sCAN baud rate settings

The sCAN API exposes baud rate settings through nrf_scan_timing_t, which is passed to nrf_scan_timing(). These parameters are translated into a value for FLPR’s internal counters.

Timing calculation

The parameter calculation follows CAN Specification 2.0 A/B and the CiA99 paper.

When the SoC runs at its highest base clock frequency, the FLPR frequency is as follows:

nRF54L15nRF54LM20

\[\text{max_device_freq_hz}=128000000\]

A time quantum is the base unit for the configuration parameters.

\[\text{tq} = \left\lfloor \frac{\text{max_device_freq_hz}} {\text{nrf_scan_timing_t.prescaler} \cdot \text{desired_baud_rate}} \right\rceil\]

The timing segments make up each transmitted bit. The total number of time quanta in each transmitted bit is calculated as follows:

\[\text{num_tq_per_bit} = 1 + \text{prop_seg} + \text{phase_seg1} + \text{phase_seg2}\]

Timing constraints

The timing parameters must meet the following constraints:

• prescaler must be at least 8.

• prop_seg and phase_seg1 must each be between 1 and 8.

• phase_seg2 must be between 1 and phase_seg1.

• The sum of prop_seg, phase_seg1, and phase_seg2 must be at least 7.

• sjw must be between 1 and the lower of phase_seg1 and 4.

Example configuration

The following example configures a baud rate of 1 Mbps:

nrf_scan_timing_t m_scan_timing = {
    .prescaler = 8,
    .prop_seg = 1,
    .phase_seg1 = 7,
    .phase_seg2 = 7,
    .sjw = 1
};