Abstract:
A reproduction apparatus and a reproduction method by which an error of time information that arises from interruption of power supplied to a timer that manages the term of term-managed contents data is minimized to allow accurate term management of the contents data. The timer produces time information when power is supplied to the timer from a cell, but the timer stops operating when no power is supplied thereto. The time information produced by the timer is stored into a memory, and the memory holds the stored time information when no power is supplied to the timer. When power from the cell is restored to the timer, the timer is set accordingly to the time information stored in the memory, so that the timer may thereafter produce correct time information thereby allowing term management of the term-managed contents data to be performed accurately.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a reproduction apparatus and a reproduction method wherein a term of term-managed contents data is managed by a timer. 
     In recent years, such a service as to allow an information processing apparatus such as a personal computer to access an electrical music distribution (EMD) server through a predetermined network to receive contents such as music data from the EMD server so that the user of the information processing apparatus may enjoy the contents has been and is being popularized. Among contents distributed in this manner, some contents are distributed free of charge on condition that enjoyment of the contents is permitted only within a predetermined limited period, for example, for advertisement. 
     An apparatus which handles contents whose term for enjoyment is limited as described above must include a clock function in order to manage the term. Further, power supply is temporarily interrupted upon exchange of a battery or the like, and in order to prepare for such temporary power supply interruption, also it is necessary for an apparatus of the type described to include a power supply backup function. 
     However, in order to provide a power supply backup function, different power supply wiring line systems must be designed for circuit blocks for which power supply backup is required and circuit blocks for which power supply backup is not required. Therefore, the apparatus of the type described above has a subject to be solved in that it is complicated in circuit configuration and miniaturization of the circuit is difficult. 
     Further, where an exchangeable primary cell is used as the backup power supply for the power supply, such a trouble may possibly occur that time information is lost because the time within which the power supply can be backed up elapses during an exchanging operation process of the primary cell. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a reproduction apparatus and a reproduction method by which the error of time information which arises from interruption of power supply to a timer which manages a term of term-managed contents data is minimized to allow accurate term management. 
     In order to attain the object described above, according to an aspect of the present invention, there is provided a reproduction apparatus which operates with a battery for reproducing term-managed main data, comprising main data storage means for storing the term-managed main data, term data storage means for storing term management data to be used for the term-management of the main data, time counting means operating with the battery for counting time, holding means for holding time information counted by the time counting means also when power is not supplied thereto from the battery, and control means for controlling the holding means to hold the time information counted by the time counting means at a predetermined time 
     According to another aspect of the present invention, there is provided a reproduction apparatus which operates with a battery for reproducing main data term-managed based on term management information, comprising time counting means operable only while power is supplied thereto from the battery for counting time to be used for the term management, holding means for holding the time counted by the time counting means while power from the battery is not supplied to the time counting means, and control means for controlling reproduction of the main data based on the term management information and the time information counted by the time counting means. 
     According to a further aspect of the present invention, there is provided a reproduction method for a reproduction apparatus which reproduces term-managed main data using a battery as a power supply, comprising the steps of reading, from a timer which operates with the power supply from the battery to count time and stops the time counting when the power is not supplied from the battery, time information to be used for the term management of the main data and writing the time information into a nonvolatile memory which holds data even when the power is not supplied thereto from the battery, and setting the time information written in the nonvolatile memory to the timer when the power is supplied again after the power supply from the battery is interrupted. 
     The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic view showing a configuration of an information processing system to which the present invention is applied; 
     FIG. 2 is a block diagram showing an internal configuration of a personal computer shown in FIG. 1; 
     FIG. 3 is a perspective view showing an appearance of a portable device shown in FIG. 1; 
     FIGS. 4A to  4 E are schematic views of the portable device of FIG. 3 as viewed in different directions; 
     FIG. 5 is a block diagram showing an internal configuration of the portable device of FIG. 3; 
     FIG. 6 is a diagrammatic view illustrating a data structure of digital music contents used in the information processing system of FIG. 1; 
     FIGS. 7 and 8 are diagrammatic views illustrating a different data structure of a header of the digital music contents illustrated in FIG. 6; 
     FIGS. 9A to  9 C are diagrammatic views illustrating copying of digital music contents; 
     FIG. 10 is a block diagram showing another internal configuration of the portable device of FIG. 3; and 
     FIG. 11 is a flow chart illustrating time management executed by the portable device of FIG.  10 . 
