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Dual Wire CAN Physical Layer and Data Link Layer Specification
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WORDLWIDE
ENGINEERING
STANDARDS
General Specification
Electrical/Electronic
GMW3122
Dual Wire CAN Physical Layer and Data Link Layer Specification
© Copyright 2005 General Motors Corporation All Rights Reserved
November 2005
Originating Department: North American Engineering Standards
Page 1 of 42
1 Introduction
1.1 Scope. This document specifies the physical
layer requirements for a Carrier Sense Multiple
Access/Collision Resolution (CSMA/CR) data link
which operates on a dual wire medium to
communicate among Electronic Control Units
(ECU) on road vehicles at normal transmission
rates of:
High Speed Bus 500 kbit/sec
Medium Speed Bus 95.24 and 125 kbit/sec
This document is to be referenced by the particular
Component Technical Specification (CTS) which
describes any given ECU in which the dual wire
data link controller and physical layer interface is
located. The performance of the data link layer and
physical layer is specified in this document. ECU
environmental and other requirements shall be
provided in the Component Technical
Specification. Functional as well as parameter
requirements in this document generally apply over
the applicable operating conditions and aging. This
includes, for example, operating ambient
temperature, operating supply voltage and age drift
over component life time unless otherwise noted.
The intended audience includes, but is not limited
to, ECU suppliers, component release engineers,
platform system engineers and semiconductor
manufacturers of CAN controller and CAN
transceiver ICs.
1.2 Mission/Theme. This specification describes
the physical layer requirements for a dual wire data
link capable of operating with CSMA/CR protocols
such as CAN version 2.0A (standard frame
format). All ECUs shall tolerate CAN version 2.0B
(29 bit identifier extended frame format) messages,
i.e. ECUs may not disturb such messages unless
bit errors were detected. This serial data link
network is intended for use in applications where a
high data rate is required.
1.3 Requirement Wording Conventions. Within
this document the following conventions are
applied:
The word “Shall” shall be used in the following
ways:
a. To state a binding requirement on the network
or the nodes which comprise the network,
which is verifiable by external manipulation
and/or observation of a node or the network.
b. To state a binding requirement upon a node’s
requirements document that is verifiable
through a review of the document.
The word “Must” shall be used to state a binding
requirement upon nodes on the network
components which will have a corresponding ECU
or component requirements document. These
requirements will be verified as part of the
component verification.
The word “Should” denotes a preference or
desired conformance.
Note: In the event of a conflict between the text of
this specification and the documents cited herein,
the text of this specification takes precedence.
Note: Nothing in this specification supersedes
applicable laws and regulations unless a specific
exemption has been obtained.
2 References
Note: Only the latest approved standards are
applicable unless otherwise specified.
2.1 External Standards/Specifications.
ISO 11898-1 ISO 21848-2
ISO 11898-2 SAE J2284-3
ISO 16845 SAE J2284-1
2.2 GM Standards/Specifications.
GME6718 GMW3097
GME14010 GMW3172
GMW3001 GMW3173
GMW3059 GMW3191
GMW3091 GMW8763
3 Requirements
3.1 Physical and Data Link Layer
Characteristics.
3.1.1 Data link layer and two-wire physical layer
according to ISO 11898 (high-speed CAN physical
layer).
Copyright GM Worldwide
Reproduced by IHS under license with GMW
Licensee=Panasonic Automotive Systems Co of America/5946710001
Not for Resale, 01/27/2006 09:11:17 MST
No reproduction or networking permitted without license from IHS
--`,,`,,`,````,```````,``,,`,`,-`-`,,`,,`,`,,`---
GMW3122 GM WORLDWIDE ENGINEERING STANDARDS
© Copyright 2005 General Motors Corporation All Rights Reserved
Page 2 of 42 November 2005
3.1.2 Capable of operating with CAN 2.0A protocol
messages and tolerates CAN 2.0B protocol
messages. If platform-specific documents or
SSTS/CTS require conformance to CAN 2.0B, then
the applicable interfaces shall be capable to
transmit and receive standard as well as extended
frame format messages at any time during
operation, that is support the protocol CAN 2.0B
running in mixed-mode operation.
