ISO/FDIS 14908-2

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14908-2
ISO/TC 205
Interconnection of information
Secretariat: ANSI
technology equipment — Control
Voting begins on:
Network Protocol —
2011-01-04
Part 2:
Voting terminates on:
2011-03-04
Twisted-pair communication

Interconnexion des équipements des technologies de l'information —
Protocole de réseau de contrôle —
Partie 2: Communication de paire torsadée


Please see the administrative notes on page iii

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ISO/FDIS 14908-2:2011(E)
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ISO/FDIS 14908-2:2011(E)
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ISO/FDIS 14908-2:2011(E)
In accordance with the provisions of Council Resolution 15/1993, this document is circulated in the
English language only.


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ISO/FDIS 14908-2:2011(E)
Contents Page
Foreword.v
Introduction.vi
1 Scope .1
2 Normative references .1
3 Network overview .1
4 System specifications .2
4.1 General aspects .2
4.2 Cable .2
4.3 Topology.2
4.4 Cable termination.2
4.5 Segment configuration.3
4.6 Power specifications .3
5 Link power.4
5.1 General.4
5.2 Source.4
5.3 Power supply requirements.5
5.4 Passive coupler circuit.7
6 Node specifications.8
6.1 Link power.8
6.2 Hot plugging.8
6.3 Transmitter/receiver interface to the MAC sub-layer.8
6.4 Impedance . 12
7 Communication parameters . 13
Annex A (informative) Environmental specifications. 14
Bibliography. 15

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ISO/FDIS 14908-2:2011(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 14908-2 was prepared by CEN/TC 247, was adopted, under the fast track procedure, by joint Technical
Committee ISO/IEC JTC 1, Information technology, and was assigned to SC 25, Interconnection of
information technology equipment. It was then transferred to ISO/TC 205, Building environment design.
ISO 14908 consists of the following parts, under the general title Interconnection of information technology
equipment — 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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ISO/FDIS 14908-2:2011(E)
Introduction
This International Standard has been prepared to provide mechanisms through which various vendors of local
area control networks may exchange information in a standardized way. It defines communication capabilities.
This International Standard is to be used by anyone involved in design, manufacture, engineering, installation
and commissioning activities.
The International Organization for Standardization (ISO) and the 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.
ISO and the IEC take no position concerning the evidence, validity and scope of this patent right.
The holder of this patent right has assured ISO and the 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 patent rights is registered with ISO and the 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.



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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 14908-2:2011(E)

Interconnection of information technology equipment —
Control Network Protocol —
Part 2:
Twisted-pair communication
1 Scope
This part of ISO 14908 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 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 part of ISO 14908 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 which control the operation of the physical layer, are also specified.
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.
ISO 14908-1:2011, Interconnection of information technology equipment — Control Network Protocol —
Part 1: Protocol Stack
ISO/IEC 15018:2004, 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.
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ISO/FDIS 14908-2:2011(E)
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.
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. Physical layer repeaters shall
not be interconnected in such a way as to create a loop.
Each port of a physical layer repeater shall meet the specifications stated in 6.2, 6.3.3, and 6.4. The delay
through the repeater shall not exceed 36 µs.
4.4 Cable termination
4.4.1 Free-topology segment
A free-topology segment shall have a single termination. If the segment is locally powered, an RC network as
shown in Figure 1 shall be used, with R1 = 52,3 Ω ± 1 %, 1/8 W. The termination may be located anywhere on
the segment. If the segment is link-powered, the termination shall be provided by the link power source. See
Figure 5. The link power source and termination may be located anywhere on the segment.
4.4.2 Bus topology segment
A bus topology segment shall have two terminations, one at each end of the bus. If the segment is locally
powered, an RC network as shown in Figure 1 shall be used, with R1 = 105 Ω ± 1 %, 1/8 W at each end. If the
segment is link-powered, the link power source shall provide one termination. See Figure 5. The other
termination shall be an RC network as shown in Figure 1, with R1 = 105 Ω ± 1 %, 1/8 W.
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ISO/FDIS 14908-2:2011(E)

Key
1 Network Connection
Figure 1 — Termination
4.5 Segment configuration
A free-topology twisted-pair channel shall support up to 128 link-powered or 64 locally-powered nodes at a
maximum bit error rate of 1 in 100 000. Both types of nodes shall be supported on a given segment, provided
the following constraint is met:
(1 ×+ number of link powered nodes) (2 × number of locally powered nodes) ≤ 128
Table 1 shows the maximum bus length for a bus-topology segment.
Table 2 shows the maximum node-to-node distance and maximum wire length for a free-topology segment.
The distance from each node to each of the other nodes and to the link power source shall not exceed the
maximum node-to-node distance. If multiple paths exist, e.g., a loop topology, then the longest path shall be
used for the calculations. The maximu
...