Guide · Bus systems

CAN & CAN-FD — the nervous system of the vehicle.

For decades, the CAN bus has connected ECUs robustly and cost-effectively. CAN-FD extends it for the growing data volumes of modern vehicles.

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How CAN works

CAN (Controller Area Network) is a differential two-wire bus: the information is carried in the voltage difference between two lines, which makes it robust against interference. All nodes listen in; there is no master.

Arbitration — who is allowed to transmit?

Several nodes can start at the same time. Through dominant and recessive bits, the message with the highest priority automatically prevails: whoever sends a recessive bit but sees a dominant one on the bus backs off. This avoids collisions without losing time.

Classic CAN vs. CAN-FD

Classic CAN: up to 8 bytes of payload per frame, up to 1 Mbit/s.
CAN-FD (Flexible Data-Rate): up to 64 bytes of payload and a faster data phase (e.g. 2/5/8 Mbit/s). The arbitration phase stays at the classic bit rate (≤ 1 Mbit/s) — this makes CAN-FD backward-compatible and able to coexist with CAN 2.0 devices.

Why it matters

More payload and a higher data rate on the same robust principle — ideal for data-rich functions (e.g. battery management). And: the differential bus is only truly immune to interference if the layout is right.

Frequently asked questions

Is CAN-FD compatible with classic CAN?

Arbitration uses the same bit rate as classic CAN, so CAN-FD devices can coexist with existing CAN 2.0 networks. However, pure CAN 2.0 controllers do not understand CAN-FD frames — the network design must take this into account.

Why is CAN so immune to interference?

Thanks to differential transmission: a common-mode disturbance affects both lines equally and largely cancels out in the difference. Provided that grounding and termination are clean.

Sources: CAN FD (Wikipedia), Kvaser — CAN & CAN FD.