Abstract:
Write data, when given from a host via an interface, are temporarily stored in a buffer memory of a disk control unit. A number-of-chips managing unit manages the number of memory chips executing writing operations. If the number of memory chips in the process of writing operations does not reach a fixed number, the write data are transferred to the memory chips allocated to, corresponding write areas. Whereas if the number of memory chips in the process of writing operations reaches the fixed number, the write data are transferred after an end of the writing operations to the memory chips in the process of writing operations. An entire electric current during the writing operation of a disk card can be thereby restricted.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a nonvolatile semiconductor disk device (hereinafter referred to as a “disk card”) as one of peripheral function extender cards of a personal computer (hereinafter abbreviated to a “PC”), etc., and also relates to writing control to this disk card.  
           [0002]    The disk card as a peripheral device of the PC is stored with data.  
           [0003]    Then, the disk card is capable of holding a content of the storage without requiring a power supply.  
           [0004]    Next, a nonvolatile semiconductor memory such as, e.g., a flash memory is employed as a storage medium of the disk card.  
           [0005]    This nonvolatile semiconductor memory is stored with the data in such a form as to be formatted to a fixed size called a sector as in the case of the disk device like a flexible disk and a hard disk.  
           [0006]    Incidentally, the disk card in a name card size becomes, with increases by leaps in storage capacity of the semiconductor memory, capable of storing the data of several tens of Mega bytes.  
           [0007]    This disk card is used for storing data about a picture photographed by, e.g., a digital camera in the way of utilizing merits of being small in size but large in capacity and of the storage content being held even when switching off the power supply.  
           [0008]    Next, the disk card with a completion of the photography is taken out of the digital camera and set in the PC, and the image data stored thereon can be read and digitally processed.  
           [0009]    [0009]FIG. 2 is a diagram showing one example of a conventional disk card.  
           [0010]    This disk card includes an interface unit  10  connected to a host  1  such as the digital camera and the PC, a central processing unit (hereinafter abbreviated to a “CPU”)  20  for executing whole control within the disk card by transmitting and receiving a variety of control signals to and from this host  1 , a disk control unit  30  for controlling a transfer of the data to the host  1 , an internal bus  40  through which to transfer the data inwardly the disk card, and a storage unit  50  for storing the data.  
           [0011]    Then, the disk control unit  30  has a buffer memory  31  for temporarily holding sector-basis data given from the host  1 .  
           [0012]    The sector contains e.g., 536-bytes data in such a fixed format that a header portion containing data about a validity, etc. of this sector and a correction code for correcting an error are added to, e.g., 512-bytes data.  
           [0013]    The disk control unit  30  incorporates a function to write sector-basis data to the corresponding storage unit  50  via the internal bus  40  on the basis of an address signal given via the interface unit  10 , and to read the sector-basis data stored in the storage unit  50 .  
           [0014]    The storage unit  50  is constructed of a plurality (e.g.,  15  pieces) of memory chips  50   a ,  50   b , . . . ,  50   n  connected in common to the internal bus  40 .  
           [0015]    Addresses different from each other are allocated to these memory chips  50   a - 50   n.    
           [0016]    Then, each of the memory chips  50   a - 50   n  has the same construction, and includes a buffer memory  51  for temporarily holding the sector-basis data and a nonvolatile semiconductor memory  52  for storing the sector-basis data.  
           [0017]    The nonvolatile semiconductor memory  52  is capable of holding a content of the storage even if a supply of the power supply is stopped.  
           [0018]    Each of the memory chips  50   a - 50   n  has a memory control unit  53  for controlling a transfer of the sector-basis data between the buffer memory  51  and the nonvolatile semiconductor memory  52 .  
           [0019]    Next, in this disk card, when the host  1  issues a command to write the data, the write data is temporarily held in the buffer memory  31  within the disk control unit  30  via the interface unit  10 .  
           [0020]    The data held in the buffer memory  31  is transferred to and held in the buffer memory  51  in one of the memory chips  50   i  (however, i=a to n) which corresponds, to the address thereof via the internal bus  40 .  
           [0021]    The data held in the buffer memory  51  in the memory chip  50   i  is written to a predetermined storage area in the nonvolatile semiconductor memory  52  under the control of the memory control unit  53 .  
