top of page
Writer's pictureInflux Technology

CAN VS CAN FD - Know The Difference

CAN FD is an advanced version of CAN. The significant difference lies in the data rate it can offer. Original CAN offers 11-bit (standard) and 29-bit (extended) data rates, whereas CAN FD offers flexible data rates, ranging from 0-64 bytes per frame. BOSCH developed both to support the ever-growing need for data and technology in the automotive industry. BOSCH originally made the Controlled Area Network Bus (CAN Bus), a communication protocol for automotive applications. With vehicle innovation and multiple ECU's coming into the picture, there was a need for a communication method that could cope with ever-growing complexity, speed, and lots of data. CAN bus played an essential role, preventing the need for miles of wire for communication between different modules. On the other hand, CAN FD was released as an advancement to the original CAN-Bus protocol when the features offered by the original CAN started falling short of the technology it had to support. CAN Flexible Data rate (specified in ISO 11898-1:2015) is practically a more capable CAN. This flexible signal transmission provides automotive electronics communication with increased bandwidth, and all the required functionality cost-effectively. Moreover, it offers upgradation to almost every feature CAN holds and is a better alternative for more advanced data and bandwidth requirements. The original CAN 2.0 bus has many features that make it an ideal choice for applications where the number of ECU’s is more and the bandwidth utilization is less. CAN bus supports a maximum message payload of 8 bytes per frame at a maximum data rate of 1Mbps. CAN FD supports a flexible message payload, ranging from 0, 8, 12, 16, 20, 24, 32, 48, 64 bytes per frame at 2, 5 and 8 Mbps. The CAN FD Protocol also has two independent bit rates for the arbitration and data phases. The arbitration phase use the same bit timing as the original CAN, but the data bit rate is either similar or higher than the arbitration bit rate.

The below table consists of a few basic differences between a original CAN and CAN FD:

CAN: Controller Area Network Bus (CAN) a communication protocol for automotive applications. /  Offers fixed DLC rate of 8 bytes. /  Ideal choice for applications where the number of ECUs is more and the bandwidth utilisation is less. / Offers maximum data rate of 1Mbps./ No upward compatibility. CAN FD: Controlled Area Network with Flexible Data Bus (CAN FD). Offers an upgrade to almost every feature of CAN. / Supports a flexible message payload ranging from 0 to 64 bytes. /  Flexible signal transmission provides better functionality for advanced data and bandwidth applications. / Offers 2, 5 and 8Mpbs of data rates. /  Downward compatible with original CAN.

There are many more differences that can be understood by knowing both the technologies in detail. The knowledge of frame formats, error handling techniques, and other features give a clearer picture of how one differs from the other.

Frame Formats:


Frame Format for a standard CAN bus (11 bit)

ARBITRATION FIELD   ADDRESS FIELD   BUS idle in recessive state   DATA   SOF 12245   891011TDRSRY 1   CONTROL FIELD   T DLC   STANDARD CAN DATA FRAME   BUS ide in recessive srate   CRC ACK EOF   SOF-Start of Frame   RTR-Remate Request Frame   IDE-Identifier Extension Bit   RSRV Reserve bit   DILC Data Length Code   CRC-Cyclic Redundancy Check   ACK-Acknowledgement bit   EOF-End of Frame

  • SOF: Start of Frame. Marks the beginning of the data frame. (A dominant 0)

  • ADDRESS FIELD: This field decides the priority of the data. The lower the address higher the priority. An address with a maximum number of dominant "0" will hold the highest priority. No two nodes can transmit the same message address at the same time.

  • RTR: Remote Transmission Request is used to request data from the nodes that are not needed to send the data continuously. This is used if any node wishes to communicate with another specific node. This directly reduces congestion on the bus as direct communication takes place between the nodes.

  • ARBITRATION FIELD: The arbitration process is the one that helps in deciding which node gets to play master for a given point of time. Any node that transmits a logical "1" when another node transmits a logical 0 "drops out" or loses the arbitration. This means that the node that transmits the first "1" loses arbitration; a dominant "0" always wins. The node that fails arbitration re-queues its message for re-transmission, and the CAN frame bit-stream continues without error until only one node is left transmitting.

  • IDE: Identifier Extension Bit is for future use/extension. A recessive IDE will result in another 18 bits of the address.

