Densoshisutemu

摘要

PURPOSE:To prevent system interruptions in a system which performs information transmission between plural terminals, by controlling the supply of a back- up electric power to a terminal whose power supply is downed based on the operating condition of the other terminals at the time when the power supply to the terminals is downed. CONSTITUTION:Plural terminals are connected in a form of a loop with an optical fiber 13 and controlling lines 14 and 15 of DC power supply. An interface circuit 1 receives a DC power supply from a signal processing section 7 through a power supply line 18 and a relay driving line 17, operates a transmission-reception module 16, and transmits signals to the processing section 7 through a signal line 19. When the power supply of the processing section 7 is not made, relays A and B do not operate, a contact (a) is disconnected, and a contact (b) is connected to a contact (c). In this case, when the other terminals operate, the electric power from the driving line 17 of the operating terminals closes the contact (a) by operating the relay A through the lines 14 and 15, and the module 16 is operated by connecting a back-up power source 20 to the module 16, and thus, interruptions of information transmission of the system are prevented.