3
CANopen access procedure
20
Festo – GDCP-CMMP-M3/-M0-C-CO-EN – 1510b – English
3
CANopen access procedure
3.1
Introduction
CANopen makes available a simple and standardised possibility to access the parameters of the motor
controller (e.g. the maximum motor current). To achieve this, a unique number (index and subindex) is
assigned to each parameter (CAN object). The totality of all adjustable parameters is designated an
object directory.
For access to the CAN objects through the CAN bus, there are fundamentally two methods available: a
confirmed access type, in which the motor controller acknowledges each parameter access (via so-
called SDOs), and an unconfirmed access type, in which no acknowledgement is made (via so-called
PDOs).
Confirmation from
the controller
Order from controller
Control
system
CMMP
SDO
Confirmation from
the controller
Control
system
CMMP
PDO
(transmit PDO)
Data from controller
Control
system
CMMP
PDO
(receive PDO)
Fig. 3.1
Access procedure
As a rule, the motor controller is parametrised and also controlled via SDO access. In addition, other
types of messages (so-called communication objects), which are sent either by the motor controller or
the higher-level controller, are defined for special application cases:
Communication objects
SDO
Service Data Object
Used for normal parametrisation of the motor controller.
PDO
Process Data Object
Fast exchange of process data (e.g. actual speed) possible
SYNC
Synchronisation Message
Synchronisation of multiple CAN nodes
EMCY
Emergency message
Transmission of error messages
NMT
Network management
Network service: All CAN nodes can be worked on
simultaneously, for example.
HEART
BEAT
Error Control Protocol
Monitoring of the communications participants through
regular messages.
Tab. 3.1
Communication objects
