Patent ID: 8321037

Claim:
A PLC distributed control system, comprising: a plurality of PLCs each including a communicating unit, wherein each PLC of the plurality of PLCs includes, a first storage unit that stores output schedule definition frames corresponding to other PLCs, wherein each output schedule definition frame corresponding to a respective other PLC is formed of output schedule definition information, which define, by respective bits, whether or not output variables that simulate output coils in a ladder diagram executed on the PLC are scheduled to be output to a respective other PLC, a second storage unit that stores reference schedule definition frames corresponding to the other PLCs, wherein each reference schedule definition frame corresponding to a respective other PLC is formed of reference schedule definition information, which define, by respective bits, whether or not output variables that simulate output coils in a ladder diagram executed on the respective other PLC are scheduled to refer to every output variable, a transmitter that transmits the output schedule definition frames or the reference schedule definition frames to other PLCs; a receiver that receives other output schedule definition frames or other reference schedule definition frames from the other PLCs; a collating unit that collates, bit by bit, the other output schedule definition frames or the other reference schedule definition frames received from the other PLCs with the output schedule definition frames and the reference schedule definition frames stored in the first and second storing units, on a corresponding frame basis for each respective other PLC, respectively, and a normal communication start deciding unit that decides whether or not a normal communication in the PLC distributed control system is started, based on a collated result by the collating unit, wherein the normal communication is inhibited in response to an inconsistency in at least one bit as a result generated by the collating unit.