           [0022]    At this time, a transfer time of the data transferred from the host  1  to the buffer memory via the interface unit  10  and the buffer memory  31 , is on the order of several hundred μs.  
           [0023]    On the other hand, for instance, a time of several ms is required for writing the data temporarily held in the buffer memory  51  to the semiconductor memory  52 .  
           [0024]    For this purpose, the storage unit  50  is divided into a plurality of memory chips  50   a - 50   n , and each memory chip, e.g.,  50   a  is provided with the buffer memory  51  and the nonvolatile semiconductor memory  52 .  
           [0025]    Then, the data is independently written to the nonvolatile semiconductor memory  52  from each of the buffer memories  51 . With this operation, there can be substantially equivalently executed the writing process to the disk card from the host  1 .  
           [0026]    On the other hand, under the control of the CPU  20 , when the host  1  issues a command to read the data, a reading command is given to the memory chip  50   a  stored with the data to be read.  
           [0027]    Then, the sector-basis data is read from the corresponding storage area in the nonvolatile semiconductor memory  52 .  
           [0028]    The thus read data is temporarily held in the buffer memory  51  and thereafter held in the buffer memory  31  within the disk control unit  30  via the internal bus  40 .  
           [0029]    The data written to the buffer memory  31  is further transferred to the host  1  via the interface unit  10 .  
           [0030]    There arise, however, the following problems inherent in the prior art disk card.  
           [0031]    In the disk card, the storage unit  50  is divided into the plurality of memory chips  50   a - 50   n  in order to substantially equivalently hold an access speed for high-velocity writing and reading processes in the interface unit  10 .  
           [0032]    Next, each of the memory chips  50   a - 50   n  is provided with the buffer memory  51 .  
           [0033]    Then, the disk card is capable of equivalently executing the writing operations at the high speed by executing the writing operations to the memory chips  50   a - 50   n  in parallel.  
           [0034]    An electric current necessary for the writing operation per memory chip is on the order of, e.g., 15 mA.  
           [0035]    A total operation current, when the number of the memory chips  50   a - 50   n  in the process of the simultaneous writing operations increases, becomes large.  
           [0036]    Accordingly, only the storage unit  50  requires a current of approximately 150 mA when ten pieces of memory chips  50   i  are in the simultaneous writing operations.  
           [0037]    Therefore, the host  1  must include a power supply having a current capacity allowing for it.  
           [0038]    The thus constructed disk card is used not only simply as a peripheral device of the PC but also for storing data about photographed picture in such a way as to be attached to, e.g., a digital camera.  
           [0039]    The digital camera is driven by a battery and therefore has a limit in terms of being supplied with a large current when writing the image data.  
           [0040]    It is a primary object of the present invention, which was contrived to obviate the problems inherent in the prior art described above, to provide a disk card requiring no large current of a power supply by restricting the number of memory chips  50   a - 50   n  in the process of simultaneous writing operations.  
         SUMMARY OF THE INVENTION  
         [0041]    To accomplish the above object, a nonvolatile semiconductor disk device according to the present invention is a disk card comprising an interface unit for transferring data given from outside, a plurality of memory chips each including a nonvolatile semiconductor memory for storing data and a buffer memory for temporarily holding the data to write the data to the semiconductor memory, and a control unit for outputting the data transferred via the interface unit, reading the data from a corresponding memory chip in accordance with a designation given from outside and outputting the data to the interface unit. The control unit monitors the number of simultaneous writing processes that are simultaneously being executed in the plurality of memory chips, and controls the outputs of the data given from outside to the corresponding memory chips so that the number of simultaneous writing processes does not exceed a predetermined number.  
           [0042]    Next, in the nonvolatile semiconductor disk device, the control unit has a function added thereto, to output the data to the memory chips and thereafter to start monitoring a completion of the writing processes to the memory chips after an elapse of a fixed time substantially corresponding to a necessary writing time in the memory chips.  
           [0043]    Then, the nonvolatile semiconductor disk device is so constructed as to take a card-like configuration as a disk card and to be attachable and detachable to the processor through the interface unit.  
           [0044]    The nonvolatile semiconductor disk device, since the disk card is constructed as described above, exhibits the following operations.  
           [0045]    The control unit, when the data is transferred from the processor via the interface unit, checks the number of memory chips that are now in the process of the writing operations.  
