CiA® 102
CAN
Physical layer for industrial applications
Version: 3.0.0
05 February 2010
CAN in Automation (CiA) e. V.
HISTORY
Date
1994-04-20
2008-04-10
2010-02-05
Physical layer for industrial applications –
Changes
Publication of version 2.0 as draft standard
Publication of version 3.0 as draft standard proposal
Entirely reviewed; references to CiA 301 and CiA 303-1 included.
Publication of version 3.0 as draft standard
General information on licensing and patents
CAN in AUTOMATION (CiA) calls attention to the possibility that some of the elements of this
CiA specification may be subject of patent rights. CiA shall not be responsible for identifying
any or all such patent rights.
Because this specification is licensed free of charge, there is no warranty for this
specification, to the extent permitted by applicable law. Except when otherwise stated in
writing the copyright holder and/or other parties provide this specification “as is” without
warranty of any kind, either expressed or implied, including, but not limited to, the implied
warranties of merchantability and fitness for a particular purpose. The entire risk as to the
correctness and completeness of the specification is with you. Should this specification prove
failures, you assume the cost of all necessary servicing, repair or correction.
Trademarks
CANopen® and CiA® are registered community trademarks of CAN in Automation. The use is
restricted for CiA members or owners of CANopen® vendor ID. More detailed terms for the
use are available from CiA.
© CiA 2010
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or
utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm,
without permission in writing from CiA at the address below.
CAN in Automation e. V.
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DE - 90429 Nuremberg, Germany
Tel.: +49-911-928819-0
Fax: +49-911-928819-79
Url: www.can-cia.org
Email: headquarters@can-cia.org
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Physical layer for industrial applications –
CONTENTS
1 Scope ............................................................................................................................. 4
2 Normative references ...................................................................................................... 4
3 Definitions and abbreviations .......................................................................................... 4
3.1 Definitions ............................................................................................................. 4
3.2 Abbreviations ......................................................................................................... 4
4 Physical signalling .......................................................................................................... 4
4.1
Introduction ........................................................................................................... 4
4.2 Device design ........................................................................................................ 5
4.3 System design ....................................................................................................... 5
5 Physical medium attachment ........................................................................................... 5
Introduction ........................................................................................................... 5
5.1
5.2 Device design ........................................................................................................ 5
5.3 System design ....................................................................................................... 5
6 Medium dependent interface ........................................................................................... 6
6.1
Introduction ........................................................................................................... 6
6.2 Device design ........................................................................................................ 6
6.3 System design ....................................................................................................... 6
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Physical layer for industrial applications –
1 Scope
This specification describes the Controller Area Network physical layer for general industrial
applications using transmission rates of up to 1 Mbit/s. In addition to the internationally
standardized high-speed transceiver, it specifies a number of transmission rates in order to
achieve a generic compatibility between CAN devices, in particular with CANopen devices.
This specification is suitable for all CAN tools and generic interface devices (e.g. USB/CAN
dongles) to be used for CAN-based industrial networks.
2 Normative references
/CiA301/
/CiA303-1/
CiA 301, CANopen application layer and communication profile
CiA 303-1, CANopen additional specification – Part 1: Cabling and connector
pin assignment
/ISO11898-1/ ISO 11898-1, Road vehicles – Controller area network (CAN) – Part 1: Data
link layer and physical signalling
/ISO11898-2/ ISO 11898-2, Road vehicles – Controller area network (CAN) – Part 2: High-
speed medium access unit
/ISO11898-5/ ISO 11898-5, Road vehicles – Controller area network (CAN) – Part 5: High-
speed medium access unit with low-power mode
3 Definitions and abbreviations
3.1 Definitions
For the purposes of this specification, the definitions given in /ISO11898-1/, /ISO11898-2/,
and /ISO11898-5/ apply.
3.1.1 CAN device
electronic control unit featuring a CAN controller chip and a CAN transceiver chip
3.1.2 T-connector
passive component comprising three connectors
3.2 Abbreviations
CAN
EMC
GND
LC
SHLD
RC
TVS
Controller Area Network
Electro-magnetic compatibility
Ground
Inductor capacitor
Shield
Resistor capacitor
Transient voltage suppression
4 Physical signalling
4.1
Introduction
The settings of bit-timing parameters for CAN controller chips are not standardized in
/ISO11898-1/.
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Physical layer for industrial applications –
4.2 Device design
Normally, the device designer sets the bit-timing parameters. One of the transmission rates as
specified in /CiA301/ shall be used. For convenience, the recommended bit-rates are shown
in Table 1.
