The Sercos III specifications provide for three possible network topologies: ring, line, and double line.
The Modicon M262 Motion Controller supports line topologies:
Each telegram “begins” and “ends” at the master. This is possible due to full duplex operation.
Each slave has two communication ports, P1 and P2. The ports are interchangeable. The telegrams for a cycle originate from the master. They are transmitted to the first slave on the line which receives them via its receive port (P1 in the figure), reads the MDTs and, if necessary, writes data to the slot reserved to it in the ATs. The first slave then forwards the telegrams via its transmit port (P2 in the figure) to the next slave on the line. This procedure is repeated until the last Sercos device on the line is reached.
The last slave detects no further Sercos device on the line and redirects the telegrams back to the master (loopback). On their way back to the master, the telegrams pass each slave a second time in reverse order.
The last slave on the line also makes the received telegrams (Sercos and Ethernet/IP) available at its transmit port (P1 in the figure). This feature enables, for example, hot-plugging of additional Sercos devices and transmission of the telegrams to devices using other protocols.
