OPERATION IN THE CANOPEN NETWORK
6 OPERATION IN THE CANOPEN NETWORK
6.1 ACCESS TO THE DATA
Each slave of the CANopen network has a list called object dictionary that contains all the data accessible via network.
Each object of this list is identified with an index, which is used during the equipment configuration as well as during
message exchanges. This index is used to identify the object being transmitted.
6.2 CYCLIC DATA
Cyclic data is the data normally used for status monitoring and equipment control. For CANopen protocol, the
interface supports 4 receive PDOs and 4 transmit PDOs.
It is necessary the configuration to be made both at the slave and master.
6.3 ACYCLIC DATA
In addition to the cyclic data, the interface also provides acyclic data via SDO. Using this type of communication, you
can access any equipment parameter. Access to this type of data is commonly done using instructions for reading
or writing data, which should indicate the index and sub-index to the desired parameter. The item 7.4 describes how
to address the parameters for SSW900 soft-starter.
6.4 COMMUNICATION OBJECTS - COB
There is a specific set of objects that are responsible for the communication among the network devices. Those
objects are divided according to the type of data and the way they are sent or received by a device. The following
communication objects (COBs) are described by the specification:
Table 6.1:
Types of Communication Objects (COBs)
Type of object
Description
Service Data Object (SDO)
SDO are objects responsible for the direct access to the object dictionary of a device. By means
of messages using SDO, it is possible to indicate explicitly (by the object index) what data is being
handled. There are two SDO types: Client SDO, responsible for doing a read or write request to
a network device, and the Server SDO, responsible for taking care of that request. Since SDO are
usually used for the configuration of a network node, they have less priority than other types of
message.
Process Data Object (PDO)
PDO are used for accessing equipment data without the need of indicating explicitly which dictionary
object is being accessed. Therefore, it is necessary to configure previously which data the PDO will
be transmitting (data mapping). There are also two types of PDO: Receive PDO and Transmit PDO.
They are usually utilized for transmission and reception of data used in the device operation, and for
that reason they have higher priority than the SDO.
Emergency Object (EMCY)
This object is responsible for sending messages to indicate the occurrence of errors in the device.
When an error occurs in a specific device (EMCY producer), it can send a message to the network.
In the case that any network device be monitoring that message (EMCY consumer), it can be
programmed so that an action be taken (disabling the other devices, error reset, etc.).
Syncronization Object (SYNC)
In the CANopen network, it is possible to program a device (SYNC producer) to send periodically
a synchronization message for all the network devices. Those devices (SYNC consumers) will then
be able, for instance, to send a certain datum that needs to be made available periodically.
Network Management (NMT)
Every CANopen network needs a master that controls the other devices (slaves) in the network.
This master will be responsible for a set of services that control the slave communications and their
state in the CANopen network. The slaves are responsible for receiving the commands sent by
the master and for executing the requested actions. The protocol describes two types of service:
device control service, with which the master controls the state of each network slave, and error
control service (Node Guarding an Heartbeat), with which the device sends periodic messages to
inform that the connection is active.
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