Abstract:
The invention provides a compact and highly reliable electronic apparatus that can be driven by a small-capacity battery, and that can achieve high-speed continuous driving of a load by quickly judging the recovery state of the battery after driving the load. More particularly, the invention provides an electronic apparatus includes a power supply, a load, a load driver for driving the load by the power supply, a power supply state detecter for outputting power supply recovery information by measuring physical quantity of the power supply at predetermined intervals of time after the driving of the load is stopped, and a controller for instructing the load driver to drive the load, based on the power supply recovery information supplied from the power supply state detecter.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electronic apparatus powered by a battery, and more particularly to an electronic apparatus that achieves high-speed driving of a load by quickly detecting the recovery of the battery after driving the load. 
     BACKGROUND OF THE INVENTION 
     A variety of battery-powered portable electronic apparatuses, including electronic wristwatches and mobile phones, have been introduced into the market. These electronic apparatuses are equipped with high power consuming loads, such as a motor, a buzzer, an illumination device, etc., in order to implement the required functions. Batteries are used as power supplies to drive these high power consuming loads. Most of the batteries used as power supplies in such portable electronic apparatuses are secondary batteries. In recent years, high-performance batteries that are small in size, but large in capacity, such as lithium-ion batteries, have been developed. 
     However, the performance and functionality of such portable electronic apparatuses has been increasing rapidly, and the number of loads mounted therein has also been increasing. On the other hand, portability and aesthetics are important considerations in the design of portable electronic apparatuses. For example, electronic wristwatches are becoming increasing thin and light-weight. As a result, batteries that can be mounted in them have to be made smaller and thinner, resulting in a situation where the battery capacity decreases and the battery output impedance degrades when the number of loads to be driven is increasing. In this way, the power supply design for portable electronic apparatuses is becoming increasingly constrained, and there is therefore a need for a power supply system that controls the battery as a power supply and the driving of a load in a more efficient manner. 
     In view of the above situation, it is known to provide a battery-powered electronic apparatus equipped with a voltage judging means that judges the recovery state of a battery after driving a load (refer, for example, to Patent Document 1). 
     The prior art voltage judging method disclosed in Patent Document 1 will be described below.  FIG. 14  is a block diagram showing the configuration of a paging receiver equipped with a voltage judging means as disclosed in Patent Document 1, and  FIG. 15  is a characteristic diagram of a battery mounted in the paging receiver. 
     The paging receiver  50  is an electronic apparatus equipped with the prior art voltage judging means, and has a function to receive a paging signal addressed to it and to display the received information. A reception processing unit  51  detects and demodulates a radio signal received via an antenna ANT. An ID-ROM  52  is a nonvolatile memory for storing address data, etc. of the paging receiver  50 . A signal processing unit  53  drives the reception processing unit  51  intermittently. 
     A control unit  54  is constructed from a CPU, etc., and carries out processing, such as incoming call processing and voltage judgment processing, by controlling the various units in the paging receiver  50  in accordance with a control program stored in a ROM  55 . A RAM  56  is used as a working area by the control unit  54 , and stores various register and flag data. A voltage measuring circuit  57  measures the voltage of the battery  63 , and generates a detection signal Sd when the voltage Vd of the battery  63  drops below a voltage V 12  (to be described later) or a detection signal Su when it exceeds a voltage V 11  (to be described later). 
     A display driver  58  receives display data from the control unit  54 , and displays the data on a display unit  59  constructed from an LCD panel or the like. A key input unit  60  is constructed from various key switches (for example, a power switch and a reset key), and generates a switch signal that matches the operation of each key switch. A driver  61 , in response to an annunciator driving signal supplied from the control unit  54 , drives a speaker  71  that produces an alerting sound indicating the arrival of an incoming call, a vibrator  72  that produces vibration to indicate the arrival of an incoming call, and an LED  73  that illuminates when an incoming call arrives. A voltage raising circuit  62  is constructed from a DC/DC converter, and raises the voltage of the battery  63  for output during high load operation. The high load operation here refers, for example, to the operation in which the driver  61  drives any one of the annunciators, the speaker  71 , the vibrator  72 , or the LED  73 , when an incoming call arrives. 
     Next, the voltage judging operation in the paging receiver  50  will be described with reference to  FIGS. 14 and 15 . 
     First, when the power switch on the key input unit  60  is turned on, the control unit  54  performs initialization and enters an intermittent receive mode to wait for the arrival of an incoming call. When an incoming radiowave is detected, thus detecting the arrival of an incoming call, the address data of the detected incoming radiowave is compared with the address data stored in the ID-ROM  52  to determine whether they match or not. If the two addresses match, processing is performed to capture the received data into a receive buffer. Upon recognizing, as a result of the signal capturing processing, that the paging is addressed to the paging receiver  50 , the control unit  54  supplies an annunciator driving signal to the driver  61  which thus drives the speaker  71 , the vibrator  72 , or the LED  73  to annunciate the incoming call. 
     When the high load operation for driving the speaker  71 , the vibrator  72 , or the LED  73  is performed in this way, the voltage Vd of the battery  63  begins to drop at time t 101  at which the high load operation is started, as shown in  FIG. 15 . The battery voltage Vd drops to the voltage V 12  at time t 102  at which the high load operation ends. At the high load operation end time t 102 , the internal timer of the control unit  54  is started. At voltage judging time t 103  when a predetermined time has elapsed, the voltage measuring circuit  57  measures the battery voltage Vd. 
     Starting from the high load operation end time t 102 , the battery voltage Vd gradually recovers and rises. At the voltage judging time t 103 , if the battery voltage Vd is higher than the voltage V 11  (as indicated by the voltage characteristic BT 1 ), the operation continues by returning to the incoming call waiting state. On the other hand, at the voltage judging time t 103 , if the battery voltage Vd is not higher than the voltage V 11  (as indicated by the voltage characteristic BT 2 ), it is determined that the battery  63  is unable to drive the load. Then, a message saying, for example, “BATTERY IS LOW. REPLACE BATTERY.” is displayed on the display unit  59 , urging the user to replace or recharge the battery, while stopping the operation of the reception processing unit  51 . 
     In this way, the prior art electronic apparatus equipped with the voltage judging means disclosed in Patent Document 1 checks the voltage recovery state when a predetermined time has elapsed after stopping the high load operation. Accordingly, the prior art electronic apparatus can avoid to a certain extent the problem of immediately stopping the operation or urging the user to replace the battery by determining that the battery is low even when the battery voltage just drops temporarily. 
     The electronic apparatus equipped with the prior art voltage judging means disclosed in Patent Document 1 judges the voltage after a predetermined time (voltage recovery period) has elapsed after stopping the high load operation. Accordingly, when the battery is in a nearly fully charged condition, for example, since the battery recovers quickly after stopping the high load operation, time loss occurs in judging the recovery state of the battery. As a result, when driving a load repeatedly, or when driving a plurality of loads sequentially in succession, there arises the serious problem that the load or loads cannot be driven quickly. 
     Furthermore, since the voltage recovery characteristic of the battery after stopping the high load operation greatly varies depending on ambient temperature and other load driving conditions, it is difficult to accurately judge the recovery state of the battery with the prior art judging method that measures the voltage only once after the predetermined time (voltage recovery period) has elapsed. Such a judging method requires that the detection margin be increased in order to compensate for the poor accuracy in the detection of the battery recovery state. However, if the detection margin is increased, the voltage recovery period has to be set longer, which makes it further difficult to achieve high speed load driving, and an electronic apparatus having excellent response characteristics cannot be achieved. If such a prior art power supply system is applied to a portable electronic apparatus that requires a compact and thin design, the operation will become unstable because of insufficient capacity of the power supply, and it is extremity difficult to achieve a highly reliable product. 
     It is also known to provide a battery-driven power tool equipped with a battery-driven power source (motor) and having a remaining capacity detection circuit that detects the remaining capacity of the battery (refer to Patent Document 2). This remaining capacity detection circuit judges the remaining capacity of the battery by detecting whether the time rate of change of battery voltage when a predetermined time has elapsed after power is turned off to the power source exceeds a predetermined value. Accordingly, in the battery-driven power tool disclosed in Patent Document 2, the remaining capacity of the battery can be detected with relatively good accuracy by minimizing the effects due to the condition (such as the load condition) of the power source. 
     The electronic apparatus disclosed in Patent Document 2 is designed to judge the remaining capacity of the battery by the time rate of change of battery voltage when a predetermined time has elapsed after power is turned off to the power source. However, in the electronic apparatus disclosed in Patent Document 2, when, for example, the battery is in a nearly fully charged condition, and the battery recovers quickly after turning off power to the power source, time loss occurs in judging the recovery state of the battery, as in the case of the electronic apparatus disclosed in Patent Document 1. Accordingly, the electronic apparatus disclosed in Patent Document 2 involves the same problem as the electronic apparatus disclosed in Patent Document 1, that is, the power source such as the motor cannot be quickly operated repeatedly.
     Patent Document 1: Japanese Unexamined Patent Publication No. 2000-156722 (page 4, FIG. 1)   Patent Document 2: Japanese Unexamined Patent Publication No. 2003-25252 (page 6, FIG. 2)   

     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an electronic apparatus that can solve the above problem. 
