Table of Contents
Advertisement
Inertial Measurement Unit IMUF99*B16
Parameterization Using the CANopen Engineering Tool with CANopen Objects
6
Parameterization Using the CANopen Engineering Tool
with CANopen Objects
6.1
CANopen Overview
What Is CANopen?
CANopen is a multimaster-compliant fieldbus system based on the CAN (Controller Area Net-
work).
Devices on the CAN 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).
Collision Avoidance means that the dominant signal "0" overwrites the recessive signal "1" in
the event of simultaneous access. The node that sends the "1" detects this and aborts the data
transfer. As a result, messages with a lower identifier have higher priority and messages with
higher priority are not interrupted by these procedures.
Each device monitors the fieldbus and can send messages whenever the fieldbus is free. The
device with the highest priority, i.e., the lowest CAN identifier, receives the access right.
Devices with a lower priority interrupt the transmission and make a further access attempt once
the fieldbus becomes free. However, this also means that there is no guaranteed transmission
time for a message and that it is better to avoid excessive bus loading.
In CANopen the CAN identifier is encoded in a COB ID (Communication Object Identifier). This
object type encodes also if the message is active or other CAN frame specific options. The
CAN identifier for a CANopen message is made up of the function code and the node ID num-
ber.
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 immediate data
•
•
•
•
•
Messages for network management (NMT)
For controlling the state machine of the CANopen device and for monitoring the network
nodes
What is the difference between PDO and SDO?
PDO and SDO are 2 types of communication objects in CANopen that are used to exchange
data between different devices within the network.
PDO (Process Data Object): PDOs are used for the cyclic exchange of process data between
the participants of a CANopen network. They are used to transfer immediate data such as sen-
sor measurements, actuator controls or status information between the devices. PDOs are sent
and received at regular time intervals and are usually restricted to a limited amount of data.
SDO (Service Data Object): SDOs are used for the non-cyclical exchange of parameterization
and diagnostic data. They enable the reading, writing and parameterization of data objects in
the devices. Unlike PDOs, which are sent cyclically, SDOs are only used when a parameteriza-
tion change or data exchange outside of the cyclical PDO exchange is required. SDOs offer
greater flexibility in configuring and diagnosing devices, but also require more communication
effort and latency than PDOs.
26
Any length
Transmission "on request"
SDOs of a device are combined in the object directory
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
Advertisement
Table of Contents