NOTE Not all CAN transceiver chips compliant to /ISO11898-2/ support the lower bit-rates. Also high-clocked
CAN controller chips are not always able to support the lower bit-rates.
It is recommended to parameterize the CAN controller chips regarding the sample point as
specified in /CiA301/.
Table 1 – Recommended bit rates
Bit rate
1 Mbit/s
800 kbit/s
500 kbit/s
250 kbit/s
125 kbit/s
50 kbit/s
20 kbit/s
10 kbit/s
Nominal bit time
1 µs
1,25 µs
2 µs
4 µs
8 µs
20 µs
50 µs
100 µs
4.3
System design
All devices in a network shall use the very same bit-rate. The configured sample points should
be the same or as close as possible to each other. Using different sample point configurations
may lead to shorter network length or require more accurate oscillators in order to achieve a
suitable resynchronization.
5 Physical medium attachment
5.1
Introduction
Devices connected to networks compliant to this specification shall use transceiver chips
compliant to /ISO11898-2/ or /ISO11898-5/. The low-power mode of transceiver chips
compliant to /ISO11898-5/ does not fall into the scope of this specification.
5.2 Device design
In order to increase EMC performance and to protect the transceiver chip, the device designer
may use additional circuitry such as bi-directional TVS diodes, metal oxide varistors,
crowbars, or RC/LC filters.
5.3
System design
In order to increase EMC performance and to protect the transceiver chip, the system
designer may use (biased) split termination resistors and other additional circuitry (e.g. ferrite
bead, common mode choke, or feed-through capacitors). It is also possible to shield the bus-
line cable.
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Physical layer for industrial applications –
6 Medium dependent interface
6.1
Introduction
The network topology is a two-wire bus-line (CAN_H and CAN_L) with common return
(CAN_GND) being terminated at both ends by resistors representing the characteristic
impedance of the bus-line. The pin assignments for different connectors are recommended in
/CiA303-1/. For general-purpose applications
to use 9-pin D-sub
connectors.
is recommended
it
6.2 Device design
There are two basic concepts how to connect the device to the bus-lines:
•
Interconnected bus line sections – The bus lines consist of a number of sections, which are
interconnected; two options are allowed:
o A T-connector is used to interconnect the bus-line sections and the CAN device.
o The CAN device provides two bus connectors, interconnecting the bus line
• Undivided bus-line – The bus-line consists of a single cable without interconnecting
devices (device: one plug connector; bus-line: one socket connector per device, plus one
socket and one plug connector with termination resistors on both ends).
The plug connectors shall not provide external power supply for transceiver and optocouplers.
6.3
System design
The wiring topology should be as close as possible to a single line structure, in order to
minimize reflections. The maximum network length depends on the selected bit-rate and the
location of the sample point. The maximum length of the network shall not exceed 1 000 m.
The system designer should consider the general recommendations given in /CiA303-1/.
For network length below 40 m it is recommended to use a 124-Ω resistor to terminate the
bus-lines at both network ends. For other network lengths, general recommendations are
given in /CiA303-1/.
The ground pins of all transceiver chips are interconnected. The parameters of specific
resistance per stub-cable length, total network length, current, and location of the power
supply input should be chosen in a way, that the difference between ground potentials of the
transceiver chips does not exceed 2 V.
NOTE At bus line lengths greater than 40 m, the specific resistance of the bus cable should be lower than the
value given in /ISO11898-2/. The recommendations given in /CiA303-1/ should be considered.
If necessary, galvanic isolation may be applied, in order to reduce the current through the
ground line. In general, it is advantageous to locate the power supply input in the centre of
the bus-lines. It is recommended that the external positive power supply is in the range +7 V <
V+ < +13 V with a maximum of up to 100 mA. Other values should be double-checked with the
used connectors in the entire network.
NOTE
transceiver chips.
If the devices use 24-V or higher voltage power supplies, it is recommended to select appropriate CAN
The bus wires may be routed parallel, twisted and/or shielded, depending on the EMC
requirements. If non-terminated stub-cables are used, the maximum length of them should be
considered, for details see /CiA303-1/. The cable stubs should be as short as possible,
especially at higher bit-rates. At 1 Mbit/s, the length of the cable-stubs should not exceed
0,3 m (see /ISO11898-2/); this includes also the device-internal cable stubs.
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Physical layer for industrial applications –
It is possible to use repeater devices to increase the number of bus nodes, which are
connected to the network system. From the data link layer point of view, it is one logical
network comprising several segments. Repeaters are also used to increase the allowed
distance between the bus nodes.
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