Operation And Communication; Data Exchange In The Canopen Bus; General Information About Canopen - Pepperl+Fuchs PGV F200 Manual

PGV...-F200/-F200A...-B16-V15

Operation and communication

5 Operation and communication
5.1

Data Exchange in the CANopen Bus

5.1.1

General Information about CANopen

CANopen is a multimaster-compliant fieldbus system based on the CAN (Controller Area
Network).
Figure 5.1
Devices on the CANopen fieldbus communicate via message identifiers rather than via
addresses. This allows all devices to access the fieldbus at any time. Fieldbus access is
according to the CSMA/CA principle (Carrier Sense Multiple Access/Collision Avoidance).
Each device intercepts the fieldbus and can send messages whenever the fieldbus is free. If
two devices start an access at the same time, the device with the highest priority, i.e., the
lowest identifier, is assigned the access right. Devices with a lower priority interrupt the data
transfer and make a further access attempt once the fieldbus becomes free.
Any device can receive the messages. An acceptance filter ensures that messages are
received only by the intended devices. Data is transferred via message telegrams. Message
telegrams consist of a COB ID (Communication Object Identifier) and a maximum of 8
subsequent bytes. The COB ID dictates the priority of the messages. The COB ID is made up
of the function code and the node number.
The function code describes the message type:
Message with service data (SDO)
For parameterization of object directory entries
•
•
•
•
Message with process data (PDO)
For transmitting real-time data
•
•
•
•
Messages for network management (NMT)
For controlling the finite state machine of the CANopen device and for monitoring the
nodes
Further objects such as synchronization object (SYNC), time stamp and error messages
(EMCY).
The most important attributes of the process data objects (PDOs) and service data objects
(SDOs) are shown in the table below.
40
Any length
Cyclical transmission
SDOs of a device are combined in the object directory
Mailbox is placed on a (server) SDO, 36 bytes long
Maximum 8 bytes long
Cyclical or event-controlled transmission
Distinction between send (max. 512) and receive PDOs (max. 512)
In the CAN, PDOs occupy their own identifier