| 摘要 |
PURPOSE:To prevent a call from being affected by the fault of a power source even when it occurs, by providing an independent power disconnection detection circuit in respective system between duplexed MPR and CPR. CONSTITUTION:The power disconnection detection circuits 7 are provided in all of the CPRs #00-#N0 and #01-#N1 of both systems and MPRs #0 and #1 of both systems. When the disconnection of the power circuit 5 of the interme diate CPR of the CPRs #00-#N0 where the power disconnection detection circuits 7 are connected in series is generated, no operation of the power discon nection detection circuit 7 of the CPR #k0 is performed. Thereby, the output resistance of the power disconnection detection circuit 7 of the CPR #k0 becomes high impedance, and the input terminal 7a of the power disconnection detection circuit 7 of the CPR #k-10 at the preceding stage becomes high impedance, As a result, the high impedance is transferred to the CPR #i0 one after another, and finally, the input of the system switching circuit 8 of the MPR #0 becomes a high level, then, the system switching circuit 8 switches an operating system from a system 0 to a system 1 immediately. Thus, the operating system is switched immediately to a waiting system when the fault of power disconnection at one of the CPRs of the operating system is generated.
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