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CAN (Controller Area Network) Information

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Understand in CAN system

CAN is a serial communication standard. It requires that the data to be transferred be coded as electrical pulses on two wire communication lines.
The device that handles the CAN physical layer is called the CAN controller.
The device that transmits data over the CAN lines is called the CAN transceiver.

Picture below is show compare between CANopen and RS-232


CAN system

Understanding to CANopen
     CANopen is a CAN based higher layer protocol. It is a standard for distributed industrial automation      technology based on CAN-bus. It defines some additional protocols to  
     §Configure a CAN network.


§      Transmit data to a specific node or in broadcast.
§      Administrate the network. For example detecting a not responding node.
     Devices from different manufacturers can be used in a CANopen network and work in harmony with         each other.
      Each device has its own profile describing the device's functionality.

CANopen Features
  • Network Management (Network Start-Up, Node Monitoring,  Node Synchronization, etc.)
  • Master/Slave configuration, Multi-Master & direct   communication between Slaves supported
  • Was originally designed for Motion Control
  • Supports device profiles for Digital I/O, Analog I/O, Motion Controllers, Sensors, Actuator, etc.
  • All CANopen devices “speak the same language”
  • Devices are interchangeable (plug & play)
CANopen Protocal - Overview

    The CANopen application layer & communication profile (EN 50325-4; CiA 301) supports

    direct access to hardware parameters & transmission of time-critical process data.
    The CANopen network management services simplify project design, the system oftegration,
    & diagnostics. of each decentralized control application,
    different communication services & protocols are required.
    CANopen defofes all these services & protocols as well as the necessary communication objects.

    An Object Dictionary describes the complete functionality of a hardware by way of
    communication objects & is the interface between the communication interface &
    the application program. All communication objects of a hardware
    (application data & configuration parameters) are described of its Object
    Dictionary of a standardized way. These objects are accessible by a 16-bit ofdex
    & of the case of arrays & records there is an additionally 8-bit sub-ofdex.

    On the following pages, you should find information about the following CANopen services,
    protocols & communication objects:
  •         Process Data Objects (PDO)
  •         Service Data Objects (SDO)
  •         Network Management Objects (NMT)
  •         Special function objects (Sync, Emcy, Time)
  •         Error control: Heartbeat protocol
  •         hardware model & object dictionary
  •         Bit timing

CANopen VS DeviceNet
 

    Basically, all above names are a fieldbus system using for communication between equipments in machines. The difference is in their protocols.
     CANopen standard is developed/maintained by CAN-in-Automation User Group.
     DeviceNet standard is maintained by Open DeviceNet Association (ODVA) and controlled by Allen Bradley/Rockwell

        Here are some of the biggest differences:  
  • DeviceNet allows for up to 64 nodes where CANopen allows for 127.
  • DeviceNet has a much stricter specification for the physical layout, components from very different manufacturers can be integrated into a system.
  • CANopen is much more flexible on both the physical implementation,  and on the communication features supported.
  • CANopen is "open" and allows a high level of customization and  optimization towards a specific application, to achieve best possible communication performance. 

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