     FIG. 12 is a second flow chart illustrating time management executed by the portable device of FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, there is shown an information processing system in the form of an audio data management system to which the present invention is applied. In the audio data management system shown, a personal computer  1  is connected to a network  2  which may be a local area network, the Internet or the like. The personal computer  1  converts audio data, that is, contents, received from an EMD server  4 - 1 ,  4 - 2  or  4 - 3  or read from a CD (Compact Disk), which is hereinafter described, into data compressed in accordance with a predetermined compression system such as, for example, the ATRAC (Advanced TRansform Acoustic Coding) 3 (trademark), encrypts the compressed data in accordance with an encryption system such as the DES (Data Encryption Standard) and records the encrypted compressed data. It is to be noted that, in the following description, where there is no necessity to distinct the EMD servers  4 - 1 ,  4 - 2  and  4 - 3  individually from one another, each of them is referred to merely as EMD server  4 . This similarly applies also to other similar elements. 
     The personal computer  1  records utilization condition data representative of utilization conditions of recorded encrypted contents in a corresponding relationship to the contents. The utilization condition data represent that the contents corresponding thereto can be utilized by three portable devices  6 - 1 ,  6 - 2  and  6 - 3  simultaneously, can be copied or can be moved to the other personal computer or computers. 
     The personal computer  1  stores the recorded encrypted contents into a portable device  6  connected thereto and updates, in response to such storage into the portable device  6 , the utilization condition data corresponding to the stored contents. This operation of the personal computer  1  is hereinafter referred to as check-out. Further, the personal computer  1  erases contents stored in a portable device  6  connected thereto from the portable device  6  and updates the utilization condition data corresponding to the erased contents. This operation of the personal computer  1  is hereinafter referred to as check-in. 
     An EMD registration server  3  transmits, in response to a request of the personal computer  1  when the personal computer  1  starts acquisition of contents from an EMD server  4 , an authentication key necessary for mutual authentication between the personal computer  1  and the EMD server  4  to the personal computer  1 , and transmits, if necessary, a program for connection to the EMD server  4  to the personal computer  1 , through the network  2 . 
     Each EMD server  4  supplies, in response to a request of the personal computer  1 , contents to the personal computer  1  by transmission through the network  2 . Contents supplied from the EMD servers  4 - 1 ,  4 - 2  and  4 - 3  are data compressed in accordance with the same compression system or different compression systems. Further, contents supplied from the EMD servers  4 - 1 ,  4 - 2  and  4 - 3  are data encrypted in accordance with the same encryption system or different encryption systems. 
     If a CD is set in position into a CD player connected to the personal computer  1 , then the personal computer  1  can acquire an attribute of the set CD or an attribute of contents recorded on the CD from a WWW (World Wide Web) server  5 - 1  or  5 - 2  connected thereto through the network  2 . 
     In particular, each of the WWW servers  5 - 1  and  5 - 2  supplies, for example, the name of an album or a distributor of a CD from which contents are read and the title or the name of the composer of a musical composition of data corresponding to the contents read from the CD to the personal computer  1  through the network  2  in response to a request of the personal computer  1 . 
     Each portable device  6  stores contents supplied thereto from the personal computer  1 , that is, checked out contents, into a memory or the like provided therein. The portable device  6  reproduces the stored contents and outputs the reproduced contents to a headphone not shown or the like. The user can remove the portable device  6 , in which contents are stored, from the personal computer  1 , carry the portable device  6 , reproduce the stored contents from the portable device  6  and enjoy music or the like corresponding to the contents by means of the headphone or the like. 
     FIG. 2 shows a configuration of the personal computer  1 . Referring to FIG. 2, a central processing unit (CPU)  11  actually executes various application programs and an operating system (OS). A read-only memory (ROM)  12  generally stores programs to be used by the CPU  11  and basically fixed data from among parameters for use for arithmetic operation. A random-access memory (RAM)  13  stores programs to be used in execution of the CPU  11  and parameters which vary suitably during execution of such programs. The CPU  11 , ROM  12  and RAM  13  are connected to one another by a host bus  14  which may be a CPU bus or the like. 
     The host bus  14  is connected through a bridge  15  to an external bus  16  such as a PCI (Peripheral Component Interconnect/Interface) bus. 