3.1.3 Supports the enhanced protocol for extended
clock tolerance
3.1.4 Only performs bit re-synchronization on
recessive to dominant bus signal edges
3.1.5 Meets GMW3173 GMLAN architecture and
bus wiring requirements
3.1.6 Complies to GMW3097GS and
GMW3091GS EMC requirements
3.1.7 Intended to operate at ground offset voltages
of up to 2V temporarily
3.2 Bus Operation.
3.2.1 General Requirements on Bus Operation
for 12V-Powered Devices. Per default the bus
network when awake shall be fully functional - i.e.
nodes shall be able to transmit and receive data -
when the supply voltage at the ECU power input
pins is within a range as specified in GMW3172
and/or the applicable CTS and/or SSTS document.
Note: In any case bus communication shall be
supported down to (at least) 9.0 V as measured at
the ECU power/ground input pins.
Note: The requirement “shall support
communication” does not imply that valid sensor
data or actuator function must be supported at this
voltage.
Note: Those devices which are involved in the
vehicle immobilization function in some fashion
typically need to support bus communication down
to a supply voltage of 6.0 V.
If local ECU supply voltage had decreased below
the specified minimum value, then the ECU shall
resume bus receive and transmit capability within a
time as specified in the ECU Component Technical
Specification. The time is measured from the point
in time when the voltage increases to a level of
0.5 V higher than the specified minimum supply
voltage until bus receive and transmit capability is
resumed. If no time is specified in the CTS, then
the ECU shall resume bus receive and transmit
capability within t
rsm
(See section 3.10). In
addition, if local ECU supply voltage decreases
below the specified minimum value, then the ECU
shall continue to support bus receive and transmit
capability for a time of t > 2 ms.
Note: Operation at battery voltages of less than
approximately 6.5 V typically implies usage of a
low-dropout voltage regulator.
The bus network shall support communication
between powered nodes even when only two of
the nodes on each network are sufficiently
powered and the rest of the nodes are non-
powered or under powered. Under powered is
when battery voltage at the ECU power input pins
is within the range of 0 V to 6.0 V unless otherwise
specified, see applicable SSTS and/or CTS.
Nodes that are not able to communicate without
disturbing the communication between other
nodes, e.g. due to non-powered or under powered
conditions, shall not be allowed to communicate.
Nodes shall, under these conditions, close down
communication circuits in a controlled manner.
Nodes that are in sleep condition shall not disturb
communication between other nodes.
In addition, ECU’s that transmit and receive
message frames which are required to support
engine start such as immobilizer data or Crank
command shall support communication in the
range of 16 V to 18 V for 1 hour and 18 V to 26.5 V
for 1 minute (jump start condition) unless otherwise
specified (see, e.g., GMW3172GS).
3.2.2 General Requirements on Bus Operation
for 42V-Powered Devices. If an ECU is supplied
exclusively by 42V nominal power as main supply,
then it shall comply to the following requirements
on bus operation:
3.2.2.1 The bus network when awake shall be fully
functional (i.e., device shall be able to transmit and
receive data) when the battery voltage at the ECU
power input pins is within the range of 21.0 V to
50.0 V.
3.2.2.2 Devices that are relevant for vehicle
functions at crank and/or which are not permitted
to perform a reset or re-initialization during an
engine Start & Stop cycle, shall be fully functional
(i.e., devices shall be able to transmit and receive
data) when a supply voltage starting profile
according to ISO 21848-2 is applied. The ECU
shall support error-free bus communication during
and after the complete ISO 21848-2 starting
profile.