  • RSRV: Reserve Bit. As the name suggests, it is kept for future up-gradations. • DLC: Data Length Code (0-8 bytes).

  • DATA: User-defined data (0-64 bits).

  • CRC: Cyclic Redundancy Check for error/data corruption detection.

  • ACK: Acknowledgement by the receiving end.

  • EOF: End of Frame (7s bit recessive "1" s)


Frame Format for CAN FD

BUS idle in recessive state   SOF IDENTIFIER   RIEFBE RDDDRS SELFSI   DATA LENGTH CODE (4bit)   DATA (0-64 bytes)   15, 17 OR 21 BIT CRC   CAAE RCCO CKKF D D   INTER FRAME SPACE (3bit)   BUS idle in recessive state   CAN FD DATA FRAME   SOF Start of Frame   RRS Remote Request Substitution   IDE Identifier Extension Bit   EDL-Extended Data Length   FDF Flexible Data Rate Format   BRS-Bit Rate Switch   ESI Error State Indicator   CRCD-CRC Delimiter   ACKD-Acknowledgement Delimiter has context menu

The Frame Formats for original CAN and CAN FD may not seem very different. But a few added fields in a CAN FD frame format are not present in the CAN bus.


  • RRS: Remote Request Substitution (always a dominant 0). The remote frames are not at all supported in CAN FD. (In original CAN, there is RTR (Remote Transmission Request) for identifying the data frames and remote frames)

  • EDL: Extended Data Length (always a recessive 1) for managing larger payloads and faster bit-rates in CAN FD.

  • FDF: Flexible Data Rate Format (always a recessive 1) used to indicate Flexible data frame format usage.

  • BRS: Bit Rate Switch helps determine the bit rate of a data frame. 1. Dominant 0 signifies that the arbitration rate for the CAN FD data frame is up to 1Mbit/sec.

    2. Recessive 1 signifies a higher/faster arbitration rate for the CAN FD data frame ranging up to 5Mbit/sec.


  • ESI: Error State Indicator

    1. A dominant 0 indicates the error-active mode.

    2. A recessive 1 indicates the error-passive mode.


  • DLC: Data Length Code is a 4-bit code in CAN FD which denote the number of data bytes in the frame. (DLC values ranging from 1001 to 1111 are used to specify the data lengths of 12, 16, 20, 24, 32, 48, and 64 bytes).

  • CRC: The Cyclic Redundancy Check is 17 bits long for up to 16 bytes of data or 21 bits for 20-64 bytes. Its length depends upon the length of EDL and DLC bits. CAN FD always uses 4-fixed stuff bits that improve communication reliability.


Features of CAN and CAN FD:


Original CAN

  • CAN uses pair of twisted wire cables.

  • It offers easy and simplified handling.

  • Multiple ECU’s can be connected on the same CAN-BUS.

  • Developed to support and enable high speed and efficient communication in automobiles.

  • It has reduced weight and wire costs.

  • Error reduction.

  • A quick exchange of data. Uses arbitration process; hence top priority data get access of the bus.

  • Scope for upgradation.

  • Standard CAN 2.0A allows 11Bit data transmission (meaning, a total of 2048 different unique messages can be introduced).

  • Extended CAN 2.0B allows 29Bit data transmission (that sums up to 536+ million messages).


In addition to all the features that the original CAN offer, CAN FD has:


  • Flexibility to switch between faster and slower data rates.

  • Increased Protocol efficiency.

  • Reduced protocol overhead.

  • Allows more data to fit into a single message.

  • Better reliability. • Improved network bandwidth.

  • Up to 30 times more efficient and faster communication between multiple ECU’s.

  • Decreased number of undetected errors with advanced CRC.


Influx provides you with a wide variety of products that support CAN and CAN FD to cater to the automotive industry's ever-changing needs.


ReXgen AIR CAN To Cloud device from Influx Technology

The ReXgen Air CAN to Cloud is a fully adaptable data logger designed to capture and access a wide range of data, including CAN, CAN FD, LIN, GNSS, IMU, as well as digital and analog inputs, all from a remote location. It seamlessly connects with your existing instrumentation, ensuring smooth integration into your current workflow. ReXgen AIR allows you to break away from proprietary solutions, granting you full and precise control over your data.





328 views0 comments

Comments


bottom of page