     A keyboard  18  is operated by the user in order to input various instructions to the CPU  11 . A mouse  19  is operated by the user in order to designate or select a point on a screen of a display unit  20 . The display unit  20  may be a liquid crystal display apparatus or a CRT (Cathode Ray Tube) and displays various kinds of information in the form of a text or an image. A hard disk drive (HDD)  21  drives a hard disk not shown to record or reproduce a program to be executed by the CPU  11  or information onto or from the hard disk. 
     A drive  22  reads out data or a program recorded on a magnetic disk  41 , an optical disk  42  including a CD, a magneto-optical disk  43  or a semiconductor memory  44 , which is loaded therein, and supplies the data or program to the RAM  13  connected thereto through an interface  17 , the external bus  16 , the bridge  15  and the host bus  14 . 
     The portable devices  6 - 1 ,  6 - 2  and  6 - 3  are connected to universal serial bus (USB) ports  23 - 1 ,  23 - 2  and  23 - 3  by predetermined cables, respectively. Each USB port  23  outputs data supplied thereto from the HDD  21 , CPU  11  or RAM  13  through the interface  17 , external bus  16 , bridge  15  and host bus  14  to a portable device  6  connected thereto. In this instance, the data outputted to the portable device  6  include, for example, contents, a command of the portable device  6  or the like. 
     A speaker  24  outputs predetermined sound corresponding to contents based on data or an audio signal supplied thereto from the interface  17 . 
     The keyboard  18 , mouse  19 , display unit  20 , HDD  21 , drive  22 , USB ports  23 - 1 ,  23 - 2  and  23 - 3 , and speaker  24  are connected to the interface  17 , which is in turn connected to the CPU  11  through the external bus  16 , bridge  15  and host bus  14 . 
     A communication section  25  is connected to the CPU  11  through the external bus  16 , bridge  15  and host bus  14 . 
     The communication section  25  is connected also to the network  2 , and places data of a request for registration or a request for transmission of contents supplied thereto from the CPU  11  or the HDD  21  into a packet of a predetermined system and transmits the packet through the network  2 . Further, the communication section  25  outputs, for example, an authentication key or data of contents or the like placed in a packet received through the network  2  to the CPU  11 , RAM  13  or HDD  21 . 
     Now, the portable device  6  is described. FIG. 3 shows an appearance of the portable device  6 . Referring to FIG. 3, the portable device  6  includes a casing  50  of a substantially cylindrical profile. The casing  50  has various operation switches and operation buttons, a display window  51  for a display section and so forth provided on a circumferential face thereof. 
     Different circumferential face portions of the portable device  6  when the casing  50  is rotated successively by 45 degrees around an axis thereof where the circumferential face portion on which the display window  51  is provided is defined as the front face are described with reference to FIGS. 4A,  4 B,  4 C and  4 D. 
     As seen from FIG. 4A, a sound volume upper limit fixation switch  52  for fixing an upper limit to the sound volume to one end side of the casing  50  in its longitudinal direction is provided for sliding movement on a left side face of the casing  50 . A USB connector cover  53  made of a plastic material is provided on the left side face of the casing  50  such that it opens or closes up a hole not shown in which a USB (Universal Serial Bus) connector is accommodated. 
     The USB connector cover  53  actually closes up, when the USB connector is not used, the hole in such a manner that it is integrated with the casing  50  to protect the USB connector. On the other hand, when the USB connector is to be used, the USB connector cover  53  can open the hole so that the USB connector can be connected to the personal computer  1  by a USB cable  91  hereinafter described with reference to FIG.  5 . 
     Meanwhile, as shown in FIG. 4B, at a portion from a substantially mid portion to one end of the front face of the casing  50 , a sound volume up button  54 , a sound volume down button  55 , a fast feed button  56 , a fast return button  57 , the display window  51  and a shift button  58  are provided in order. Further, a reproduction/stop button  59  which can input a reproduction instruction and a stop instruction is provided on one end face of the casing  50  which is shown in FIG.  4 E. 
     On the front face of the casing  50 , a display section  85  shown in FIG. 5 which is provided below the display window  51  performs display in response to various operations, and the displayed contents of the display section  85  can be presented through the display window  51 . 
     The shift button  58  functions, if the fast feed button  56  is depressed while it is kept depressed, as an operation button for changing over the reproduction mode together with the fast feed button  56 . Further, the shift button  58  functions, if the fast return button  57  is depressed while it is kept depressed, as an operation button for changing over the sound volume mode together with the fast return button  57 . 