           [0046]    Then, the control unit outputs the data to the relevant memory chips if the number of the memory chips in the writing processes is less than a predetermined number.  
           [0047]    The control unit, if the number of the memory chips in the writing processes is the predetermined number, does not output the data to the relevant memory chips till the number of the simultaneous writing processes becomes less than the predetermined number.  
           [0048]    Then, the control unit outputs the data to the memory chips just when the number of the simultaneous writing processes becomes less than the predetermined number.  
           [0049]    Next, the nonvolatile semiconductor disk device exhibits the following operations.  
           [0050]    The control unit checks the number of the memory chips that are now in the writing processes when the data is transferred from the processor via the interface unit.  
           [0051]    Then, the control unit, if the number of the memory chips in the writing processes is less than the predetermined number, outputs the data to the relevant memory chips.  
           [0052]    Subsequently, the control units, after an elapse of a fixed time substantially corresponding to a necessary write time, starts monitoring whether or not the writing processes are completed.  
           [0053]    On the other hand, the control unit, if the number of the memory chips in the writing processes, does not output the data to the relevant memory chips till the number of the simultaneous operations becomes less than the predetermined number.  
           [0054]    Then, the control unit, if the number of the simultaneous writing operations is less than the predetermined number as a result of monitoring the completion of the writing processes, outputs the data to the memory chips, and the data is written to the semiconductor memory in the memory chip.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0055]    Other objects and advantages of the present invention will become apparent during the following discussion in conjunction with the accompanying drawings, in which:  
         [0056]    [0056]FIG. 1 is a diagram showing a construction of a disk card in a first embodiment of the present invention;  
         [0057]    [0057]FIG. 2 is a diagram illustrating a construction of a prior art disk card; and  
         [0058]    [0058]FIG. 3 is a diagram illustrating a configuration of a disk control unit in the disk card in a second embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0059]    First Embodiment  
         [0060]    [0060]FIG. 1 is a diagram showing a construction of a disk card in a first embodiment of the present invention.  
         [0061]    Referring to FIG. 1, the elements common to those of the prior art disk card shown in FIG. 2 are marked with the common numerals.  
         [0062]    This disk card takes a card-like configuration in a name card size enough to be attachable to a digital camera, etc.  
         [0063]    The disk card includes an interface module (e.g., an interface unit)  10 , control modules (e.g., a CPU  20  and a disk control unit  30 A), an internal bus and a storage unit  50 .  
         [0064]    The interface unit  10  is, as in the case of the prior art disk card, connected to a host  1  such as a digital camera and a PC.  
         [0065]    Then, the interface unit  10  pursuant to, for example, the ATA (Advanced Technology Attachment) Standards defined as hard disk standards proposed by IBM in U.S.A., is connected to the host  1  and transmits and receives data and a variety of control signals.  
         [0066]    A CPU  20  for controlling the whole units within the disk card and a disk control unit  30 A incorporating functions different from those in the prior art, are connected to the interface unit  10  in the same way with the prior art.  
         [0067]    This disk control unit  30 A includes a buffer memory  31 , having storage capacity for a plurality of sectors, for temporarily storing sector-basis data (e.g., 536 bytes) given from the host  1 .  
         [0068]    Therefore, as far as empty sectors exist in the buffer memory  31 , the disk control unit  30 A is capable of inputting the sector-basis data from the host irrespective of an operating status of the storage unit  50 .  
         [0069]    The disk control unit  30 A monitors the number of simultaneous operations of memory chips  50   a - 50   n , in the storage unit  50  in addition to the conventional functions described above.  
         [0070]    Then, the disk control unit  30 A has a number-of-chips managing unit  32  for controlling so as not to simultaneously execute writing operations to more than a predetermined number of memory chips  50   i  (however, i=a−n).  
         [0071]    The number-of-chips managing unit  32  has, e.g., three pieces of unillustrated registers  32   a  for registering addresses of the memory chips  50   i  that are in the process of writing operations.  
         [0072]    The internal bus  40  is a common bus for transferring the data between the disk control unit  30 A and the storage unit  50 .  
         [0073]    Then, the internal bus  40  is constructed of an address line, a data line and a control line.  
         [0074]    The storage unit  50  consists of a plurality (e.g., 15 pieces) of memory chips  50   a - 50   n  connected in common via the internal bus in the same way with the prior art.  
