ISO/TS 21815-2:2021

TECHNICAL ISO/TS
SPECIFICATION 21815-2
First edition
2021-07
Earth-moving machinery — Collision
warning and avoidance —
Part 2:
On-board J1939 communication
interface
Engins de terrassement — Avertissement et évitement de collision —
Partie 2: Interface de communication embarquée
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 5
5 Logical interface . 5
5.1 Logical groups . 5
5.2 Negotiation . 6
5.3 Initialisation . 6
5.4 Operation . 6
6 Physical interface . 7
6.1 General . 7
6.2 Machine connector . 7
6.3 CxD connector . 8
6.4 Override switch . 9
6.5 Physical layer .10
7 J1939 communication protocol .10
7.1 General .10
7.2 PGN:CxD»machine status .11
7.2.1 General.11
7.2.2 PGN description .12
7.2.3 SPN structure .14
7.3 PGN:CxD»MachineCommand .37
7.3.1 General.37
7.3.2 PGN description .37
7.3.3 SPN structure .39
7.4 PGN:Machine»CxDr eply .43
7.4.1 General.43
7.4.2 PGN description .45
7.4.3 SPN structure .46
7.5 PGN:Machine»CxDdata (PR OPULSION) .54
7.5.1 General.54
7.5.2 PGN description .55
7.5.3 SPN structure .56
7.5.4 PROPULSION subsystem .57
7.6 PGN:Machine»CxDstatus .62
7.7 PGN:Machine»CxDcommand .62
7.8 PGN:CxD»MachineR eply .63
7.9 PGN:CxD»MachineData .63
7.10 PGN:Time/ Date .63
8 Documentation .64
8.1 Machine documentation .64
8.2 System documentation.64
Annex A (informative) Communication sequences .66
Annex B (informative) Trust mechanisms .74
Annex C (informative) Implementation examples for override and standby modes .80
Bibliography .82
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
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 127, Earth-moving machinery,
Subcommittee SC 2, Safety, ergonomics and general requirements.
A list of all parts in the ISO 21815 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2021 – All rights reserved

Introduction
The increasing use of detection systems and avoidance technology has been supporting operators to
safely operate machines in the field of mining and construction. At the same time, there are demands to
set standards for machines and systems detecting, alerting and intervening to mitigate collision risk.
There are currently two existing standards in the field: ISO 16001 and ISO 17757. These standards
provide guidance for visibility aids and object detection systems and for autonomous and semi-
autonomous machines, however, there is currently no standard that describes collision risk awareness,
warning signals and collision avoidance actions of the machinery operated by humans where there is a
risk of collision.
Collision warning and avoidance systems are developing technologies; and the algorithms are not yet
mature and well understood. This document is intended to foster innovation and accelerate the pace of
improvements in new collision warning and avoidance technologies. The performance requirements of
this document are technology neutral and do not specify technologies to meet the requirements.
The systems described in this document are intended to assist the operator of the machine. As current
technologies are unable to achieve full collision warning/avoidance in every situation, the responsibility
for safe operation of the machine remains with the operator of the machine.
This document defines a protocol for communication between a machine and a connected device to
allow the connected device to command the machine to slow down, stop or to maintain a stationary
state where the machine can move in a linear (i.e. forwards-backwards) direction along a travel path.
Machines with rotational movements (e.g. excavators) and machines with compound movements (e.g.
machines with booms) are only considered to the extent of the linear component of their travel.
The machine manufacturer may be flexible in deciding which method is most appropriate for their
machine. Some applications can be delivered with basic functionality (e.g. without the use of registers).
Regardless of which approach is selected, the connected device has a means to discover the capabilities
of the machine.
Annex B outlines a mechanism for establishing trust between the machine and the connected device
based on the exchange of certificates at the session layer as defined by the machine manufacturer.
The message structure for the session layer can be different to the message structure defined in this
document.
The specification of the J1939 protocol in this document does not preclude the development of other
communication interfaces that can support collision warning and avoidance functionality. At the time of
publishing this document, protocols have only been defined for SAE J1939 due to the general availability
of CAN 2.0 interfaces on machinery and devices providing collision warning and avoidance functions.
