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Sercos-III-Information
3 Sercos-III-Information
Sercos III (Serial Realtime Communication System) is a real-time Ethernet
technology and is the third generation of the non-proprietary Sercos bus system
according to IEC 61491.
From drives and controls to I/O peripherals, all automation components are easily
compined to form an understandable and capable overall system. With real-time and
innovative features, sercos provides maximum performance and flexibility in all
applications.
3.1 Sercos-III-Communication cycle
Figure 1: Sercos-III-Communication cycle
Sercos III uses the IEEE 802.3 compliant Ethernet protocol type 0x88CD to send data
in cyclic telegrams. The exchanged data can be addressed via standardized
parameter numbers (IDN´s) of the encoder and generic device profile.
Telegrams
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Device channels are allocated to each slave in the MDT and AT. The slaves read data
from and write data to the channels. Up to four MDTs and four ATs are sent from the
master per clock cycle depending on the data volume.
The conventional Ethernet communication is handled outside the Sercos-III-Telegrams
in a so-called Unified Communication Channel (UCC). Thus, Sercos-III-Devices can
be addressed directly by means of the MAC or IP address.
Sercos-III-Telegrams contain a Sercos-III-Header and a data field which are
embedded in the Ethernet frame.
The MDT and AT data fields are sub-divided into different sub-fields
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Master-Data-Telegram (MDT): Command data from the master to the slaves
Acknowledge-Telegram (AT): Status data from the slaves to the master and to
other slave devices
Hot-Plug field: Integration of slaves during operation
Service-channel field (SVC): Exchanging of acyclic data
Real-time data field: Exchanging of acyclic data, cyclic or synchronous data
TR - ECE - BA - DGB - 0105 - 03
Printed in the Federal Republic of Germany
08/31/2017