|Sercos I & II are the first two generations of the Sercos interface, both of which generally use ASICS (Application Specific Integrated Circuits) as bus controllers and fiber optics as the transmission medium. (Some uniquely-designed bus controllers do exist.)
The difference between the two is that Sercos I uses an ASIC that operates at 2 and 4 Mbit/sec (now obsolete) and Sercos II uses an ASIC that operates at 2/4/8/16 Mbit/sec, downward compatible with the Sercos I ASIC. Except for the difference in speeds, the descriptions in this section apply to both versions.
Devices in Sercos I and II-based motion control systems are connected via fiber optic rings using a master/slave configuration. A typical system may include several rings, with up to 254 devices per ring. A Sercos interface master controls each ring, assigning timeslots to ensure deterministic and collision-free access for all slaves.
In order to ensure strict synchronization of multiple axes and a predictable update time at each axis, a Sercos motion control acts as a master, with the drives as slaves. The drives are only permitted to respond to queries from the motion control. Note that the new Sercos-III supports slave-to-slave data transfer.