CANopen Basics - Introduction
CANopen is a standardized application for distributed automation systems based on CAN (Controller Area Network)
offering the following performance features:
- Transmission of time-critical process data according to the producer consumer principle
- Standardized device description (data, parameters, functions, programs) in the form of the so-called "object dictionary". Access to all "objects" of a device with standardized transmission protocol according to the client-server principle
- Standardized services for device monitoring (node guarding/heartbeat), error signalisation (emergency messages) and network coordination ("network management")
- Standardized system services for synchronous operations (synchronization message), central time stamp message
- Standardized help functions for configuring baud rate and device identification number via the bus
- Standardized assignment pattern for message identifiers for simple system configurations in the form of the so-called "predefined connection set"
|Device profile for generic I /O modules (CiA 401, V3.0)
||Device profile drives and motion control (CiA 402, V2.0)
||Interface and device profile for IEC 61131-3 programmable devices (CiA 405, V2.0)
|CANopen application layer and communication profile (CiA 301, V4.1, also EN 50325-4) and CANopen framework for CANopen managers and programmable CANopen devices (CiA 302, V3.4)
|CAN data link layer (ISO 11898:2003)
|CAN physical layer (ISO 11898:2003)
The document CiA 301 "CANopen Application Layer and Communication Profile" is the CANopen basic
specification and is available via the user organization "CAN-in-Automation e.V." (CiA) in Erlangen, Germany.
Extended communication mechanisms are described in CiA 302: "Framework for Programmable Devices", in
particular PLCs, HMIs or CANopen tools.
The specification proposals CiA 303, CiA 305 and CiA 306 define standards and recommendations for cables,
pin assignments, SI units, the layer setting services (LSS) and the specification of an electronic data sheet (EDS).
All CANopen specifications were developed by member companies of the CiA and are freely available without
usufruct. An overview of the CANopen device and application profiles is given in the section
Device and Application Profiles .
Physical structure of a CANopen network
The underlying CAN architecture defines the basic physical structure of the CANopen network. Therefore,
a line (bus) topology is used. To avoid reflections of the signals, both ends of the network must be terminated.
In addition, the maximum permissible branch line lengths for connection of the individual network nodes are
to be observed.
The recommended permissible bit rates for a CANopen network are given in CiA 301: 10 kbps, 20 kbps, 50 kbps,
125 kbps, 250 kbps, 500 kbps, 800 kbps and 1000 kbps. In CiA 301 a recommendation for the configuration of the
bit timing is also given.
Additionally, for CANopen, two additional conditions must be fulfilled:
Unfortunately there are no mechanisms automatically ensuring these conditions. The system integrator
has to check the bit rate and node-ID of every single network node when wiring a network and adjust if necessary.
Normally the node-ID is configured directly on the device via DIP-switches or hexadecimal rotary switches.
Alternative solutions require setting of these parameters via two reserved CAN identifiers by software with
the aid of the so-called "LSS-service" (layer setting service) as described in CiA 305.
- All nodes must be configured to the same bit rate and
- No node-ID may exist twice.