TECHNICAL SPECIFICATION ISO/TS 21815-2:2021(E)
Earth-moving machinery — Collision warning and
avoidance —
Part 2:
On-board J1939 communication interface
1 Scope
This document describes the on-board J1939 communication interface between a connected device
and mobile machines for use in earth-moving, mining and road construction applications to enable
interventional collision avoidance actions defined in ISO 21815-1 based on the SAE J1939 protocol. This
interface is intended for use by a collision avoidance system (CAS) device integrated independently
from the original machine providing intervention signals to slow down, stop or prevent motion of the
machine. The protocol defined by this document can also be used to provide input information for a
collision warning system (CWS).
This document is not intended for plug-and-play implementation of CAS or CWS on the machine.
Additional details not fully described in this document can be negotiated by the CAS or CWS
manufacturer and the machine manufacturer to enable functionality.
This document does not preclude the possibility of the machine manufacturer or the CxD manufacturer
developing alternative on-board communication interfaces.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 19014-3, Earth-moving machinery — Functional safety — Part 3: Environmental performance and test
requirements of electronic and electrical components used in safety-related parts of the control system
SAE J1939-15, Reduced Physical Layer, 250 kbits/sec, UN-Shielded Twisted Pair (UTP)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
collision warning system
CWS
system which detects intended objects in the collision risk area, evaluates the collision risk level and
provides a warning to the operator
[SOURCE: ISO 21815-1:—, 3.8]
3.2
collision avoidance system
CAS
system which detects intended objects in the collision risk area, evaluates the collision risk level and
provides interventional collision avoidance action (3.9)
[SOURCE: ISO 21815-1:—, 3.9]
3.3
CxS
CWS (3.1) or CAS (3.2) or both
[SOURCE: ISO 21815-1:—, 3.10]
3.4
CxS device
CxD
proximity detection system
device with sensors providing CxS (3.3) functions to detect objects in the proximity of the machine,
assess the collision risk level, warn the operator of the presence of object(s) for CWS (3.1), and/
or provide signals to the machine control system to initiate the appropriate interventional collision
avoidance action (3.9) on the machine for CAS (3.2)
Note 1 to entry: Proximity detection system (PDS) is a colloquial industry term for a physical device providing
CWS or CAS functionality.
3.5
on-board communication interface
bi-directional connection between a CxD (3.4) and the machine in a CWS (3.1) or CAS (3.2)
Note 1 to entry: The CxS (3.3) may utilise information sent from the machine via the on-board communication
interface to improve the estimation of the collision risk level. Only a CAS can initiate interventional collision
avoidance action (3.9) over the on-board communication interface.
3.6
register
storage location on the machine side of the on-board communication interface (3.5) that may be read and
optionally written to by the CxD (3.4)
Note 1 to entry: Changing the value of a register does not immediately initiate an interventional collision
avoidance action (3.9).
3.7
parameter
type of register (3.6) that is used to store configuration information
EXAMPLE Software revision, timeout, max speed for emergency stop.
3.8
setpoint
type of register (3.6) that is used by the machine to respond to an interventional collision avoidance
action (3.9)
EXAMPLE Minimum braking, maximum throttle, maximum speed.
3.9
action
message sent from the CxD (3.4) to the machine to change an internal register (3.6), or to initiate a
machine function
EXAMPLE Reduce speed, apply brakes, inhibit motion.
2 © ISO 2021 – All rights reserved

3.10
enquiry
message sent from the CxD (3.4) to the machine to read an internal register (3.6), or request a machine
capabilityEXAMPLE Slow down, emergency stop, controlled stop.
3.11
instruction
action (3.9) or enquiry (3.10) issued by the CxD (3.4)
3.12
reply
response (3.35) of the machine to an instruction (3.11) from the CxD (3.4)
3.13
logical group
grouping of related information or instruction (3.11) elements into a coherent message, sent from the
CxD (3.4) to the machine or from the machine to the CxD over the on-board communication interface
(3.5)
3.14
+bat
system voltage of the machine as defined by the machine manufacturer
Note 1 to entry: Typical voltages are 12 V or 24 V DC.
