ISO/IEC 14908-2:2012

INTERNATIONAL ISO/IEC
STANDARD 14908-2
First edition
2012-02-15
Information technology — Control
network protocol —
Part 2:
Twisted pair communication
Technologies de l'information — Protocole de réseau de contrôle —
Partie 2: Communication de pair torsadée

Reference number
©
ISO/IEC 2012
©  ISO/IEC 2012
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ii © ISO/IEC 2012 — All rights reserved

14908-2 © ISO/IEC:2012 (E) - 2 -
Contents
Introduction .5
1 Scope. 7
2 Normative references. 7
3 Network overview . 7
4 System specifications. 7
4.1 General aspects. 7
4.2 Cable. 8
4.3 Topology . 8
4.3.1 Free or bus topology. 8
4.3.2 Repeater . 8
4.4 Cable Termination . 8
4.4.1 Free-topology segment . 8
4.4.2 Bus topology segment. 8
4.5 Segment configuration. 9
4.6 Power specifications. 9
5 Link power . 9
5.1 General . 9
5.2 Source . 10
5.3 Power supply requirements. 10
5.4 Passive coupler circuit. 13
6 Node specifications. 14
6.1 Link power . 14
6.2 Hot plugging . 14
6.3 Transmitter/receiver interface to the MAC sub-layer. 14
6.3.1 Physical layer protocol data unit. 14
6.3.2 Frame format. 15
6.3.3 Transmit waveform. 16
6.4 Impedance. 19
7 Communication parameters . 20
Annex A (informative). 21
Environmental specifications. 21
Bibliography . 22

Figures
Figure 1 — Termination.8
Figure 2 — Link Power Source.10
Figure 3 — Power supply output ripple voltage requirement .11
Figure 4 — Power supply startup interval behavior .12
Figure 5 — Coupler circuit schematic.13
Figure 6 — Physical layer protocol data unit .15

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Figure 7 — Frame format for compliant transmitter. .15
Figure 8 — Idealised transmit waveform - zero bit.16
Figure 9 — Idealised transmit waveform - one bit.17
Figure 10 — Maximum voltage spectrum over frequency relative to peak.18
Figure 11 — Minimum impedance – powered and unpowered node.19
Tables
Table 1 — Bus-Topology Distance Specifications .9
Table 2 — Free-Topology distance specifications .9
Table 3 — Power supply requirements.11
Table 4 — Coupler circuit bill of materials .14
Table 5 — Link power requirements.14
Table 6 — Communication parameters for interoperable transceiver.20

Table A. 1 —Representative environmental specifications for nodes .21

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Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical Commission)
form the specialized system for worldwide standardization. National bodies that are members of ISO or IEC
participate in the development of International Standards through technical committees established by the
respective organization to deal with particular fields of technical activity. ISO and IEC technical committees
collaborate in fields of mutual interest. Other international organizations, governmental and non-governmental, in
liaison with ISO and IEC, also take part in the work. In the field of information technology, ISO and IEC have
established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the national bodies casting a vote.
ISO/IEC 14908-2 was prepared by CEN/TC 247 and was adopted, under a special “fast-track procedure”, by
Joint Technical Committee ISO/IEC JTC 1, Information technology, in parallel with its approval by the national
bodies of ISO and IEC.
ISO/IEC 14908 consists of the following parts, under the general title Information technology — Control network
protocol:
 Part 1: Protocol stack
 Part 2: Twisted pair communication
 Part 3: Power line channel specification
 Part 4: IP communication
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Introduction
This International Standard has been prepared to provide mechanisms through which various vendors of
local area control networks may exchange information in a standardised way. It defines communication
capabilities.
This International Standard is to be used by all involved in design, manufacture, engineering, installation
and commissioning activities.
The International Organization for Standardization (ISO) and International Electrotechnical
Commission (IEC) draw attention to the fact that it is claimed that compliance with this
International Standard may involve the use of patents held by Echelon Corporation.
The ISO and IEC take no position concerning the evidence, validity and scope of this patent right.
The holder of this putative patent right has assured the ISO and 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 holder of the putative patent rights is
registered with the ISO and IEC. Information may be obtained from:
Echelon Corporation, 4015 Meridian Avenue, San Jose, CA 94304, USA, phone +1-408-
938-5234, fax: +1-408-790-3800 http://www.echelon.com.
Attention is drawn to the possibility that some of the elements of this International Standard may
be the subject of patent rights other than those identified above. ISO and IEC shall not be held
responsible for identifying any or all such patent rights.

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INFORMATION TECHNOLOGY – CONTROL NETWORK PROTOCOL –

Part 2: Twisted pair communication
1 Scope
This International Standard specifies the control network protocol (CNP) free-topology twisted-pair
channel for networked control systems in local area control networks and is used in conjunction with
ISO/IEC 14908-1. The channel supports communication at 78,125 kbit/s between multiple nodes, each of
which consists of a transceiver, a protocol processor, an application processor, a power supply and
application electronics.
This International Standard covers the complete physical layer (OSI Layer 1), including the interface to
the Media Access Control (MAC) sub-layer and the interface to the medium. Parameters that are
controlled by other layers but control the operation of the physical layer are also specified.
2 Normative references
The following referenced documents are indispensable for the application of this International Standard.
For dated references, only the edition cited applies. For undated references, the latest edition of the
referenced document (including any amendments) applies.
ISO/IEC 14908-1:2012, Information technology – Control network protocol – Part 1: Protocol stack.
ISO/IEC 15018, Information technology - Generic cabling for homes.
3 Network overview
The CNP free-topology twisted-pair channel supports up to 128 nodes on a single network segment with
an optional link power source that supplies DC power to the nodes on the network. The channel is
specified to support free-topology wiring, and will accommodate bus, star, loop, or any combination of
these topologies. The total network length and number of nodes may be extended by use of CNP channel
physical layer repeaters, or CNP compliant routers. The channel data rate is 78,125 kbit/s. Nodes can be
either locally powered or link powered. A link-powered node derives its power from the network. The
power is delivered on the same two conductors that carry data. Nodes are polarity-insensitive with
respect to data as well as DC power. A locally powered node derives its power from a local source. The
data is transmitted using Differential Manchester encoding, which is polarity-insensitive.
4 System specifications
4.1 General aspects
This section specifies the cable type used, terminations required with bus or free topology, maximum
node counts and distances for link and locally powered schemes, and the maximum steady state power
that can be drawn from the link power supply.

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4.2 Cable
The cable shall conform to 9.4 of ISO/IEC 15018:2004.
4.3  Topology
4.3.1 Free or bus topology
The network may use either a singly-terminated free topology or a doubly-terminated bus topology.
4.3.2 Repeater
Two network segments may be interconnected with a channel physical layer repeater. No more than one
physical layer repeater shall be in a path between any two nodes on a network
...