Semiconductor memory unit used as external storage
First Claim
1. A semiconductor memory unit operated by supplying electric power from a first power source, used so as to be cut off at a predetermined time, said semiconductor memory unit comprising:
- volatile memory means for storing data that can be accessed by a host unit coupled to said semiconductor memory unit, said volatile memory means maintaining the data while electric power is being supplied;
a battery used as a back-up power source for said volatile memory means;
a second power source, said second power source being available continuously when there is no service interruption of said second power source; and
power supply control means, coupled to said first power source, said battery and said second power source for switching a power source by which electric power is supplied to said volatile memory means from said first power source to said second power source when said first power source is cut off, and for switching electric power from said second power source to said battery when a service interruption of said second power source occurs, said power supply control means including first detection means for detecting whether or not said first power source is cut off, second detection means for detecting whether or not service interruption of said second power occurs, and selecting means for selecting the power source by which electric power is supplied to said volatile memory means from among said first and second power sources and said battery based on results obtained by said first detection means and said second detection means, said selecting means including first means for selecting said first power source when said first detection means detects that said first power source is not cut off, second means for selecting said second power source when said first detection means detects that said first power source is cut off, and third means for selecting said battery when said first detection means detects that said first power source is cut off and said second detection means detects that service interruption of said second power source occurs.
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Accused Products
Abstract
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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Citations
7 Claims
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1. A semiconductor memory unit operated by supplying electric power from a first power source, used so as to be cut off at a predetermined time, said semiconductor memory unit comprising:
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volatile memory means for storing data that can be accessed by a host unit coupled to said semiconductor memory unit, said volatile memory means maintaining the data while electric power is being supplied; a battery used as a back-up power source for said volatile memory means; a second power source, said second power source being available continuously when there is no service interruption of said second power source; and power supply control means, coupled to said first power source, said battery and said second power source for switching a power source by which electric power is supplied to said volatile memory means from said first power source to said second power source when said first power source is cut off, and for switching electric power from said second power source to said battery when a service interruption of said second power source occurs, said power supply control means including first detection means for detecting whether or not said first power source is cut off, second detection means for detecting whether or not service interruption of said second power occurs, and selecting means for selecting the power source by which electric power is supplied to said volatile memory means from among said first and second power sources and said battery based on results obtained by said first detection means and said second detection means, said selecting means including first means for selecting said first power source when said first detection means detects that said first power source is not cut off, second means for selecting said second power source when said first detection means detects that said first power source is cut off, and third means for selecting said battery when said first detection means detects that said first power source is cut off and said second detection means detects that service interruption of said second power source occurs. - View Dependent Claims (2, 3, 4)
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5. A semiconductor memory unit operated by supplying electric power from an independent power source, used so as to be cut off at a predetermined time, said semiconductor memory unit comprising:
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a volatile memory; a system power source; an all day power source; a battery; and a power supply controller, said controller selectively connecting said system power source, said all day power source and said battery to said volatile memory. - View Dependent Claims (6, 7)
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Specification