     Further, as shown in FIG. 4C, a hold switch  60  is provided for sliding movement on one end side of the right side face of the casing  50  such that, for example, if it is slidably moved to the one end side of the casing  50 , then inputting of various operation buttons is invalidated, and this state can be maintained. 
     In addition, as shown in FIG. 4D, a dry cell accommodation section  62  into which a driving dry cell  61  of the AA size can be loaded is provided on one end side of the rear face of the casing  50 , and a lid member  63  for closing up the dry cell accommodation section  62  is removably mounted on the rear face of the casing  50 . Consequently, if the lid member  63  is removed, then the driving dry cell  61  can be loaded into the dry cell accommodation section  62  and can be unloaded from the dry cell accommodation section  62 . Further, if the lid member  63  is mounted while the driving dry cell  61  is loaded in the dry cell accommodation section  62 , then the lid member  63  prevents the driving dry cell  61  from coming out of the dry cell accommodation section  62 . 
     Further, a jack holding portion  65  for holding a headphone jack  64  and a clip member  66  for attaching the casing  50  to a breast pocket or the like of an outerwear of a user are provided in a juxtaposed relationship in a longitudinal direction of the casing  50  on one end side of the rear face of the casing  50 . Further, an annular strap metal member  67  is provided at a predetermined position of the rear face of the casing  50  adjacent the jack holding portion  65  and the clip member  66  and displaced from the center of gravity of the portable device  6 . 
     The strap metal member  67  is mounted for pivotal motion within a range of approximately 180 degrees between a position in which it contacts with the jack holding portion  65  and another position in which it contacts with the clip member  66  with respect to the back face of the casing  50 . If the strap metal member  67  is pivoted uprightly, then various kinds of straps can be attached to and removed from the strap metal member  67 . 
     The portable device  6  is configured, different from a recording and reproduction apparatus having a mechanical recording and reproduction mechanism such as a hard disk drive, such that, where digital music contents C 1  as data supplied from the personal computer  1  are recorded into a semiconductor flash memory  80  provided in the inside of the portable device  6  as shown in FIG. 5, music data D 1  of the digital music contents C 1  can be reproduced without suffering from temporary interruption of reproduction even if the portable device  6  is in such an environment that vibrations are applied thereto. 
     Now, an internal configuration of the portable device  6  is described with reference to FIG.  5 . The portable device  6  includes a power supply circuit  71  which converts a power supply voltage supplied from the driving dry cell  61  into internal power of a predetermined voltage and supplies the internal power to a central processing unit (CPU)  72  and other circuit blocks to drive the entire portable device  6 . 
     If the portable device  6  is connected to the personal computer  1  through a USB connector  73  by a USB cable  91 , then it supplies digital music contents C 1  transferred in bulk from the personal computer  1  to the CPU  72  through an internal bus  75  under the control of a USB controller  74 . 
     The digital music contents C 1  have a frame configuration wherein one packet is formed from 64 bytes and are transferred at the transfer rate of 12 Mbit/sec from the personal computer  1 . One packet of the digital music contents C 1  includes a header H 1  and music data D 1  as seen in FIG.  6 . The header H 1  has a “file ID”, a “header size”, a “contents key” for encryption, a “file size”, a “code ID”, a “file name” and “file information” placed therein. The header H 1  further has “reproduction limitation data”, a “reproduction start date”, a “reproduction end date”, a “reproduction allowed time number” and an “actual reproduction time number” placed therein as reproduction control information necessary for a reproduction limitation process. 
     Actually, each piece of information placed in the header H 1  is represented by a hexadecimal digit. As seen in FIG. 7, the “header size” represents the data length of the header H 1 , and in this instance, it is 33 bytes. The “file size” represents the data length of the file of the music data D 1 , and in this instance, it is 33 bytes. The “contents key” is cipher key data to be used for decryption of the music data D 1  illustrated in FIG. 6, and actually, the digital music contents C 1  is transferred in a state further encrypted with a common session key between the personal computer  1  and the portable device  6 . 
     Actually, when the personal computer  1  and the portable device  6  are connected to each other, the portable device  6  must be authenticated by the personal computer  1 . In this instance, for example, authentication of the challenge-response system is performed between the personal computer  1  and the portable device  6 . Incidentally, in the portable device  6 , a digital signal processor (DSP)  76  takes charge of a decryption process when authentication of the challenge-response system is performed. 
