Abstract:
A circuit for an integrated interface of a PDA and a wireless communication system is suitable for integrating the PDA and the wireless communication system. The circuit includes a first serial port has two terminals, in which one of the two terminals is electrically connected to the PDA, and another one of the two terminals is electrically connected to the wireless communication system. The first serial port is used to bi-directionally transmit a control signal between the PDA and the wireless communication system. A second serial port has two terminals, in which one of the two terminals is electrically connected to the PDA, and another one of the two terminals is electrically connected to the wireless communication system. The second serial port is used to bi-directionally transmit data between the PDA and the wireless communication system.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of a prior application Ser. No. 10/249,403, filed Apr. 7, 2003. The prior application Ser. No. 10/249,403 claims the priority benefit of Taiwan application serial no. 91118369, filed on Aug. 15, 2002. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of Invention  
         [0003]     The present invention generally relates to a circuit and operating method for an integrated interface of a PDA and a wireless communication system, and more particularly, to a circuit, operating method for executing turn-on-device, power-saving, power-shortage determining, and power-charging for the integrated interface of a PDA and a wireless communication system. Description of Related Art  
         [0004]     In line with personal computer capability enhancement, the demands of portable computers increase accordingly and their functions are getting more and more mature. In the beginning, portable computer meant a lighter weight desktop computer that had to use household power supply. However, along with the development of LCD and the long-term battery, the notebook started to be accepted and used widely. The weight of a general notebook is about 2.5 kg to 3.5 kg. Therefore, the notebook indeed provides a perfect portability while keeping the complete functionality of a personal computer.  
         [0005]     Since the notebook has acquired excellent performance in the market, many people have aggressively dedicated themselves to the development of a smaller computer. However, due to the limitation of display size and suitable input equipment, the development of the smaller computer had limited improvement. Nevertheless, finally there has been one smaller computer to breakthrough the difficulties mentioned above and be well accepted in the market. This is a computer that uses few buttons and a touch screen as input equipment, generally called the Personal Digital Assistant (PDA).  
         [0006]     With PDA&#39;s high portability, plus the Optical Character Recognition (OCR) software, there is no much difference between a PDA and a general notebook in the convenience level of data input anymore. Therefore, the PDA is getting more and more popular in the market. The most common purpose of the general PDA is to provide the related information for daily living, such as calendar, railroad/bus time table, telephone numbers, and even domestic maps, etc. The general reason why a user uses a PDA is for its excellent portability, with which a user can get the information mentioned above to use a telephone at any time, any place. In order to contact with others at any time and any place, or to acquire the most updated and suitable information, a different sort of the wireless communication systems such as the Global System for Mobile (GSM) system or the General Packet Radio Service (GPRS) system are used to communicate with others, or through these wireless communication systems connecting to the Internet to acquire the most updated information. Either one of the above is a wonderful option.  
         [0007]     However, PDA and all other wireless communication systems are sold independently in the current market. Therefore, besides purchasing a PDA and wireless communication systems, in order to connect to the Internet and acquire information easily, it is also necessary to purchase an appropriate network interface or use a more expensive infrared communication device to have mutual information exchange between a PDA and a wireless communication system. Therefore, users not only have to consider the compatibility between different products when they are purchased, but also have to carry all kinds of equipment for providing interfaces, which is really troublesome.  
       SUMMARY OF THE INVENTION  
       [0008]     The present invention provides a circuit and operating method for an integrated interface of a PDA (Personal Digital Assistant) and a wireless communication system. The interface between the PDA and the wireless communication system is provided to integrate the PDA and the wireless communication system, and to further enhance the whole utilization between the PDA and the wireless communication system.  
         [0009]     The present invention provides a circuit and operating method for integrated interface of PDA and wireless communication system. It is suitable for integrating the PDA and the wireless communication system. The circuit includes two serial ports, the serial ports are electrically connected between the PDA and the wireless communication system, and one of the two ports is used to transmit a control signal, and another one of the two ports is used to transmit a data signal.  
