SLLA521B January   2022  – June 2022 TCAN1145-Q1 , TCAN1146-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction – Partial Networking
  4. 2Partial Networking Application
    1. 2.1 Modes of Operation and Partial Networking
    2. 2.2 Sleep Mode and Partial Networking
    3. 2.3 Wake-Up Frame
    4. 2.4 Classical High-speed CAN, CAN FD, and PN
    5. 2.5 Mixed Network Information
  5. 3CAN Frames and Wake-up Frames
    1. 3.1 CAN Frame Structure
    2. 3.2 Wake-up Frames
      1. 3.2.1 ID Field Match
      2. 3.2.2 Data Length Code (DLC) Match
      3. 3.2.3 Data Match
      4. 3.2.4 CRC Match
      5. 3.2.5 Acknowledge Match
    3. 3.3 Error Counter
    4. 3.4 Selective Wake FD Passive
  6. 4Selective Wake Registers
  7. 5Configuring Partial Networking
    1. 5.1 Valid CAN Message ID Example
    2. 5.2 Valid Data Example
  8. 6Summary
  9. 7References
  10. 8Revision History

2.3 Wake-Up Frame

Before the enabled PN CAN transceiver correctly receives and interprets the Wake-Up Frame (WUF), the receiver must synchronize to the CAN data rate. To save cost, the local PN transceiver uses an internal oscillator that can have a variance of ± 3% compared to the CAN controllers on the network. To properly decode CAN frames, the device must first synchronize its internal clock to the clock of the controllers sending CAN frames. This is accomplished by analyzing CAN frames and comparing the length of received bits versus its own expected length, and then making bit length adjustments. This can take several CAN frames before the PN CAN transceiver locking step is complete.

The ISO 11898-2:2016 CAN standard allows up to four CAN frames at 500 kbps or 8 CAN frames at 1 Mbps for the transceiver to lock on to the data rate, not including the first CAN frame that contains the WUP, which starts after tBias. Correct decoding of these frames is not required, and does not cause the internal frame error counter to increment. The transceiver can receive a valid WUF after it successfully syncs to the CAN data rate. See Section 3 for clarification on the wake-up frame.

During this process, CAN bus data does not get passed through to the transceiver RXD pin. Once the PN-enabled ECU receives this valid WUF, it fully wakes up and transitions to standby mode. Other nodes that did not wake from this WUF must continue to remain in Sleep mode, decoding CAN frames and looking for their matching WUF pattern. If the transceiver does not receive a valid WUF, and the ISO defined tSILENCE timer expires (timeout for bus inactivity), the ECU will re-enter deep sleep and bias the bus back to ground. Keep in mind that if other nodes are communicating, the CAN network will stay biased to 2.5 V and will no longer be in the deep sleep state but is still consuming less current than ECUs in standby or normal mode.