     It is also an object of the present invention to provide an electronic apparatus that can achieve high-speed continuous driving of a load by quickly judging the recovery state of a battery after driving the load. 
     It is a further object of the present invention to provide a compact and highly reliable electronic apparatus that can be driven by a small-capacity battery. 
     An electronic apparatus according to the present invention includes a power supply, a load, load driver for driving the load by the power supply, power supply state detecter for outputting power supply recovery information by measuring physical quantity of the power supply at predetermined intervals of time after the driving of the load is stopped, and a controller for instructing the load driver to drive the load, based on the power supply recovery information supplied from the power supply state detecter. With this configuration, the recovery state of the battery can be judged quickly after stopping the driving of the load. Accordingly, the electronic apparatus according to the present invention can advance the timing of the next load driving in accordance with the recovery state of the battery, can achieve high-speed continuous driving of the load, and can perform highly reliable driving using a small-capacity battery. 
     Preferably, in the electronic apparatus according to the present invention, the power supply state detecter compares the physical quantity of the power supply with a reference value at the predetermined intervals of time and, when the physical quantity of the power supply exceeds the reference value, outputs the power supply recovery information as determines that the power supply has recovered sufficiently to be able to drive the load, and the load driver resumes the driving of the load in accordance with the drive instruction supplied from the control means. Since the recovery state of the power supply is judged by comparing the physical quantity of the power supply with the reference value at the predetermined intervals of time, the recovery state of the power supply can be detected accurately and quickly, and high-speed driving of the load can be achieved. 
     Preferably, in the electronic apparatus according to the present invention, the power supply state detecter makes the measurement at intervals of time shorter than a recovery time that the power supply takes to recover sufficiently to be able to drive the load. With this configuration, since the recovery state of the power supply after stopping the driving of the load can be measured meticulously and accurately, high-speed and highly reliable driving of the load can be achieved. 
     Preferably, in the electronic apparatus according to the present invention, the controller varies the predetermined intervals of time at which the power supply state detecter makes the measurement and/or the reference value in accordance with the recovery state of the power supply. With this configuration, since the power supply measuring time intervals can be properly set by making the measuring time intervals shorter when the power supply can recover quickly and longer when the power supply is slow to recover, the battery life of the electronic apparatus can be extended by reducing wastage of power consumption due to needless measurement operations. 
     Preferably, in the electronic apparatus according to the present invention, the controller sets the predetermined intervals of time differently toward the end of the measurement than at the beginning of the measurement. With this configuration, since the measuring time intervals can be properly adjusted in accordance with the recovery state of the power supply, not only can the measurement be made with high accuracy, but the battery life of the electronic apparatus can be extended by reducing wastage of power consumption due to needless measurement operations. 
     Preferably, in the electronic apparatus according to the present invention, the control means varies the detection frequency with which the power supply state detecter performs detection, in accordance with the recovery state of the power supply. With this configuration, since the power supply detection frequency after stopping the driving of the load is varied in accordance with the recovery state of the power supply, the load can be driven continuously in accordance with the recovery state of the power supply, and high-speed driving of the load can thus be achieved. 
     Preferably, in the electronic apparatus according to the present invention, when the measurement has been performed a predetermined number of times, or when a predetermined time has elapsed from the start of the measurement, if it is determined that the power supply has not recovered sufficiently to be able to drive the load, the controller causes the electronic apparatus to move to a power recovery mode in which priority is given to making the power supply recover. With this configuration, when the power supply becomes unable to drive the load because of reduced power supply capacity, the electronic apparatus can be made to move to the power supply recovery mode for the power supply to recover, or can be switched to a light load driving mode to prevent overdischarging of the power supply. 
     Preferably, in the electronic apparatus according to the present invention, the load has different driving conditions, and the controller varies one or all of the predetermined intervals of time, the predetermined number of times, the predetermined elapsed time, and the reference value in accordance with the driving conditions of the load. Since the recovery state of the power supply after stopping the driving of the load can be properly measured and evaluated for the load having different driving conditions, the timing for driving the load can be advanced in accordance with the recovery state of the power supply. Accordingly, with this configuration, high-speed driving can be achieved that matches the load having different driving conditions. 
     Preferably, the electronic apparatus according to the present invention further includes storage for storing past detection conditions including the predetermined intervals of time, the reference value, the predetermined number of times, or the predetermined elapsed time. With this configuration, by storing the detection conditions for the power supply state detecter and by retrieving the stored contents, the drive instruction for the next load driving and the detection conditions for detecting the recovery state of the power supply can be properly determined. 
     Preferably, in the electronic apparatus according to the present invention, the control means varies, based on the past detection conditions stored in the storage, one or all of the predetermined intervals of time, the reference value, and measurement start time to be allowed after stopping the driving of the load until starting the measurement. Since the most recent recovery state of the power supply is checked by retrieving the detection information from the storage, and since the detection conditions for the next load driving are varied in accordance with the thus checked power supply recovery state, the detection accuracy of the power supply recovery state can be enhanced, while reducing the loss of the measurement operation. 
     Preferably, in the electronic apparatus according to the present invention, the load is constructed to be driven intermittently, and the controller, based on the past detection conditions stored in the storage, adjusts intervals at which the load is driven intermittently, and instructs the load driver to drive the load intermittently at the adjusted intervals. 
     Preferably, the electronic apparatus according to the present invention further includes storage for storing past detection conditions concerning the predetermined intervals of time, the reference value, the predetermined number of times, or the predetermined elapsed time, and the controller varies, based on the past detection conditions stored in the storage, the detection frequency with which the power supply state detecter performs detection. Since the most recent recovery state of the power supply is checked by retrieving the detection information from the storage, and since the detection frequency with which to detect the recovery of the power supply after stopping the driving of the load is varied based on the retrieved information, the load can be driven continuously in accordance with the recovery state of the power supply, and thus high-speed driving of the load can be achieved. 
     Preferably, in the electronic apparatus according to the present invention, the electronic apparatus has a plurality of loads, the load driver drives the plurality of loads individually, the power supply state detecter outputs the power supply recovery information for the plurality of loads by measuring the physical quantity of the power supply for the plurality of loads at predetermined intervals of time after the driving of each of the plurality of loads is stopped, and the controller instructs the load driver to drive the plurality of loads individually, based on the power supply recovery information supplied from the power supply state detecter. With this configuration, since the recovery state of the power supply can be judged quickly after stopping the driving of each of the plurality of loads, the timing of the next load driving can be advanced in accordance with the recovery state of the power supply, and thus high-speed driving can be achieved for the plurality of loads. 
     Preferably, in the electronic apparatus according to the present invention, the plurality of loads have different characteristics, and the controller sets one or all of the predetermined intervals of time, the predetermined number of times, the predetermined elapsed time, and the reference value individually for the plurality of loads. Since the recovery state of the power supply after stopping the driving of the respective loads can be properly measured and evaluated for the plurality of loads having different characteristics, the timing for driving the respective loads can be advanced in accordance with the recovery state of the power supply, and thus high-speed driving can be achieved for the plurality of loads having different characteristics. 
     Preferably, in the electronic apparatus according to the present invention, the plurality of loads have different driving conditions, and the controller sets one or all of the predetermined intervals of time, the predetermined number of times, the predetermined elapsed time, and the reference value individually in accordance with the driving conditions. Since the recovery state of the power supply after stopping the driving of the respective loads can be properly measured and evaluated for the loads having different driving conditions, the timing for driving the respective loads can be advanced in accordance with the recovery state of the power supply, and high-speed driving can be achieved for the plurality of loads having different driving conditions. 
     Preferably, the electronic apparatus according to the present invention further includes storage for storing past detection conditions including the predetermined intervals of time, the reference value, the predetermined number of times, or the predetermined elapsed time for the plurality of loads, wherein based on the past detection conditions stored in the storage, the controller varies, for each of the plurality of loads, one or all of the predetermined intervals of time, measurement start time to be allowed after stopping the driving of each of the plurality of loads until starting the measurement, the reference value, the predetermined number of times, the predetermined elapsed time, and the detection frequency with which the power supply state detecter performs detection. Since the most recent recovery state of the power supply can be checked for each of the plurality of loads by retrieving the detection information from the storage, and since the detection information can be shared among the plurality of loads, the detection conditions and detection frequency can be properly varied for each load based on the detection information. Accordingly, even when driving the loads by a small-capacity battery, high-speed driving that matches the plurality of loads can be achieved, and wastage of power consumption can be reduced. 
     Preferably, in the electronic apparatus according to the present invention, the power supply is a battery, the physical quantity that the power supply state detecter measures is the battery voltage of the battery, and the reference value is a reference voltage. 
     Preferably, in the electronic apparatus according to the present invention, the load is any one of a motor, a vibrator, an audio device, an illumination device, a display device, a communication device, an imaging device, or a sensor. 
     According to the present invention, since the recovery state of the battery can be judged quickly after stopping the driving of the mounted load, it has become possible to advance the timing of the next load driving in accordance with the recovery state of the battery. 
     Further, according to the present invention, it has become possible to achieve high-speed continuous driving of the load. 
     Furthermore, according to the present invention, it has become possible to achieve highly reliable driving of the load using a small-capacity battery. 
