ISO 20794-2:2020

Road vehicles — Clock extension peripheral interface (CXPI) — Part 2: Application layer

This document describes the application layer protocol including the application measurement and control data management, message transfer and fault management. The application and application layer contain the following descriptions: — message structure; — communication method; — network management (optional); — measurement and control data; and — error handling. This document also specifies: — the service interface; and — the service interface parameters.

Véhicules routiers — Interface du périphérique d'extension d'horloge (CXPI) — Partie 2: Couche Application

General Information

• Status: Published
• Publication Date: 04-Feb-2020
• ICS: 43.040.15 - Car informatics. On board computer systems
• Technical Committee: ISO/TC 22/SC 31 - Data communication
• Drafting Committee: ISO/TC 22/SC 31/WG 3 - In-vehicle networks
• Current Stage: 6060 - International Standard published
• Start Date: 05-Feb-2020
• Due Date: 07-Dec-2019
• Completion Date: 05-Feb-2020

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 20794-2
First edition
2020-02
Road vehicles — Clock extension
peripheral interface (CXPI) —
Part 2:
Application layer
Véhicules routiers — Interface du périphérique d'extension d'horloge
(CXPI) —
Partie 2: Couche Application
Reference number
ISO 20794-2:2020(E)
©
ISO 2020

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ISO 20794-2:2020(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ISO 20794-2:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 3
4.1 Symbols . 3
4.2 Abbreviated terms . 3
5 Conventions . 4
6 Introduction to application and application layer . 4
6.1 Application properties . 4
6.2 Application layer properties . 4
6.3 Message transmission . 4
6.4 Communication methods . 4
6.5 Message types . 5
6.6 Error handling . 5
7 Service interface parameters (SIP) . 5
7.1 SIP — General . 5
7.2 SIP — Data type definitions . 5
7.3 SIP — Mtype, message type . 6
7.4 SIP — ReqId, request identifier . 6
7.5 SIP — ReqTypeId, request type identifier . 6
7.6 SIP — PDU, protocol data unit . 6
7.7 SIP — Length, length of PDU . 6
7.8 SIP — ev_wakeup_ind, event wake-up indication (optional) . 6
7.9 SIP — cmd_wakeup_req, command wake-up request . 7
7.10 SIP — NMInfo, network management information . . 7
7.11 SIP — SCT, sequence count . 8
7.12 SIP — Result, result . 8
8 SI — Service interface (SI) definition to application and lower OSI layers .8
8.1 SI — A_Data.req and A_Data.ind service interface . 8
8.2 SI — A_Data.req and A_Data.ind service interface parameter mapping . 9
9 Application (APP) . 9
9.1 APP — Message exchange . 9
9.2 APP — Communication methods . 9
9.2.1 APP — General . 9
9.2.2 APP — Event-triggered method .10
9.2.3 APP — Polling method . .10
9.3 APP — Network management (NM) .11
9.3.1 APP — General .11
9.3.2 APP — Normal, standby, and sleep states .12
9.3.3 APP — Normal state .13
9.3.4 APP — Sleep state (optional) .14
9.3.5 APP — Standby state (optional) .14
9.3.6 APP — Wake-up/sleep function (optional) .14
9.3.7 APP — Wake-up/sleep sequence parameter .24
9.4 APP — Multi clock master sequence processing .24
9.5 APP — Measurement and/or control data .25
9.5.1 APP — Publisher and subscriber data .25
9.5.2 APP — Measurement and/or control data management .26
9.5.3 APP — Measurement and/or control data types.26
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9.5.4 APP — Measurement and/or control data consistency .26
9.5.5 APP — Assignment of ReqId . .27
9.5.6 APP — Priority of ReqId .27
9.6 APP — Error handling .28
9.6.1 APP — General .28
9.6.2 APP — CXPI network error.28
9.6.3 APP — Network management information .29
9.6.4 APP — SCT, sequence count (optional) .30
9.6.5 APP — Sequence count (SCT) error (optional) .31
9.6.6 APP — Transmission prohibition . .31
9.6.7 APP — Retransmission . .32
9.6.8 APP — Error notification on CXPI network (optional).32
10 Application layer (AL) .33
10.1 AL — Message exchange .33
10.2 AL — Message structure .34
10.3 AL — Request protected type identifier field .35
10.4 AL — Request protected identifier field .35
10.4.1 AL — General .35
10.4.2 AL — Judgment of received message .35
10.5 AL — Response field (A_PDU) .35
10.5.1 AL — General .35
10.5.2 AL — A_PDU . .35
10.5.3 AL — Wake-up indication and request .36
10.6 AL — Error detection .36
Bibliography .37
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ISO 20794-2:2020(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.
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
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
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 22, Road vehicles, Subcommittee SC 31,
Data communication.
A list of all parts in the ISO 20794 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.
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ISO 20794-2:2020(E)

