CANopen

showstack / protocols / canopen

Also called CANopen CC, CiA 301.

CiA's standardized application layer and communication profile riding on a CAN bus, giving devices a shared object dictionary and PDO/SDO messaging so drives, sensors and I/O from different vendors share one bus. It increasingly turns up in stage automation and rigging motion control, where the CiA 402 drive profile standardizes controller-to-servo-drive messaging.

Machinery and motionOpen, free sign-upCAN in AutomationVerified

Stewarded by CAN in Automation (CiA).

Control Small, urgent, must arrive

Small messages that either repeat constantly or fire once. Bandwidth is almost never the problem.

What kills it. Latency and loss on the messages that fire once. A repeating level survives a dropped packet; a GO does not.

The four flows, and why the model is worth having →

What goes wrong

CANopen CC bit rate is fixed network-wide and trades off against cable length; CiA specifies 10 kbit/s to 1000 kbit/s. Reusing a bit rate chosen for a short rack-to-rack link on a long touring cable run is a classic cause of bus errors that only appear once the cable is stretched out on site.

The 11-bit CAN identifier splits into a 4-bit function code and 7-bit node ID, capping a single CANopen network at 127 nodes (0 reserved for broadcast); large automation systems need multiple buses/gateways well before that limit in practice.

CiA itself warns that "some vendors implement only a subset of the mandatory functions and parameters, but still claim CiA 402 conformity," so two devices that both claim CiA 402 support are not guaranteed to interoperate on motion commands without testing.

The full CiA 301/402 specification text requires a free CiA account and login to download (status "Public Available Specification"); it is not a plain public URL, which trips up integrators expecting a direct PDF link.

What speaks CANopen (1)

Product	Direction	Notes
CODESYS CODESYS Group	bidirectional	Standard.

Typical use

Servo drive, VFD and motor-controller networking within winches, hoists and automated scenery machines (CiA 402 profile)
Sensor and I/O integration on machine-control buses inside automation racks and control cabinets
General industrial embedded device networking wherever many low-cost nodes need to share one bus

Sources

CANopen history (first published November 1994 as CiA 301) — CAN in Automation (CiA) primary
CANopen (bit rates 10 kbit/s-1000 kbit/s, application layer over ISO 11898) — CAN in Automation (CiA) primary
CiA 402: CANopen device profile for drives and motion control (conformance caveat quote) — CAN in Automation (CiA) primary
Technical documents (PAS/Technical Report documents free after registration or CiA membership login) — CAN in Automation (CiA) primary
CANopen (127-node limit from the 7-bit node ID field) — Wikipedia

Understand the mechanism

Robots, animatronics and connected things Code on a show

Something wrong, or missing?

Known gaps on this entry: default_ports, implementations. If you can source one of them, that is a ten minute pull request.

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