What Is CAN FD?

CAN FD (CAN with Flexible Data-rate) is an upgrade to the Controller Area Network protocol that lets each message carry more data, faster. Bosch introduced it in 2012 and it was standardised in ISO 11898-1:2015, where the original protocol is now called Classical CAN.

Classical CAN has two limits that modern vehicles and machines run into. Each frame carries only 8 bytes of data, so more than half of every frame is overhead such as identifiers and checksums. And the whole bus runs at one speed, at most 1 Mbit/s, because every node must be able to check each bit during arbitration.

CAN FD lifts both limits while keeping what makes CAN reliable. Frames carry up to 64 bytes. Arbitration, where nodes compete for the bus, still runs at the normal rate, typically 500 kbit/s, but once a node has won, it switches to a faster data-phase bit rate, typically 2 to 5 Mbit/s, for the payload and checksum. The result is several times more useful data through the same pair of wires.

A CAN FD frame looks much like a Classical CAN frame, with a few new control bits that tell every node how to read the rest of it:

CAN is now a family of three generations on the same physical layer of twisted pair, termination and differential signalling. CAN XL is the newest and reaches into territory previously served by automotive Ethernet.

The data rates CAN FD can reach depend on the transceivers, cable length and how many stubs hang off the bus. 2 Mbit/s is common in vehicles. 5 Mbit/s and above needs short stubs, careful termination and transceivers rated for it, and is usually checked on the real wiring harness.

CAN FD controllers can send and receive Classical CAN frames, so a CAN FD computer can join an existing CAN network and talk to it normally. The reverse is not true. A Classical CAN controller that sees a CAN FD frame treats it as an error and destroys it with an error frame, which disrupts the whole bus.

That leaves three options. Keep CAN FD traffic on a separate bus, run every node at CAN FD, or use transceivers with partial networking or FD-tolerant behaviour, which keep older nodes quiet while FD frames pass. Higher-layer protocols have followed: J1939-22 brings CAN FD to heavy vehicles and CANopen FD to industrial automation.

CAN FD fills the gap between Classical CAN and Ethernet: more data than CAN can carry, with CAN’s low cost, priority-based timing and noise immunity.

A CAN FD port on a computer needs a CAN FD controller, a CAN FD-rated transceiver and a driver. On Linux, CAN FD interfaces appear through SocketCAN, so standard tools can configure both bit rates and capture traffic. Termination matters as much as on Classical CAN: the bus needs 120 ohm at each end, and a switchable resistor in the computer saves an external plug. On vehicles, pair it with ignition control that shuts the computer down cleanly when the engine stops.

Within the Advantech range we list, the MIC-713 Jetson computers have a nine-pin CAN FD port with switchable 120 ohm termination beside optically isolated digital I/O, and the T5000 version of the MIC-742-AT Jetson Thor computer has four CAN FD ports for motor controllers and vehicle networks.

We build in-vehicle, robot and industrial computers with CAN FD fitted and configured as standard, set the termination and bit rates to match your network, and load the drivers before the system ships.