CAN FD

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CAN FD (CAN with Flexible Data-Rate) is an extension to the original CAN bus protocol specified in ISO 11898-1.[1] Developed in 2011 and released in 2012 by Bosch, CAN FD[2] was originally created in response to the requests of automakers for more accurate, "real-time" data. Just like with classic CAN, this protocol is designed to record and transmit data, including errors, between devices and microcontrollers without the use of a central, "host" computer. CAN FD is primarily designed to meet the needs of automakers, however, the pervasiveness of classic CAN indicates the inclusion of this improved protocol across a variety of applications, including defense, industrial automation, autonomous devices, underwater vehicles and medical equipment.

CAN FD versus classic CAN[edit]

CAN FD was created to accommodate increases in bandwidth requirements within automotive networks. The CAN FD protocol has brought the software closer to "real time" through the minimization of delays between an instruction and transfer of data (latency) and higher bandwidth.

CAN FD also allows for more storage capacity in the CAN-frame. While classic CAN has the capacity to hold 8 bytes of data within the CAN-frame, CAN FD can hold up to 64. This is accomplished through a decrease in relative overhead and improvements to software simplicity and efficiency when transmitting large data objects.

The CAN-FD Busload that was developed by "De Andrade's" equation which is based on Tindel's equation.[1][3][4]

β = τ/ω (1) (β = Busload) , (τ = time of slow bits more faster bits) , ω ( time in seconds of measurement). τ = Ts + Tf (2)

The CAN-FD protocol defines five different error detection mechanisms: Two of them work at the bit level, and the other three at the message level. They are (i) Bit Monitoring, (ii) Bit Stuffing, (iii) Frame Check, (iv) Acknowledgement Check and (v) Cyclic Redundancy Check. There are two options of CRC which should be denoted as for CRC length of 17 bits or for CRC length of 21 bits.


Ts = ([(SOF+ID+r1+IDE+EDL+r0+BRS/2+CRCdel/2)* 1,2]+ACK+DEL+EOF+IFS)/t_x (3) Tf = (〖[(D〗_f+BRS/2+ESI+DLC+CRCdel/2)*1,2]+〖CRC〗_17+5)/t_y (4)

where SOF (Start of Frame) + ID ( Identifier) + r1 (reserved bit 1) + IDE + EDL( Extended Data Length) + r0(reserved bit 0) + BRS/2 (Bit Rate Switch) + CRCdel/2 (CRC delimiter)= 17 bits, 1.2 is the factor of the worst case bit stuffing, which means it is necessary to divide by 5. It is considered BRS and CRCdel divided by 2, because they are exactly in the shift of bit rate transition. The ACK (Acknowledge) + DEL (Delimiter) + EOF (End-of-Frame) + IFS (Interframe Spacing) = 12 bits without bit stuffing. The CAN-FD payload size may be 0, 8, 12, 16, 20, 24, 32, 36, 48, 64 Bytes. t_X is the transmission bandwidth for the message header (up to 1 Mbps).

For data < 16 Bytes

β= ( (SOF+ID+r1+IDE+EDL+r0+BRS/2+CRCdel/2 * 1,2)+ACK+DEL+EOF+IFS)/t_x + (〖[(D〗_f+BRS/2+ESI+DLC+CRCdel/2 )*1,2]+〖CRC〗_17+5)/t_y )/ω (5)

For data >= 16 Bytes β= ( (SOF+ID+r1+IDE+EDL+r0+BRS/2+CRCdel/2 * 1,2)+ACK+DEL+EOF+IFS)/t_x + (〖[(D〗_f+BRS/2+ESI+DLC+CRCdel/2 )*1,2]+〖CRC〗_21+6)/t_y )/ω (6)

CAN FD also has decreased the number of undetected errors through increases in the performance of the CRC-algorithm.[5] In addition, CAN FD is compatible with existing CAN 2.0 networks, allowing the new protocol to function on the same network as classic CAN.[6] CAN FD has been estimated to transmit data up to 30 times faster than classic CAN.

Due to higher communication speed, CAN FD constraints are tougher in terms of line parasitic capacitances. Therefore, all components on the line have seen their "capacitance" budget reduced compared to regular CAN bus. That is the reason why semiconductor suppliers have released new components approved by car makers. This approval reflects the need for interoperability between all CAN FD systems. Indeed, selected ESD protection components are compatible with all transceivers (CAN or CAN FD) and withstand ISO7637-3.[7]

Despite a higher stand-off voltage (37 V), devices for truck applications must also comply with the low capacitance requirement (3.5 pF).[8]

CAN FD in action[edit]

CAN FD is predicted to be in most vehicles by 2019/2020.[9]

CAN FD supporters[edit]

Some of the companies behind the new standard include STMicroelectronics, Infineon,[10] NXP, Texas Instruments, Kvaser, Daimler and GM.

See also[edit]

References[edit]

  1. ^ a b "CAN in Automation (CiA): CAN FD - The basic idea". www.can-cia.org. Retrieved 2017-01-25.
  2. ^ "Bosch CAN FD Specification Version 1.0 (released April 17th, 2012)" (PDF). Retrieved 2019-01-02.
  3. ^ de Andrade, R.; Hodel, K. N.; Justo, J. F.; Laganá, A. M.; Santos, M. M.; Gu, Z. (2018). "Analytical and Experimental Performance Evaluations of CAN-FD Bus". IEEE Access. 6: 21287–21295. doi:10.1109/ACCESS.2018.2826522. CC-BY icon.svg This article contains quotations from this source, which is available under the Creative Commons Attribution 3.0 (CC BY 3.0) license.
  4. ^ https://www.teses.usp.br/teses/disponiveis/3/3140/tde-06082015-111553/publico/Dissertacao_Ricardo_rev2_17.pdf
  5. ^ https://www.kvaser.com/wp-content/uploads/2016/10/comparing-can-fd-with-classical-can.pdf
  6. ^ "High speed CAN FD bus is coming to cars, says Microchip". Electronics Weekly. 2015-10-26. Retrieved 2017-01-26.
  7. ^ "CAN bus ESD protection for 12V systems". STMicroelectronics-ESDCAN03-2BWY.
  8. ^ "CAN bus ESD protection for 24V systems". STMicroelectronics-ESDCAN05-2BWY.
  9. ^ "CAN 2020: The future of CAN technology". www.can-cia.org. Retrieved 2017-01-26.
  10. ^ Kelling, Ursula (April 2014). "Infineon Microcontrollers" (PDF). CAN Newsletter Online. Retrieved June 2, 2019.

External links[edit]