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Wake-Up Pattern in CAN / CAN FD Networks

Last updated: 2019-04-10
Wake-Up Pattern Definition in ISO 11898-5:2007

A wake-up is defined as 1 to n dominant levels of at least tFilter separated by a recessive level.

tFilter: 500 ns to 5 μs

  • Dominant network level > 5 μs causes a wake-up
  • 500 ns < dominant network level is filtered
  • 500 ns < dominant network level < 5 μs may cause a wake up (transceiver dependent)

These conditions are fulfilled for 200 kBit/s -> 1 bit is longer than 5 μs!

That means each CAN frame can be used to wake up the network!

Wake up generation at 500 kBit/s:

Wake up with classical base format frames (CBFF):

  • The following three dominant bits fulfill the wake-up condition (1 bit == 2 μs -> 3 bit == 6 μs):
    • RTR, IDE, and r0 (ISO 11898-1:2003)
    • RTR, IDE and FDF (ISO 11898-1:2016)

    Figure 1: Wake-Up with a Classical Base Format Frame

Wake up with classical extended format frames (CEFF):

  • The following three dominant bits fulfill the wake-up condition (1 bit == 2 μs -> 3 bit == 6 μs):
    • RTR, r1, and r0 (ISO 11898-1:2003)
    • RTR, FDF and r0 (ISO 11898-1:2016)

    Figure 2: Wake-Up with a Classical Extended Format Frame

Note: The recessive level separating the dominant wake up pulses is not specified.

Wake-Up Pattern Definition in ISO 11898-2:2016
Classical CAN Networks

A wake up is defined as two consecutive dominant network levels for at least tFilter separated by a recessive network level for at least tFilter.

A wake-up pattern can be generated at 500 kBit/s:

  • With one CAN frame that provides two dominant phases with at least 3 bits length separated by a recessive phase of 3 bits
  • With two CAN frames each providing a dominant phase of at least 3 bits length
    • The EOF/IFS field in between the two CAN frames serves as recessive phase (see Figure 1, Figure 2)

CAN FD Networks

CAN FD base format frames (FBFF) only provide two consecutive dominant bits:

  • RSS, IDE

    Figure 3: Wake-Up with a FD Base Format Frame

CAN FD extended format frames (FEFF) do not provide any specific consecutive dominant bits

Therefore, for CAN FD a second filter time is introduced:

tCanActivityFilterShort: 150 ns to 1.8 μs (1.8 μs slightly shorter than a bit time at 500 kBit/s == 2 μs)

A wake-up pattern can be generated at 500 kBit/s in the arbitration phase:

  • With one CAN FD frame that provides two dominant phases with at least 1 bit length separated by a recessive phase of 1 bit
  • With two CAN FD frames each providing a dominant phase of at least 1 bit length
    • The EOF/IFS field in between the two CAN FD frames serves as recessive phase (see Figure 3)

References:
  • ISO 11898-1:2003: Road Vehicles – Controller Area Network (CAN) – Part1: Data Link Layer
  • ISO 11898-1:2015: Road Vehicles – Controller Area Network (CAN) – Part1: Data Link Layer
  • ISO 11898-5:2007: Road Vehicles – Controller Area Network (CAN) – Part5: High-Speed medium access unit with low power mode
  • ISO 11898-2:2016: Road Vehicles – Controller Area Network (CAN) – Part5: High-Speed medium access unit
  • CiA 601-1: CAN FD node and system Design Part1: Physical interface implementation
  • International CAN Conference (iCC) 2017 Proceedings: The new wake-up pattern for a robust system

 
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2019-04-10
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