Patent ID: 8738808

Claim:
A programmable logic controller (PLC) system comprising: a PLC including a first connection terminal connected to an extended input/output (I/O) module, and a first communication terminal connected to a communication line to a remote I/O module; the remote I/O module including a second communication terminal, and configured to communicate data of the PLC with the PLC through the first and second communication terminals; and the extended I/O module including a second connection terminal, and mounted to the PLC to communicate the data of the PLC through the first and second connection terminals, wherein the PLC comprises: a first communication unit configured to communicate with the remote I/O module, a second communication unit configured to communicate with the extended I/O module, first and second switching units configured to perform switching operation to communicate with either or both of the remote I/O module and the extended I/O module, a third switching unit configured to perform a switching operation to configure a ring topology with the remote I/O module and the extended I/O module, and a first control unit configured to control the first, second, and third switching units.