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Introduction to Sercos interface
Advantages
Applications Types
Sercos III
Sercos I and II
Fiber Optics
ASICs
Timing & Interface
Sercos IDNs
I/O Functions
Cycle Times
Cyclic Operation
System Safety
Packaging Profile
Sercos Standardization
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.

Topology

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.


Communications Structure

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.