CAN / CAN FD Bit Timing Calculator

Calculate CAN bit rate, sample point and time quanta, or find timing counts for a target. Uses documented Bosch M_CAN limits, with standard and split termination calculations.

Method, formulas and references

CAN time quanta and sample point

With functional counts, tQ = BRP / CAN clock, bit time = (1 + TSEG1 + TSEG2) × tQ, and sample point = (1 + TSEG1) / (1 + TSEG1 + TSEG2). The synchronisation segment is one TQ. Register fields use count minus one.

The model follows Bosch M_CAN revision 3.3.1. The search checks legal segment ranges and keeps SJW no larger than either segment. TDC restricts the data prescaler to one or two. Both phases must be configured for CAN FD; its data rate must be at least the nominal rate. This tool evaluates one phase at a time. Device integration, propagation budget, oscillator tolerance and TDC configuration need separate checks.

Termination circuit calculations

Two end resistors RT present RT/2 in parallel. A split end termination uses two RT/2 resistors; the ideal common-mode capacitor sees their parallel combination RT/4. Its RC corner is 1/[2π(RT/4)C]. Differential resistor power follows V²/R. These are circuit calculations, not a maximum permitted CAN bit rate.

Data sources

Bosch M_CAN User’s Manual, revision 3.3.1 (11 March 2023)
§2.3.4 DBTP and §2.3.8 NBTP: functional segment counts, prescaler limits, bit-time equations and zero-based register fields. Data-phase prescaler is limited to 1 or 2 with TDC enabled.
Texas Instruments SLLA270 — Controller Area Network Physical Layer Requirements
§4.5: matched terminations at the two ends of high-speed CAN; standard and split termination. Split-filter corner and resistor dissipation are derived here from the ideal circuit.

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