         [0010]     In a preferred embodiment of the present invention, the circuit provided by the present invention further comprises a power system, wherein the power system provides power to the PDA and the wireless communication system, and also provides a power-shortage signal to the PDA and the wireless communication system when power is insufficient. In another preferred embodiment of the present invention, the power system determines a method for supplying power to a PDA according to an idle signal received from the PDA. Moreover, in another embodiment of the present invention, the power system provides a charging signal to the wireless communication system when it is charged from outside, and the wireless communication system determines the charging mode according to the charging signal and the power system potential.  
         [0011]     The present invention further provides an operating method for an integrated interface of a PDA and wireless communication system. The interface used by the operating method comprises a PDA-turn-on-wireless-communication-system signal line, a PDA-reset-wireless-communication-system signal line, a PDA-state signal line, wireless-communication-system-state/wake-up-PDA signal line and two serial ports. Wherein, one of the two ports located between the PDA and the wireless communication system is used to transmit the control signal and the status data of the wireless communication system state such as the antenna intensity and the battery capacity by using the multi-channel method, and another one of the two ports is used to transmit a digital data signal.  
         [0012]     In an embodiment of the present invention, the following turn-on-device method is further used by the operating method according to the present invention in the first time PDA power-on: turning on the PDA first, and further checking the status of the wireless communication system. If the status of the wireless communication system observed is turn-on during the checking process, the wireless communication system is reset via the PDA-reset-wireless-communication-system signal line; otherwise, if the status of the wireless communication system is turn-off, the wireless communication system is turned on and reset via the PDA-turn-on-wireless-communication-system signal line. After performing the reset operation of the wireless communication system mentioned above, the status of the wireless communication system is further checked after waiting for a certain period of time. If the status of the wireless communication system observed is normal in the present time&#39;s wireless communication system status checking, the first time turn-on-device is completed; otherwise, if the status of the wireless communication system observed is abnormal, the error message is displayed to notify the external that power on of the wireless communication system turn-on-device has failed.  
         [0013]     In another preferred embodiment, the operating method according to the present invention further comprises a set of power management system. This comprises a power-saving method, a power-shortage determining method, and a battery charging method. On the power-saving aspect, the preferred embodiment of the present invention transmits a wireless communication system state signal to the PDA when the wireless communication system starts to operate from a standby state. Meanwhile, if the PDA is currently used, the normal procedure is processed accordingly. If the PDA is in a sleep state, the PDA is wakened by the subsequent wake-up-PDA signal. However, the input source of the audio element in the PDA is switched to the wireless communication system under both states mentioned above to facilitate the usage of the wireless communication system. When the wireless communication system operates continuously and the PDA does not have any operation for a certain period of time, the PDA is switched to the sleep state.  
         [0014]     Moreover, in the power-shortage determining method used by a preferred embodiment of the present invention, the power potential is divided into three different levels from high to low. For convenience of explanation, the potential levels from high to low are herein called the first potential, the second potential and the third potential, respectively. The power-shortage determining method used by the preferred embodiment of the present invention issues a power-shortage signal when the power potential starts to be lower than the second potential, and continuously issues the power-shortage signal until the power potential is greater than or equal to the first potential. Furthermore, if the power potential is in between the first potential and the second potential and there is no power-shortage signal, the system is operated normally. Finally, if the power potential is lower than the third potential, it is fully discharged. Moreover, in a preferred embodiment of the present invention, for example, the first potential mentioned above is about 3.6 V, the second potential is about 3.5 V, and the third potential is about 3.2 V.  
         [0015]     The battery charging method used by another preferred embodiment of the present invention is suitable for charging the device that uses a battery as power and is charged via an external charging cable. The device further has an external charging circuit for charging a battery, and the wireless communication system has an internal charging circuit for charging a battery, too. The battery charging method performs a small-current charging via the external charging circuit mentioned above by using the external charging cable when the battery is empty, and tries to turn on the wireless communication system during the period when performing the small-current charging. After the wireless communication system is successfully turned on, when the battery potential achieves a first predetermined value, the internal charging circuit is turned on to perform charging. Furthermore, the battery can issue a charging signal to the wireless communication system when the external charging cable mentioned above connects to it, so that the wireless communication system can recognize the current charging status.  
