| 摘要 |
A semiconductor memory unit is operated by supplying an electric power from a system power source (200 v) used so as to be cut off at a predetermined time. The semiconductor memory unit includes a volatile memory for storing data that can be accessed by a host unit coupled to the semiconductor memory unit, a battery used as a back-up power source for the volatile memory, and a power supply controller, coupled to the system power source, the battery and an all-day service power source (100 v) having a capacity less than that of the system power source, for switching a power source by which electric power is supplied to the volatile memory from the system power source to the all-day service power source when the system power source is cut off, and for switching it from the all-day service power source to the battery when a service interruption of the all-day service power source occurs.
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