...
The LEDs on our master hardware have a wide variety of states to get a first hint of what might be the issue:
Topology Error
One of the most crucial parts and often the cause of issues is the cabeling / topology of the EtherCAT network. Our master firmware is really strict about proper topology.
...
To determine the difference between the configured and the real topology use the Diagnosis and do a "Online Comparison". This will also show, if all the device descriptions used match the real hardware, according to the parameters: Vendor ID, product code and Revision.
Configuration does not Match
If you get one of the following Errors: 0xC0D5001D or 0xC0D5001E it means either the Output or the Input Configuration does not match.
...