         [0016]     In a preferred embodiment of the present invention, the charging method is switched to the constant voltage charging when the battery potential achieves a second predetermined value that is higher than the first predetermined value mentioned above. When the battery potential falls in between the first predetermined value and the second predetermined value, the charging process can be further divided into multiple charging segments. These charging segments are distinguished from each other by using the battery potential and use charging speeds with different current values respectively.  
         [0017]     The present invention further provides an operating method for an integrated interface of a PDA and a wireless communication system, suitable for integrating the PDA and the wireless communication system. The operating method comprises using at least one serial port to transmit a control signal and data between the PDA and the wireless communication system. In addition, when the PDA is turned on, the PDA is turned on, and the wireless communication system is turned on by the PDA.  
         [0018]     In summary, the circuit and operating method for the integrated interface of a PDA and wireless communication system integrates a PDA and wireless communication system by using two serial ports, and further defines an integrated set of operating methods, so that the PDA and the wireless communication system can easily communicate and exchange messages with each other. However, since the serial port is a well developed interface, it is not necessary to spend much effort on it to tune it or design a new communication protocol for it when it is used by the operating method disclosed by the present invention. Moreover, its price is cheap and its cost is lower than the cost needed by the infrared system or the bluetooth system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention. In the drawings,  
         [0020]      FIG. 1  schematically shows a block diagram for the integrated interface circuit of a preferred embodiment according to the present invention;  
         [0021]      FIG. 2  schematically shows a block diagram for the integrated interface circuit of another preferred embodiment according to the present invention;  
         [0022]      FIG. 3  schematically shows a step flow chart of a preferred embodiment that is included in the operating method for the integrated interface provided by the present invention related to the operation for turning on the system first time;  
         [0023]      FIG. 4  schematically shows a step flow chart of the process included in the operating method for the integrated interface of a preferred embodiment according to the present invention related to the power-saving method;  
         [0024]      FIG. 5  schematically shows a flow chart of the steps included in the operating method for the integrated interface of a preferred embodiment according to the present invention related to power charging;  
         [0025]      FIG. 6A  schematically shows a sketch map of the potential levels used by a preferred embodiment according to the present invention; and  
         [0026]      FIG. 6B  schematically shows a flow chart of the steps included in the operating method for the integrated interface of a preferred embodiment according to the present invention related to the power-shortage determining method. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]      FIG. 1  schematically shows a block diagram for the integrated interface circuit of a preferred embodiment according to the present invention. The circuit for the integrated interface of the PDA (Personal Digital Assistant) and the wireless communication system shown in  FIG. 1  transmits signal between the PDA  102  and the wireless communication system  104  to integrate and make them into a whole. In the present embodiment, the circuit for the integrated interface comprises a PDA-turn-on-wireless-communication-system signal line  130 , a PDA-reset-wireless-communication-system signal line  132 , a PDA-state signal line  134 , a wireless-communication-system-state/wake-up-PDA signal line  136 , two serial ports  110  and  112 , and a power system  106 . Wherein, the serial port  110  transmits the control signal and the status data of the wireless communication system state such as the antenna intensity and the battery capacity by using a multi-channel method, and the serial port  112  is dedicated to transmit the digital data signal. Under normal situations, the digital data signal transmitted between these two elements (usually, it is an audio signal) occupies a very long time period on the serial port. Therefore, the present invention transmits the control signal and the digital data signal via separate serial ports respectively to avoid prolonging the time for transmitting the control signal when the PDA  102  and the wireless communication system  104  transmit the digital data signal to each other. Moreover, the integrated interface does not interrupt the digital data transmission and does not impact the real timing of the digital data due to the requirement of transmitting the control signal.  