     It has also becomes possible to achieve highly reliable driving of the load without having to employ a technique that enhances the detection accuracy of the battery recovery state by mounting a temperature sensor for measuring the ambient temperature of the battery. Mounting such a temperature sensor would not be advantageous as it would lead to increased system size and increased power consumption. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram schematically showing the configuration of an electronic watch as an electronic apparatus according to the present invention. 
         FIG. 2  is a flowchart explaining the basic operation of the electronic watch. 
         FIG. 3  is a timing chart explaining the load driving operation in the electronic watch when its battery is in a fully charged condition. 
         FIG. 4  is a timing chart explaining the load driving operation in the electronic watch when its battery is in a medium state of charge condition. 
         FIG. 5  is a timing chart explaining the load driving operation in the electronic watch when the battery state of charge is low. 
         FIG. 6  is a timing chart explaining the effect of varying the time intervals at which the battery voltage of the electronic watch is measured. 
         FIG. 7  is a timing chart explaining the effect of varying the detection frequency of the battery voltage in the electronic watch. 
         FIG. 8  is a timing chart explaining the effect of varying the time intervals of the battery voltage measurement according to different load driving conditions of the electronic watch. 
         FIG. 9  is a diagram schematically showing the configuration of a multi-function electronic watch as an electronic apparatus according to the present invention. 
         FIG. 10  is a flowchart explaining operation when driving a plurality of loads in the multi-function electronic watch. 
         FIG. 11  is a timing chart explaining the operation for driving the plurality of loads in the multi-function electronic watch. 
         FIG. 12  is a flowchart explaining the driving operation when the plurality of loads to be driven in the multi-function electronic watch have different characteristics. 
         FIG. 13  is a timing chart explaining the driving operation when the plurality of loads to be driven in the multi-function electronic watch have different characteristics. 
         FIG. 14  is a block diagram schematically showing the configuration of a paging receiver equipped with a voltage judging means according to the prior art. 
         FIG. 15  is a characteristic diagram of a battery mounted in the prior art paging receiver. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments of the present invention will be described in detail below with reference to the drawings. 
       FIG. 1  is a diagram schematically showing the configuration of an electronic watch as an electronic apparatus according to a first embodiment of the present invention. 
     In the electronic watch  1  shown in  FIG. 1 , the hour, minute, and second hands on the display unit are driven by a single motor. In  FIG. 1 , an oscillation circuit  3  causes a quartz crystal  2  as a reference signal source to oscillate and thus output a reference clock P 1 . A frequency dividing circuit  4  takes the reference clock P 1  as an input and outputs a second signal P 2  of 1 Hz. 
     A battery  5  as a power supply is a small secondary battery, and preferably a lithium-ion battery. However, the kind of the battery used as the battery  5  is not limited to a lithium-ion battery. The voltage at the positive terminal  5   a  of the battery  5  is the battery voltage Vbt, and the voltage at the negative terminal  5   b  is a zero voltage Vz. The voltage at the positive terminal  6   a  of a solar battery  6  is the solar voltage Vso, and the negative terminal  6   b  is connected to the negative terminal  5   b  of the battery  5 . Based on the solar voltage Vso supplied from the solar battery  6 , a charge control circuit  7  applies a charge voltage V 1  to the positive terminal  5   a  of the battery  5 . Thus, the battery voltage Vbt as the output of the battery  5  and the charge voltage V 1  are at the same potential. 
     A battery state detection circuit  10  as a power supply state detecting means comprises a timer  11 , a dividing circuit  12 , a reference voltage generating circuit  13 , and a comparator circuit  14 . The dividing circuit  12  is connected to the positive terminal  5   a  and negative terminal  5   b  of the battery  5 , and outputs a battery dividing voltage V 2  by dividing the potential difference between the battery voltage Vbt and the zero voltage Vz (i.e., the electromotive force of the battery  5 ) by a prescribed factor. The reference voltage generating circuit  13  is constructed from a D/A conversion circuit, and outputs a prescribed reference voltage V 3 . The comparator circuit  14  is constructed from an analog comparator, and outputs a battery recovery signal P 4  as battery recovery information by comparing the battery dividing voltage V 2  with the reference voltage V 3  each time a timer signal P 3  is output from the timer  11 . 
     In the present embodiment, the battery state detection circuit  10  is constructed mainly from analog circuits. Alternatively, it may be constructed to output the battery recovery signal P 4  by digital processing, for example, by converting the battery voltage Vbt of the battery  5  into a digital signal and comparing the digital signal with the reference value. 
     A control circuit  20  as a control means for controlling the entire operation of the electronic watch  1  operates by executing firmware stored in its internal ROM (not shown). The control circuit  20  generates a motor control signal P 5  for output, based on the second signal P 2  supplied from the frequency dividing circuit  4 . Further, the control circuit  20  generates a battery detection control signal P 6  based on the battery recovery signal P 4  supplied from the battery state detection circuit  10 , and outputs the battery detection control signal P 6  to the battery state detection circuit  10 . 
     A load driving circuit  30  as a load driving means takes the motor control signal P 5  as an input and generates a motor driving signal P 7  for output. A stepping motor  31  (hereinafter simply called “the motor”) is driven by the motor driving signal P 7  and drives the hour, minute, and second hands on the display unit  32 . 
     As shown, the battery voltage Vbt output from the battery  5  is supplied to the oscillation circuit  3 , the frequency dividing circuit  4 , the control circuit  20 , the load driving circuit  30 , and the battery state detection circuit  10 , and is used to power the respective circuits. The zero voltage Vz of the battery  5  is also connected to the respective circuits, but the connections are not shown here. Preferably, the circuits constituting the electronic watch  1  are implemented on a single-chip microcomputer, but the implementation of the circuits need not be limited to a single-chip microcomputer. 
     Next, the operation of the electronic watch  1  shown in  FIG. 1  will be described. 
     First, an overview of the time-keeping operation of the electronic watch  1  will be given. In  FIG. 1 , when the solar battery  6  is exposed to ambient light, the solar battery  6  generates power and produces an electromotive force which is supplied as the solar voltage Vso to the charge control circuit  7 . Upon receiving the solar voltage Vso, the charge control circuit  7  outputs the charge voltage V 1  and thus starts to charge the battery  5 . When the battery  5  is charged, and the battery voltage Vbt reaches a specified voltage, the oscillation circuit  3  starts operating to drive the quartz crystal  2  and output the reference clock P 1 . 
     The frequency dividing circuit  4  frequency-divides the reference clock P 1 , and outputs a timing signal P 2  which is supplied to the control circuit  20 , the load driving circuit  30 , and the battery state detection circuit  10 . The timing signal P 2  includes a signal, for example, a signal of 1 Hz, necessary for the operation of each of the above-mentioned circuits. The control circuit  20  outputs the motor control signal P 5  synchronized to the thus supplied timing signal P 2 . 
     The load driving circuit  30 , based on the supplied timing signal P 2  and motor control signal P 5 , outputs the motor driving signal P 7  to drive the motor  31  so as to advance the second hand on the display unit  32  by one second. The motor driving signal P 7  for driving the motor  31  is one that consumes the largest current in the electronic watch  1 . Accordingly, each time the motor driving signal P 7  is output, a large current is supplied from the battery  5  to the load driving circuit  30 , and the battery voltage Vbt of the battery  5  temporarily drops. 
     The battery state detection circuit  10  has the function of judging the recovery state of the battery  5  by detecting the change in the battery voltage Vbt associated with the driving of the motor  31 . The operation of the battery state detection circuit  10  will be briefly described below. 
     Each time the battery detection control signal P 6  is output from the control circuit  20 , the timer  11  in the battery state detection circuit  10  is set to a predetermined timer value and starts counting based on the timing signal P 2 . When the count value of the timer  11  reaches zero, the timer signal P 3  is output. Instead of receiving the timing signal P 2 , the timer  11  may contain an internal signal source. 
     The comparator circuit  14  compares the battery dividing voltage V 2  with the reference voltage V 3  in synchronism with the timer signal P 3 , and outputs the battery recovery signal P 4  as battery recovery information if the battery dividing voltage V 2  is higher than the reference voltage V 3 . The comparator circuit  14  is configured to compare the battery dividing voltage V 2  with the reference voltage V 3  in intermittent fashion based on the timer signal P 3  from the timer  11 , but the dividing circuit  12  and the reference voltage generating circuit  13  may also be configured to operate in intermittent fashion based on the timer signal P 3 . Operating both the dividing circuit  12  and the reference voltage generating circuit  13  in intermittent fashion is preferable because the battery state detection circuit  10  can then be operated at low power. 
     Since the battery dividing voltage V 2  is a voltage obtained by dividing in a manner accurately proportional to the battery voltage Vbt, the operation of the comparator circuit  14  is equivalent to comparing the battery voltage Vbt with the reference voltage V 3 . The reference voltage V 3  is set to a voltage value such that, when the battery dividing voltage V 2  exceeds the reference voltage V 3 , it can be determined that the battery  5  has recovered to a level that can drive the motor  31  as a load. In other words, when the battery recovery signal P 4  is output from the comparator circuit  14 , this indicates that the battery  5  has recovered sufficiently to be able to drive the motor  31 . Accordingly, when the battery recovery signal P 4  is input, the control circuit  20  recognizes that the battery  5  has recovered sufficiently to be able to drive the motor  31 , and proceeds to execute the next cycle of motor driving. The reference voltage V 3  here can be varied as desired by the battery detection control signal P 6  that the control circuit  20  outputs. 
