SERCOS III requires dedicated hardware on both the Master and the Slave side. Such SERCOS III hardware relieves the host CPU of all communication tasks, and ensures quick real-time data processing and hardware-based synchronization. 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. Daisy chain or closed ring cabling is required for the network nodes. 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 will actually yield a single ring already, whereas a proper ring topology will produce a double ring, allowing for redundant data transfer. Cross-traffic is enabled by the two communication interfaces every node is equipped with: 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 a communication cycle, with no need to route their data through the Master.

Besides the real-time channel, which uses time slots with reserved bandwidths to ensure collision-free data transfer, SERCOS III also provides for an optional non-real-time channel. Nodes are synchronized on the hardware level, with a cue taken straight from the first real-time telegram at the beginning of a communication cycle. The Master Synchronization Telegram (MST) is embedded into the first telegram for that purpose. Keeping synchronization offsets below 100 nanoseconds, a hardware-based procedure compensates for runtimes and runtime variations resulting from the Ethernet hardware. Various network segments may use different cycle clocks and still achieve fully synchronized operation.