         [0028]     Furthermore, although it is not shown in  FIG. 1  precisely, the power system  106  used by the present embodiment supplies power to the PDA  102  and the wireless communication system  104  for their operation via related circuits, respectively. In addition, for the convenience of power management, the power system  106  of the present embodiment further provides a power-shortage signal to the PDA  102  and the wireless communication system  104  respectively via the signal line  120  when the power is insufficient. Moreover, the power system  106  further provides a charging signal to the wireless communication system  104  via the charging signal line  124 . With the message provided by the charging signal, the wireless communication system  104  can determine the magnitude of the current and the charging circuit used for charging.  
         [0029]     Moreover, in the present embodiment, in order to provide a further power management method, the PDA  102  transmits an idle signal to the power system  106  via the idle signal line  122  after it is idle for a certain period of time, so that the power system  106  can determine the magnitude of the power supplied to the PDA  102 .  
         [0030]      FIG. 2  schematically shows a detailed block diagram for the integrated interface circuit of another preferred embodiment according to the present invention. The device  20  comprises a PDA  202 , a wireless communication system  252 , a power system  280 , and an integrated interface composed of a serial port  22  and a serial port  24 . Wherein, the PDA  202  portion comprises a processor  204 , an LCD (liquid crystal display)  206 , a touch panel  208 , an ASIC (Application Specific Integrated Circuit)  210 , a universal I/O chip  212 , an external universal I/O chip  214 , an external device interface (RS232/IR)  216 , a USB (Universal Serial Bus)  218 , a keyboard  220 , a memory  222 , an audio element  224 , and an extended memory card  230 . The wireless communication system  225  portion comprises a processor  254 , a built-in memory  256 , a SIM card  258 , a keyboard  260 , a vibrating element  262 , an LED  264 , an analog Codec (coder/decoder)  266  with an internal charging circuit  268  included in it, and a wireless communication element  270  used for sending and receiving the electromagnetic wave signal. Moreover, the power system  280  used by the present embodiment is composed of the battery  282  and the external charging circuit  284 . In addition, in the integrated interface used to communicate between the PDA  202  and the wireless communication system  252 , the serial port  22  is used to transmit a control signal, and the serial port  24  is used to transmit a digital data signal. In order to have those skilled in the related art have better understanding of the technique contents of the present invention, the circuit block diagram shown in  FIG. 2  is exemplified hereinafter to describe operating methods for the PDA and the wireless communication system provided by the present invention in detail. Furthermore, in order to reduce the complexity of drawings, the signal lines shown in  FIG. 1 , including the PDA-turn-on-wireless-communication-system signal line  130 , the PDA-reset-wireless-communication-system signal line  132 , the PDA-state signal line  134 , and the wireless-communication-system-state/wake-up-PDA signal line  136  are not shown in  FIG. 2 . However, in order to achieve all specific functions, these signal lines are required under certain circumstances.  
         [0031]     Referring to both  FIG. 2  and  FIG. 3  simultaneously,  FIG. 3  schematically shows a step flow chart of a preferred embodiment that is included in the operating method for the integrated interface provided by the present invention and related to the operation for turning on the system first time. It has to be specified that the wording of the “turning on the system first time” used herein is switching the state of the PDA  202  from turn-off state to turn-on state. For example, the turn-on operation performed after the battery is exhausted or the PDA  202  is turned off to replace the battery belongs to the range of “turning on the system first time”. Moreover, although the global system for mobile (GSM) is used as an example of the embodiment for the wireless communication system  252  in the present embodiment, it does not mean that the present invention is only suitable for the circumstance of the GSM combination, other wireless communication systems, such as the general packet radio service (GPRS) can also be applied with the same method.  
         [0032]     In the embodiment as shown in  FIG. 3 , at first, for example, a keyboard is used by the user to turn on the device  20  for the first time after it is manufactured from the factory (step S 302 ). Since the power system  280  currently used usually stores enough power for its operation, the system will turn on the PDA  202  first (step S 304 ). Certainly, if the power system  280  does not store enough power to turn on the PDA  202 , the device  20  cannot be turned on.  
