CAN interface configuration

The CAN interface of the EL6751 is configured via the StartUp SDOs of the objects 0xF800, 0x8000 and 0x8001 (optional) in the PREOP state.

CAN interface configuration 1:
Flow chart for CAN interface startup

After a power-on, the EL6751 is in the INIT state and has no CAN configuration. The CAN controller is in the OFFLINE state.

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.