3.15
key switch
device used by the operator to turn on or turn off the machine
3.16
isolator switch
disconnect switch
device used by the operator to isolate the batteries or electrical supply to the machine
3.17
+bat(switched)
machine system level voltage that is turned on or off through the key switch (3.15)
3.18
+bat(un-switched)
voltage that is not affected by the state of the key switch (3.15), but is affected by the isolator switch
(3.16)
3.19
CxD harness
auxiliary wiring between the machine connector and the CxD (3.4) connector
3.20
CxD bus
CAN-bus communication path between the machine and the CxD (3.4) terminated by 120 Ohm resistors
at each end
3.21
CxD branch
machine-to-CxD bus or CxD-to-CxD bus wiring connection
3.22
PowerOn()
startup sequence for the machine that enables CxD (3.4) operation
3.23
doNegotiation()
automatic or semi-automatic process that verifies the credentials of the CxD (3.4) attached to the
machine and returns permissions for the CxD to send commands to the machine and receive machine
information
3.24
enableTimeout()
automatic process that enables an automatic timer that counts down to zero and sets a flag that there
has been a communications error on the J1939 on-board communication interface (3.5)
3.25
resetTimeout()
automatic process that resets the automatic timer and clears the error flag indicating that the J1939 on-
board communication interface (3.5) is functioning normally
3.26
doEmergencyStop()
automatic process that initiates an emergency stop on the machine
3.27
doControlledStop()
automatic process that initiates a controlled stop on the machine
3.28
doSlowDown()
automatic process that slows down the machine
3.29
doStandDown()
automatic process that brings the machine to a halted state
3.30
doBypassPropulsion()
instruction to bypass the propulsion system
3.31
doApplyPropulsionSetpoints()
activation of braking, throttle, speed setpoint (3.8) registers (3.6)
3.32
doMotionInhibit()
automatic process that prevents a machine from moving while stationary
3.33
doNormalOperation()
instruction (3.11) for the machine to continue with normal operation or return to normal operation
Note 1 to entry: This instruction has the effect of cancelling any other interventional collision avoidance action
(3.9) that is already in progress.
3.34
challenge
unique message issued by the machine to the CxD (3.4) to which a valid reply (3.12) is expected
3.35
response
reply (3.12) by the CxD (3.4) to the challenge (3.34) issued by the machine to establish trust
4 © ISO 2021 – All rights reserved

4 Symbols and abbreviated terms
PGN parameter group number (see SAE J1939)
SPN suspect parameter number (see SAE J1939)
0xHH 8-bit hexadecimal value in the range 0x00 to 0xFF
0bB 1-bit binary value in the range 0b0 to 0b1
0bBB… N-bit binary value
5 Logical interface
5.1 Logical groups
The logical connections for the on-board J1939 communication interface between the CxD and the
machine are shown in Figure 1.
Figure 1 — Overview of logical CxD-machine interface
The logical groups defined for the on-board J1939 communication interface are:
— CxD»MachineStatus – this logical group of instructions allows the CxD to read or write to machine
registers and detect the health of the communication interface.
NOTE 1 This logical group is used to provide machine status information to the CxD and allow the CxD to
inspect and modify machine registers.
Information sent over this logical group may be sent at the maximum data rate supported by the
machine.
— CxD»MachineCommand – instructions sent by CxD to machine to confirm or activate machine functions
(e.g. slow down, stop, inhibit motion).
NOTE 2 This logical group is used to initiate interventional collision avoidance actions at the specified
broadcast rate (see 7.3).
— Machine»CxDreply – response of machine to instructions sent by the CxD over CxD»MachineStatus or
CxD»MachineCommand, which may include:
— successful execution of the instruction;
— an error was encountered while executing the instruction;
— the instruction is not supported by the machine.
The machine may limit the maximum data rate over the communication interface by delaying the
response.
— Machine»CxDdata – data provided by machine to the CxD.
— Time/Date – information sent by machine to CxD or from CxD to machine to synchronise system
clocks (see 7.10).
The enquiries and actions within each of these logical groups are described more fully in 5.2 to 5.4.
