Abstract: A programmable controller has a first (executing) CPU unit and a second (standby) CPU unit for a duplexed operation. Each CPU unit stores CPU version indicating its functionality and function version indicative of the functionality of the user program stored in itself. Before the duplexed operation is started, the first CPU unit acquires the unit version of the second CPU unit, compares it with the function version stored in itself and judges from this comparison whether a duplexed operation is possible or not. Only if it is judged that the duplexed operation is possible, the first CPU unit copies the user program stored in itself to the second CPU unit together with the function version and the duplexed operation is started.

Abstract: A programmable controller includes two CPU units each having a detachably attached special-function module for carrying out a calculation process, each of the two CPU units recognizing conditions of the other CPU unit, one of them becoming an active unit and the other becoming a standby unit such that when the active unit fails and goes down the standby unit is switched to become active and resumes operations. The special-function module attached to the active CPU unit becomes an active module and carries out control processes with the active CPU unit and the other special-function module attached to the standby CPU unit becomes a standby module.

Abstract: A programmable controller has two communication units connected to a same network and a CPU unit. These two communication units are both identified by same unit-identifying data such as node numbers and unit numbers and function such that one of them operates in an active mode and the other operates in a standby mode. Each of these communication units, when in the active mode, operates to carry out data exchanges with the CPU unit and other nodes connected to the network and, when in standby mode, is prevented from carrying out any data exchange with the other nodes connected to the network. When the communication unit in the active mode fails and goes down, the one in the standby mode is switched to the active mode and carries out the data change. This mode-switching operation is carried out in response to a command from the CPU unit although it may be so arranged that the communication units communicate with each other and switch their modes by informing the occurrence of a failure to the other unit.

Abstract: A programmable controller has a first (executing) CPU unit and a second (standby) CPU unit for a duplexed operation. Each CPU unit stores CPU version indicating its functionality and function version indicative of the functionality of the user program stored in itself. Before the duplexed operation is started, the first CPU unit acquires the unit version of the second CPU unit, compares it with the function version stored in itself and judges from this comparison whether a duplexed operation is possible or not. Only if it is judged that the duplexed operation is possible, the first CPU unit copies the user program stored in itself to the second CPU unit together with the function version and the duplexed operation is started.

Abstract: A programmable controller includes two CPU units each having a detachably attached special-function module for carrying out a calculation process, each of the two CPU units recognizing conditions of the other CPU unit, one of them becoming an active unit and the other becoming a standby unit such that when the active unit fails and goes down the standby unit is switched to become active and resumes operations. The special-function module attached to the active CPU unit becomes an active module and carries out control processes with the active CPU unit and the other special-function module attached to the standby CPU unit becomes a standby module.

Abstract: A programmable controller has two communication units connected to a same network and a CPU unit. These two communication units are both identified by same unit-identifying data such as node numbers and unit numbers and function such that one of them operates in an active mode and the other operates in a standby mode. Each of these communication units, when in the active mode, operates to carry out data exchanges with the CPU unit and other nodes connected to the network and, when in standby mode, is prevented from carrying out any data exchange with the other nodes connected to the network. When the communication unit in the active mode fails and goes down, the one in the standby mode is switched to the active mode and carries out the data change. This mode-switching operation is carried out in response to a command from the CPU unit although it may be so arranged that the communication units communicate with each other and switch their modes by informing the occurrence of a failure to the other unit.