
e/T
62056-21 © IEC:2002 – 31 –
IEC  731/02
Figure 5 – Test arrangement for the transmitter
4.3.5.3 Receiver
A transmitter which is positioned at a distance a = 10 mm (±1 mm) on the optical axis from
the receiver in the tariff device or the reading head generates a signal with a radiation strength
E over a defined reference surface (optically active area).
e/R
The following limiting values apply:
ON-condition: receiver definitely ON at E ≥ 200 µW/cm² (ON = SPACE = Binary 0)
e/R
OFF-condition: receiver definitely OFF at E ≤ 20 µW/cm² (OFF = MARK (quiescent state) =
e/R
Binary 1)
IEC  732/02
Figure 6 – Test arrangement for the receiver

62056-21 © IEC:2002 – 33 –
4.3.5.4 Environmental lighting condition
The optical path (data transmission) shall not be affected by surrounding light with an intensity
of up to 16 000 lux (light composition comparable with daylight, including fluorescent light).
4.3.5.5 Environmental temperature condition
The reference temperature is 23 °C ± 2 °C.
5 Character transmission
5.1 Type of transmission
Asynchronous serial bit (Start – Stop) transmission according to ISO/IEC 1177:1985, half-duplex.
5.2 Transmission speed
Initial baud rate – 300
Standard baud rates – 300, 600, 1 200, 2 400, 4 800, 9 600, 19 200
Special baud rate – as desired.
NOTE The maximum speed may be limited by the reading head or the optical port or the ITU-T Recommendation
V.28 limitations in the tariff device.
5.3 Signal quality
According to ISO/IEC 7480:1991:
– category 1 for the transmitter;
– category A for the receiver.
5.4 Character format
Character format according to ISO/IEC 1177:1985.
(1 start bit, 7 data bits, 1 parity bit, 1 stop bit).
NOTE Protocol mode E (see 6.4.5) may use byte transparency, 1 start bit, 8 data bits, 1 stop bit (e.g. see Annex E).
5.5 Character code
Character code according to ISO/IEC 646:1991, international reference version. For local use,
a national replacement code can be used.
NOTE Protocol mode E (see 6.4.5) may use byte transparency.
5.6 Character security
With parity bit, even parity according to ISO/IEC 1177:1985.
NOTE Protocol mode E (see 6.4.5) may use byte transparency, specific security may be used.

62056-21 © IEC:2002 – 35 –
6 Data transmission protocol
6.1 General
The protocol offers five alternative protocol modes, which can be used by the tariff device: A,
B, C, D and E. Mode selection is a subset of ISO/IEC 1745, basic mode control procedures.
Data exchange is bi-directional in protocol modes A, B, C and E and is always initiated by the
HHU with a transmission of a request message. In protocol modes A to C, the HHU acts as a
master and the tariff device acts as a slave. In protocol mode E, the HHU acts as a client and
the tariff device acts as a server. These protocol modes permit meter reading and
programming. Protocol mode E may be a transparent binary mode.
Data exchange is unidirectional in protocol mode D and permits readout only. The information
flows from the tariff device to the HHU. Data transmission is initiated, for example by operating
a push button or other sensor on the tariff device.
The protocol mode used by the tariff device is indicated to the HHU by the identification
message. Protocol modes A to D are identified by the baud rate identification character (see
item 13 in 6.3.3) while protocol mode E is identified by an escape sequence (see items 23 and
24 in 6.3.2). Protocol mode E enables to use various protocols, one of them being the
METERING HDLC protocol as described in Annex E.
6.2 Calculation of the block check character
The readout of data may be performed without block check character. Whenever used, the
block check character shall comply with ISO/IEC 1155:1978.
IEC  733/02
NOTE The scope of the block check character BCC is as specified in ISO/IEC 1745:1975, and is from the
character immediately following the first SOH or STX character detected up to and including the ETX character
which terminates the message. The calculated BCC is placed immediately following the ETX.
Figure 7 – Setting up a block check character (example according to ISO/IEC 1155)

