Patent Publication Number: US-2005138311-A1

Title: Method and circuit for preservation of user data in a mobile terminal

Description:
PRIORITY  
      This application claims priority to an application entitled “Method and Circuit for Preservation of User Data in Mobile Terminal” filed in the Korean Intellectual Property Office on Dec. 23, 2003 and assigned Serial No. 2003-95128, the contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to mobile terminals, and more particularly to a method and a circuit for preserving user data in a mobile terminal.  
      2. Description of the Related Art  
      Generally, mobile terminals including a mobile communication terminal, PDA (Personal Digital Assistant), and PDA phones, temporarily store user data, that is being processed, in volatile memory such as a SRAM (Static Random Access Memory). The user data refers to data that can be modified, added or deleted using functions such as a phone book, scheduler, address list, alarm, memo, voice message, and photograph function embedded in a mobile terminal. While such user data is stored in the volatile memory, the battery power of the mobile terminal may change from a low level to an off state. In such an event, the user data stored in the volatile memory will be lost.  
      As a solution to this problem, user data stored in a volatile RAM (Random Access Memory) can be backed up in nonvolatile flash memory when the amount of remaining battery power becomes lower than some predetermined level. Since the user data stored in the volatile memory is backed up in the flash memory before power-off, it can be preserved even if the battery power level is changed from the low level to the off state.  
      Also, users may inadvertently drop their mobile terminals during a call or other operations, thereby causing the batteries to separate from the main body. In case of a sudden power loss caused by the battery separation, the user data stored in the volatile memory cannot be backed up or preserved in the nonvolatile memory.  
      To prepare for such a case, a backup battery can be embedded in a mobile terminal to supply backup power to the volatile memory. While the main battery power is in a normal state, it is supplied as an operation power to the volatile memory and charges the backup battery. During a power failure, the backup battery serves as a source of operation power supplied to the volatile memory. Accordingly, even if the main battery is suddenly separated from the mobile terminal during a call or other operations, the user data stored in the volatile memory can be preserved.  
      However, an embedded backup battery increases the size of a mobile terminal. Due to limitations in size of mobile terminals, only small-capacity backup batteries can be used as backup batteries in mobile terminals. Since such backup batteries are unstable in voltage and vulnerable to noise, they cannot ensure the complete preservation of user data stored in a volatile memory.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a method and a circuit for stably preserving user data temporarily stored in a volatile memory of a mobile terminal, without using a backup battery for backing up the operation power for the volatile memory.  
      In order to accomplish the above object of the invention, whenever there is a change in the user data temporarily stored in the volatile memory, the changed user data is formatted in a file and backed up or saved in a nonvolatile memory. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a block diagram of a user data preservation circuit according to the present invention;  
       FIG. 2  is a flow chart of a process of backing up user data according to the present invention; and  
       FIG. 3  is a map of a flash memory for storing a backed-up user data file according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.  
       FIG. 1  is a block diagram showing a user data preservation circuit according to the present invention. As shown in  FIG. 1 , a SRAM (Static Random Access Memory)  102  can be used as volatile memory, while a flash memory  104  can be used as nonvolatile memory. A CPU (Central Processing Unit)  100  is a main controller of a mobile terminal that adopts the user data preservation circuit as shown. The CPU  100  temporarily stores user data such as a phone book, scheduler, address list, alarm, memo, voice message and photograph function, that is being processed during implementation of functions in the SRAM  102 .  
      An operation power Vo that operates the CPU  100 , SRAM  102  and flash memory  104  is supplied from a power switching circuit  108 . The power switching circuit  108  supplies either a battery power V+ of a battery (not shown) of the mobile terminal or a charging power of a super capacitor  110  as the operation power Vo to the CPU  100 , SRAM  102  and flash memory  104  according to the output from a power failure detecting circuit  106 .  
      The power failure detecting circuit  106  is a comparator for comparing a voltage level of the battery power V+ with a predetermined reference level. When the voltage level of the battery power V+ becomes lower than the reference level, the power failure detecting circuit  106  determines that the battery power has terminated. At that time, the power failure detecting circuit  106  outputs a power failure detecting signal to the power switching circuit  108  and applies the same signal as an interrupt signal to the CPU  100 .  
      When the battery power V+ is normal, that is, when no power failure detecting signal is applied from the power failure detecting circuit  106 , the power switching circuit  108  supplies the battery power V+ as the operation power Vo to the CPU  100 , SRAM  102  and flash memory  104 . At this time, the power switching circuit  108  also applies the battery power V+ to the super capacitor  110  so as to charge the super capacitor  110 . The super capacitor  110  is generally a short-time power backup capacitor with high capacity. The present invention uses a super capacitor capable of supplying the operation power Vo, for example, over one second.  
      If the battery is suddenly separated from the mobile terminal, the power failure detecting circuit  106  will detect the power failure caused by the battery separation. The power switching circuit  108  will then supply the charging power of the super capacitor  110  as the operation power Vo to the CPU  100 , SRAM  102  and flash memory  104 . Accordingly, the CPU  100 , SRAM  102  and flash memory  104  can normally operate for a short time, i.e., for one second or so. Since the power failure detecting circuit  108  must be operating during the time of separation of the battery from the mobile terminal, the charging power of the super capacitor  110  is also used as the operation power for the power failure detecting circuit  108 .  
      When there is a change in the user data temporarily stored in the SRAM  102 , the CPU  100  formats the changed user data in a file and flushes the file to be backed up or saved in the flash memory  104 .  
       FIG. 2  is a flow chart showing the operations of the CPU  100 . When any modification, addition or deletion is made to the user data temporarily stored in the SRAM  102  at step  200 , the CPU  100  proceeds with step  204 . At step  204 , the changed user data is formatted in a file. At step  206 , the CPU  100  determines the position in the flash memory  104  to which the formatted user data file should be backed up or saved. At step  208 , the user data file is flushed or copied to the flash memory  104  to be backed up or saved. Upon completion of the backup process, the CPU  100  returns to step  200 . Whenever there is a change in the user data temporarily stored in the SRAM  102 , the changed user data is backed up in the flash memory  104  by the process as shown in  FIG. 2 .  
      Therefore, through the use of the present invention, the user data stored in the SRAM  102  can be preserved even when the battery is separated from the mobile terminal during a call or other operations. Also, since the user data, if changed, is formatted in a file and backed up or saved in the flash memory  104 , it can be easily managed as files. When the mobile terminal resumes a normal operation upon backup of the user data or insertion of the separated battery, the user data is moved again or restored to the SRAM  102  to be readily processed.  
      It is also likely that the battery may be separated from the mobile terminal during the process of backing up the changed user data in the flash memory  104 . In such an event, the charging power of the super capacitor  110  is supplied as the operation power Vo to the CPU  100 , SRAM  102  and flash memory  104 . Also, the power failure detecting circuit  106  applies an interrupt signal for informing the CPU  100  about the power failure. Accordingly, the process of backing up the changed user data in the flash memory  104  can be completed normally even if the battery is suddenly separated. Upon recognizing the occurrence of battery separation, the CPU  100  performs all predetermined routines for a power-off mode and turns off the mobile terminal in a normal fashion, while the charging power of the super capacitor  110  is being supplied.  
      As explained above, whenever any change to the user data temporarily stored in the volatile memory is made, the present invention stores the changed user data as a file in the nonvolatile memory, thereby ensuring stable preservation of the user data. The present invention can preserve the user data, without using a backup battery for backing up the operation power of the volatile memory.  
      Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims, including the full scope of equivalents thereof.