SERCOS III

Sercos III is the third generation of the Sercos interface, a standardized open digital interface for the communication between industrial controls, motion devices, input/output devices, and Ethernet nodes, such as PCs. Sercos III applies the hard real-time features of the Sercos interface to Ethernet.

SERCOS III

STANDARDS BODY, TITAN AND PHILOSOPHY

A freely available real-time communication standard for digital drive interfaces, SERCOS III not only specifies the hardware architecture of the physical connections, but also a protocol structure and an extensive range of profile definitions. For SERCOS III, effectively the third generation of the SERCOS Interface (SERCOS, Serial Realtime Communication System) that was originally introduced to the market in 1985, Standard Ethernet according to IEEE 802.3 serves as the data transfer protocol. This communication system is predominantly used in motion control-based automation systems. A registered association, SERCOS International, supports the technology‘s ongoing development and ensures compliance with the standard.

ARCHITECTURAL PHILOSOPHY: OPEN SOFTWARE/MODIFIED ETHERNET

SERCOS-III uses the Ethernet physics (100Mbps) and the Ethernet telegram while retaining the existing SERCOS mechanisms. SERCOS-III is likewise based on a time slot mechanism in which bandwidth is reserved for the isochronous (real-time channel) and asynchronous (IP channel) data traffic. SERCOS-III works without hubs or switches. Each station has a special integrated ASIC or FPGA with two communication ports, enabling it to be connected via line or ring topology. Eliminating the switches means shorter cycle times can be implemented, though at the cost of flexibility in the network topology.

While specific hardware is categorically needed for the slave, a software solution is also feasible for the master. The SERCOS user organization provides a SERCOS III IP core to support FPGA-based SERCOS III hardware development. SERCOS III uses a summation frame method. Network nodes must be deployed in a daisy chain or a closed ring. Data is processed while passing through a device, using different types of telegrams for different communication types. Due to the full-duplex capability of the Ethernet connection, a daisy chain actually constitutes a single ring, whereas a proper ring topology will in effect provide a double ring, allowing for redundant data transfer. Direct cross-traffic is enabled by the two communication ports on every node: in a daisy chain as well as a ring network, the real-time telegrams pass through every node on their way back and forth, i.e. they are processed twice per cycle. Hence, devices are capable of communicating with each other within one communication cycle, with no need to route their data through the master.

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