Features

Fundamental Properties and Fields of Application

CANOPEN is a standardized layer 7 protocol used for decentralized industrial automation systems based on the Controller Area Network (CAN) and the CAN Application Layer (CAL). CANOPEN is based on a communication profile containing the determination of basic communication mechanisms and their descriptions, such as the mechanisms used for exchanging process data in real-time or for sending alarm telegrams. This common communication profile is the basis for the various CANOPEN device profiles. The device profiles describe the specific functionality and/or the parameters of a device class. Such device profiles are available for the most important device classes used in industrial automation, such as digital and analog I/O modules, sensors, drives, control units, regulators, programmable controllers or encoders. Further device profiles are projected.

The central element of the CANOPEN standard is the device functionality description in an object directory (OD). The object directory is divided into one general area containing information about the device (e.g. device identification, manufacturer’s name, etc.) as well as communication parameters, and the device-specific area describing the particular functionality of the device. These properties of a CANOPEN module are documented in the form of a standardized “electronic data sheet” (EDS file).

A CANOPEN network can consist of a maximum of 128 modules, one NMT master and up to 127 NMT slaves. In contrast to the typical master-slave systems (e.g. PROFIBUS systems), the meanings of the terms master and slave are different for CANOPEN. In operational mode, all modules are independently able to send messages via the bus. Moreover, the master is able to change the operating mode of the slaves. The CANOPEN master is normally implemented by a PLC or a PC. The bus addresses of the CANOPEN slaves can be set in the range between 1 and 127. The device address results in a number of identifiers occupied by this module.

CANOPEN supports transmission rates of 10 kbit/s, 20 kbit/s, 50 kbit/s, 125 kbit/s, 250 kbit/s, 500 kbit/s, 800 kbit/s and 1 Mbit/s. Each CANOPEN device has at least to support a transmission rate of 20 kbit/s. Other transmission rates are optional.

Standardization: CANOPEN

BOSCH CAN specification - version 2.0, part A and part B

ISO 11898

CiA DS 201 V1.1 - CAN Application Layer

CiA DS 301 V3.0 - CAL based Communication Profile for Industrial Systems

CiA DS 301 V4.02 - CANOPEN Application Layer and Communication Profile

CiA DS 401 V2.1 - CANOPEN Device Profile Generic I/O modules

CiA DS 402 V2.0 - CANOPEN Device Profile Driver and Motion Control

CiA DS 406 V3.0 - CANOPEN Device Profile Encoder

Terms, Definitions and Abbreviations

CANOPEN

CAL CAN Application Layer
CAN Controller Area Network
CiA CAN in Automation e.V.
DLC Data Length Code
EDS Electronic Data Sheet
ISO International Standardization Organization
NMT Network Management
OD Object Directory
PDO Process Data Object
RTR Remote Transmission Request
SDO Service Data Object

CANOPEN

  • Operating mode CANOPEN-Master
  • Process image with a maximum of 57344 I/O points
  • Supports min. boot-up, emergency messages and life guarding
  • Supported PDO modes: Event-controlled, synchronous, cyclic and remote PDO transmission
  • Integrated device profiles: CiA DS-401, CiA DS-402 and CiA DS-406

CAN (additional functionality, not necessary \ for pure CANOPEN operation)

  • Support of 11 bit identifiers according to CAN 2.0 A and 29 bit identifiers according to CAN 2.0 B
  • Transmission and reception of any CAN telegrams via function blocks in the user program

Transmission technique

  • ISO 11898, potential separated
  • Transfer rates of 20 kbit/s, 125 kbit/s, 250 kbit/s, 500 kbit/s and 1 Mbit/s
  • Bus length up to 1000 m at 20 kbit/s and up to 40 m at 1 Mbit/s
  • One bus can have up to 128 subscribers (master + 127 slaves)
  • 5-pin COMBICON connector for bus

Communication

  • Message-oriented bus access, CSMA/CA
  • Predefined master-slave connections
  • 8 bytes of non-fragmented user data, for fragmentation any size is possible
  • Synchronization of inputs and/or outputs via synchronous PDOs

Protection functions

  • Message transfer with Hamming distance HD = 6
  • CAN fault recognition mechanisms via 15 bit CRC, frame check, acknowledge, bit monitoring and bit stuffing
  • Incorrect parameter settings are avoided because bus subscribers with faulty parameters are not included in the user data operation.
  • Adjustable behavior on subscriber failure. System continues normal operation and the error is indicated at the master or the entire system is stopped.
  • Response monitoring of the subscribers (node guarding)