Introduction
ISO 20794 (all parts) specifies the application (partly), application layer, transport layer, network
layer, data link layer, and physical layer requirements of an in-vehicle network called "clock extension
peripheral interface (CXPI)".
CXPI is an automotive low-speed single-wire network. It is an enabler for reducing vehicle weight and
fuel consumption by reducing wire counts to simple devices like switches and sensors.
CXPI serves as and is designed for automotive control applications, for example door control group,
light switch, and HVAC (Heating Ventilation and Air Conditioning) systems.
The CXPI services, protocols, and their key characteristics are specified in different parts according to
the OSI layers.
— Application and application layer:
— application measurement and control data communication to exchange information between
applications in different nodes based on message communication;
— wake-up and sleep functionality;
— two kinds of communication methods can be selected at system design by each node:
i) the event-triggered method, which supports application measurement- and control-based
(event-driven) slave node communication, and
ii) the polling method, which supports slave node communication based on a periodic master
schedule;
— performs error detection and reports the result to the application;
— application error management.
— Transport layer and network layer:
— transforms a message into a single packet;
— adds protocol control information for diagnostic and node configuration into each packet;
— adds packet identifier for diagnostic and node configuration into each packet;
— performs error detection and reports the result to higher OSI layers.
— Data link layer and physical layer:
— provides long and short data frames;
— adds a frame identifier into the frame;
— adds frame information into the frame;
— adds a cyclic redundancy check into the frame;
— performs byte-wise arbitration and reports the arbitration result to higher OSI layers;
— performs frame type detection in reception function;
— performs error detection and reports the result to higher OSI layers;
— performs Carrier Sense Multiple Access (CSMA);
— performs Collision Resolution (CR);
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ISO 20794-2:2020(E)