     When continuously performing the high load driving operation, such as when continuously driving the motor  31  fast forward in order, for example, to adjust the time on the electronic watch  1 , the recovery state of the battery  5  must be accurately judged. Otherwise, the battery  5  may be overdischarged, resulting in an abnormal decrease of the battery voltage Vbt, and the operation of the electronic watch  1  may stop. In this way, an important point of the present invention is to properly detect the state of the battery  5  during the high load driving operation such as when driving the motor  31  fast forward, and to achieve safe and quick driving of the load in accordance with the recovery state of the battery  5 . 
       FIG. 2  is a flowchart for explaining the basic operation of the electronic watch. 
     Referring to the flowchart of  FIG. 2 , one example of the battery state detection operation performed during the fast forward driving of the motor  31  will be described in detail below. 
     First, the electronic watch  1  is set, for example, to a time adjusting mode to adjust the time, and the motor  31  is driven fast forward (step ST 1 ). Usually, this fast forward driving is performed by outputting 60 pulses of the motor driving signal P 7  in one fast forward driving operation and thereby causing the second hand to make one revolution, that is, advancing the second hand by one minute. 
     Next, the control circuit  20  of the electronic watch  1  determines whether the one fast forward driving operation (for adjusting the time forward by one minute) is completed or not, that is, whether the motor  31  has stopped or not (step ST 2 ). If the answer is NO, the process waits until the motor  31  stops, and if the answer is YES (the motor  31  has stopped), the process proceeds to the next step. 
     Next, the control circuit  20  of the electronic watch  1  determines whether the time adjustment is completed or not (step ST 3 ). If the answer is YES, the fast forward driving of the motor  31  is stopped, and the time adjusting mode is terminated; if the answer is NO (the time adjustment is not completed yet), the process proceeds to the next step. 
     Next, the control circuit  20  of the electronic watch  1  outputs the battery detection control signal P 6 , and thus sets the timer  11  in the battery state detection circuit  10  to a predetermined value (that defines a time interval during which to measure the battery voltage) and causes the timer  11  to start counting down (step ST 4 ). 
     The battery state detection circuit  10  of the electronic watch  1  waits until the timer  11  counts down to zero and, when the count value reaches zero (that is, the timer expires), the timer  11  outputs the timer signal P 3  (step ST 5 ). 
     Then, in response to the timer signal P 3 , the comparator circuit  14  in the battery state detection circuit  10  of the electronic watch  1  compares the battery dividing voltage V 2  with the reference signal V 3  (step ST 6 ). That is, each time the timer  11  expires and outputs the timer signal P 3 , the comparator circuit  14  determines whether or not the battery dividing voltage V 2  obtained by dividing the battery voltage Vbt is higher than the reference signal V 3 . 
     Next, the control circuit  20  of the electronic watch  1  determines whether or not the battery recovery signal P 4  has been output from the battery state detection circuit  10  (that is, whether or not the battery  5  has recovered sufficiently to be able to drive the motor  31 ) (step ST 7 ). If the answer is YES, the process returns to step ST 1  to resume the fast forward driving of the motor  31 , and the process from step ST 1  to step ST 7  is repeated. If the answer is NO (not recovered yet), the process proceeds to the next step. 
     If the answer in step ST 7  is NO, the control circuit  20  of the electronic watch  1  increments its internal measuring counter (not shown) by  1  (step ST 8 ). 
     Next, the control circuit  20  of the electronic watch  1  determines whether or not the measuring counter has counted up to a predetermined value (which indicates a predetermined number of times of the measurement) (step ST 9 ). If the answer is NO, that is, if the predetermined number of times is not reached yet, the process returns to step ST 4  to continue the measurement of the battery voltage Vbt, and the process from step ST 4  to step ST 9  is repeated until the predetermined number of times is reached. 
     If the answer in step ST 9  is YES, the control circuit  20  moves to a power supply recovery mode by determining that, even after performing the measurement the predetermined number of times, the battery  5  has not recovered sufficiently to be able to execute the next cycle of fast forward driving. In the power supply recovery mode, the fast forward driving of the motor is stopped, and an alarm indication (for example, the second hand is advanced by two seconds) is produced to warn the user that the battery capacity is low, thus actively urging the user to recharge the battery  5 . During the power recovery mode, high load driving operations such as the one performed in the time adjusting mode are not performed until the battery  5  is recharged. 
     In steps ST 8  and ST 9 , the number of times that the measurement made is counted when determining whether the battery  5  has recovered or not, but the battery recovery control method is not limited to this specific one. For example, the time elapsed from the start of the measurement may be measured, and control may be performed to move to the power supply recovery mode when the battery recovery signal P 4  is not output even after a predetermined time has elapsed. Furthermore, since the predetermined number of times of the measurement or the predetermined elapsed time based on which to judge the recovery state of the battery  5  can be varied by the control circuit  20 , these parameters may be varied in accordance with the power supply specification of the electronic watch  1 . 
       FIG. 3  is a timing chart explaining the load driving operation in the electronic watch when the battery is in a fully charged condition. 
     Referring to the timing chart of  FIG. 3 , a description will be given of one example of the fast forward driving of the motor when the battery  5  is in a nearly fully charged condition. 
     First, suppose that the electronic watch  1  is set to the time adjusting mode and the motor driving signal P 7  is output to start the fast forward driving of the motor (timing T 1 ). As earlier described, one fast forward driving operation of the motor is performed by outputting 60 pulses of the motor driving signal P 7  and thereby causing the second hand to make one revolution. This fast forward driving operation consumes high power from the battery  5 . Accordingly, during the period from the start (timing T 1 ) of the fast forward driving to the end (timing T 2 ) of one fast forward driving operation, the battery voltage Vbt drops to the voltage Vbt 2  as shown in the figure. 
     Next, when the one fast forward driving operation ends (timing T 2 ), the battery state detection circuit  10  starts to measure the battery voltage Vbt. That is, the measurement by the comparator circuit  14  (that is, the comparison between the battery dividing voltage V 2  and the reference voltage V 3 ) is preformed at predetermined intervals of time under the control of the timer  11 . Measurement sampling M 1  shown in  FIG. 3  shows the timing with which the measurement is preformed by the comparator circuit  14  at the predetermined intervals of time. Since the battery  5  is in a nearly fully charged condition, the battery voltage Vbt of the battery  5  quickly rises to the no-load voltage Vbt 1  after the end of the fast forward driving operation. Accordingly, by the second timing of the measurement sampling M 1 , the battery voltage Vbt of the battery  5  has risen to a level higher than the reference voltage V 3  by reference to which the battery recovery state is judged. 
     The battery recovery signal P 4  is output from the comparator circuit  14  in synchronism with the second timing of the measurement sampling M 1  (as indicated by arrow A 1 ). When the battery recovery signal P 4  is received, the control circuit  20  determines that the battery  5  has recovered, and instructs the battery state detection circuit  10  to stop the measurement. Further, the control circuit  20  outputs the motor control signal P 5  as a drive instruction for the next fast forward driving operation, and resumes the fast forward driving of the motor  31  (next timing T 1 ). Thereafter, the timings T 1 , T 2 , T 1 , T 2 , etc. are repeated in sequence, as long as the fast forward driving of the motor  31  continues. 
     In this way, when the battery  5  is in a nearly fully charged condition, the battery recovery can be quickly detected after the start of the measurement sampling M 1 . As a result, the repeating cycle of the fast forward driving (the period from one timing T 1  to the next timing T 1 ) becomes almost equal to the fast forward driving period (that is, the period from timing T 1  to timing T 2 ), thus achieving the speedup of the fast forward driving. 
       FIG. 4  is a timing chart explaining the load driving operation in the electronic watch when the battery is in a medium state of charge condition. 
     Referring to the timing chart of  FIG. 4 , a description will be given of one example of the fast forward driving of the motor when the battery  5  is in a medium state of charge condition. 
     First, suppose that the electronic watch  1  is set to the time adjusting mode and the motor driving signal P 7  is output to start the fast forward driving of the motor (timing T 4 ). This fast forward driving operation consumes high power from the battery  5 . Accordingly, during the period from the start (timing T 4 ) of the fast forward driving to the end (timing T 5 ) of one fast forward driving operation, the battery voltage Vbt drops to the voltage Vbt 2  as shown in the figure. 
     Next, when the one fast forward driving operation ends (timing T 5 ), the battery state detection circuit  10  starts to measure the battery voltage Vbt. The measurement by the comparator circuit  14  (that is, the comparison between the battery dividing voltage V 2  and the reference voltage V 3 ) is preformed at predetermined intervals of time under the control of the timer  11 . Measurement sampling M 2  shown in  FIG. 4  shows the timing with which the measurement is preformed by the comparator circuit  14  at the predetermined intervals of time. Since the battery  5  is in a medium state of charge condition, the battery voltage Vbt of the battery  5  rises to the no-load voltage Vbt 1  over a certain length of time after the end of the fast forward driving operation. Accordingly, only after the measurement sampling M 2  has been repeated several times, can the battery voltage Vbt of the battery  5  exceed the reference voltage V 3  by reference to which the battery recovery state is judged. 
