SERCOS interface

Sercos ( SErial Realtime COmmunication system ), the automation bus, is a world standard digital interface for communication between controllers and fieldbus (IEC 61491 and EN 61491 ). This is very precise and real-time synchronization of controllers, servo drives, inputs and outputs, frequency converters, encoders, cameras, etc.


Mid-80s developed the ZVEI and the German Machine Tool Builders ' Association (VDW ) the specifications for an open digital interface.

The first generation sercos I was recognized in 1995 and worked at a transmission rate of 2 or 4 Mbit / s

The second generation sercos II was introduced in 1999 and works with up to 16 Mbit / s and has a service channel for transmission of asynchronous data.

The third generation sercos III is used since 2005 in components.

Transmission medium

The transmission medium is an optical waveguide - ring for sercos I and II used for sercos III communicating across the physical medium of Ethernet, later is still a variant added which is constructed as in sercos I and II via a fiber optic ring.


Properties of sercos III are:

  • Collision-free transmission by means of a time -slot mechanism
  • Highly efficient communication protocol
  • Up to 511 participants
  • Synchronization, for example, 66 axes with a cycle time of 1 ms and a jitter of less than 20 nsec.

Sercos, the automation bus is supported by sercos International eV (SI). As part of this industry association for the standardization and user support take place.