Wake-Up Pattern in CAN / CAN FD Networks
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.
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 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)
- 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