     After the measurement sampling M 2  has been repeated at predetermined intervals of time, the battery recovery signal P 4  is output from the comparator circuit  14  in synchronization with the timing when the battery voltage Vbt exceeds the reference voltage V 3  (as indicated by arrow A 2 ). When the battery recovery signal P 4  is received, the control circuit  20  determines that the battery  5  has recovered, and instructs the battery state detection circuit  10  to stop the measurement. Next, the control circuit  20  outputs the motor control signal P 5  as a drive instruction for the next fast forward driving operation, and resumes the fast forward driving of the motor  31  (next timing T 4 ). Thereafter, the timings T 4 , T 5 , T 4 , T 5 , etc. are repeated in sequence, as long as the fast forward driving of the motor  31  continues. 
     In this way, when the battery  5  is in a medium state of charge condition, the measurement sampling M 2  is repeated several times until the battery  5  recovers and, when the battery  5  has recovered, the recovery of the battery  5  can be quickly detected. As a result, while the repeating cycle of the fast forward driving (the period from one timing T 4  to the next timing T 4 ) becomes longer than that when the battery  5  is in a nearly fully charged condition shown in  FIG. 3 , the fast forward driving can be repeatedly performed in the shortest possible time in accordance with the recovery state of the battery  5 . 
       FIG. 5  is a timing chart for explaining the load driving operation in the electronic watch when the state of charge of the battery is low. 
     Referring to the timing chart of  FIG. 5 , a description will be given of one example of the fast forward driving of the motor when the state of charge of the battery  5  is low. 
     First, suppose that the electronic watch  1  is set to the time adjusting mode and the motor driving signal P 7  is output to start the fast forward driving of the motor (timing T 7 ). This fast forward driving operation consumes high power from the battery  5 . Accordingly, during the period from the start (timing T 7 ) of the fast forward driving to the end (timing T 8 ) of one fast forward driving operation, the battery voltage Vbt drops to the voltage Vbt 2  as shown in the figure. 
     Next, when the one fast forward driving operation ends (timing T 8 ), the battery state detection circuit  10  starts to measure the battery voltage Vbt. In other words, the measurement by the comparator circuit  14  (i.e., the comparison between the battery dividing voltage V 2  and the reference voltage V 3 ) is preformed at predetermined intervals of time under the control of the timer  11 . Measurement sampling M 3  shown in  FIG. 5  shows the timing with which the measurement is preformed by the comparator circuit  14  at the predetermined intervals of time. Since the state of charge of the battery  5  is low, the battery voltage Vbt of the battery  5  rises nearly to the no-load voltage Vbt 1  over a considerable length of time after the end of the fast forward driving operation. Accordingly, only after the measurement sampling M 3  has been repeated a considerable number times, does the battery voltage Vbt of the battery  5  exceed the reference voltage V 3  by reference to which the battery recovery state is judged. 
     After the measurement sampling M 3  has been repeated many times at predetermined intervals of time, when the battery voltage Vbt exceeds the reference voltage V 3  (as indicated by arrow A 3 ) the battery recovery signal P 4  is output from the comparator circuit  14 . When the battery recovery signal P 4  is received, the control circuit  20  determines that the battery  5  has recovered, and instructs the battery state detection circuit  10  to stop the measurement. Then, the control circuit  20  outputs the motor control signal P 5  as a drive instruction for the next fast forward driving operation, and resumes the fast forward driving of the motor  31  (next timing T 7 ). Thereafter, the timings T 7 , T 8 , T 7 , T 8 , etc. are repeated in sequence, as long as the fast forward driving of the motor  31  continues. 
     In this way, when the state of charge of the battery  5  is low, the measurement sampling M 3  is repeated many times until the battery  5  recovers and, when the battery  5  has recovered, the recovery of the battery  5  can be quickly detected. As a result, while the repeating cycle of the fast forward driving (the period from one timing T 7  to the next timing T 7 ) becomes longer than that when the battery  5  is in a medium state of charge condition shown in  FIG. 4 , the fast forward driving can be repeatedly performed in the shortest possible time in accordance with the recovery state of the battery  5 . 
     As previously described in connection with step ST 9  in the flowchart of  FIG. 2 , the measuring operation of the battery state detection circuit  10  is terminated by determining whether the measurement has been performed a predetermined number of times (or when a predetermined elapsed time has elapsed). Accordingly, if the battery  5  does not recover even after the predetermined condition is reached, the fast forward driving is stopped, and the electronic watch  1  moves to the battery recovery mode. 
     As described above, in the electronic apparatus according to the present invention, the battery voltage is measured at predetermined intervals of time after stopping the driving of the load and, when it is determined that the battery has recovered sufficiently to be able to drive the load, the next cycle of load driving is immediately executed. In this way, since the electronic apparatus according to the present invention can advance the load driving timing in accordance with the recovery state of the battery, high-speed driving of the load can be achieved in accordance with the recovery state of the battery. In particular, in an electronic watch equipped with a secondary battery that is charged by a solar battery or the like, as in the present embodiment, it is often the case that the secondary battery is used in a nearly fully charged condition. Accordingly, the present invention can be applied with great advantage to an electronic watch equipped with a solar battery, because significant speedup of the fast forward driving of the motor can then be achieved. 
     Further, in the electronic apparatus according to the present invention, when the driving capability of the battery is low because of low battery level or low ambient temperature, or when the battery is small and its capacity as a power supply is limited, since the load is driven in accordance with the battery capacity after waiting until the battery recovers, optimum load driving that does not cause an overloaded condition can be achieved for various driving conditions. Furthermore, when the battery is unable to recover sufficiently to be able to drive the load, the electronic apparatus according to the present invention moves to the power supply recovery mode to allow the battery to be recharged or switches to a light load driving mode to prevent overdischarging of the battery, thus ensuring high reliability. 
       FIG. 6  is a timing chart for explaining the effect of varying the time intervals at which the battery voltage of the electronic watch is measured. 
     In the first embodiment, when the fast forward driving of the motor  31  ends, the battery state detection circuit  10  starts to measure the battery voltage Vbt. However, the measurement of the battery voltage Vbt can be performed in various ways, some examples of which will be described below with reference to  FIG. 6 . 
     In  FIG. 6 , measurement sampling M 10  is an example in which the battery voltage Vbt is measured at relatively short time intervals (for examples, at intervals of 25 mS) immediately following the end (timing T 10 ) of the fast forward driving of the motor  31 . The measurement sampling M 10  is similar in timing to the measurement sampling M 1  shown in  FIG. 3 , the measurement sampling M 2  shown in  FIG. 4 , and the measurement sampling M 3  shown in  FIG. 5 . Further, since the measurement time interval is relatively short, the measurement sampling M 10  is suitable for detecting the recovery of a battery that is in a fully charged condition or in a medium state of charge condition. 
     Measurement sampling M 11  is an example in which the battery voltage Vbt is measured at relatively long time intervals (for examples, at intervals of 50 mS) immediately following the end (timing T 10 ) of the fast forward driving of the motor  31 . Since the measurement time interval is relatively long, the measurement sampling M 11  is suitable for detecting the recovery of a battery that takes time to recover because of low state of charge or a battery whose capacity is small. 
     Measurement sampling M 12  is an example in which the measurement of the battery voltage Vbt is started after waiting for a predetermined time (Tw) to elapse from the end (timing T 10 ) of the fast forward driving of the motor  31 . Since the measurement is started after a predetermined time has elapsed from the end of the fast forward driving, the measurement sampling M 12  is suitable for detecting the recovery of a battery that takes time to recover because of low state of charge or a battery whose capacity is small. 
     Measurement sampling M 13  is an example in which the battery voltage Vbt is measured first at relatively short time intervals (for examples, at intervals of 25 mS) immediately following the end (timing T 10 ) of the fast forward driving of the motor  31  and then, after a predetermined time has elapsed, at relatively long time intervals (for examples, at intervals of 50 mS) toward the end of the measurement period. Since the measurement time interval differs between the first half and second half of the measurement period, the measurement sampling M 13  is a sampling scheme that can address various situations regardless of whether the battery is in a fully charged condition and can therefore recover quickly or in a low state of charge condition and therefore takes time to recover, whether the capacity of the battery is small, or whether the battery is operated at normal temperatures or at low temperatures. 
     Any of the measurement sampling schemes M 11  to M 13  described above for the measurement of the battery voltage Vbt can be used in the electronic watch  1  described with reference to  FIGS. 1 to 5 . As described above, the measurement sampling can be implemented in various ways, but in any measurement sampling, it is important that, after stopping the driving of the load, the battery voltage be measured in succession at intervals of time shorter than the recovery time of the battery. 
     Further, the measurement sampling scheme can be dynamically selected according to the state of charge of the battery, the ambient temperature, the differences in battery capacity due to the size and characteristics of the battery, etc., in such a manner that when the battery  5  is in a state that can quickly recover, the measurement sampling M 10  is selected thereby detecting the recovery of the battery quickly and, when the battery  5  is in a state that takes time to recover, the measurement sampling M 11  or M 12  is selected thereby reducing the loss of the measurement operation. By changing the measurement sampling in this way, not only can optimum load driving that matches the state of the battery be achieved, but the battery life of the electronic apparatus can be extended by reducing wastage of power consumption due to needless measurement operations. 