5.2 Negotiation
A higher level of sequence of negotiation and credentials may be used to protect the machine against
access from an unauthorized CxD or connection of an unauthorised device to the interface. The
negotiation sequence may be independently developed by the machine manufacturer and CxD supplier
for exclusive use on a specific machine and may include:
— protocol version;
— machine model ID;
— machine generation / revision / series;
— other information defined by machine manufacturer and CxD manufacturer.
The CxD may pass credential information to the machine in a predefined sequence agreed between
the CxD manufacturer and the machine manufacturer. Basic authentication methods are described in
7.2.3.1 (refer to NEGOTIATE_NOP description in Table 8).
A mechanism for establishing trust between the machine and the CxD is described in Annex B.
The machine may refuse to reply to or acknowledge all other instructions until after the negotiation
sequence has been completed successfully.
Once negotiation has been successfully completed, the CxD shall send a PROTOCOL_NOP instruction
within the specified maximum interval to avoid a timeout of the communication link.
5.3 Initialisation
After successful completion of the negotiation sequence, the CxD should read the contents of all
registers defined on the machine and discover the capabilities of the machine using the mechanisms
described in 7.2.
The CxD may read or write to registers after startup of the machine or at any time while the machine is
running.
5.4 Operation
After negotiation and initialisation have been completed, the CxD may initiate interventional collision
avoidance actions which are supported by the machine, including:
— motion inhibit;
— emergency stop;
— controlled stop;
— slow down;
— stand down;
— bypass propulsion;
— apply propulsion setpoints;
— no operation (NOP) – do nothing.
6 © ISO 2021 – All rights reserved

The machine may not support all interventional collision avoidance actions listed here. The CxD should
discover the capabilities of the machine during initialisation.
Some interventional collision avoidance actions may require pre-conditions to be met, e.g. the machine
is stationary before motion inhibit is applied, maximum machine speed for emergency stop, valid
setpoint values provided by CxD.
Examples are shown for the PROPULSION subsystem only. Additional interventional collision avoidance
actions may be defined in other subsystems.
6 Physical interface
6.1 General
The connection between the machine and the CxD is defined in 6.2 to 6.5.
The connectors specified in 6.2 to 6.5 can be unsuitable for the specific requirements of machines
working in hazardous atmospheres. Alternative connector and connection arrangements may be used
in these cases.
6.2 Machine connector
The physical connector on the machine shall be Deutsch DT-Series 12-pin plug part DT06-12SC-EP06
1)
(Key C) shown in Figure 2 or equivalent . The pin connections and pin definitions are shown in Table 1.
Dimensions in millimetres (inches)
Figure 2 — Machine physical connector - Deutsch DT-series 12 pin, part DT06-12SC-EP06
(Key C)
1) Deutsch DT-Series 12-pin plug part DT06-12SC-EP06 (Key C) is an example of a suitable connector that
is available commercially. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of this product.
Table 1 — Machine pin connections
Pin Machine Comment
1 n/a Reserved for future use by the ISO 21815 series
2 +bat(un-switched) 10A (maximum)
3 -bat 0V/GND Common ground, 0V from battery supply
4 +bat(switched) 10 A (maximum) switched from ignition key
5 CAN HI SAE J1939 CAN-bus (High)
6 CAN LO SAE J1939 CAN-bus (Low)
7 n/a Reserved for future use by the ISO 21815 series
8 n/a Reserved for future use by the ISO 21815 series
9 n/a Reserved for future use by the ISO 21815 series
10 n/a Reserved for future use by the ISO 21815 series
11 Override A Override switch (see Table 2)
12 Override B Override switch (see Table 2)
The maximum combined load from pin 2 and pin 4 shall not exceed 10 A. An alternative source of power
should be obtained from the machine for CxS devices that exceed the combined requirements of pin 2
and pin 4.
NOTE For some machines the additional power requirement of the CxD can require modification to the
machine electrical system (e.g. larger alternator, reduction in electrical loads, changes to wiring harness).
The +bat(switched) or +bat(un-switched) battery lines should not be routed around the isolator switch
to connect directly to the battery.
The machine should provide protection for short circuit or overcurrent fault conditions on pin 2 and pin
4, e.g. circuit breaker, resettable fuse, fuseable link.
