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

3.1 CAN Frame Structure

To understand how Wake Up Frames (WUF) are used in CAN partial networking, it is important to first understand the structure of a CAN frame. In Figure 3-1, a high signal represents the CAN bus is recessive (logic 1), while a low signal represents the CAN bus is dominant (logic 0).

There are two formats used which are based upon the number of ID bits. As shown in Figure 3-1 there is an 11-bit ID format known as Classic Base Frame Format (CBFF) and a 29-bit ID format know as Classic Extended Frame Format (CEFF). The following is a list of the names and description:

  • IDLE – When the CAN bus is in an idle state, the bus will be recessive, or ‘1.’
  • SOF – Start of Frame, a dominant bit, or ‘0.’
  • ID[10:0], the Base ID in CBFF, or EXT_ID[28:18], the first 11 bits of the Extended ID in CEFF. These share the same configuration bits.
  • EXT_ID[17:0], the remaining 18 bits of the Extended ID in CEFF
  • RTR – Remote Transmission Request. A ‘1’ indicates a remote frame (will have a zero length DLC). A ‘0’ indicates a data frame. For a WUF, this bit must be ‘0.’
  • IDE – Identifier. A ‘1’ indicates CEFF (extended ID), while a ‘0’ indicates CBFF (base ID)
  • FDF – FD Format indicator which states whether the frame is classic CAN,(0), or CAN FD (1). For a WUF, this bit must be ‘0.’ Note that for CAN-FD frames, the structure following this FDF bit is different from either Classical CAN frame, and is not described here.
  • DLC – Four-bit Data Length Code states how many data bytes are in the frame. Values of 8-15 will be interpreted as 8 bytes
  • SRR – Substitute RTR. Will always be a ‘1.’
  • r1 – Reserved bit. Will always be a ‘0.’
  • CRC – 15-bit Cyclic Redundancy Check which is used to determine the integrity of the information
  • Del – Delimiter bits. Will always be ‘1.’
  • ACK – Acknowledge. The sender of the CAN frame will transmit a ‘1,’ while all of the receivers of the CAN frame will transmit a ‘0’ if the CRC is correct, or a ‘1’ if the CRC is incorrect
Figure 3-1 CAN Frame Structure