Sercos 3

Sercos 3 is the third and as such, the latest model of the Sercos interface automation bus series, which was first marketed in 1985. Since then, the Sercos series has developed into a worldwide standard in automation technology, based on good quality and, in terms of the product innovations, low interference susceptibility. In 1995, Sercos Interface was named as worldwide standard for motion control communication. Today, Sercos has over 2 million installed Sercos nodes in approximately 350,000 applications.

The Innovations with Sercos III

Easy Slave - The new Innovation of the Automation Bus

Because of the development of the easy slave chips, Sercos III is not only suited to drives (as was the case with the two predecessors in the Sercos series) but now also for the I/O slaves as well. Sercos slave devices can now be added flexibly and without much effort. These I/O slaves are synchronized in the Sercos cycle, whereby the connection to the sensor and the actuator layer can be achieved even easier. The Easy Slave single-chip controller supports up to 32 bytes of output data and 32 bytes of input data in the real-time channel. 

The new Sercos Monitor

The processes in the Sercos III network can be analyzed and traced most accurately by the Sercos monitor. These analyses and evaluations can be performed in real-time as well as through network records.
The typical characteristics of the Sercos III network, e.g. the topology or the communication phases, can be seen through the user-friendly program interface. By means of filter settings, the monitor view always meets the requirements of the user with regard to the program. As such, the desired information can be found accurately and in the shortest time.

Networking of the Systems using Ethernet Technology

In Sercos III, networking is now realized via Fast Ethernet technology. The Ethernet standard is best suited for networking the increasingly complex automation components within a network and it also meets the technical requirements. The Ethernet technology makes data transfer possible that is 10 to 100 times higher than conventional fieldbuses. Furthermore peripheral, drive, safety and office communication are combined into one medium.


Functionality of Sercos III

Sercos III supplements the mechanisms of the predecessor products in the Sercos series with Ethernet technology. Telegram data are transmitted in the real-time channel with high protocol efficiency. However, other Ethernet telegrams can also be transferred into a non-real-time channel. This varies depending on the application requirements. The Sercos III communication is based on the parameters specified by the configuration. Sercos III is provided with the most important communication channels and device profiles:

1. Real-time Communication Channels
M/S device channel:
Data exchange between the master and slaves
CC device channel (Cross Communication):
Data exchange between control units or peripheral slaves
Service channel:
Service data exchange
SMP (Sercos Messaging Protocol):
Transfer of function data
Sercos Safety:
Exchange of safety-relevant data in a CC device channel

2. Universal Communication Channel
The connection of any Ethernet devices (for example notebook) is enabled by standard Ethernet, as well as transfer of protocols in the Unified Communication Channel (UCC).

3. Device Profiles
Motion profile:
For controlling Sercos motion control parameters
Drive profile:
For controlling drives

4. Energy Profile
Enables an energy-saving operation of the machines operating with Sercos III

IP Communication

The conventional IP communication takes place outside the Sercos III network, which is based on communication by means of telegrams.This IP communication is realized in the Unified Communication Channel (UCC). Examples for this type of communication include e-mail and web services.

Communication via the High-performance Protocol

Matched to the automation industry, Sercos III uses high-performance protocols. The data are sent in cyclic telegrams. Standardized by the parameters of the device profiles, these make the communication channels mentioned above available. A distinction is made between two telegram types:

Master Data Telegram (MDT)
The master sends data to the slaves.

Answer Telegram (AT)
The slaves send data to the master and other slave devices.

At the time of initialization, each slave is assigned device channels in the MDT and in the AT with which it receives or sends telegrams.

Depending on the quantity of data, up to 4 MDT and 4 AT are sent by the master.

Telegram Structure

The clear and robust data structure of Sercos III increases operational reliability and provides for transparent, traceable processes within the network. Installation diagnoses on any network nodes also can be realized easily.
The Sercos III telegrams consist of a Sercos III header and a data field, which is embedded in the Ethernet frame. The header provides information about the position of the telegrams, as well as the phase of the network at a specified time. The data fields of MDT and AT can be subdivided into three areas:

1. Hot-plug field:
Details of the slaves newly coupled to the network

2. Service channel field:
Device channels which serve to configure the slaves

3. Real-time data field:
Device channel of the slaves in order to send (MDT) or receive (AT) cyclic real-time data.


Integrated Safety with Sercos III

The CIP Safety On Sercos protocol transfers data that guarantee safety in the Sercos Interface network. This eliminates the need for an additional safety bus that normally would assume this function. CIP Safety On Sercos transfers the data in the same way as normal standard data, i.e. on the same medium. With this, the functionality of the safety protocols lies in the terminal devices. This enables simultaneous operation of standard and safety devices in the Sercos Interface network. This safety is guaranteed for all communication levels and channels.