CANopen vs CAN Bus: What's the Difference? (Explained)

This article is part of the CAN & CANopen family. If you're new to CAN start with CAN Bus Protocol Explained (arbitration, frames, errors), or the CAN wiring and termination guide for physical-layer rules. For the full family landing with links to CANopen, J1939, DeviceNet, and CAN FD, visit the CAN & CANopen category hub.

Many engineers compare CANopen vs CAN bus as though they are competing technologies. In reality, they are different layers of the same communication stack. CAN provides reliable message transport, while CANopen defines how devices exchange meaningful information.

Short version: they are not alternatives. CANopen runs on CAN. Asking which to choose is like asking whether to use HTTP or Ethernet — one sits on top of the other, and a working system needs both.

The confusion is understandable, because vendors write "CAN interface" and "CANopen interface" on datasheets as though they were two options at the same level. They aren't. And the difference between them determines whether two devices from different manufacturers will talk to each other or just share a cable.

The layer picture

In OSI terms, CAN defines the physical and data link layers, while CANopen defines higher-layer communication services. Think of it as two floors of the same building.

CAN — standardized in ISO 11898 — is the bottom floor. It defines how bits get onto the wire and how simultaneous transmissions resolve. Specifically: differential signalling with dominant and recessive bits, identifier-based arbitration so the lowest identifier wins without any data being lost, frame formats, error detection, and fault confinement that escalates a failing node out of the conversation.

What CAN does not define is what any of it means. An identifier is just a number. Eight bytes of payload are just eight bytes. There is no concept of a parameter, a device type, a configuration mechanism, or a way to move more data than fits in a single frame.

CANopen — specified in CiA 301 and standardized as EN 50325-4 — is the floor above. It takes CAN's frames and imposes meaning: an object dictionary that gives every device parameter an address, SDO transfers for configuration, PDO mapping for cyclic process data, NMT states, SYNC for coordinated sampling, heartbeat monitoring, EMCY error reporting, and device profiles that make instruments from different vendors behave alike.

CAN gets bits from A to B reliably. CANopen decides what those bits mean and how devices agree about them.

What each layer actually gives you

Notice the last row. Every CAN wiring rule applies to a CANopen network without modification — two 120 Ω terminators, short stubs, one bit rate for everyone. A CANopen network with a missing terminator fails exactly like any other CAN network with a missing terminator. The CAN wiring and termination guide covers all of it.

What "raw CAN" actually means

Plenty of devices genuinely do use CAN without a higher-layer protocol. The manufacturer defines its own identifier scheme and payload layout, documents it, and that's the protocol.

Because there is no standardized application layer, every manufacturer invents its own message format. This works, and it's common in embedded and automotive systems where one organization controls every node. The cost is that nothing is portable. Your identifier map is yours alone. Adding a device from another vendor means an integration project. There is no standard way to configure a parameter, discover a device, or ask whether a node is alive.

That's precisely the gap higher-layer protocols exist to fill — CANopen for machines, J1939 for vehicles and engines, DeviceNet for CIP-based device networks. Each takes CAN's frames and imposes a different set of conventions on them.

How to tell what a device actually speaks

This is the practical question behind most searches for this comparison.

"CAN interface" on a datasheet usually means raw CAN with a manufacturer-defined message set. You'll need the vendor's protocol documentation, and the device will not interoperate with anything it wasn't designed alongside.

"CANopen interface" means the device implements the object dictionary, SDO and PDO services, and NMT states. It will respond to a standard CANopen configuration tool without any vendor-specific software.

Two quick tests. Ask whether an EDS file exists — the electronic data sheet describing the object dictionary. Only CANopen devices have one. And ask whether the device has a node ID rather than just a set of identifiers; CANopen devices are addressed by node ID, and their default identifiers derive from it.

If a device speaks raw CAN and you need it on a CANopen network, the options are a gateway or a custom master. There is no configuration setting that turns one into the other — the difference is in the firmware.

Can they share a bus?

Physically, yes. Electrically they're identical, so raw CAN frames and CANopen frames coexist on one pair as long as everyone runs the same bit rate.

Practically, be careful. CANopen's default identifier allocation reserves specific ranges for its own services — NMT commands, SYNC, EMCY, the default PDOs and SDOs for each node ID. A raw CAN device transmitting on an identifier that collides with one of those will cause behaviour that looks like a CANopen fault and isn't.

There's a tooling problem too. Even when identifier conflicts are avoided, diagnostic tools may struggle because raw CAN traffic does not follow CANopen conventions — a CANopen analyzer will show the frames but cannot interpret them, and they clutter the view of the traffic you're actually trying to read.

If you must mix, map the identifiers deliberately and keep the raw traffic clear of CANopen's reserved ranges. And remember that identifier value equals bus priority — a chatty raw device on a low identifier will win arbitration over the CANopen traffic that matters.

CAN vs CANopen: which should you use?

Use raw CAN when you control every node, the message set is small and stable, and the cost of an extra protocol stack matters — deeply embedded products, cost-driven designs, one-vendor systems.

Use CANopen when devices come from more than one supplier, when you want standard configuration tooling instead of custom software, when device profiles let you swap a drive without rewriting control code, or when you need the services CAN doesn't provide — segmented transfers, coordinated sampling, standardized health monitoring.

The decision isn't really CAN versus CANopen. It's whether you want to define and maintain your own conventions, or adopt ones that already exist and that other vendors already implement.

FAQ

Is CANopen the same as CAN?

No. CAN is the data link and physical layer standardized in ISO 11898 — frames, arbitration, error handling. CANopen is an application layer built on top of it, adding the object dictionary, SDO and PDO communication, NMT states, and device profiles. Every CANopen network is a CAN network; not every CAN network is CANopen.

Can a CANopen device work on a plain CAN bus?

Electrically yes, functionally no. It will transmit and receive frames, but nothing on a raw CAN network knows how to configure it, start it into the operational state, or interpret its PDOs. Without a CANopen master it stays in pre-operational and sends no process data.

Do I need CANopen to use CAN?

No. Many systems use raw CAN with a manufacturer-defined message set, which is entirely valid where one organization controls every node. What you give up is interoperability and standard tooling.

How do I know if my device supports CANopen?

Look for an EDS file, a node ID setting, and documentation referring to the object dictionary, SDOs, or PDOs. A device with a manufacturer-specific identifier table and no EDS is raw CAN.

Is CANopen slower than raw CAN?

The wire speed is identical — same bit rates, same frames. CANopen adds structure, and an SDO transfer carries more overhead than a hand-crafted message. But PDOs are designed for exactly this: the mapping is agreed in advance, so a PDO carries process data with no addressing overhead at all, matching what a well-designed raw CAN message would achieve.

Does CANopen use CAN FD?

Traditional CANopen was designed for Classical CAN. Modern CANopen FD (CiA 1301) extends the protocol to operate over CAN FD while preserving the same application-layer concepts such as the object dictionary, PDOs, and SDOs. The device model you learn on Classical CANopen carries over.

Can CANopen and J1939 run on the same bus?

Not sensibly. Both define their own use of the CAN identifier field, and their allocations conflict. Where both are needed, a gateway between two separate buses is the normal arrangement.