     The authentication of the challenge-response system is authentication of the type wherein, to a challenge which is a predetermined value produced by the personal computer  1 , the portable device  6  responds with a response as a value produced using a secret key possessed commonly with the personal computer  1 . Since the challenge is changed every time, even if the response is tapped, there is no possibility that it may be re-used. Therefore, mutual authentication can be performed in safe by the authentication procedure of the challenge-response system. 
     The “codec ID” is an ID number representative of a decompression system to be used for reproduction of the music data D 1  of the digital music contents C 1  by the portable device  6 . A decompression system corresponding to a data compression system called ATRAC (Adaptive TRansform Acoustic Coding) 3 is allocated to the ID number “1”, and another decompression system corresponding to another data compression system called MP3 (MPEG Audio Layer-3) is allocated to the ID number “0”. 
     The “file name” is data in the form of an ASCII (American National Standard Code for Information Interchange) code obtained by conversion of, for example, a file name “ABCD.AAC” of the digital music contents C 1 . The “file information” is data in the form of an ASCII code obtained by conversion of the name of the tune, the name of the artist, the name of the lyric writer, the composer and so forth of the digital music contents C 1 . 
     The “reproduction limitation data” is data representative of whether or not reproduction limitation to the reproduction allowed period or the reproduction allowed time number is applied to the digital music contents C 1  to be reproduced by the portable device  6 . Only when there is some limitation to the reproduction allowed time number, “1” is applied to the “reproduction limitation data”, and only when there is some limitation to the reproduction allowed period, “2” is applied to the “reproduction limitation data”. But when there is no limitation to reproduction, for example, where the digital music contents C 1  have been acquired by purchase, “0” is applied to the “reproduction limitation data”. 
     The “reproduction start date” and the “reproduction end date” are data indicative of the range within which reproduction is allowed when the “reproduction limitation data is “2”. For example, where the “reproduction start date” and the “reproduction end date” are “00040F” and “00070F”, they indicate that the period from “Apr. 15, 2000” to “Jul. 15, 2000” is the range within which reproduction is allowed. 
     Similarly, the “reproduction allowed time number” and the “actual reproduction time number” are data indicative of a maximum number of times determined in advance by which reproduction is allowed and an actual updated time number updated by the CPU  72  when a reproduction process is executed, respectively, when the “reproduction limitation data” is “1” or “2”. For example, if the “reproduction allowed time number” and the “actual reproduction time number” are “02” and “01”, respectively, then they indicate that the “reproduction allowed time number” is “2” times and the “actual reproduction time number” is “1” time. 
     Incidentally, in the header H 1  of the digital music contents C 1  to which reproduction limitation only with regard to the reproduction allowed time number is applied, for example, as seen in FIG. 8, the “reproduction limitation data” is “1”; the “reproduction start date” and the “reproduction end date” are “000000” and “000000”, respectively; and the “reproduction allowed time number” and the “actual reproduction time number” are “0a” and “05”, respectively. In particular, it can be seen that there is no limitation to the reproduction allowed period by the “reproduction start date” and the “reproduction end date”, but the “reproduction allowed time number” is “10” times, and the “actual reproduction time number” at present is “5”. 
     Referring back to FIG. 5, the portable device  6  receives a writing instruction of the digital music contents C 1  transferred thereto from the personal computer  1  together with the digital music contents C 1 . When the CPU  72  receives the write instruction, it controls a flash memory controller  79  in accordance with a main program read out from a ROM  78  and stored into a RAM  77  to write the digital music contents C 1  into the semiconductor flash memory  80 . 
     In the semiconductor flash memory  80 , a reproduction code for reproducing the music data D 1  in accordance with a decompression system suitable for the music data D 1  of the digital music contents C 1  compressed in accordance with a predetermined compression system is stored in advance. Accordingly, if a reproduction instruction is inputted to the CPU  72  of the portable device  6  through an operation key controller  81  in response to a depression operation of the reproduction/stop button  59  by the user, then the CPU  72  reads out a reproduction code from the semiconductor flash memory  80  and the music data D 1  of the digital music contents C 1  and transfers them to a RAM not shown of the DSP  76 . 
