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CAN Bus Bit Timing Calculator

Work out can bus bit timing instantly with clear inputs, formula shown and shareable results.

About CAN Bus Bit Timing Calculator

CAN bit time is divided into time quanta, and the prescaler is the clock divided by bit rate times quanta per bit. Bus length is limited by propagation delay because arbitration requires every node to see the bit within one bit time: roughly 40 m at 1 Mbit/s and 500 m at 125 kbit/s.

Formula

CAN timing

prescaler = f / (bitrate x tq per bit); usable length scales inversely with bit rate

Worked example

With the default values below, CAN Bus Bit Timing Calculator returns Baud rate prescaler of 5. Change any input above and every figure here is recalculated in your browser.

Inputs used

CAN clock
40 MHz
Target bit rate
500 kbit/s
Time quanta per bit
16 tq
Bus length
40 m

Results

Baud rate prescaler
5
Actual bit rate
500.00 kbit/s
Bit rate error
0.0000% %
Maximum bus length at this rate
40 m

Step by step

  1. 1Values used
  2. 2CAN timing
  3. 3Baud rate prescaler= 5
  4. 4Actual bit rate= 500.00 kbit/s
  5. 5Bit rate error= 0.0000 %
  6. 6Maximum bus length at this rate= 40 m

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is CAN length limited by bit rate?

Non-destructive arbitration needs the signal to reach the far end and back within the sample point of the same bit, so the bit time must exceed twice the propagation delay.

What must match between nodes?

Bit rate exactly, and the sample point closely. Mismatched sample points cause intermittent errors that only appear under load.

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