       FIG. 7  is a timing chart for explaining the effect of varying the detection frequency of the battery voltage in the electronic watch. 
     The operation for varying the detection frequency of the battery voltage will be described with reference to  FIG. 7 . In  FIG. 7 , it is assumed that the battery  5  in the electronic watch  1  is in a nearly fully charged condition and that the ambient temperature is in a normal temperature range, the battery thus being in a state that can recover quickly. 
     First, suppose that the electronic watch  1  is set to the time adjusting mode and the fast forward driving of the motor is started (timing T 11 ). As earlier described, one fast forward driving operation of the motor is performed by outputting 60 pulses of the motor driving signal P 7  and thereby causing the second hand to make one revolution. This fast forward driving operation consumes high power from the battery  5 . Accordingly, during the period from the start (timing T 11 ) of the fast forward driving to the end (timing T 12 ) of one fast forward driving operation, the battery voltage Vbt drops to the voltage Vbt 2  as shown in the figure. 
     Next, when the one fast forward driving operation ends (timing T 12 ), the battery state detection circuit  10  starts to measure the battery voltage Vbt, and the measurement by the comparator circuit  14  is preformed at predetermined intervals of time under the control of the timer  11 . Measurement sampling M 20  shows the timing with which the comparator circuit  14  operates. In this case, since the battery  5  is in a nearly fully charged condition and can therefore recover quickly, the battery voltage Vbt of the battery  5  quickly rises to the no-load voltage Vbt 1  after the end of the fast forward driving operation. By the second timing of the measurement sampling M 20 , the battery voltage Vbt of the battery  5  has risen to a level higher than the reference voltage V 3  by reference to which the battery recovery state is judged. 
     The battery recovery signal P 4  is output from the comparator circuit  14  in synchronism with the second timing of the measurement sampling M 20  (as indicated by arrow A 4 ). When the battery recovery signal P 4  is received, the control circuit  20  determines that the battery  5  has recovered, and instructs the battery state detection circuit  10  to stop the measurement, and the fast forward driving of the motor  31  is resumed (next timing T 11 ). At this point, the control circuit  20  realizes that the battery recovery signal P 4  is output at the second timing of the measurement sampling M 20 . Accordingly, the control circuit  20  determines that the battery  5  is in a state that can recover quickly, and performs the next fast forward driving operation by setting the number of output pulses of the motor driving signal P 7 , for example, to twice the usual number, i.e., to 120, thereby causing the second hand to make two revolutions. 
     It therefore follows that the next measurement sampling M 20  is performed after the end (timing T 13 ) of the second fast forward driving operation, that is, after the end of the 120th pulse of the motor driving signal P 7 . However, since the battery  5  is in a nearly fully charged condition, and the ambient temperature is within the normal temperature range, there will be no problem in the operation of the watch if the number of times that the recovery state of the battery  5  is detected (the detection frequency) is reduced to increase the amount of fast forward driving. In other words, when the battery  5  is in a state that can recover quickly, the detection frequency of the battery voltage Vbt can be reduced to increase the amount of fast forward driving; i.e., by reducing the time loss that may occur when detecting the recovery state of the battery  5 , speedup of the fast forward driving of the motor  31  can be achieved. 
     Furthermore, since the detection frequency of the battery voltage Vbt decreases, the power consumption associated with the measurement operation can be reduced, which serves to extend the battery life of the electronic apparatus. If the quick recovery state of the battery  5  can be maintained, the extended fast forward driving operation may be performed repeatedly as shown in the figure. On the other hand, when the capacity of the battery  5  becomes low, or when the driving capability of the battery  5  has dropped due to low ambient temperature, and the recovery of the battery  5  becomes slow, the number of output pulses of the motor driving signal P 7  per fast forward driving operation may be reduced from the usual 60 pulses to, for example, 30 pulses, contrary to the control shown in  FIG. 7 . 
     In this case, since the recovery state of the battery  5  can be detected more frequently by increasing the detection frequency of the battery voltage Vbt for the amount of load driving, if the driving capability of the battery  5  drops due to reduced capacity of the battery  5 , etc., highly reliable load driving can be achieved. The number of output pulses of the motor driving signal P 7  per fast forward driving operation is not limited to the above specific numbers, but can be determined as desired in accordance with the specification of the electronic watch. 
       FIG. 8  is a timing chart explaining the effect of varying the time intervals of the battery voltage measurement according to different load driving conditions of the electronic watch. 
     The control for varying the detection condition of the battery voltage measurement according to different load driving conditions of the electronic watch will be described with reference to  FIG. 8 . Usually, the motor used in the electronic watch can be driven in both forward and backward directions, but it is known that the backward driving, which requires supplying complex drive pulses to the motor  31 , consumes power three times that required for the forward driving. In this way, for the same load (motor), the power consumption varies according to different driving conditions, and thus the load for the battery may vary. 
       FIG. 8  shows the operation for setting the time intervals of the measurement sampling differently when driving the motor  31  backward than when driving it forward. As shown in  FIG. 8 , when driving the motor forward, since the load is relatively light, the drop in battery voltage Vbt due to the forward driving is small, and the battery voltage Vbt drops to the voltage Vbt 2 . On the other hand, when driving the motor backward, since the load is heavy, the drop in battery voltage Vbt due to the backward driving is large, and the battery voltage Vbt drops to the voltage Vbt 3 . 
     The control circuit  20  addresses the quick recovery of the battery  5  by setting shorter the time intervals of the measurement sampling M 21  performed to measure the battery voltage Vbt after the forward driving. It also addresses the slow recovery of the battery  5  by setting longer the time intervals of the measurement sampling M 21  performed to measure the battery voltage Vbt after the backward driving. In this way, when the time intervals of the measurement sampling M 21  performed to measure the battery voltage Vbt are varied according to different load driving conditions, not only can the speedup of the load driving be achieved by properly detecting the recovery of the battery  5 , but wastage of power consumption due to needless measurement operations can be reduced by reducing the loss of the measurement operation. 
       FIG. 8  has shown the case where the time intervals at which to measure the battery voltage Vbt are varied according to different driving conditions of the motor  31  as the load, but the voltage detection condition to be varied is not limited to the above one. For example, the detection conditions for the battery voltage Vbt, such as the measurement time intervals, the value of the reference voltage V 3 , the number of times of the measurement to be made, the elapsed time, etc., can be varied differently according to different load driving conditions, to achieve load driving and battery state detection that properly address the differences in the load driving conditions. 
     Further, the differences in the load driving conditions are not limited to the above-described differences associated with the forward/backward driving of the motor  31 . For example, in the forward driving of the motor, the driving conditions are different when driving the motor to move the hand fast forward than when driving the motor to move the hand by one second in normal operation. By varying the detection conditions for the battery voltage Vbt, such as the measurement time intervals, the value of the reference voltage V 3 , the number of times of the measurement to be made, the elapsed time, etc., differently according to such differences in the load driving conditions, proper load driving and proper battery state detection can be achieved. 
     It should also be noted that the battery voltage Vbt of the battery  5  varies depending on the state of charge of the battery, ambient temperature, etc. In the electronic watch, it is usual to perform control for stable motor driving by varying the drive pulse shape of the motor driving signal P 7  in accordance with the change of the battery voltage Vbt. When the drive pulse shape is varied in accordance with the change of the battery voltage Vbt, the load for the battery  5  also varies. Accordingly, if the detection conditions for the battery voltage Vbt are also varied in accordance with the change of the drive pulse shape, the reliability of the load driving can be further enhanced. 
     As described above, in the electronic apparatus according to the present invention, since the load is driven by quickly detecting the recovery state of the battery after stopping the driving of the load, as shown in the first embodiment, high-speed driving of the load that matches the state of charge of the battery can be achieved. Furthermore, in the electronic apparatus according to the present invention, since the battery voltage detection conditions, such as the measurement time intervals, the value of the reference voltage V 3 , the number of times of the measurement to be made, the elapsed time, etc., can be properly varied in accordance with the recovery state of the battery, the load driving conditions, etc., stable load driving can be accomplished even when driving the load by a small-capacity battery. 
       FIG. 9  is a diagram schematically showing the configuration of a multi-function electronic watch as an electronic apparatus according to a second embodiment of the present invention. 
     The feature of the multi-function electronic watch  40  shown in  FIG. 9  is that the electronic watch is constructed to drive the display unit by three motors and includes a buzzer, an illumination device, a sensor, etc. The same component elements as those shown in the block diagram of the first embodiment are designated by the same reference numerals, and the configuration and operation of such component elements will not be discussed in detail herein. 
     In  FIG. 9 , the quartz crystal  2 , the oscillation circuit  3 , the frequency dividing circuit  4 , the battery  5 , the solar battery  6 , the charge control circuit  7 , and the battery state detection circuit  10  are the same as those in the electronic watch  1  shown in  FIG. 1 , and the description thereof will not be repeated here. A control circuit  21  as a control means is similar in function to the corresponding circuit in the electronic watch  1 , but differs by the inclusion of a storage circuit  22  as a storage means. The control circuit  21  further outputs a buzzer control signal P 10 , an LED control signal P 11 , and a sensor control signal P 12 . 
