Static information storage and retrieval – Read/write circuit – Bad bit
Reexamination Certificate
2002-03-13
2003-11-11
Tran, M. (Department: 2818)
Static information storage and retrieval
Read/write circuit
Bad bit
C365S185090
Reexamination Certificate
active
06646931
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor storage device such as a semiconductor card, equipped with flash memories of which the number of rewriting actions is limited, and particularly to a semiconductor storage device having spare sectors for replacing error sectors in rewriting data and arranged to give a warning when the number of rewriting actions is close to its limit.
2. Description of the Prior Art
Recently, as semiconductor storage devices such as semiconductor cards using flash memories have been increased in storage capacity scale, they are now used as data storage devices in mobile terminals such as portable information apparatuses (PDAs) or factory automation system (referred to as “FA”, hereinafter). In particular, FA system requires a higher level of environmental durability and commonly employs a hard disk drive. Recently, many FA systems utilize semiconductor cards which have much higher environmental durability.
For example, a flash ATAPC card, compact flash (registered trademark) card and flash drive are used as the semiconductor storage device for a substitute for a hard disk drive in various applications. These examples include nonvolatile or flash memories built therein, each memory having a floating gate structure of memory cells and capable of writing and reading data with protocols compatible with a hard disk drive.
A flash memory has a floating gate structure where the number of rewriting actions is limited. It is hence schemed for increasing the operating life of the flash memory to prepare and use spare sectors (blocks) for replacing error sectors (blocks) of which the number of rewriting actions is exhausted. Accordingly, as each flash memory is increased in the number of rewriting actions more than that of rewritable actions per sector (block), it can favorably be used in a semiconductor storage device.
However, when all the spare sectors (blocks) are used up and another error sector (block) is generated in the rewriting, the semiconductor storage device fails to replace the error sector (block) with a spare one and will thus be defective due to causing a rewriting error.
Such a conventional semiconductor storage device having a flash memory includes no means for notifying a host apparatus of the exhaustion condition of the spare sectors (blocks). This results in that the operating life of the conventional semiconductor storage device is identified only at the time when a rewriting error suddenly occurs during a continuous operation.
FIG. 8
is a block diagram showing a conventional semiconductor card as a semiconductor storage device equipped with flash memories. As shown in the figure, the semiconductor card
82
comprises a card controller
83
, flash memories
84
, and a power supply circuit
86
. The card controller
83
includes a CPU
85
, a buffer portion
88
, and an error correction coding circuit
89
(referred to as “ECC circuit”, hereinafter). The card controller
83
is linked with an oscillator
87
. The card controller
83
executes data transmission to and from an external system
81
of various data signals including I/O signals, address signals, and control signals.
The operation of the conventional semiconductor card will now be explained in brief. When acknowledging a message of a command received from the external system
81
, the card controller
83
starts control actions for implementation of the command. The control actions of the card controller
83
are basically programmed and executed by the CPU
85
provided in the card controller
83
. The read and write actions on the flash memories
84
are based on data transfer via the buffer portion
88
built in the card controller
83
.
Generally, as each flash memory has a limited life in rewriting defective sectors, the semiconductor card prepares spare storage areas for prolonging the life of rewriting actions. The spare storage areas of the semiconductor card have specific rewritable size at each replacement action and entire replacement storage size, which are individually determined and managed depending on the type of equipped flash memories and the controlling method.
The conventional semiconductor card is designed to notify the external system
81
of the occurrence of error only when the spare storage areas have been used up and a counteraction is needed, but not give an early warning to the system
81
before the spare storage areas are exhausted. In other words, exhaustion of the spare storage areas is not known before the occurrence of error is notified. Therefore, the degree of the used spare storage areas is hardly examined, which results in that the rewriting action may exceed the rewritable limit without precaution. This disables the function of the flash memories and causes the semiconductor card to have an erratic action.
When the conventional flash memory provided in the semiconductor card is used in an FA system, the end of the rewriting life of the flash memories may suddenly cause an error, which hence results in functional faults of the system such as a sudden stop of the system line. It is thus urgently necessary to provide a method of warning that the life of the semiconductor card in storage capacity thereof comes close to its end or limit.
SUMMARY OF THE INVENTION
The present invention has been developed for eliminating the foregoing drawbacks and its object is to provide a system and a method of generating a warning signal in a semiconductor card equipped with a set of flash memories which is arranged for examining a remaining size of a spare storage area in rewriting actions to judge that the life of each flash memory comes close to its end before the flash memory is completely used up, thus preventing any malfunction derived from careless use after the end of the life.
It is another object of the present invention to provide a semiconductor storage device having flash memories capable of rewriting data in sector (block) units, employing a command for examining consumption of spare sectors (blocks) and the storage device is arranged for, when receiving the command from an external system such as a host apparatus, notifying the host apparatus of the consumption of spare sectors (blocks) that the number of spare sectors (blocks) comes close to its end. Namely, the time for replacement of the semiconductor device with a new device is notified before any fault resulting in malfunction occurs in the system.
For achievement of the above objects, a first aspect of the present invention provides a semiconductor storage device equipped with flash memories each having a limited size of a spare storage area, which comprises: an error decision unit for judging whether or not an error occurs during writing of data; a replacing unit for rewriting data to the spare storage area when the error decision unit judges that an error occurs; a spare area size calculating unit for calculating a remaining size of the spare storage area after the data has been re-written to the spare storage area; a spare area checking unit for comparing the remaining size of the spare storage area with a predetermined value; and a warning generator for generating a warning when the remaining size of the spare storage area is smaller than the predetermined value.
In this arrangement, the replacing unit may acquire a start address of the spare storage area from a spare storage area management table which is saved in a management area of each flash memory to thereby rewrite the data to the spare storage area of the acquired address, and after the completion of the data rewriting, the replacing unit updates the spare storage area management table and a logic-to-physic conversion table saved in the management area.
A second aspect of the present invention provides a warning generating system of a semiconductor storage device exchanging commands and data with an external system, the semiconductor storage device being equipped with flash memories each having a limited size of a spare storage area, where the system comprises: an erro
Kimura Masatoshi
Mizoguchi Shinichi
Shinohara Takayuki
McDermott & Will & Emery
Mitsubishi Denki & Kabushiki Kaisha
Tran M.
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