     The DSP  76  corrects errors of the music data D 1  of the digital music contents C 1  in accordance with a Cyclic Redundancy Check (CRC) system based on the reproduction code transferred thereto from the semiconductor flash memory  80 , decompresses, reproduces and supplies the error-corrected music data D 1  to a digital/analog (D/A) converter  82 . 
     The D/A converter  82  converts the reproduced music data D 1  into an analog music signal and transmits the analog music signal to an amplifier  83 . The amplifier  83  amplifies the music signal to a predetermined level and outputs the amplified music signal to a headphone not shown from the headphone jack  64  so that the reproduced music is presented to the user through the headphone. 
     The portable device  6  further includes a liquid crystal display (LCD) controller  84 , which is controlled by the CPU  72 , to display such information as a reproduction mode state, a sound quality mode for equalization adjustment, a tune number, a reproduction time, a processing state such as reproduction, stopping, fast feeding or fast returning, a sound volume and a battery remaining capacity on the display section  85 . 
     The portable device  6  further includes an electrically erasable programmable read only memory (EEPROM)  86  having a storage capacity smaller than that of the semiconductor flash memory  80 . In the EEPROM  86 , the number of all digital music contents C 1  written in the semiconductor flash memory  80 , the block positions of the semiconductor flash memory  80  in which the individual digital music contents C 1  are stored and other various kinds of memory information are stored. 
     A real time clock (RTC)  87  of the portable device  6  is provided to count up the time to perform time management for the digital music contents C 1  to which some reproduction limitation is applied. A backup power supply circuit  88  serves as a power supply exclusively for the real time clock  87  and may be a primary cell such as a button cell, a capacitor or the like. The backup power supply circuit  88  allows the counting up of the time to be continued by the real time clock  87  even when the supply of power from the driving dry cell  61  is stopped. 
     Digital music contents C 1  to be stored into the semiconductor flash memory  80  of the portable device  6  are first downloaded from an EMD server  4  into the personal computer  1  through the network  2  as seen in FIG.  9 A. Then, the digital music contents C 1  downloaded in the personal computer  1  are supplied to and stored into the semiconductor flash memory  80  of the portable device  6  as seen in FIG.  9 B. 
     In this instance, also time information T1 including the year, month and day regarding the time is supplied from a real time clock (RTC) circuit not shown built in the personal computer  1  to the portable device  6  as seen in FIG.  9 C. The thus supplied time information T1 is written into the EEPROM  86  of the portable device  6 . The portable device  6  uses the time information T1 and the clock signal of the real time clock  87  to perform time management of the digital music contents C 1  to which some reproduction limitation is applied. 
     The time management by the portable device  6  is performed by the real time clock  87  counting up the time with reference to the time information T1 supplied thereto from the personal computer  1  to normally produce the latest time information T11′. Then, if the r issues an instruction to reproduce digital music contents C 1  stored in the semiconductor flash memory  80  and having some reproduction limitation applied thereto, then it is discriminated whether or not the time information T11′ managed by the real time clock  87  is time later than the “reproduction end date” specified in the header H 1  of the digital music contents C 1 , and only if it is discriminated that the time information T11′ is not later time, reproduction of the digital music contents C 1  is started. 
     In this manner, also the portable device  6  supervises the term of digital music contents C 1  to which some reproduction limitation is applied and can execute such an appropriate process based on the supervision that reproduction of the digital music contents C 1  is started or is not permitted. 
     Since the backup power supply circuit  88  for exclusive use for the real time clock  87  is provided in the portable device  6  as shown in FIG. 5, time management can be executed irrespective of the state of the driving dry cell  61 . 
     However, since the backup power supply circuit  88  requires holding of charge, in order to assure the backup for a predetermined period of time, a certain physical size is required for the backup power supply circuit  88 , and it is difficult to miniaturize the backup power supply circuit  88 . Further, in order to back up only the real time clock  87 , designing of a power supply wiring scheme separate from that for the other circuit elements is required for the real time clock  87 . Even if the backup power supply circuit  88  is provided taking such a situation into consideration, the backup cannot be performed without any restriction, but may not possibly be performed because the user is puzzled in exchange of the cell or the portable device  6  is left after the cell is removed. This may result in such a disadvantage that, since the time T11 produced by the real time clock  87  is reset to an initial state, time in the past is produced in error and this disables enjoyment of digital music contents C 1  to which a limitation to the utilization term is applied. 
