14.6.3.7 Recommendations for Bit Time Configuration

The following recommendations should be considered when configuring the bit time:

  • Select the highest available CAN clock frequency:
    • Short TQ leads to high resolution to select the sample point.
    • Use 20 MHz, 40 MHz or 80 MHz for FCAN.
  • Select the lowest NBRP and DBRP:
    • Low BRP leads to short TQ.
    • NSYNC and DSYNC will be short and reduce the quantization error.
    • The receiving node can synchronize more accurately to the transmitting node.
  • Set NBRP equal to DBRP:
    • Identical TQ in both phases prevents quantization errors during Bit Rate Switching.
  • Use the same Nominal Sample Point (NSP) and Data Sample Point (DSP) in all nodes on the CAN FD network:
    • Different sample points in the different nodes lead to different lengths of the BRS and CRC delimiter bits and introduce phase errors when switching the bit rate.
    • NSP need not be equal to the DSP.
    • The SSP can be different in differing CAN FD nodes.
  • Select the largest possible NSJW and DSJW:
    • Maximizes the oscillator tolerance.
    • Allows the receiving nodes to quickly resynchronize to the transmitting nodes.
  • Enable automatic TDC for DBR of 1 Mbps and higher:
    • Automatic TDC measurement compensates for transmitter delay variations.