Devices, that are not relevant to vehicle functions
during crank and/or that are allowed to perform
reset or re-initialization during an engine Start &
Stop cycle, shall not cause error conditions to
occur on the bus, i.e., there shall be no error
frames during and after the application of the crank
pulse. The device shall resume bus communication
within t ≤ t
rsm
after the supply voltage has reached
Copyright GM Worldwide
Reproduced by IHS under license with GMW
Licensee=Panasonic Automotive Systems Co of America/5946710001
Not for Resale, 01/27/2006 09:11:17 MST
No reproduction or networking permitted without license from IHS
--`,,`,,`,````,```````,``,,`,`,-`-`,,`,,`,`,,`---
GM WORLDWIDE ENGINEERING STANDARDS GMW3122
© Copyright 2005 General Motors Corporation All Rights Reserved
November 2005 Page 3 of 42
a level of 21 V unless otherwise specified in the
applicable SSTS or CTS.
3.2.2.3 High Speed Bus networks shall operate if
only two of the nodes on each network are
sufficiently powered and the rest of the nodes are
not powered or are in a low supply voltage
condition. Low supply voltage in this context
means the battery voltage at the ECU power input
pins is less than 21.0 V.
3.2.2.4 High Speed Bus Nodes that are not able to
communicate without disturbing the communication
of other nodes while in low supply voltage
condition shall automatically disable
communication under that condition. Such nodes
shall close down their communication function in a
controlled manner while in low supply voltage
condition.
3.2.2.5 Nodes that are in sleep condition shall not
disturb communication of other nodes.
3.2.2.6 Physical interface drivers which are not
powered or under-powered shall not disturb the
communication on the network.
3.2.3 Bus Operation During Crank. Table 1
describes the bus network functionality during
crank. Please refer to the applicable CTS, SSTS or
platform-specific technical document to determine
which devices are required to support this function
during crank.
Note: Each ECU that is supposed to contribute
data for engine start purposes (e.g., immobilizer
data) needs to support bus transmission function
during Crank, depending on platform- or vehicle-
specific requirements.
Voltage levels and timing of the Crank pulse are
specified in GMW3097GS and GMW8763 (PPEI).
Table 1: ECU Functional Status at Crank
Period Description
Run/Crank Transition The bus network shall be fully functional, nodes shall be able to transmit and receive
data
Crank
1
Bus functionality during this period shall be stated in the Component Technical
Specification. Under no circumstances shall any node disturb ongoing bus
communication. Ongoing message transmissions should be concluded normally, e.g.
without causing error conditions on the bus.
Crank
2
See Crank
1
Crank
3
Upon return of power nodes shall resume data receive and transmit function within a
time period being specified in the Component Technical Specification. If such time is
not specified in the CTS and/or SSTS, then the node shall resume receive/transmit
function within t ≤ t
rsm
(See section 3.10). Under no circumstances shall any node
disturb ongoing bus communication, e.g. due to start-up initiation.
Crank/Run Transition The bus network shall be fully functional, nodes shall be able to transmit and receive
data
3.2.3.1 Transferred 42V Crank Pulse To 14V
Side (e.g., via 42V/14V DC/DC converter). All
designated ECU’s shall be fully functional (i.e.,
device shall be able to transmit and receive data
on high-speed CAN) when a test pulse according
to the table below is applied. Designated ECUs
shall support error-free bus communication and are
not allowed to perform reset or re-initialization
during and after the complete test pulse.
Note: See the CTS, SSTS and or platform-specific
technical document to determine which devices
shall support operation while a transferred crank
pulse is present.