Alternate compatible connector body styles may be used depending on the preferred method of
connection, e.g. bulkhead / chassis, in-line connection.
All unused cable entries and cavities should be plugged to preserve the IP rating of the connector.
6.3 CxD connector
The physical connector on the CxD shall be Deutsch DT-series 12-pin receptacle part DT04-12PC-BE02
2)
(Key C) shown in Figure 3 or equivalent . The pin connections are identical to the machine connector
(see Table 1).
2) Deutsch DT-series 12-pin receptacle part DT04-12PC-BE02 (Key C) is an example of a suitable connector that
is available commercially. This information is given for the convenience of users of this document and does not
constitute an endorsement by ISO of this product.
8 © ISO 2021 – All rights reserved

Figure 3 — CxD physical connector - Deutsch DT-series 12 pin, part DT04-12PC-BE02 (Key C)
The maximum combined load from pin 2 and pin 4 shall not exceed 10 A.
Alternate compatible connector body styles may be used depending on the preferred method of
connection, e.g. bulkhead / chassis, in-line connection.
6.4 Override switch
An override signal may be implemented on the machine to notify the CxD that the operator has
determined that the collision avoidance action may be overridden.
If provided by the machine, the override signal shall be implemented by parity switches connected to
override A (pin 11) and override B (pin 12) with the states defined in Table 2.
Table 2 — CxD Override switch
Override A Override B
Value
Pin 11 Pin 12
Open Open Connection fault
Open Closed Override enabled
Closed Open Override disabled
Closed Closed External fault
Key
Closed  short to 0V/GND
Open    machine voltage (e.g. +bat)
If provided by the machine, the maximum sinking load on either override A or override B shall be 1 A at
the system voltage of the machine as defined by the machine manufacturer.
NOTE Typical voltages for +bat (un-switched) and +bat (switched) are 12 V or 24 V DC.
If provided by the machine, the override A and override B contacts shall be maintained in the closed
state when the override signal is indeterminate (e.g. during the startup sequence).
The override signal can be provided by a momentary action change-over switch, relay contacts, low
impedance electronic switch with de-bounce provisions, or other means. Refer to Annex C for example
implementations of the override functionality.
Transient states lasting less than 100 ms shall be ignored by the CxD.
6.5 Physical layer
The physical layer shall comply with SAE J1939-15. Both the machine connector and the CxD connector
shall be CxD branches from the CxD harness as shown in Figure 4.
Figure 4 — Physical layer
The topology for the CxD harness should be a direct point to point connection with termination resistors
at each end.
The CxD harness should be separated from the machine control bus by a suitable gateway.
The use of unshielded twisted pair (UTP) for the physical layer of the CxD harness shall meet the
requirements defined in SAE J1939-15, including:
a) Connection of the CxD device to the CxD bus shall not exceed the maximum permitted number of
nodes – typically 10 nodes maximum. The machine manufacturer shall state the number of nodes
attached to the aux CxD bus in the factory default configuration of the machine.
b) Connection of the CxD device to the CxD bus shall not exceed the maximum physical bus length
(40 m) and CxD branch limits (3 m). If the physical length of the CxD harness in the factory default
configuration of the machine exceeds 1 m, the machine manufacturer shall state any physical
limitations that should be taken into account before connection of the CxD.
The physical layer consisting of the CxD and CxD harness (e.g. conduit, braid, cable ways) shall meet the
environmental protection requirements of ISO 19014-3.
7 J1939 communication protocol
7.1 General
The connections for the on-board communication interface between the CxD and machine shown in
Figure 1 allows information to be passed between the CxD and the machine within the logical groups
defined in Table 3. The functions provided within each logical group (for a specific subsystem, if
specified) are shown in the right columns.