         [0033]     After the PDA  202  is turned on in step S 304 , the PDA  202  starts checking the status of the GSM  252  (step S 306 ). Meanwhile, since the PDA  202  has been turned on, the processor  204  recognizes the status of the GSM  252  via the GSM-state/wake-up-PDA signal line  136 . If the GSM  252  has been turned on, the PDA  202  transmits the PDA-reset-GSM signal to the processor  254  via the PDA-reset-GSM signal line  132  to reset the GSM  252  (step S 312 ). Otherwise, if the GSM  252  is found to be turned off in step S 306 , the PDA  202  transmits the PDA-turn-on-GSM signal to the processor  254  via the PDA-turn-on-GSM signal line  130  to turn on the GSM  252  (step S 308 ). After the GSM  252  has been turned on in step S 308  and after waiting for a predetermined period of time (step S 310 ), the PDA  202  performs the operation for resetting the GSM  252  as mentioned above (S 312 ).  
         [0034]     After the reset operation in step S 312 , the PDA  202  starts waiting for another predetermined period of time (step S 314 , and this predetermined period of time can be different from the waiting time in step S 310  mentioned above). After waiting, the PDA  202  checks the status of the GSM  252  again (step S 316 ). If the result of checking indicates the GSM  252  operates normally, the turn-on process is completed. Otherwise, if the result of checking indicates the GSM  252  does not operate normally yet (step S 318 ), the steps S 314 -S 316  are processed repeatedly to confirm the actual status of the GSM  252  under the circumstance that the waiting time does not exceed the length of the predetermined period of time. If the GSM  252  cannot operate normally even after waiting for the predetermined period of time, the device  20  issues an error message to notify the user that the GSM  252  turn on operation failed. In the present invention, the error message may comprise a flashing light, displaying a string on the PDA  202  or sounding a warning beep.  
         [0035]     Although the embodiment mentioned above uses the circumstance that the device  20  is turned on the first time by the keyboard after it has been manufactured from the factory as a major foundation for description, all other methods for turning on the device that comply with the definition of “turning on device first time” can be used with the method mentioned above. For example, under the circumstance that the power of the power system  280  is completely exhausted and the device  20  has to rely on recharging via the external charging cable for resuming its operation, after the charging cable is plugged into the device  20  and starts charging the power system  280  (step S 330 ), the power system  280  is charged gradually (step S 332 ). Then, the device  20  tries to turn on the PDA  202  (step S 334 ), and if the PDA  202  cannot be turned on yet, the device  20  charges the power system  280  continuously; if the power stored in the power system  280  is large enough to turn on the PDA  202 , the process turns into the step S 304  to turn on the PDA  202 , and subsequently performs the turn-on-device operation mentioned above.  
         [0036]     Moreover, the method provided by the present embodiment is also suitable for the general turn-on-device process after some minor modification. As shown in  FIG. 3 , after the PDA  202  passes the general normal reset operation (step S 340 ), step S 306  and its subsequent processes can be continued to complete the turn-on-device process.  
         [0037]     It has to be specified herein, that when a system is charging, since there may be some leak of electricity between those two systems (PDA  202  and GSM  252 ), it may result in a certain unstable state, and thus the GSM  252  has to be reset after the PDA  202  is turned on to prevent the phenomenon of disorder from happening. Optionally, a switch can be designed in the power terminal of the GSM  252 , and after the PDA  202  becomes stable, the PDA  202  turns on this switch to supply power to the GSM  252 . Therefore, the GSM  252  is ensured not to be turned on before the main controller (i.e. PDA  202 ) and thus will not lose its control.  
