SERCOS III

SERCOS III is an open, Ethernet-based real-time communication protocol for automation devices. It uses Fast Ethernet at 100 Mbps full duplex and summation-frame transmission, with configurable communication cycles from 31.25 μs to 65 ms and synchronization accuracy below 1 μs. It supports ring, line and star/tree topologies, direct cross communication between slaves, and safety functions up to SIL3 with CIP Safety according to IEC 61508.

Source checked4/4 values · 2026-10-25

Specification

2 sources

Transports	ethernet l2
Architecture	master slave
Encoding	binary
Standard body	IEC
Standard ref	IEC 61784, IEC 61158, IEC 61800-7

Study notes

Communication cycle time is configurable between 31.25 μs and 65 ms.
Synchronization accuracy is less than 1 μs.
Process data is consolidated into one summation-frame telegram rather than transmitted in individual telegrams.
Hot plugging does not affect real-time or synchronization characteristics.
TCP/IP and other Ethernet-based protocols can share the same cable with real-time data.
Sercos slaves can communicate directly with one another through cross communication.
Supported topologies include ring, line, and star/tree structures.
Ring redundancy is supported.
Devices and their positions in the topology are recognized automatically.
Drives can be parameterized over Sercos without a separate configuration device.
Sercos uses IEEE 802.3 Ethernet physics and copper or fiberglass cables.

Safety

Safety functions up to SIL3 can be implemented with CIP Safety on Sercos according to IEC 61508.
Safety-relevant and non-safety-relevant data are transferred over the same cable.
CIP Safety routing allows devices to communicate safely outside network boundaries.
In a ring configuration, cable breaks are recognized within 25 μs and data is lost for at most one cycle.