CANopen over EtherCAT

The CANopen over EtherCAT (CoE) protocol enables the complete CANopen profile family to be utilized via EtherCAT. The SDO protocol is used directly, so that existing CANopen stacks can be used practically unchanged. Optional extensions are defined that lift the 8-byte limit and enable complete readability of the object list.

The process data are organized in process data objects (PDO), which are transferred using the efficient means of EtherCAT - naturally without 8-byte limit. All CANopen profiles - including the drive profile (DS 402) - are fully usable, and devices based on it can be transferred to EtherCAT very easily.

Apart from a few details, the EtherCAT state machine of the slave corresponds to the CANopen state machine, so that only a limited number of changes are required. To enable less ambiguous start-up behavior, a further state called "safe operational" is defined, to which inputs that are already valid are transferred, while the outputs remain in safe state.

The AX2000 contains the CANopen profile, to implement the technical drive functions:

1. There are 8 fixed PDO configurations. No other information can be configured in the cyclic data exchange. The PDO configurations are to be considered as "constant configurations".
2. If other information is required, this can only be read and written asynchronously via ADS (entirely normal CAN objects). Almost every item of information is available as a CAN object (SDO): see examples in the appendix, e.g., the drive's error codes or warnings etc.).
3. Resolver: one motor rotation has a fixed 20 bit resolution
   (see ASCII parameter <PRBASE> equal to 20).

State machine