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

2.4 Classical High-speed CAN, CAN FD, and PN

The ISO 11898-2:2016 standard covers the physical layer for high-speed CAN, CAN FD and PN. PN uses classical high-speed CAN for waking up an ECU but does not preclude the CAN network from using CAN FD during normal CAN traffic. CAN FD communication would typically generate a CAN error when used on a classic CAN node; the standard overcame this by using the CAN FD Format indicator (FDF) bit in the CAN packet. The FDF bit set to 1b indicates that the packet is CAN FD. This bit allows a PN-enabled CAN transceiver to determine if the frames are CAN FD.

PN-capable CAN transceivers have the ability to decide whether to indicate an error or to ignore the CAN FD frames by programming a SW_FD_PASSIVE bit. When this bit is set to 1b, CAN FD frames are ignored, which is known as CAN FD passive.

The benefit for using classical high-speed CAN for WUF is that a PN-enabled CAN transceiver does not need a precise internal clock. If a CAN FD frame was to be used, the CAN transceiver needs a 0.5% tolerant crystal to decode the WUF which adds system level cost.