62056-21 © IEC:2002 – 37 –
6.3 Message definitions
Explanations of message contents see 6.3.14.
6.3.1 Request message
Opening message from the HHU to the tariff device. The device address is optional.
I ? Device address ! CR LF
1) 9) 22) 2) 3) 3)
6.3.2 Identification message
Answer of a tariff device. Fields 23) and 24) are optional, they are part of field 14).
I X X X Z \ W Identification CR LF
1) 12) 12) 12) 13) 23) 24) 14) 3) 3)
6.3.3 Acknowledgement/option select message
Negotiation of advanced features (only used in protocol mode C and E).
ACK V Z Y CR LF
4) 10) 13) 11) 3) 3)
6.3.4 Data message (except in programming mode)
Normal response of a tariff device, for example the full data set (not used in protocol mode E).
STX Data block ! CR LF ETX BCC
5) 15) 2) 3) 3) 6) 8)
6.3.5 Acknowledgement message
If appropriate, see also flow charts in the annexes.
ACK
4)
6.3.6 Repeat-request message
If appropriate, see also flow charts in the annexes.
NAK
16)
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6.3.7 Programming command message
Used for programming and block oriented data transfer, see also 6.5.
SOH C D STX Data set ETX BCC
17) 18) 19) 5) 20) 6) 8)
6.3.8 Programming command message using optional partial blocks
Used for long messages, see also 6.5 and flow charts in the annexes (only in protocol
mode C).
SOH C D STX Data set EOT BCC
17) 18) 19) 5) 20) 7) 8)
6.3.9 Data message (programming mode)
Used for block oriented data transfer, see also 6.5 and flow charts in the annexes.
STX Data set ETX BCC
5) 20) 6) 8)
6.3.10 Data message (programming mode) using optional partial blocks
Used for long messages of block oriented data transfer, see also 6.5 and flow charts in the
annexes (only in protocol mode C).
STX Data set EOT BCC
5) 20) 7) 8)
6.3.11 Error message (programming mode)
Used for block oriented data transfer, see also flow charts in the annexes.
STX Error message ETX BCC
5) 21) 6) 8)
6.3.12 Break message (programming mode)
Used for block oriented data transfer, see also flow charts in the annexes.
SOH B 0 ETX BCC
17) 18) 19) 6) 8)
6.3.13 Block message (other protocols)
Block messages are used in conformance with the protocol selected, as specified in "other
protocol", see 6.4.5 and Annex E.

62056-21 © IEC:2002 – 41 –
6.3.14 Explanations of message contents
1) Start character "/" (forward oblique, code 2FH).
2) End character "!" (exclamation mark, code 21H).
3) Completion character (CR, carriage return, code 0DH; LF, line feed, code 0AH).
4) Acknowledge character (ACK, acknowledge, code 06H).
5) Frame start character (STX, start of text code 02H) indicating where the calculation of BCC
shall start from. This character is not required if there is no data set to follow.
6) End character in the block (ETX, end of text, code 03H).
7) End character in a partial block (EOT, end of text block, code 04H).
8) Block check character (BCC), if required, in accordance with the characters 5) and 6).
Items 5) and 6) do not apply when the data block is transmitted without check characters.
9) Transmission request command "?" (question mark, code 3FH)
10) Protocol control character (see 6.4.5.2).
11) Mode control character (see 6.4.5.3).
12) Manufacturer's identification comprising three upper case letters except as noted below:
If a tariff device transmits the third letter in lower case, the minimum reaction time t for the
r
device is 20 ms instead of 200 ms. Even though a tariff device transmits an upper case
third letter, this does not preclude supporting a 20 ms reaction time.
These letters shall be registered with the administrator: The FLAG Association (see the
foreword).
13) Baud rate identification (for baud rate changeover)
The request message, the identification message and the acknowledgement/option select
message are transmitted at the initial rate of 300 Bd (except protocol mode D). The baud
rate of the data message depends on the baud rate determined by the protocol.
a) Protocol mode A (without baud rate changeover)
Any desired printable characters except "/", "!" and as long as they are not specified for
protocol mode B or protocol mode C.
b) Protocol mode B (with baud rate changeover, without acknowledgement/option select
message)
A -  600 Bd
B - 1 200 Bd
C - 2 400 Bd
D - 4 800 Bd
E - 9 600 Bd
F - 19 200 Bd
G, H, I - reserved for later extensions.
c) Protocol mode C and protocol mode E (with baud rate changeover, with
ackn
...