Abstract: A communication system includes a master device and a slave device that perform, at predetermined periods, communication for sharing storage data stored in a cyclic memory. The master device transmits communication data that includes (i) identification information distinguishing a period relating to the communication data from other periods before and after the period and (ii) target information indicating whether the communication data is a target that is to be communicated by the communication at the predetermined periods or is an exception to be excluded from being the target. The slave device discards the received communication data when (i) the target information included in the received communication data indicates that the communication data is the target and (ii) a period indicated by the identification information included in the communication data is different from a current period, and processes the communication data.

Abstract: A communication system includes a master device and a slave device that perform, at predetermined periods, communication for sharing storage data stored in a cyclic memory. The master device transmits communication data that includes (i) identification information distinguishing a period relating to the communication data from other periods before and after the period and (ii) target information indicating whether the communication data is a target that is to be communicated by the communication at the predetermined periods or is an exception to be excluded from being the target. The slave device discards the received communication data when (i) the target information included in the received communication data indicates that the communication data is the target and (ii) a period indicated by the identification information included in the communication data is different from a current period, and processes the communication data.

Abstract: A received-data writer of a network unit records first data in a first data area when a flag is set indicating that a write is allowed, and records second data in a second data area. The first data are data for which data consistency is to be guaranteed among received data that is received from the first slave station and a second slave station, and the second data are data for which real-timeliness is to be guaranteed among the received data. A first transferrer of a CPU transfers the first data recorded in the first data area to a first storage at an interval of a first transfer period when the flag is set indicating that a read is allowed. A second transferrer of the CPU transfers the second data recorded in the second data area to a second storage at an interval of a second transfer period.

Abstract: A received-data writer of a network unit records first data in a first data area when a flag is set indicating that a write is allowed, and records second data in a second data area. The first data are data for which data consistency is to be guaranteed among received data that is received from the first slave station and a second slave station, and the second data are data for which real-timeliness is to be guaranteed among the received data. A first transferrer of a CPU transfers the first data recorded in the first data area to a first storage at an interval of a first transfer period when the flag is set indicating that a read is allowed. A second transferrer of the CPU transfers the second data recorded in the second data area to a second storage at an interval of a second transfer period.

Abstract: A programmable logic controller includes a state monitoring unit to monitor a state of another programmable logic controller that is a counterpart in the duplication, and a system switching control unit to transmit, to a slave device, status information including information indicating whether the programmable logic controller is a control system or a standby system, to receive the control data that is addressed to the programmable logic controller that is the control system and is transmitted from the slave device in a case where the programmable logic controller is the control system, and to switch the programmable logic controller to the control system when hindrance in the another programmable logic controller is detected in a case where the programmable logic controller is the standby system.

Abstract: A programmable logic controller includes a state monitoring unit to monitor a state of another programmable logic controller that is a counterpart in the duplication, and a system switching control unit to transmit, to a slave device, status information including information indicating whether the programmable logic controller is a control system or a standby system, to receive the control data that is addressed to the programmable logic controller that is the control system and is transmitted from the slave device in a case where the programmable logic controller is the control system, and to switch the programmable logic controller to the control system when hindrance in the another programmable logic controller is detected in a case where the programmable logic controller is the standby system.