     The storage circuit  22  is constructed from a RAM or a nonvolatile memory or the like, and stores the detection conditions such as the time intervals at which the battery state detection circuit  10  measures the battery voltage Vbt. It is advantageous to construct the storage circuit  22  from a RAM because of its low power consumption, but in that case, it is preferable to perform control so that, when the battery voltage Vbt drops, the data stored in the RAM storage circuit  22  is saved to a nonvolatile memory (not shown) built into the control circuit  21 . 
     A motor driving circuit  33  as a load driving means outputs motor driving signals P 7   a , P 7   b , and P 7   c  based on the timing signal P 2  supplied from the frequency dividing circuit  4  and the motor control signal P 5  supplied from the control circuit  21 . A second motor  34  drives the second hand on the display unit  41  in accordance with the motor driving signal P 7   a  input to it. An hour/minute motor  35  drives the hour/minute hands on the display unit  41  in accordance with the motor driving signal P 7   b  input to it. A date indicator motor  36  drives the date indicator on the display unit  41  in accordance with the motor driving signal P 7   c  input to it. 
     A buzzer driving circuit  37  as a load driving means takes the buzzer control signal P 10  as an input and outputs a buzzer driving signal P 13 . An LED driving circuit  38  as a load driving means takes the LED control signal P 11  as an input and outputs an LED driving signal P 14 . A sensor driving circuit  39  as a load driving means takes the sensor control signal P 12  as an input and outputs a sensor driving signal P 15 . 
     The buzzer  42  as a load produces an alarm sound or the like in accordance with the buzzer driving signal P 13  input to it. The LED  43  as a load operates in accordance with the LED driving signal P 14  input to it, and illuminates the display unit  41  so that the display unit  41  can be viewed in darkness. The sensor  44  as a load measures depth of water, temperature, etc., in accordance with the sensor driving signal P 15  input to it. 
     As shown, the battery voltage Vbt of the battery  5  is supplied to the oscillation circuit  3 , the frequency dividing circuit  4 , the control circuit  21 , the battery state detection circuit  10 , the motor driving circuit  33 , the buzzer driving circuit  37 , the LED driving circuit  38 , and the sensor driving circuit  39 , and is used to power the respective circuits. The zero voltage Vz of the battery  5  is also connected to the respective circuits, but the connections are not shown here. Preferably, the circuits constituting the multi-function electronic watch  40  are implemented on a single-chip microcomputer, but the implementation of the circuits need not be limited to a single-chip microcomputer. 
     Next, the operation of the multi-function electronic watch  40  according to the second embodiment will be described. The motor driving circuit  33  drives the respective loads, i.e., the hand motor  34 , the hour/minute motor  35 , and the date indicator motor  36 , in accordance with the motor control signal P 5  supplied from the control circuit  21 . The motor driving signals P 7   a  to P 7   c  each require supplying a large drive current to the corresponding motor; accordingly, each time any one of the motor driving signals P 7   a  to P 7   c  is output, a large current is supplied from the battery  5 , and the battery voltage Vbt of the battery  5  temporarily drops. The battery state detection circuit  10  has the function of judging the recovery state of the battery  5  by detecting the change in the battery voltage Vbt associated with the driving of each motor. Since the basic operation of the battery state detection circuit  10  is the same as that described in the first embodiment, it will not be further described herein. 
     The buzzer driving circuit  37 , the LED driving circuit  38 , and the sensor driving circuit  39  drive the buzzer  42 , the LED  43 , and the sensor  44 , respectively, in accordance with the respective control signals supplied from the control circuit  21 . When driving any one of the buzzer  42 , the LED  43 , and the sensor  44 , the corresponding drive current is supplied from the battery  5 , and the battery voltage Vbt of the battery  5  temporarily drops. The battery state detection circuit  10  has the function of judging the recovery state of the battery  5  by detecting the change in the battery voltage Vbt associated with the driving of the buzzer  42 , the LED  43 , or the sensor  44 , as in the case of the motor driving. 
       FIG. 10  is a flowchart explaining operation when driving a plurality of loads in the multi-function electronic watch. 
     Referring to the flowchart of  FIG. 10 , the battery recovery state detection and load driving operation when driving a plurality of loads will be described below by taking as an example the case where the hand motor  34  and the date indicator motor  36  are driven in the multi-function electronic watch  40 . 
     First, suppose that the multi-function electronic watch  40  is operating normally and the frequency dividing circuit  4  is performing time-keeping operation based on the reference clock P 1  (step ST 11 ). 
     Then, when one second has elapsed, the frequency dividing circuit  4  outputs the second signal P 2  (step ST 12 ). Here, when one second has not yet elapsed, the process waits in step ST 12 . 
     Next, the control circuit  21  retrieves the past detection conditions stored in the storage circuit  22 . Then, based on the past detection conditions, the control circuit  21  varies, as needed, the detection conditions for the battery voltage Vbt, such as the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the number of times of the measurement or the elapsed time, the detection frequency, etc., and outputs the battery detection control signal P 6  (step ST 13 ). When detecting the battery voltage Vbt for the first time, and when no past detection conditions are stored in the storage circuit  22 , the control circuit  21  sets prescribed standard detection conditions (initial values). 
     Then, the control circuit  21  outputs the motor control signal P 5 , in response to which the motor driving circuit  33  outputs the motor driving signal P 7   a  and drives the second motor  34  to advance the second hand by one second (step ST 14 ). 
     Next, the battery information detection circuit  10  sets the timer  11  based on the battery detection control signal P 6 , and outputs the reference voltage V 3  from the reference voltage generating circuit  13 . Further, in the battery information detection circuit  10 , the comparator circuit  14  compares the battery dividing voltage V 2  with the reference voltage V 3  at predetermined intervals of time, and measures the battery voltage Vbt to detect the recovery state of the battery  5  (step ST 15 ). 
     When the battery  5  recovers, and the battery recovery signal P 4  is output, the control circuit  21  stores in the storage circuit  22  the detection conditions (the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the number of times of the measurement made or the time elapsed until the battery recovers, etc.) obtained from the driving of the second motor  34 . On the other hand, when the battery  5  does not recover even after the measurement has been made the predetermined number of times, the process moves to the battery recovery mode, as in the flowchart of  FIG. 2  shown in the first embodiment; this operation flow is the same as that in the first embodiment, and therefore will not be described in detail herein. 
     Next, the control circuit  21  checks the internally stored time-keeping information, and determines whether there is a need to advance the date indicator (step ST 16 ). If the date of the time-keeping information has changed, there is a need to advance the date indicator, so that the answer in step ST 16  is YES, and the control circuit  21  proceeds to the next step. On the other hand, if the date of the time-keeping information has not changed yet, there is no need to advance the date indicator, so that the answer in step ST 16  is NO, and the control circuit  21  returns to step ST 11 . In other words, the process from step ST 11  to step ST 16  is repeated as long as the date remains unchanged. The hour/minute motor  35  is driven once in every minute, but the operation is basically the same as that of the second hand  34  and, therefore, will not be described here. 
     Next, the control circuit  21  retrieves the past detection conditions stored in the storage circuit  22 , determines the detection conditions for the battery voltage Vbt, and outputs the battery detection control signal P 6  (step ST 17 ). The detection conditions retrieved here from the storage circuit  22  represent the information obtained when the second motor  34  was driven in the immediately preceding period. However, when driving the date indicator motor  36  for the first time, the detection conditions, such as the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the prescribed number of times of the measurement or the elapsed time, the detection frequency, etc., are determined by varying the conditions, as needed, based on the detection conditions for the battery voltage Vbt associated with the load driven in the immediately preceding period. 
     For example, when the detection conditions associated with the second motor  34  driven in the immediately preceding period show that the battery  5  recovered quickly, the control circuit  21  addresses the quick recovery of the battery by setting shorter the time intervals at which the battery voltage Vbt is measured after driving the date indicator motor  36 . On the other hand, for example, when the detection conditions associated with the second motor  34  driven in the immediately preceding period show that the battery  5  was slow to recover, the control circuit  21  addresses the slow recovery of the battery by setting longer the time intervals at which the battery voltage Vbt is measured after driving the date indicator motor  36 . 
     Next, the control circuit  21  outputs the motor control signal P 5 , in response to which the motor driving circuit  33  drives the date indicator motor  36  fast forward (step ST 18 ). Since the date indicator motor  36  cannot advance the date indicator by one day in a single fast forward driving operation (for example, 60 pulses), the fast forward driving of the date indicator motor  36  is performed in a number of steps. 
     When one fast forward driving operation of the date indicator motor  36  ends, the battery state detection circuit  10  sets the timer  11  based on the battery detection control signal P 6 , and outputs the reference voltage V 3  from the reference voltage generating circuit  13 . Further, in the battery state detection circuit  10 , the comparator circuit  14  compares the battery dividing voltage V 2  with the reference voltage V 3  at predetermined intervals of time, and measures the battery voltage Vbt to detect the recovery state of the battery  5  (step ST 19 ). 
     Here, when the battery  5  recovers, and the battery recovery signal P 4  is output, the control circuit  21  newly stores in the storage circuit  22  the detection conditions (the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the number of times of the measurement made or the time elapsed until the battery recovers, etc.) obtained from the fast forward driving of the date indicator motor  36 . On the other hand, when the battery  5  does not recover even after the measurement has been made the predetermined number of times, the process moves to the battery recovery mode, as in the first embodiment; this operation flow is the same as that in the first embodiment and, therefore, will not be described in detail herein. 
