Up to 127 logical devices may be addressed in a CANopen network. One of these devices must have CANopen Master functionality. This means that the Master can monitor other devices called Slaves and change their states. Each device is uniquely identified by its node address (1 to 127).
There are two fundamental types of communication over the bus under CANopen. Service data objects (SDO) permit optional access to any desired entries in the object directory. Since these entries frequently exceed the maximum allowable size of a CAN message, i.e. 8 bytes, segmenting of data is performed by the SDO. An SDO is used exclusively for communication between two partners. If the same information is to be sent from one device to a number of other devices, the use of Process Data Objects (PDO) is appropriate. In principle a PDO is a CAN message that is fully configurable. This configuration is performed by entries in the object directory.
Advantages of using CANopen
CANopen offers a very flexible structure that enables its use in a wide variety of application areas. Its range of application extends from industrial automation to medical engineering to motor vehicle applications. In open systems it is quite easy to expand a network by adding other devices that support CANopen. It even makes sense to use CANopen in closed proprietary networks. In that case CANopen serves as a quasi toolbox, and only the right tools for the job need to be taken from it.