Duplex system

A duplex system comprising duplicated processor devices, in which one of the processor devices is a control side processor device which controls an input module and an output module, and the other of the processor devices is a standby side processor device,

• wherein each of the processor devices comprises:
• a first copying section which writes data written in a memory of the processor device, into a same address of a memory of the other processor device;
• a second copying section which divides all data in the memory of the processor device to sequentially write all data into the memory of the other processor device periodically;
• an error detecting section which checks the data written in the memory of the processor device;
• and
• an error check register which sets an error bit when the error detecting section detects an error, and
• after the first copying section and the second copying section write data into a memory of the standby side processor device, the control side processor device checks an error bit of an error check register of the standby side processor device.