         [0075]    These memory chips  50   a - 50   n , to which addresses different from each other are allocated, each take the same configuration, and respectively have a buffer memory  51  for temporarily storing the sector-basis data and a nonvolatile semiconductor memory  52  for storing the sector-basis data.  
         [0076]    Each nonvolatile semiconductor memory  52  has a storage capacity of, e.g., an 8M bits, and contents of the storage are held even if a supply of the power supply is stopped.  
         [0077]    Then, each of the memory chips  50   a - 50   n  has a memory control unit  53  for controlling a transfer of the sector-basis data between the buffer memory  51  and the nonvolatile semiconductor memory  52 .  
         [0078]    Next, operations of the thus constructed disk card will be explained.  
         [0079]    Write data is, when the host  1  issues a command to write the data, temporarily written to the buffer memory  31  in the disk control unit  30 A via the interface unit  10 .  
         [0080]    The three registers  32   a  within the number-of-chips managing unit  32  are registered with the addresses of the memory chips  50   i  in the process of the writing operations.  
         [0081]    Then, the number-of-chips managing unit  32  checks contents of these three registers  32   a  when the data writing command is given thereto.  
         [0082]    If there exists an empty-status register  32   a  registered with no address, the address of the memory chip  50   i  to which the data is to be written is registered in this empty-status register  32   a.    
         [0083]    Subsequently, the write data is outputted to that memory chip  50   i.    
         [0084]    Thus, the data writing operation is started in the memory chip  50   .    
         [0085]    After outputting the write data, the disk control unit  30 A periodically monitors statuses of the memory chips  50   i  n the process of the writing operations, the addresses of which are registered in the three registers  32   a , thereby monitoring a completion of the writing operation.  
         [0086]    In monitoring the status, for instance, a reading command is issued to the memory chip  50   i , and, if a response therefrom is a BUSY status, it is judged that the writing operation is uncompleted.  
         [0087]    On the other hand, if the three registers  32   a  are all in use just when the host  1  issues the data writing command, and even when executing no writing operation to the data writing target memory chip  50   i , the output of the write data to the memory chip  50   i  from the disk control unit  30 A remains stopped till a completion of the writing operations to the memory chips  50   i  the addresses of which are registered in the three registers  32   a.    
         [0088]    Then, when the completion of the writing operations to the one memory chips is detected by a status monitoring process, the addresses of the memory chips  50   i  are registered to the empty registers  32   a , and the writing command is given to the memory chips  50   i.    
         [0089]    Thus, the disk control unit  30 A in the disk card in accordance with the first embodiment incorporates the number-of-chips managing unit  32  for monitoring the number of the memory chips  50   a - 50   n  which operate simultaneously, whereby it never happens that the memory chips  50   i  exceeding the number of chips that is preset by the number-of-chips managing unit  32  simultaneously perform the writing operations.  
         [0090]    Accordingly, a consumption electric current of the storage unit  50  that is needed when writing the data to the memory chips  50   i  comes to a maximum value corresponding to the number of chips which is set by the number-of-chips managing unit  32 .  
         [0091]    Hence, there might be such an advantage that the power supply having a large capacity is not required to be prepared for the processor  1  such as, e.g., a digital camera, etc.  
         [0092]    Further, the disk control unit  30 A includes the buffer memory  31  capable of temporarily holding plural pieces of data given from the host  1 , and therefore, even when the writing operations to the memory chips  50   i  are limited, it is feasible to receive the data from the host  1 . An influence on the processing on the side of the host  1  is thus reduced.  
         [0093]    Second Embodiment  
         [0094]    [0094]FIG. 3 is a diagram showing a construction of the disk control unit in the disk card in a second embodiment of the present invention.  
         [0095]    Referring to FIG. 3, the components common to those in FIG. 1 are marked with the common numerals.  
         [0096]    A disk control unit  30 B is substitute for the disk control unit  30 A in FIG. 1.  
         [0097]    Then, the disk control unit  30 B is constructed by adding a memory control timer  33  to the disk control unit  30 A.  
         [0098]    The memory control timer  33  has a count timer  33   a  for counting a necessary write time in the memory chip  50   i.    
         [0099]    The count timer  33   a  is a timer, when the disk card executes the writing operation for the first time, for counting the time needed for this writing operation.  
