Road vehicles - Controller area network (CAN) - Part 1: Data link layer and physical signalling
1 Scope
This document specifies the characteristics of setting up an interchange of digital information between modules implementing the CAN data link layer. Controller area network is a serial communication protocol, which supports distributed real-time control and multiplexing for use within road vehicles and other control applications.
This document specifies the Classical CAN frame format and the newly introduced CAN Flexible Data Rate Frame format. The Classical CAN frame format allows bit rates up to 1 Mbit/s and payloads up to 8 byte per frame. The Flexible Data Rate frame format allows bit rates higher than 1 Mbit/s and payloads longer than 8 byte per frame.
This document describes the general architecture of CAN in terms of hierarchical layers according to the ISO reference model for open systems interconnection (OSI) according to ISO/IEC 7498-1. The CAN data link layer is specified according to ISO/IEC 8802-2 and ISO/IEC 8802-3.
This document contains detailed specifications of the following (see Figure 2):
——logical link control sub-layer;
——medium access control sub-layer;
——physical coding sub-layer.
There are three implementation options. They are the following:
——support of the Classical CAN frame format only, not tolerating the Flexible Data Rate frame format;
——support of the Classical CAN frame format and tolerating the Flexible Data Rate frame format;
——support of the Classical CAN frame format and the Flexible Data Rate frame format.
The last option is recommended to be implemented for new designs.
Note: Implementations of the first option can communicate with implementations of the third option only as long as the Flexible Data Rate frame format is not used; otherwise, Error Frames are generated. There are opportunities to run implementations of the first option also in CAN networks using the Flexible Data Rate frame format, but these are not in the scope of this document.
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/IEC 7498-1 Information technology - Open systems interconnection - Basic reference model: The basic model
GB/T 9387.1-1998 Information technology-Open Systems Interconnection-Basic Reference Mode l- Part 1: The Basic Model (ISO/IEC 7498-1: 1994, IDT)
ISO/IEC 8802-2 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 2: Logical link control
Note: GB/T 15629.2-2008 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 2: Logical link control (ISO/IEC 8802-2:1998, IDT)
ISO/IEC 8802-3 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Standard for Ethernet
Note: GB/T 15629.3-2014 Information technology - Telecommunications and information exchange between systems - Local and metropolitan area networks - Specific requirements - Part 3: Carrier sense multiple access with collision detection(CSMA/CD)access method and physical layer specif (ISO/IEC 8802-3: 2000, MOD)
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
arbitration phase
phase where the nominal bit time is used
3.2
bit stuffing
frame coding method providing bus state changes required for periodic resynchronization when using an NRZ bit representation
Note: Whenever the transmitting logic encounters a certain number (stuff width) of consecutive bits of equal value in the data, it automatically stuffs a bit of complementary value - a stuff bit - into the outgoing bit stream. Receivers de-stuff the Data Frames and the Remote Frames, ie. the inverse procedure is carried out.
3.3
bus
topology of a communication network, where all nodes are reached by passive links which allow transmission in both directions
3.4
bus comparator
electronic circuit converting physical signals used for transfer across the communication medium back into logical information or data signals
3.5
bus driver
electronic circuit converting information or data signals into physical signals so that these signals can be transferred across the communication medium
3.6
bus state
one of two complementary logical states: dominant or recessive
Note: The dominant state represents the logical 0, and the recessive state represents the logical 1. During simultaneous transmission of dominant and recessive bits, the resulting bus state is dominant. When no transmission is in progress, the bus is idle. During idle time, it is in recessive state
3.7
classical base frame format
format for Data Frames or Remote Frames using an 11-bit identifier, which are transmitted with one single bit rate and up to and including 8 data bytes
3.8
classical extended frame format
format for Data Frames or Remote Frames using a 29-bit identifier, which are transmitted with one single bit rate and up to and including 8 data bytes
3.9
classical frame
Data Frame or Remote Frame using the Classical Base Frame Format or the Classical Extended Frame Format
3.10
content-based arbitration
CSMA arbitration procedure resolving bus- contention when multiple nodes simultaneously access the bus
3.11
data bit rate
number of bits per time during data phase, independent of bit encoding/decoding
3.12
data bit time
duration of one bit in data phase
3.13
data frame
frame containing user data (e.g. one or more signals or one or more suspect parameters of one or more process data)
3.14
data phase
phase where the data bit time is used
3.15
edge
difference in bus-states between two consecutive time quanta
3.16
error frame
frame indicating the detection of an error condition
3.17
FD enabled
able to receive and to transmit FD Frames, as well as Classical Frames
3.18
FD base frame format
format for Data Frames using an 11-bit identifier, which are transmitted with a flexible bit rate and up to and including 64 data bytes
3.19
FD extended frame format
format for Data Frames using a 29-bit identifier, which are transmitted with a flexible bit rate and up to and including 64 data bytes
3.20
FD frame
data Frame using the FD Base Frame Format or FD Extended Frame Format
3.21
FD intolerant
only able to receive or to transmit Classical Frames, disturbing FD Frames
3.22
FD tolerant
not able to receive or to transmit FD Frames but not disturbing them
3.23
frame
protocol Data Unit of the data link layer specifying the arrangement and meaning of bits or bit fields in the sequence of transfer across the transmission medium
3.24
handle
hardware object label of one or multiple LLC frames (LPDU)
3.25
higher-layer protocol
protocol above the Data Link Layer protocol according to the Open System Interconnection model
[SOURCE: ISO/IEC 7498-1]