         [0038]      FIG. 4  schematically shows a step flow chart of the process included in the operating method for the integrated interface of a preferred embodiment according to the present invention related to the power-saving method. The control process used for a general warm-turn-on-device is described herein first. Please also refer to  FIG. 2  at the same time, when the PDA  202  is in the standby state (step S 402 ), if the switch is not pressed yet, the PDA  202  keeps staying in the standby (sleep) state, and the GSM  252  enters into the sleep state (step S 404 -S 410 ). If the switch is pressed while in the standby state, the PDA  202  will wake up, and the GSM  252  is activated simultaneously (step S 404 -S 406 ). Afterwards, when the switch is pressed again (step S 408 ), the PDA  202  will enter into the standby state, and the GSM  252  enters into the sleep state. When the GSM  252  is in the sleep state, the power system  280  does not provide the high frequency (e.g.  13  MHz) power to the GSM  252 , saving power required for switching the state of the high frequency element under the standby state.  
         [0039]     Referring to both  FIG. 4  and  FIG. 2  again, when the GSM  252  is in the standby state (it does not matter whether it is sleeping or not, i.e. step S 412 ), the GSM  252  starts performing an operation for receiving a telephone signal for as long as it receives the telephone signal. Meanwhile, the GSM  252  transmits the GSM-state/wake-up-PDA signal to the processor  204  of the PDA  202  via the GSM-state/wake-up-PDA signal line  136  to wake up the PDA  202  first. After the PDA  202  is wakened, the input source of the audio element  224  is converted into the analog Codec  266  of the GSM  252 . Therefore, the electromagnetic wave received by the wireless communication element  270  can be converted into the digital (or audio) data, and outputs it to the user via the analog Codec  266  by using the audio element  224 . Moreover, if only the GSM  252  is used and there is no action applied to the PDA  202  for a certain period of time, the PDA  202  enters into the sleep state from the wake-up state to reduce the electricity wear.  
         [0040]     In addition, there is still another method for saving the electricity wear. That is, as shown in  FIG. 1 , when the PDA  102  stays in the idle state, the PDA  102  provides an idle signal to the power system  106  via the idle signal line  122 . The power system  106  changes to use a new method that saves more electricity to output power after it receives this idle signal, so as to save some electricity wear.  
         [0041]      FIG. 5  schematically shows a flow chart of the steps included in a preferred embodiment according to the present invention and related to the power charging. In order to have a better understanding, please also refer to  FIG. 2  at the same time. When the charging cable is plugged into the power system  280  and starts charging (step S 502 ), the external charging circuit  284  inside the power system  280  starts charging to the battery  282  with a small-current charging method (step S 504 ). Meanwhile, the power system  280  sends a charging signal to the GSM  252  to notify it that it is in the charging state now. After the small-current charging is started, the device  20  starts trying to turn on the GSM  252 . If the GSM  252  cannot be turned on, the small-current charging is continuously performed; otherwise, if the GSM  252  is turned on successfully, the process enters into next step&#39;s charging process (step S 506 ). After the GSM  252  is turned on successfully, the internal charging circuit  268  inside the GSM  252  starts to operate, and with this, it performs faster speed&#39;s charging to the battery  282 . For example, when the potential of the battery  282  is lower than 3.6 V, the internal charging circuit  268  uses 600 mA as the current value for the first segment&#39;s charging (step S 508 , S 510 ). When the potential of the battery  282  is in between 3.6 V and 4.2 V, the internal charging circuit  268  uses 900 mA as the current value for the second segment&#39;s charging (step S 512 , S 514 ). After the potential of the battery  282  achieves 4.2 V, the internal charging circuit  268  changes to use the constant-voltage charging method to charge the battery  282  (step S 516 ), so that the battery  282  is not damaged due to over-charging.  