     Therefore, another portable device  6  shown in FIG. 10 is configured such that the backup power supply circuit  88  is removed from the portable device  6  shown in FIG. 5 but uses a time management method described below with reference to FIG. 11 to prevent the disadvantage described above. 
     In particular, referring to FIG. 11, when digital music contents C 1  are supplied from the real time clock circuit of the personal computer  1  to the portable device  6 , also time information T1 is supplied as described hereinabove with reference to FIG. 9 in step S 1 . The portable device  6  sets the time information T1 supplied thereto to the real time clock  87  and stores the time information T1 into the semiconductor flash memory  80 . The real time clock  87  starts counting up with reference to the time information T1 set thereto and continuously performs the counting up operation to successively produce the latest time information T11′. It is to be noted that the updating of the time may otherwise be performed in such a manner that, only when the time information T1 supplied from the real time clock circuit of the personal computer  1  leads the time T11 counted by the real time clock  87 , the time information T1 is set to the real time clock  87 . This is effective to prevent the real time clock  87  from being set to wrong time when the time information T1 supplied from the personal computer  1  represents time in the past. 
     In step S 2 , it is discriminated whether or not the portable device  6  is in a standby mode. Here, the standby mode is described. For the portable device  6 , a state called standby mode is prepared in order to prevent the capacity of the driving dry cell  61  from being consumed wastefully. 
     More particularly, one of operations of the portable device  6  is a reproduction operation, and the reproduction operation is performed by reproducing music data D 1  of digital music contents C 1  stored in the semiconductor flash memory  80  under the control of the CPU  72  in response to an operation of the reproduction/stop button  59 . Then, if the reproduction/stop button  59  is operated during such reproduction, then the reproduction is stopped. 
     If the reproduction/stop button  59  is operated once again after the reproduction is stopped, then the reproduction of the music data D 1  is resumed from the position at which the reproduction has been stopped under the control of the CPU  72 . On the other hand, if several seconds or more elapse without an operation of the reproduction/stop button  59  after reproduction is stopped, then the power supply is switched into an off state and the portable device  6  enters the standby mode so that the power consumption thereby is reduced. 
     Since it is repetitively discriminated in step S 2  whether or not the portable device  6  is in such a standby mode as described above, the state of the portable device  6  is normally supervised. Then, if it is discriminated that the portable device  6  is in the standby mode or the mode of the portable device  6  has changed to the standby mode, then the processing advances to step S 3 . In step S 3 , the time information T11′ of the real time clock  87  is written or overwritten into the semiconductor flash memory  80 . 
     After the process in step S 3  is completed, it is discriminated in step S 4  whether or not six hours elapse after the point of time of storage of the latest time information T11′ into the semiconductor flash memory  80 . Here, while the time for discrimination is set to 6 hours, it may otherwise be any hours. For example, an interval timer of the CPU  72  may be set in advance so that the CPU  72  may be placed into an operating state after each 6 hours. 
     If it is discriminated in step S 4  that six hours elapse, that is, if the CPU  72  is placed into an operating state by the interval timer, then the processing returns to step S 3 , in which writing of the time information T11′ of the real time clock  87  is performed. Description of the process here in step S 3  is omitted because it is described hereinabove already. 
     On the other hand, if it is discriminated in step S 4  that six hours do not elapse, then the processing advances to step S 5 , in which it is discriminated whether or not the reproduction/stop button  59  is operated. If it is discriminated that the reproduction/stop button  59  is operated, then the processing returns to step S 2  so that the processing in steps beginning with step S 2  is repeated. However, if it is discriminated that the reproduction/stop button  59  is not operated, then the processing returns to step S 4  so that the processing in steps beginning with step S 4  is repeated. 
     Where the time management is performed in such a manner as described above, at least the time information T11′ within six hours is stored in the semiconductor flash memory  80 . While the process illustrated in FIG. 11 is described as the time management of the portable device  6  which does not include the backup power supply circuit  88  as shown in FIG. 10, it may be applied also to the time management of the portable device  6  which includes the backup power supply circuit  88  as shown in FIG.  5 . 
     In the portable device  6  shown in FIG. 10, while the driving dry cell  61  is not present as a result of removal, the production of the time T11 by the counting up of the real time clock  87  is temporarily stopped, and the time information T11′ of the real time clock  87  may possibly be lost. If power supply from the driving dry cell  61  is started after it is stopped once, then at the point of time, the CPU  72  resumes the process illustrated in FIG.  12 . Processes in steps S 2 , S 3 , S 4  and S 5  illustrated in FIG. 12 are similar to those described hereinabove with reference to FIG. 11, and overlapping description of them is omitted herein to avoid redundancy. In first step S 11  prior to step S 2 , the CPU  72  reads out the time information T11′ stored in the semiconductor flash memory  80 . 