Nominal Voltage [V] Minimum Pulse Voltage [V] Pulse Duration [Seconds] Rise and Fall Time [ms]
13.8 7 1 5
3.2.4 Tolerance of the CAN Bit Time. Any CAN
interface of an ECU must be compliant to an
overall tolerance of the CAN bit time length as
specified in 4.1 (5.1). That is, CAN bits being
transmitted by an ECU shall meet this tolerance
requirement and each ECU shall be capable to
receive messages from other ECUs which meet
this requirement. The tolerance value is applicable
Copyright GM Worldwide
Reproduced by IHS under license with GMW
Licensee=Panasonic Automotive Systems Co of America/5946710001
Not for Resale, 01/27/2006 09:11:17 MST
No reproduction or networking permitted without license from IHS
--`,,`,,`,````,```````,``,,`,`,-`-`,,`,,`,`,,`---
GMW3122 GM WORLDWIDE ENGINEERING STANDARDS
© Copyright 2005 General Motors Corporation All Rights Reserved
Page 4 of 42 November 2005
over operating conditions and aging, e.g.,
temperature, supply voltage and age drift over
specified vehicle temperature including component
life time. This is to ensure proper operation of the
network, e.g., with respect to the CAN bus
resynchronization function.
Careful analysis of the bit time tolerance is
recommended when ceramic resonators and/or
PLL clocks are considered. The permitted
tolerance of the oscillator circuit is reduced when a
PLL clock is used for the CAN data link layer
controller. For example, the suitable oscillator
tolerance would be 0.1%, for the case where the
PLL circuit would exhibit an add-on tolerance of
0.35% (at 125 or 95.2 kbit/s: 0.4%).
When a ceramic resonator with a maximum
tolerance of 0.3% is used with a PLL, the add-on
clock tolerance of the PLL is limited to 0.15% (at
125 or 95.2 kbit/s: 0.2%) over a single bit time. At
a bus speed of 500 bit/s, this is equivalent to
0.15% of 2 µs, or 3 ns maximum jitter over 2 µs. At
a bus speed of 125 kbit/s, this is equivalent to
0.2% of 8 µs, or 16 ns max jitter over 8 µs. At a
bus speed of 95.2 kbit/s, this is equivalent to 0.2%
of 10.5 µs, or 21 ns max jitter over 10.5 µs.
3.3 Wake Up Techniques. Dual wire CAN allows
three types of ECU awake/sleep techniques. If a
wakeup technique is used then it must conform to
GMW3097GS EMC requirements.
a. Selective awake by an awake pulse. When
used, it will be possible to communicate on the
dual wire CAN network without forcing nodes
that are not needed to stay awake. For details
see section 3.3.1
b. Non-selective wakeup on presence of CAN
bus communication. When used, it will force
nodes to stay awake as long as ongoing
communication occurs. This is the
recommended concept for new designs. For
details see section 3.3.2.
Attention: this concept requires to employ CAN
transceiver products which support node wakeup
upon bus traffic, see 3.11.1.2.11.
c. Non-selective awake by a continuous high
level discrete signal, typically called
“Communication Enable”. When used, it will
force nodes to stay awake as long as the
discrete signal is at a high level (example:
Ignition signal). For details see section 3.3.3.
Usage of awake/sleep techniques are optional.
Whether and how the above approaches shall be
used is to be defined in the applicable platform-
specific data bus implementation document. Note
more than one of the above concepts can apply to
a particular ECU or network. For example, it may
be necessary in a subnet for an ECU to be present
which supports wakeup on bus traffic (technique 2)
and in addition to control the discrete wakeup line
(technique 3).
3.3.1 ECU Selective Awake Using a Wake Up
Wire. ECU selective awake is accomplished by a
dedicated wire, a wake up wire.
The wake up wire is a common wire for all ECU’s
connected on the same bus. Each ECU needs one
pin assigned for this function. The below parameter
specifications of the wake up wire concept support
connection of up to 22 ECU’s. The wake up wire
signal is an input/output interface, i.e., the ECU
can send and receive the wake up signal on the
same wire.
3.3.1.1 Concept Description.
3.3.1.1.1 The wake up output requirements are:
3.3.1.1.1.1 The wake up voltage V
twu
shall be
applied on the wake up wire for a time t
twuo
.
3.3.1.1.1.2 Wake up is generated as a hardware
signal on the wake up wire. The ECU generating
this signal shall wake up or notify all ECU’s
connected on the same bus.
