Introduction Industrial Ethernet has become the de facto standard for manufacturing information networking, and the market is requesting Ethernet connectivity for servo drives. The problem is that Industrial Ethernet is characterized by high bandwidth and low hardware costs, but is not deterministic. The SERCOS interface, on the other hand, is optimized for high-speed deterministic motion control, which is required for the exact synchronization of multiple drives. SERCOS also defines a protocol structure and includes an ample variety of profile definitions for control for most motion and I/O devices. It has been successfully used on over 300,000 applications. The decision was made to combine the proven mechanisms and properties of the SERCOS interface with the high speed and low cost of the Industrial Ethernet physics, thus creating an advanced version of the most successful open motion control communications interface. Many technologies have been added to the Ethernet stack simply by adding a new protocol. But rather than put motion under TCP/IP (transmission control protocol/Internet protocol), resulting in less determinism and the added expense of switching devices, the SERCOS solution was to put the standard Ethernet TCP/IP under control of the motion bus, and use Ethernet hardware with its lower cost twisted-pair copper cable. (However, Ethernet fiber optics will be supported by SERCOS-III.) This maintains the deterministic motion control of SERCOS, allows links to the existing manufacturing communications infrastructure, provides for the possibility of new features and lowers hardware costs. And noise immunity will not be a major problem, as Ethernet's twisted pair cable is generally extremely noise immune because it uses a differential driver and receiver.