10 © ISO 2021 – All rights reserved

Table 3 — Information passed via logical interface
Logical group Description Registers
CxD»MachineStatus
Actions and enquiries sent by CxD to machine Status
that modify machine configuration
Register index
Register select
Register value
CxD»MachineCommand
Actions and enquiries sent by CxD to machine Command
that affect machine state
Register index
Register select
Register value
Machine»CxDreply
Response of machine to CxD actions or en- Status / Command
quiries
Register index
Register format
Register value
Machine»CxDdata
Data provided by machine to CxD PROPULSION subsystem:
— Speed
— Direction
— Gear position
— Payload status
— Traction control
— Rollback status
— Manual override
— Machine pitch
— Machine roll
Machine»CxDstatus
Actions and enquiries sent by machine to CxD Reserved for future use by the
that modify CxD configuration ISO 21815 series
Machine»CxDcommand
Actions and enquiries sent by machine to CxD Reserved for future use by the
that affect CxD state ISO 21815 series
CxD»MachineReply
Response of CxD to machine actions or en- Reserved for future use by the
quiries ISO 21815 series
CxD»MachineData
Data provided by the CxD to the machine Reserved for future use by the
ISO 21815 series
TD
Time/Date SAE J1939
7.2 PGN: CxD»machine status
7.2.1 General
The structure of PGN:CxD»MachineStatus is shown in Figure 5. Additional details are provided in 7.2.2
and 7.2.3.
Figure 5 — Structure of PGN:CxD»MachineStatus
Refer to Annex A for typical communication sequences and Table A.1 and Table A.2 for examples of CxD
instruction and machine responses.
7.2.2 PGN description
The CxD shall send status information to the machine via the PGN with the parameters shown in Table 4
and as defined in 7.2.3.
12 © ISO 2021 – All rights reserved

Table 4 — PGN:CxD»MachineStatus parameters
Parameter Description
PGN number 61968
PGN type PDU2_FAST
Acronym CXD1
Data length 8 bytes
Multipacket message No
a
Broadcast rate 10 ms
Message priority 3
a
The machine manufacturer may limit the rate that
instructions are executed over this PGN by delaying the reply
via PGN:Machine»CxDreply.
This PGN is intended to be used by the CxD to transmit a burst of information to the machine not
exceeding the specified broadcast rate.
The CxD may remain silent between bursts.
The CxD shall maintain the communication link in an active state by periodically sending a PROTOCOL_
NOP instruction (see Table 8) to avoid a timeout when no other instructions are being sent.
The SPN’s associated with PGN:CxD»MachineStatus are shown in Table 5.
Table 5 — SPNs for PGN:CxD»MachineStatus
SPN SPN Description
Status 1.1 8 bits Action or enquiry sent from CxD to the machine
Register index 2.1 8 bits Index to machine register
Register select 3.1 8 bits Used in conjunction with SPN:RegisterIndex to set TAG
values that enable multiple matching setpoints to be exe-
cuted via PGN:CxD»MachineCommand.
Register value_0 4.1 8 bits Least significant byte of register value specified by
SPN:RegisterIndex
Register value_1 5.1 8 bits Next significant byte of register value specified by
SPN:RegisterIndex
Register value_2 6.1 8 bits Next significant byte of register value specified by
SPN:RegisterIndex
Register value_3 7.1 8 bits Most significant byte of register value specified by
SPN:RegisterIndex
Message identifier 8.1 8 bits Identifier for message originated by the CxD e.g. incre-
menting counter
NOTE  Unless specified otherwise, least-significant-first byte ordering is used for multi-byte transfers
with individual bytes preserving J1939 bit ordering (big-endian).
The standard SAE J1939 reserved codes (see Table 6) may be used in SPN:RegisterIndex (offset = 2),
SPN:RegisterSelect (offset = 3) and where noted in 7.2.3. Generally, the reserved codes are used
to indicate missing data or an error. The use of these reserved codes in SPN:Status (offset = 1) and
SPN:MessageIdentifier (offset = 8) is not permitted.
Offset
(byte.bit)
SPN length
Table 6 — Reserved SPN values
Code MESSAGE_STATUS
0xFA GENERAL_FAULT
0xFE GENERAL_ERROR
0xFF IGNORE
Each SPN within PGN:CxD»MachineStatus is defined in more detail in 7.2.3.
7.2.3 SPN structure
7.2.3.1 SPN: Status
7.2.3.1.1 General
This SPN is used by the CxD to send an enquiry or action to a specified subsystem of the machine. Refer
to Figure 6 for a description of the SUB_SYSTEM bitfield.
The typical negotiation, initialisation and operation message sequences for this SPN are described in
Annex A.