— generates a clock, which is transmitted with each bit to synchronise the connected nodes on the
CXPI network;
— supports bit rates up to 20 kbit/s.
To achieve this, it is based on the Open Systems Interconnection (OSI) Basic Reference Model specified
[1]
in ISO/IEC 7498-1 and ISO/IEC 10731 , which structures communication systems into seven layers.
Figure 1 illustrates an overview of communication frameworks beyond the scope of this document
including related standards:
— vehicle normal communication framework, which is composed of this document, and ISO 20794-5;
[3]
— vehicle diagnostic communication framework, which is composed of ISO 14229-1, ISO 14229-2 ,
[4]
and ISO 14229-8 ;
[6]
— presentation layer standards, e.g. vehicle manufacturer specific or ISO 22901-1 ODX ;
— lower OSI layers framework, which is composed of ISO 20794-3, ISO 20794-4, ISO 20794-6, and
ISO 20794-7 conformance testing.
[4]
ISO 20794 (all parts) and ISO 14229-8 are based on the conventions specified in the OSI Service
Conventions (ISO/IEC 10731) as they apply for all layers and the diagnostic services.
Figure 1 — ISO 20794 documents reference according to OSI model
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INTERNATIONAL STANDARD ISO 20794-2:2020(E)
Road vehicles — Clock extension peripheral interface
(CXPI) —
Part 2:
Application layer
1 Scope
This document describes the application layer protocol including the application measurement and
control data management, message transfer and fault management.
The application and application layer contain the following descriptions:
— message structure;
— communication method;
— network management (optional);
— measurement and control data; and
— error handling.
This document also specifies:
— the service interface; and
— the service interface parameters.
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/IEC 7498-1, Information technology — Open Systems Interconnection — Basic Reference Model: The
Basic Model
ISO 20794-3, Road vehicles — Clock extension peripheral interface (CXPI) — Part 3: Transport layer and
network layer
ISO 20794-4, Road vehicles — Clock extension peripheral interface (CXPI) — Part 4: Data link layer and
physical layer
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 20794-3, ISO 20794-4,
ISO/IEC 7498-1, and the following 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/
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3.1
clock master
node that transmits clock (3.4) to the lower OSI layers (3.2)
3.2
lower OSI layer
below the application layer
3.3
master node
node that provides the schedule (3.10) master management (including polling method), the primary
clock (3.6), and optionally the sleep message transmission management
3.4
clock
pulse that synchronises all nodes
3.5
normal state
state which enables transmission and reception of messages
3.6
primary clock
clock (3.4) that is provided by the master node (3.3)
3.7
publisher
node providing a message response containing application measurement and/or control data
3.8
request identifier
ReqId
parameter that requests dedicated measurement and/or control data
3.9
request type identifier
ReqTypeId
parameter that enables the polling method for dedicated measurement data and/or control data
3.10
schedule
origin of periodic message transmission
3.11
secondary clock
clock (3.4) that is provided by a dedicated slave node (3.13)
3.12
sequence
transmission and reception procedure of messages
3.13
slave node
node other than master node (3.3)
3.14
subscriber
master or slave node (3.13) that receives the data within a message
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3.15
wake-up pulse
stimulus initiated by a node used for wake-up of other nodes
4 Symbols and abbreviated terms
4.1 Symbols
t time that the master node requests the clock to the lower OSI layers at the latest
clock_start_m
t time that the master node stops to request the clock after master node receives the
clock_stop_m
sleep message notification
t judgment time of the CXPI network error
cxpi_network_error
t time that each slave node transits to sleep state after the node receives the sleep
sleep_s
message notification
t minimum time that master node starts the request of any request field first for the
wakeup_m
wake-up sequence
t time that slave node starts the request of the second wake-up pulse after request of
wakeup_recovery_s
the first wake-up pulse
t maximum time until the slave node wakes up by the wake-up sequence
wakeup_s
t maximum time until master node starts the request of any request field (ReqId) or
wakeup_schedule_m
request field (ReqTypeId) first for the wake-up sequence
4.2 Abbreviated terms
AL application layer
APP application
CRC cyclic redundancy check
DLC data length code
ECU electronic control unit
LSB least significant bit
MSB most significant bit
Mtype message type
NMInfo network management information
NormalCom normal communication
OSI open systems interconnection
param parameter
PDU protocol data unit
ReqId request identifier
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ReqTypeId request type identifier
SCT sequence count
SI service interface
SIP service interface parameter
5 Conventions
This document is based on the conventions discussed in the OSI Service Conventions as specified in
ISO/IEC 10731.
6 Introduction to application and application layer
6.1 Application properties
The application has the following properties:
— communication methods;
— message types;
— network management (optional wake-up, sleep);
— state management (state machine);
— measurement and/or control data; and
— error handling.
6.2 Application layer properties
The application layer has the following properties:
— message exchange;
— message structure; and
— service interface and parameters.
6.3 Message transmission
A message consists of a request field and a response field. The node that corresponds to a request
identifier composed in the request field can transmit the response field.
6.4 Communication methods
Two communication methods are supported:
— Event-triggered method
Each node can request a request protected identifier field and response field based on an internal
event occurrence.
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— Polling method
The master node requests a request protected type identifier field (event request in polling
method) to the lower OSI layers and then each node can transmit a request protected identifier
field. The node corresponding to the request protected identifier field transmits the response field.
6.5 Message types
The application layer supports the following message types:
— request message field;
— response message field; and
— request sleep message field.
6.6 Error handling
The error handling is based on the following measures:
— CXPI network errors; and
— sequence count error (optional).
7 Service interface parameters (SIP)
7.1 SIP — General
The following subclauses specify the service interface parameters and data types, which are used by
the application and application layer services.
7.2 SIP — Data type definitions
This requirement specifies the data type definitions of the CXPI service interface parameters.
REQ 0.1 SIP — Data type definitions
The data types shall be in accordance to:
— Enum = 8-bit enumeration
— Unsigned Byte = 8-bit unsigned numeric value
— Unsigned Word = 16-bit unsigned numeric value
— Byte Array = sequence of 8-bit aligned data
— 2-bit Bit String = 2-bit binary coded
— 8-bit Bit String = 8-bit binary coded
— 16-bit Bit String = 16-bit binary coded
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7.3 SIP — Mtype, message type
This requirement specifies the message type parameter values of the CXPI service interface.
REQ 0.2 SIP — Mtype, message type
The Mtype parameter shall be of data type Enum and shall be used to identify the message type and range of
address information included in a service call.
Range:  [NormalCom, DiagNodeCfg]
7.4 SIP — ReqId, request identifier
This requirement specifies the request identifier parameter values of the CXPI service interface.
REQ 0.3 SIP — ReqId, request identifier
The ReqId parameter shall be of data type Unsigned Byte and shall contain the request identifier.
Range:  [01 to 7F ]
16 16
7.5 SIP — ReqTypeId, request type identifier
This requirement specifies the request type identifier parameter value of the CXPI service interface.
REQ 0.4 SIP — ReqTypeId, request type identifier
The ReqTypeId parameter shall be of data type Unsigned Byte and shall contain the request type identifier.
Range:  [00 ] (fixed value)
16
7.6 SIP — PDU, protocol data unit
This requirement specifies the protocol data unit parameter values of the CXPI service interface.
REQ 0.5 SIP — PDU, protocol data unit
The PDU parameter shall be of data type Byte Array and shall contain the packet data (PDU) content of the
request or response packet to be transmitted/received.
Range:  [00 to FF ]
16 16
7.7 SIP — Length, length of PDU
This requirement specifies the length of PDU parameter value of the CXPI service interface.
REQ 0.6 SIP — Length, length of PDU
The Length parameter shall be of data type Unsigned Byte and shall contain the length of the PDU
to be requested transmission/notified reception. If Mtype = NormalCom then range [00 to FF ].
16 16
7.8 SIP — ev_wakeup_ind, event wake-up indication (optional)
This requirement specifies the event wake-up indication parameter values of the CXPI service interface.
REQ 0.7 SIP — ev_wakeup_ind, event wake-up indication (optional)
The ev_wakeup_ind parameter shall be of data type Enum and shall include the event wake-up indication inf
...