CANopen system overview
The Beckhoff Embedded PCs can be ordered ex works with an optional interface, e.g. PROFIBUS, CANopen or RS232. Some of the optional interfaces can be delivered as master or slave.
The following Embedded PCs can be ordered with an optional interface:
- CX9020
- CX50x0
- CX51x0
- CX20x0
CANopen master (M510)
The optional interface M510 is a CANopen master and enables a segment-like construction of control structures in large plants and machines. Further Beckhoff fieldbus components such as Bus Couplers, Bus Terminal Controllers, drive components, etc. can be used with an Embedded PC for configuring control structures.
Fieldbus masters are used for decentralized collection of process data and signals in large machines and plants. The number of slaves that can be connected to the master is only limited by the respective bus system. Using master and slave connections makes it possible to link several Embedded PCs with each other via the fieldbus level.
The optional interfaces are detected, parameterized and configured in TwinCAT, and the connected I/O components are added. TwinCAT is also used for diagnostics.
CANopen slave (B510)
The optional interface B510 is a CANopen slave and enables an Embedded PC to be used as subordinate decentral controller for configuring complex or modular systems.
The CANopen slave receives external process data from the master and processes them or returns data from its own process periphery to the master after processing.
Like the CANopen master, the optional CANopen slave interface is parameterized and configured in TwinCAT.
Functioning
CANopen is a widely used fieldbus system, which was developed by the CAN in Automation (CiA) association and in the meantime has been adopted for international standardization.
Further Information |
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CAN in Automation (CiA) website: |
CANopen consists of the protocol definition (communication objects) and the device profiles.
The protocol definition includes the following communication objects:
- Network Management (NMT)
- Process Data Objects (PDO)
- Service Data Objects (SDO)
- And protocols with special functions
The device profiles standardize the data content for the respective device class. The term device class covers devices such as electric drives, I/O modules, sensors and controllers. The device profiles define the functionality and the structure of the object directory.
The device parameters and process data are stored in a structured object directory. Any data in this object directory is accessed via service data objects (SDO).
Process data objects (PDO) are used for fast communication of input and output data. There are, additionally, a few special objects (such as telegram types) for network management (NMT), synchronization, error messages and so on.
Communication Types
CANopen defines several communication types for process data objects:
- Event driven:
Telegrams are sent as soon as their contents have changed. This means that the process image as a whole is not continuously transmitted, only its changes. - Cyclic synchronous:
A SYNC telegram causes the modules to accept the output data that was previously received, and to send new input data. - Requested (polled):
A CAN data request telegram causes the modules to send their input data.
The required communication type is set via the transmission type parameter (see: PDO tab).
Bus access procedures
CAN operates based on the Carrier Sense Multiple Access (CSMA) method, i.e. all devices have equal rights and access the bus as soon as it is free (multi-master bus access). The exchange of messages is thus not device-oriented but message-oriented. This means that every message is unambiguously marked with a prioritized identifier.
In order to avoid collisions on the bus when messages are sent by different devices, a bit-wise bus arbitration is carried out at the start of the data transmission. The bus arbitration allocates bus bandwidth to the messages in order of priority. At the end of the arbitration phase only one bus devices occupies the bus; collisions are avoided, and the bandwidth is optimally utilized.
Configuration and parameterization
The TwinCAT System Manager allows all the CANopen parameters to be set conveniently. An "eds" file (an electronic data sheet) is available on the Beckhoff website (www.beckhoff.de) for the parameterization of Beckhoff CANopen devices using configuration tools from other manufacturers.
Certification
The Beckhoff CANopen devices have a powerful implementation of the protocol, and are certified by the CAN in Automation Association (www.can-cia.org).