Performance und Effizienz SERCOS III

What is Sercos III?

Sercos III is a further development of the existing Sercos Interface standard (IEC/EN 61491) based on the standard Ethernet, which is characterized by increased performance and efficiency. Sercos mechanisms, which were already tried and tested, for example the motion control profile specified in the Sercos standard, the telegram structure, and the hardware synchronization, were transferred to the Ethernet standard.

How does Sercos III function?

(1) Basics

To fulfill the requirement of real-time transmission, a collision-free real-time channel is connected in parallel to a non real-time channel. the telegrams defined by Sercos are transmitted with high protocol efficiency in the collision-free real-time channel. By doing this, the best possible performance of Sercos III is obtained even with a high number of users.

This parallel connection also enables transmission of any Ethernet telegrams and IP-based protocols (for example TCP/IP, UDP/IP) in the non real-time channel (also called time slot) without endangering the guaranteed cycle times of the real-time data. This enables, for example, a parameterization without continuous control with a standard notebook and Ethernet interface.
The performance and the efficiency of Sercos III are increased especially by maintaining the advantages of the approach and simultaneous enabling of new features.

This considerably widens the application range of Sercos III:

  • max. possible compatibility with the existing Sercos interface (topology, profile, telegram structures, synchronization) reduces the resulting costs.
  • Hardware costs are reduced.
  • Continuous communication with any Ethernet protocols (for example UDP/IP, TCP/IP) is enabled.
  • Direct cross communication between slaves is possible.
  • Synchronization of multiple controls/machine segments.
  • Safety data can be transmitted without interfering with the operation.
  • Increased fault tolerance, for example in case of an open circuit.

With this, the communication between the components is based on standardized parameter sets for control of device functions. These are independent of the manufacturer, as well as the hardware. When a network is initialized, the configuration specifies the different parameters forming the real-time data of a specific device channel.

By doing this, Sercos III has communication channels and device profiles for all current automation applications that increase the performance and the efficiency of Sercos III:

Real-time Communication Channels

  • M/S (master/slave) device channel: Direct exchange of function data between master and slaves 
  • CC (cross communication) device channel: Direct cross-communication between devices, either between controls (C2C) or between drive or peripheral slaves
  • SVC (service channel) channel: Exchange of service data
  • SMP (Sercos messaging protocol) time slot: Transmission of function data of multiple participants by means of a multiplex process
  • Sercos Safety: Exchange of safety data in an MS or a CC device channel. These include, for example, switch-off or acceptance signals or also safe target values.

Universal Communication Channel

  • Standard Ethernet: Connection of any Ethernet device like notebook, webcam, or I/O peripheral device
  • Other Ethernet protocols: Transmission of any Ethernet-based protocols in the Unified Communication Channel (UCC).

Device Profiles

  • Motion profile: Motion and SPS functions for control based on the Sercos motion control parameters
  • Drive profile: Functions for control of drives I/O profile
  • Energy profile

(2) Details


1. Synchronicity

Sercos III refers to the proven hardware synchronization. Each model has a special logic chip (ASIC), which coordinates the system points with each other. This makes additional expensive hubs and switches unnecessary, and the network adjusts itself mostly independently. Synchronicity thus becomes a basic characteristic of each Sercos system.
This synchronicity and the data transfer rate of 100 Mbps (Fast Ethernet) in full-duplex mode results in a min. cycle time of 31.25 microseconds and thus a maximum efficiency and performance of Sercos III.

2. Flexibility

As production processes in most cases require high flexibility, the requirements for the flexibility of the network are also high. Normally the individual components (slaves) are controlled by a control (master), which again communicate with each other via a common network segment.
However, the ability of one component to directly inform another one by cross-communication increases the performance and efficiency of Sercos III. The direct data exchange reduces the load of the central control and reduces the data traffic in the network. The decentralized control of complex production installations is based on the so-called C2C (control-to-control) cross-communication.

3. Safety

The technique of cross-communication between individual nodes not only contributes to flexibility, efficiency, and performance of Sercos III, but also increases the safety, as this makes it possible to establish a Sercos III network with a ring structure. Thus, for example, a redundant signal path can be used in the case of anopen circuit. This is not the case with the classic Ethernet. The data transfer is also safer: Sercos offers a certified security log, the Sercos Safety, which meets the requirements of the safety standard IEC 61508 up to the safety integrity level 3. Sercos Safety is safeguarded against errors like repetition, loss, insertion, wrong sequence, corruption, delay, and confusion of secure data with standard data.

4. Reliability

The combination of performance and efficiency of Sercos III, the flexible application, and checked security meets all requirements ofa modern, continuous automation network. It offers suitability for daily use through the classic Sercos protocol and security for the future by the real-time Ethernet solution.


Since October 2007, all three Sercos generations belong to the international standards IEC 61784-2 (Digital Data Communication in Control Technology) and IEC 61158 (Fieldbus for Industrial Control Systems).
First of all, Sercos III offers not only impressive performance data, but also performs complex automation tasks with high efficiency. Thus, for example, up to 330 drives with 4 bytes I/O data and each 8 digital I/E can communicate with each other in a cycle of one millisecond.
Thanks to the high efficiency and performance of Sercos III, for the foreseeable future there will be no applications that would require a higher speed of the network.
For users as well as for developers, efficiency and performance of Sercos III mean sustainability and planning security for investments in existing and new machine systems.