         [0042]      FIGS. 6A and 6B  schematically shows a sketch map of the potential levels and a step flow chart used by a preferred embodiment according to the present invention, respectively. In  FIG. 6A , the present invention divides the battery potential into five different levels, they are: full battery  60 , low battery (C)  62 , insufficient battery (A)  64 , insufficient battery (B)  66 , and complete discharge  68 , respectively. In an embodiment of the present invention, the potential represented by these levels is: full battery  60  indicates the current battery potential is above 3.8 V, low battery (C)  62  indicates the current battery potential is in 3.8V˜3.6 V, insufficient battery (A)  64  indicates the current battery potential is in 3.6V˜3.5 V, insufficient battery (B)  66  indicates the current battery potential is in 3.5V˜3.2 V, and complete discharge indicates the current battery potential is below 3.2V, respectively. Certainly, the dividing standard for the battery potential levels does not have to match the present embodiment, those skilled in the related art can appropriately adjust the dividing standard, the figures listed above are only exemplified herein and do not serve as the necessary limitation condition for the present invention.  
         [0043]     The power-shortage determining method provided by the present invention is further described in detail hereinafter. In order to have a better understanding and facilitate the explanation, please refer to both  FIG. 6A  and  FIG. 6B  at the same time. In  FIG. 6B , it is assumed that the battery  282  is in the full battery  60  state at first (step S 602 ), meanwhile all operations for the device  20  operate normally. After the device  20  continuously uses power and makes the potential of the battery  282  fall in the range of the lowest battery (C)  62  (step S 604 ), the power system  280  determines whether to issue the battery-shortage signal or not (step S 606 ).  
         [0044]     The standard used in step  606  for determining whether to issue the battery-shortage signal or not is further described hereinafter. It is assumed that the battery  282  is in low battery (C)  62 , and the devices  20  are heavy loaded, such as the state when the PDA  202  is using the audio element  224  or the GSM  252  is using telephone. Since it uses more current, the potential of the battery  282  easily falls into the range of insufficient battery (B)  66  immediately. Therefore, after the potential of the battery  282  enters into the range of the low battery (C)  62 , if the device  20  turns to heavy loading from light loading (e.g. sleep mode) suddenly, the power system  280  issues the battery-shortage signal when the potential of the battery  282  is lower than the insufficient battery (B)  66 . If the device  20  keeps staying in the light loading, the power system  280  issues the battery-shortage signal when the potential of the battery  282  is lower than the insufficient battery (A)  64 . In other words, the criteria for generating the battery-shortage signal can be adjusted automatically depending on conditions.  
         [0045]     If after step S 606 , it is determined not to issue the battery-shortage signal, the battery  282  stays in the low battery state and does not enter into the insufficient battery state; if it is determined to issue the battery-shortage signal, the power system  280  provides the battery-shortage signal to the PDA  202  and GSM  252 , respectively. This indicates the battery  282  has entered into the level of insufficient battery already (step S 608 ). To be noted, the current battery potential may fall into the level of either insufficient battery (A)  64  or insufficient battery (B)  66 . Once the power system  280  issues the battery-shortage signal, the battery-shortage signal is not released until the potential of the battery  282  is higher than that of the low battery (C)  62 . If the user continuously uses it, after the potential of the battery  282  is lower than insufficient battery (B)  66 , the power system  280  enters into the level of complete discharge and is not allowed to execute any operation.  
         [0046]     To be specified herein, since the sudden fall of the battery voltage is commonly generated when it is changed from light loading to heavy loading, the electrical energy actually stored in the battery may still be big enough to support the power that is required for normal operation. Therefore, the battery-shortage determining method provided by the present invention can avoid the condition of abnormal device turn-on and turn-off resulting from the system not recognizing the battery-shortage due to the light loading to heavy loading change by flexibly adjusting the criteria for determining battery-shortage.  
         [0047]     In summary, the advantages of the present invention are described hereinafter. The present invention transmits control signals and digital data respectively by using two serial ports, thus to simplify the communication protocol generally considered and used to transmit control signals and digital data simultaneously by using a single serial port. Moreover, not only is the hardware cost much less than the cost needed for infrared system or bluetooth system, but also provides an efficient method for managing power, so that power waste can be eliminated.  
         [0048]     Although the invention has been described with reference to a particular embodiment thereof, it will be apparent to one of the ordinary skill in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed description.