Figure 6 — Subsystem bitfields in SPN:Status
The valid enumerations for the SUB_SYSTEM bitfield are listed in Table 7.
NOTE The least significant 4-bits of SPN:Status are defined separately for each subsystem.
Table 7 — SUB_SYSTEM bitfield codes
SUB_ SYS-
Name Description
TEM
0b000 PROPULSION Propulsion subsystem
0b001 RESERVED_1 Reserved for future use by the ISO 21815 series
0b010 RESERVED_2 Reserved for future use by the ISO 21815 series
0b011 RESERVED_3 Reserved for future use by the ISO 21815 series
0b100 RESERVED_4 Reserved for future use by the ISO 21815 series
0b101 RESERVED_5 Reserved for future use by the ISO 21815 series
0b110 USER_DEFINED Available for customisation by the end user or application
0b111 PROTOCOL Protocol subsystem
14 © ISO 2021 – All rights reserved

7.2.3.1.2 SUB_SYSTEM: PROTOCOL
The format of SPN:Status for the PROTOCOL subsystem is shown in Figure 7.
Figure 7 — PROTOCOL subsystem bitfields – SPN:Status
The valid enumerations of the bitfields in SPN:Status for the PROTOCOL subsystem are listed in Table 8
and Table 9.
Table 8 — ENQ7 bitfield codes in PROTOCOL subsystem – SPN:Status
ENQ7 Name Description
0b000 PROTOCOL_ This enquiry is used by the CxD after successful completion of the negotiation
sequence to indicate to the machine that the CxD is healthy when no other
NOP
active instructions are being sent to the machine. The machine may silently
ignore this enquiry if negotiation has not been completed successfully.
Use the NEGOTIATE_NOP enquiry to verify the connection between the CxD
and the machine if negotiation has not been completed.
The machine may force the CxD to reinitiate the negotiation sequence if no
valid instructions are sent within the time specified in register INSTRUC-
TION_TIMEOUT of the protocol subsystem.
0b001 NEGOTIATE_ This enquiry is used by the CxD to indicate to the machine that the CxD
is active and ready to perform a negotiation with the machine and the
NOP
machine shall provide information to the CxD on the current state of the
interface.
The values in SPN:RegisterIndex and SPN_RegisterSelect and
SPN:RegisterValue0.3 are ignored for this enquiry and should be set to
zero (0x00).
The machine shall always respond to a NEGOTIATE_NOP enquiry with the
following information in SPN:RegisterValue0.3:
RegisterValue0: J1939 = INTERFACE_STATE
RegisterValue1: REG_FORMAT = format of a non-zero
NEGOTIATION_SEED determined by the machine
and NEGOTIATION_KEY to be provided by the CxD
RegisterValue2: UINT8 = Authentication method:
— 0x00: no authentication;
— 0x01: SEED/KEY combination;
— 0x02: SEED/KEY with tokenisation of commands;
— 0xE0-0xEF: user defined;
— other values reserved for future use by this document.
RegisterValue3: Reserved for future use by this document.
Table 8 (continued)
ENQ7 Name Description
0b010 NEGOTIATE_ A higher level of sequence of negotiation and credentials may be used to
protect the machine against access from an unauthorized CxD or connection
ENQ
of an unauthorised device to the interface. The negotiation sequence may be
independently developed by the machine manufacturer and CxD supplier for
exclusive use on a specific machine.
This enquiry may be used by the CxD to pass credential information to the
machine in a predefined sequence agreed between the CxD and machine
manufacturer.
The negotiation sequence may pass up to 32-bits per message using one of
the formats specified in Table 36.
A generic example negotiation sequence starts with the CxD requesting the seed
value for the negotiation from the machine by specifying SPN:RegisterIndex
= NEGOTIATION_SEED.
The machine should respond with the non-zero seed value in
SPN:RegisterValue0.3 in the format indicated in the reply to the NEGO-
TIATE_NOP enquiry.
The CxD can then specify the matching key value expected by the machine
in SPN:RegisterValue0.3. The machine should indicate if an error occurs
by replying with the appropriate value in the REG_FORMAT bitfield (see
Table 36). The machine should preve
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