3.3.1.1.2 The wake up input requirements are:
3.3.1.1.2.1 An ECU currently in sleep mode, that
detects a voltage in excess of Vrwu for a time
longer than trwui applied on the wake up wire, shall
switch to active mode.
3.3.1.1.2.2 The wake up pulse shall also affect an
ECU in active mode, not only an ECU that is in
sleep mode, i.e., an ECU that is in active mode
shall be able to detect the wake up pulse.
3.3.1.1.2.3 Each ECU shall be able to generate
wake up pulses and detect wake up pulses on the
wake up wire.
3.3.1.2 Wake Up Wire Basic Requirements.
3.3.1.2.1 An ECU should not change power modes
when subjected to GMW3097GS EMC conditions.
For example, the ECU shall not take
conducted/coupled immunity test conditions as
valid wake up or go to sleep events.
3.3.1.2.2 Fault tolerant modes:
3.3.1.2.2.1 ECU power loss. An ECU shall not
interfere with wake up function among other ECUs
during a loss of power or low supply voltage
condition. Upon return of power, normal wake up
operation shall resume without any operator
intervention within a time period being specified by
the ECU Component Technical Specification. If a
time period is not specified in the CTS, then the
ECU shall resume operation within t ≤ trsm. (See
Section 3.10).
Copyright GM Worldwide
Reproduced by IHS under license with GMW
Licensee=Panasonic Automotive Systems Co of America/5946710001
Not for Resale, 01/27/2006 09:11:17 MST
No reproduction or networking permitted without license from IHS
--`,,`,,`,````,```````,``,,`,`,-`-`,,`,,`,`,,`---
GM WORLDWIDE ENGINEERING STANDARDS GMW3122
© Copyright 2005 General Motors Corporation All Rights Reserved
November 2005 Page 5 of 42
3.3.1.2.2.2 Wake up wire short to ground. Wake up
function may be interrupted but there shall be no
damage to any ECU when the wake up wire is
shorted to ground or to a negative voltage down to
Vwu = –5 V. Upon removal of the wiring fault,
normal wake up operation shall resume without
any operator intervention within a time period being
specified by the ECU Component Technical
Specification. If a time period is not specified in the
CTS, then the ECU shall resume normal operation
within t ≤ trsm.
3.3.1.2.2.3 Wake up wire shorted to battery
voltage. Wake up function may be interrupted but
there shall be no damage to any ECU when the
wake up wire is shorted to a positive battery
voltage of Vwu = 16 V without time limit, 18 V for
1 h and 26.5 V for 1 minute. Upon removal of the
wiring fault, normal wake up operation shall
resume without any operator intervention within a
time period being specified by the ECU
Component Technical Specification. If a time
period is not specified in the CTS, then the ECU
shall resume normal operation within t ≤ trsm.
3.3.1.2.3 The ECU´s wake up input/output function
shall be fully functional when the ECU is powered
with a supply voltage of Vs = 6.5 V to 16.0 V.
When the ECU supply voltage has decreased
below Vs = 6.5 V, then the wake up function shall
resume operation when the supply voltage reaches
a level of Vs = 7 V or higher.
Note: This operating supply voltage range for the
wake up wire function only applies if not otherwise
specified in the applicable SSTS or CTS.
n <= 22
ECU1
ECUnECU3
ECU2
Wake up wire
Figure 1: Wake Up Wire
3.3.1.3 Wake Up Output Requirements. Note,
parameter specifications apply over operating
conditions and aging, e.g. temperature, supply
voltage and age drift over specified vehicle
temperature and component life time unless
otherwise noted.
Copyright GM Worldwide
Reproduced by IHS under license with GMW
Licensee=Panasonic Automotive Systems Co of America/5946710001
Not for Resale, 01/27/2006 09:11:17 MST
No reproduction or networking permitted without license from IHS
--`,,`,,`,````,```````,``,,`,`,-`-`,,`,,`,`,,`---
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