     Since time information is stored in the semiconductor flash memory  80  and the stored time information is rewritten at a predetermined timing in this manner, even in such a case that supply of power is interrupted, time information can always be acquired by using the stored time information. By using the time information to perform term management of digital music contents C 1  to which some limitation with regard to the term is applied, illegal utilization of the digital music contents C 1  can be prevented. 
     Further, where the portable device  6  is configured such that it does not use a backup power supply, the circuit scale of the portable device  6  can be reduced. Further, since the time information is performed in the inside of the portable device  6 , such illegal accessing of the user as to change the time information from the outside can be prevented. 
     It is to be noted that, while, in the embodiment described above, time information is stored into the semiconductor flash memory  80 , it may otherwise be stored into the EEPROM  86 . Further, while the embodiment described above handles digital music contents C 1 , the present invention can be applied also to where other data such as, for example, video data is handled. 
     Further, in the embodiment described above, it is discriminated whether or not six hours elapse after the standby mode is entered and, if it is discriminated that six hours elapse, then the time information stored in the semiconductor flash memory  80  is updated. However, alternatively the point of time at which the driving dry cell  61  is re-loaded and the power whose supply has been stopped once begins to be supplied again may be used as reference time, and the time information may be updated after each six hours elapse from the reference time irrespective of whether or not the standby mode is entered. In this instance, when the standby mode is entered, the reference time of the period of six hours may be updated at the point of time at which the standby mode is entered. 
     Furthermore, in the embodiment described above, when digital music contents are downloaded from the personal computer  1 , also the time information T1 is supplied. However, not only upon such downloading, but also when the portable device  6  and the personal computer  1  are connected to each other such as, for example, upon check-in or check-out, the time information T1 may be supplied from the personal computer  1  to the portable device  6  so that the time information stored in the semiconductor flash memory  80  and the real time clock  87  of the portable device  6  may be updated. 
     While the series of processes described above can be executed by hardware, it may otherwise be executed by software. Where the series of processes is executed by software, a program which constructs the software is installed from a recording medium into a computer incorporated in hardware for exclusive use or, for example, a personal computer for universal use which can execute various functions by installing various programs. 
     The recording medium is formed as a package medium such as, as shown in FIG. 2, a magnetic disk  41  a CD-ROM (Compact Disk-Read Only Memory) and a DVD (Digital Versatile Disk)), a magneto-optical disk  43  (including an MD (Mini-Disk)), or a semiconductor memory  44 , which is distributed to provide the program to a user separately from a computer, or as a ROM  12  or a HDD  21  on which the program is stored and which is provided in a state wherein it is installed in a computer in advance. 
     It is to be noted that, in the present specification, the steps which describe a program provided in the form of a medium may be but need not necessarily be processed in a time series in the order as described, and include processes which are executed parallelly or individually without being processed in a time series. 
     Further, the term “system” in the present specification is used to signify an entire apparatus composed of a plurality of apparatus. 
     Further, the flash memory into which contents data and reproduction limitation data are recorded need not necessarily be provided in a reproduction apparatus, but may be stored in a recording medium which can be loaded into the reproduction apparatus such that reproduction of data may be performed by a loading mechanism for a recording medium and an interface not shown provided in the reproduction apparatus. In this instance, if the time information T1 produced by the real time clock of the personal computer  1  is recorded into the recording medium loaded in the reproduction apparatus when contents data are recorded by the personal computer  1  or when the recording medium is loaded in the personal computer  1  and the time T11 of the real time clock  87  is corrected when the time in the recording medium indicates time prior to that of the real time clock  87  in the reproduction apparatus, then even when the reproduction apparatus is not connected to the personal computer  1 , the time to be produced by the real time clock  87  in the reproduction apparatus can be advanced to produce time proximate to the actual time with certainty. 
     As apparent from the foregoing description, since elapsed time with reference to the time indicated by first information stored is measured to produce second information regarding the time and the first information is updated to the produced second information at a predetermined timing, illegal use of contents can be prevented by managing a term of use of the contents using the first information and the second information. 
     While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.