Beckhoff EL6751 Documentation page 156

Parameterization and commissioning
CAN bus parameters
The CANopen configuration is carried out via SDO download in the PREOP state. The objects to be loaded
must be transmitted either with Complete Access or with consistency nesting (first set SubIndex 0 to 0, then
write SubIndex 1-n, then set SubIndex 0 to n). Care should thereby be taken to always start with object
0xF800. After receiving the object 0xF800, the EL6751 switches the CAN controller with the appropriate
baud rate from 0xF800:02 to ONLINE.
CAN interface configuration
After object 0xF800, object 0x8000 and, if Rx filter table is to be used, object 0x8001 must be transmitted.
PDO Mapping
There is one EtherCAT RxPDO and one EtherCAT TxPDO for the CAN interface. The PDO mapping of the
EtherCAT PDOs is automatically calculated by the EL6751 after the download of the object 0x8000 and can
be read. The PDO mapping objects can only be written with the values that the EL6751 has calculated itself.
The writing of the PDO mapping thus serves only to check the PDO mapping calculated by the EtherCAT
configurator and can therefore be omitted.
PDO Assign
In addition, there is one EtherCAT RxPDO and one EtherCAT TxPDO, the CAN control and CAN status.
These PDOs are selected via the PDO Assign. It should thereby be observed that the EtherCAT PDOs of the
CAN interface must appear in the PDO Assign. With regard to the order of the PDOs in the PDO Assign, it is
important to ensure that the index of the assigned EtherCAT PDO increases with each entry in the
corresponding PDO Assign object. If the EtherCAT master does not transmit any PDO Assign in the StartUp
SDOs, then PDO 0x1A85 (CAN status) is transmitted alongside the CAN interface.
Cyclic communication
During the transition to SAFEOP, the EL6751 checks the length configured in the Sync Manager channels 2
and 3 against the length calculated from PDO Mapping and PDO Assign. The SAFEOP state is only adopted
if these lengths match. In the SAFEOP state, the EL6751 can already receive CAN messages that are stored
in the local RX queue. As soon as the EL6751 has been switched to OP, the data from the EtherCAT outputs
are adopted and the CAN messages can also be exchanged via EtherCAT.
5.5.2.2 CAN interface synchronization
The CAN interface cycle, which determines the CAN messages to be sent from the EtherCAT output data
and enters the CAN messages received in the EtherCAT input data, is synchronized with the EtherCAT
cycle. Synchronization takes place by default via the Sync Manager 2 event. In Fast CAN Queue mode, the
EL6751 can also be operated in the Distributed Clocks mode; in this case, synchronization takes place via
the SYNC0 and the SYNC1 events.
Buffered CAN Queue
The following flow chart shows the sequence of the CAN cycle in the Buffered CAN Queue mode.
156 Version: 3.5 EL6751