[bartlettD]

EtherCAT is built on top of IEEE 802.3 Frames, you're right that there is a special controller but those interface over MII to a standard Ethernet PHY.

They don't look like valid Ethernet Frames, they are valid Ethernet Frames. Ethercat embeds its Ethertype within the frame the same way that other protocols do.

As you say, EtherCAT does its own thing with the frames, to get the real-time determistic performance it needs, but EtherCAT and other 802.3 Frames can co-exist.

https://www.ethercat.org/pdf/english/EtherCAT_Introduction_0...

Slide 25-32 are a good high level overview of possibilities. Slide 32 shows a setup with Co-Existance.

[PinguTS]

Thanks for referencing. I still have one of the original specification somewhere in my closet, when I was asked to review it.

They are made to look alike valid Ethernet frames. The idea was: how to make Interbus look alike Ethernet and how to make some patents to make money out of it. Originally you had to buy the controllers from Beckhoff. Now they are integrated by many µC, but still they have to pay licensing fees to Beckhoff.