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Sercos master is made available as free, open-source software

21 August, 2017

A software-based Sercos industrial Ethernet master that can be implemented on industrial automation controllers instead of needing dedicated hardware, is now available as free, open-source software. The Sercos SoftMaster package is said to offer more than 95% of the capabilities of a Sercos HardMaster hardware version.

Bosch Rexroth – the originator of Sercos – has made the Sercos SoftMaster software available on the open-source platform, It is also offering a demo Sercos driver package on a USB memory stick, called the Sercos-on-a-Stick livesystem.

Sercos (SErial Realtime COmmunication System) is a digital interface for communications between controls, drives and decentralised peripheral devices. It has been used by machinery engineers for about 25 years and has been implemented in more than 5 million real-time nodes. Its latest version, Sercos III, is an open, manufacturer-independent, Ethernet-based bus for all automation applications.

The SoftMaster system is scalable:

•  For entry-level applications with bus cycle times above 500µs, a line topology, and microsecond-range synchronicity between the system components, a standard Ethernet controller with an real-time operating system is sufficient. It is estimated that this would be suitable for at least 50% of potential applications.

•  For medium-to-high synchronicity requirements  less than 100ns and bus cycle times greater than 125µs (which covers almost all applications), a TTS-capable Ethernet controller can be used with a real-time operating system. If two of these controllers are synchronised, a ring architecture with seamless redundancy can be created.

Sercos HardMaster hardware systems will continue to be available for applications with higher bus cycle time requirements, or where the hardware and operating system platform requirements cannot be met.

The Sercos SoftMaster is intended for implementing a software-based Sercos industrial Ethernet master on industrial automation controllers.

Using a generic mode, Sercos SoftMaster can run on almost any Ethernet controller. However, telegram jitter reduces the synchronisation accuracy. For higher synchronicity and cycle time requirements, the NIC/TTS (Network Interface Controller/Time Triggered Send) mode allows the Ethernet controller to determine the telegram transmission precisely using its own timer. Software-based timing disturbances (jitter) are said to be eliminated because programs need only ensure that telegram content is fed to the Internet controller within the time window provided.

The open-source SoftMaster is available under an MIT license in which the license conditions do not require users to disclose their expertise.

A free operating system abstraction and a test application are available from Bosch Rexroth on request to

•  Sercos International and the OPC Foundation have issued a Sercos OPC UA Companion Specification Release which describes the mapping of the Sercos device model and the Sercos device profiles to OPC UA, so that functions and parameters of Sercos devices are made accessible via OPC UA in a vendor-independent manner. This initiative aims at to simplify communications between machine peripherals and supervisory IT systems and to support the requirements of Industry 4.0 regarding semantic interoperability.

On the one hand, OPC UA server functions can be implemented in a Sercos master device, such as a PLC or CNC. On the other hand, it is possible to transfer these functions to a Sercos slave device, with OPC UA accesses executed in parallel to the Sercos real-time communications or even without any Sercos real-time communications. Thus, consistent communication with OPC UA is possible down to the field level without abandoning the hard-real-time communications of the Sercos automation bus.

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