         [0100]    An output side of the count timer  33   a  is connected to a time storage register  33   b  for storing the time counted by the count timer  33   a  as a time substantially corresponding to the necessary write time.  
         [0101]    Then, three pieces of count-down timers  33   c ,  33   d ,  33   e  are connected to an output side of the time storage register  33   b , corresponding to the three registers  32   a  used for the number-of-chips managing unit  32  managing the number of chips performing the simultaneous writing operations.  
         [0102]    The count-down timers  33   c - 33   e  count down the necessary write time loaded from the time storage register  33   b  with an elapse of time.  
         [0103]    Then, the count-down timers  33   c - 33   e , when values thereof come to “0”, start monitoring the completion of the writing operations to the relevant memory chips  50   i.    
         [0104]    In the thus constructed disk card, when the host  1  issues the data writing command, the write data is temporarily written to the buffer memory  31  in the disk control unit  30 B via the interface unit  10 .  
         [0105]    Just when one of the three registers  32   a  in the number-of-chips managing unit  32  is emptied, the address of the writing target memory chip  50   i  is registered in this empty register  32 , and the write data is transferred to this memory chip  50   i .  
         [0106]    Furthermore, a content of the time storage register  33   b  is loaded into a count-down timer  33   j  (however, j=c−e) corresponding to that register  32   a.    
         [0107]    With this process, the operation of writing the data starts within the memory chip  50   i , and simultaneously the count-down timer  33   j  starts counting down.  
         [0108]    When a value of the count-down timer  33   j  comes to “0”, the disk control unit  30 B is informed of this purport, and the disk control unit  30 B monitors a status of the relevant memory chip  50   i.    
         [0109]    Thus, in the disk card in accordance with the second embodiment, the disk control unit  30  incorporates the memory control timer  33 , and just when the writing process is completed, this memory control timer  33  gives a notification.  
         [0110]    Accordingly, there is no necessity for monitoring the completion of the writing process to the memory chip  50   i  within a predetermined time required for the writing process.  
         [0111]    It is therefore of almost no necessity to implement the operation for monitoring the status, which yields such a advantage that the electric power consumed for that operation can be reduced.  
         [0112]    Note that the present invention is not limited to the embodiments discussed above but may be modified in a variety of forms, and there may be, for example, the following modified examples (a)−(e).  
         [0113]    (a) The disk card assumes the card-like configuration in the name card size so as to be attachable to the digital camera, etc., but is not confined to the card-like configuration.  
         [0114]    (b) The interface unit  10  is not limited to the ATA Standards but may be the one capable of transferring the data in accordance with a given format.  
         [0115]    (c) The number of the memory chips  50   a - 50   n , the storage capacity, the transfer speed and the size of the transfer data, are not limited to the numerical values shown in the embodiments.  
         [0116]    (d) The number-of-chips managing unit  32  restricts the number of the memory chips  50   i  operating simultaneously to “3”, however, it may be set to an arbitrary number depending on a capacity of the power supply, a data quantity and a necessary write time.  
         [0117]    (e) The memory control timer  33  shown in FIG. 3 is constructed so that the count timer  33   a  counts at first the necessary writing operation time of the memory chip  50   i , however, if the time storage register  33   b  is stored with a rough order of necessary writing operation time, the count timer  33   a  can be omitted.  
         [0118]    As discussed above in greater detail, according to the first invention, there is provided the control module for restricting the simultaneous writing operations to the memory chips by managing the output of the write data to the plurality of memory chips. It is therefore possible to prevent the power supply from making a large current flow momentarily therefrom and to thereby reduce the capacity of the power supply.  
         [0119]    According to the second invention, after the necessary write time of the memory chip has elapsed, the completion of the writing operation to that memory chip is monitored. Therefore, the unnecessary operation for monitoring is eliminated, which leads to a decrease in the consumption electric power.  
         [0120]    According to the third invention, the disk card is formed in the card-like shape and can be connected via the interface module to the host such as the digital camera, etc. Hence, the disk card is, when in use, suitably attached to the portable host having a small capacity of the power supply.  
         [0121]    It is apparent that, in this invention, a wide range of different working modes can be formed based on the invention without deviating from the spirit and scope of the invention. This invention is not restricted by its specific working modes being limited by the appended claims.