CAN Communication
CANopen Application Layer
EPOS4 Communication Guide
3-26
CCMC | 2019-11 | rel8759
3.3.2
Communication Objects
CANopen communication objects are described by the services and protocols. They are classified as fol-
lows:
•
The real-time data transfer is performed by means of Process Data Objects.
•
With Service Data Objects, read/write access to entries of a device Object Dictionary is provided.
•
Special Function Objects provide application-specific network synchronization and emergency
messages.
•
Network Management Objects provide services for network initialization, error control and device
status control.
Table 3-10
CAN communication – Communication objects
3.3.3
Predefined Communication Objects
3.3.3.1
PDO Object
PDO communication can be described by the producer/consumer model. Process data can be transmitted
from one device (producer) to one another device (consumer) or to numerous other devices (broadcasting).
PDOs are transmitted in a non-confirmed mode. The producer sends a Transmit PDO (TxPDO) with a spe-
cific identifier that corresponds to the identifier of the Receive PDO (RxPDO) of one or more consumers.
Figure 3-13
CAN communication – Process Data Object (PDO)
There are two PDO services:
•
The Write PDO is mapped to a single CAN Data frame.
•
The Read PDO is mapped to CAN Remote Frame, which will be responded by the corresponding
CAN Data Frame.
Read PDOs are optional and depend on the device capability. The complete data field of up to 8 byte may
contain process data. Number and length of a device’s PDOs are application-specific and must be specified
in the device profile.
Communication Objects
Process Data Objects (PDO)
Service Data Objects (SDO)
Special Function Objects
Synchronization Objects (SYNC)
Time Stamp Objects (not used on EPOS4)
Emergency Objects (EMCY)
Network Management Objects
NMT Message
Node Guarding Object