     Next, the control circuit  21  determines whether the advancing of the date indicator by the date indicator motor  36  is completed or not (step ST 20 ). If the answer is NO (the advancing of the date indicator is not completed yet), the process proceeds to the next step; on the other hand, if the answer is YES (the advancing of the date indicator is completed), the process returns to step ST 11  to continue the usual one-second advancing operation. 
     Next, if the answer in step ST 20  is NO, the control circuit  21  retrieves the past detection conditions stored in the storage circuit  22 , determines the detection conditions for the battery voltage Vbt, and outputs the battery detection control signal P 6  (step ST 21 ). Since the past detection conditions retrieved here from the storage circuit  22  represent the information obtained when the date indicator motor  36  was driven fast forward in the immediately preceding period, the load and driving conditions are the same, and the detection conditions for the battery voltage Vbt can be determined based on the immediately preceding battery recovery information. In this way, the electronic apparatus according to the present invention can accomplish proper load driving and battery state detection. 
     As described above, in the electronic apparatus according to the present invention, even when there are a plurality of loads providing different loads and having different load driving conditions, proper load driving that matches the recovery state of the battery can be performed. This is because, when driving the different loads in succession, the drive instruction and the detection conditions for the battery voltage Vbt for the next load to be driven are determined based on the detection conditions associated with the load driven in the immediately preceding period. Accordingly, the electronic apparatus according to the present invention can achieve not only high-speed driving of a plurality of loads but also highly reliable load driving using a small-capacity battery. 
       FIG. 11  is a timing chart for explaining the operation for driving the plurality of loads in the multi-function electronic watch. 
     Next, one example of the operation for driving the second motor  34  and the date indicator motor  36  will be described with reference to the timing chart of  FIG. 11 . As shown in  FIG. 11 , the motor driving signal P 7   a  is output at intervals of one second, as shown by timings T 20  and T 21 , to advance the second hand by one second. When the motor driving signal P 7   a  is output, the battery voltage Vbt of the battery  5  drops from the no-load voltage Vbt 1  to the load voltage Vbt 2 . 
     After driving the second motor  34 , the control circuit  21  retrieves the past detection conditions from the storage circuit  22 , and determines the detection conditions for the battery voltage Vbt. The battery information detection circuit  10  measures the battery voltage Vbt at predetermined intervals of time (measurement sampling M 30 ). When the recovery of the battery  5  is detected with the battery voltage Vbt exceeding the reference voltage V 3 , the battery information detection circuit  10  outputs the battery recovery signal P 4  to the control circuit  21 . In response to the battery recovery signal P 4 , the control circuit  21  stores the detection conditions (the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the number of times of the measurement made or the time elapsed until the battery recovers, etc.) newly obtained from the driving of the second motor  34  into the storage circuit  22  by write timing W 1 . 
     In the measurement sampling M 30  after the first driving of the second hand  34  at timing T 20 , the battery voltage Vbt is measured using the prescribed standard detection conditions (initial values). However, in the measurement sampling M 30  after the driving of the second hand  34  at timing T 21 , the detection conditions are determined based on the detection information of the battery voltage Vbt stored after the driving performed at timing T 20  one second before (as indicated by arrow A 5 ). 
     Next, the motor driving signal P 7   c  is output at timing T 22  to drive the date indicator motor  36  fast forward, and the driving stops at timing T 23 . When the motor driving signal P 7   c  is output, the battery voltage Vbt of the battery  5  drops from the no-load voltage Vbt 1  to the load voltage Vbt 3 . Since the date indicator motor  36  requires larger drive power than the second motor  34 , larger power is consumed from the battery  5 . As a result, the amount of drop in the battery voltage Vbt is larger, and the battery  5  becomes correspondingly slower to recover. 
     After stopping the fast forward driving of the date indicator motor  36 , the control circuit  21  retrieves the past detection conditions from the storage circuit  22 , and determines the detection conditions for the battery voltage Vbt. The battery information detection circuit  10  starts to measure the battery voltage Vbt at predetermined intervals of time immediately after timing T 23 . When the recovery of the battery  5  is detected with the battery voltage Vbt exceeding the reference voltage V 3 , the battery information detection circuit  10  outputs the battery recovery signal P 4  to the control circuit  21 . In response to the battery recovery signal P 4 , the control circuit  21  stores the detection conditions newly obtained from the driving of the date indicator motor  36  into the storage circuit  22  by write timing W 1 . 
     The fast forward driving of the date indicator motor  36  is performed repeatedly a number of times, as earlier described. As shown in the figure, the fast forward driving is started at timings T 22 , T 24 , T 26 , etc. and is stopped at timings T 23 , T 25 , etc. 
     In the measurement sampling M 30  after stopping the first fast forward driving of the date indicator motor  36  (timing T 23 ), the detection conditions are determined based on the detection information of the battery voltage Vbt stored after the driving of the second motor  34  performed at timing T 21  in the immediately preceding period (as indicated by arrow A 6 ). 
     Since the load characteristics and driving conditions are different between the hand motor  34  and the date indicator motor  36 , the past detection conditions stored in relation to the driving of the hand motor  34  do not perfectly match the driving of the date indicator motor  36 . However, since the detection information stored after the driving of the second motor  34  at timing T 21  represents the recovery information of the battery  5  immediately before driving the date indicator motor  36 , the information can provide sufficient information as to the state of charge of the battery  5 , the ambient temperature, etc. Therefore, the instruction for driving the date indicator motor  36  and the detection conditions for the battery voltage Vbt after the driving can be determined based on the detection conditions for the battery  5  obtained from the driving of the second motor  34 , and this has a great effect in achieving highly reliable load driving. 
     In the measurement sampling M 30  after the end (timing T 25 ) of the second fast forward driving of the date indicator motor  36 , the detection conditions are newly determined (as indicated by arrow A 7 ) based on the past detection conditions stored in the storage circuit  22  after the driving of the date indicator motor  36  in the immediately preceding period (timing T 23 ). That is, for the second and subsequent fast forward driving of the date indicator motor  36 , the drive instruction and the detection conditions for the battery voltage Vbt are determined based on the immediately preceding fast forward driving of the date indicator motor  36 . Since the detection conditions here are determined based on the detection conditions previously obtained for the same load under the same driving conditions, and since the detection conditions can be dynamically varied based on the recovery information including the state of charge of the battery  5 , the ambient temperature, etc. in the immediately preceding period, optimum load driving and battery state detection can be achieved. 
     For example, as a result of the first fast forward driving of the date indicator motor  36  (from timing T 22  to timing T 23 ), if it is determined that the battery  5  is slow to recover, the time intervals of the measurement after the second fast forward driving (from timing T 24  to timing T 25 ) can be set longer. In this way, by reducing the loss of the measurement operation and thus reducing wastage of power consumption, flexible load driving and battery state detection can be achieved. If the battery becomes even slower to recover, the detection frequency can be increased by reducing the amount of fast forward driving of the date indicator motor  36  per operation. With this arrangement, the recovery state of the battery can be detected meticulously, and highly reliable battery state detection that matches the recovery state of the battery can be achieved. 
     As described above, in the electronic apparatus according to the second embodiment of the present invention, the detection conditions obtained from the measurements performed by the power supply state detection circuit  10  are stored in the storage means and, based on the stored detection conditions, the detection conditions can be properly adjusted for the driving of the different kinds of loads that have different driving conditions. Accordingly, the present invention can be applied advantageously to a portable electronic apparatus that is small in size, and therefore imposes constraints on the power supply design, and in particular, to a multi-function electronic apparatus that is equipped with a plurality of loads. 
       FIG. 12  is a flowchart explaining the driving operation when the plurality of loads to be driven in the multi-function electronic watch have different characteristics. 
     Referring to the flowchart of  FIG. 12 , the load driving operation will be described by taking as an example the operation in the stopwatch mode for the case where two entirely different loads, the buzzer and the motor, are driven in succession. The following description is given by assuming that, in the multi-function electronic watch  40  shown in  FIG. 9 , the date indicator motor  36  is replaced by a 1/20-second stepping motor  36   a  (not shown) which is driven by the motor driving signal P 7   c  to advance the second hand by 1/20-second increments. 
     First, in the stopwatch mode, the control circuit  21  in the multi-function electronic watch  40  determines whether the start switch not shown is depressed or not (step ST 31 ). If the answer is NO, the process remains in the standby state, but if the answer is YES (switch ON), the process proceeds to the next step. 
     Next, if the answer in step ST 31  is YES (switch ON), the control circuit  21  retrieves the past detection conditions stored in the storage circuit  22 , newly determines the detection conditions for the battery voltage Vbt, and outputs the battery detection control signal P 6  (step ST 32 ). When detecting the battery voltage Vbt for the first time, and when no past detection conditions are stored in the storage circuit  22 , the control circuit  21  sets prescribed standard detection conditions (initial values). 
     Next, the control circuit  21  outputs the buzzer control signal P 10 , in response to which the buzzer driving circuit  37  drives the buzzer  42  to produce a prescribed buzzer sound (step ST 33 ). The reason for producing the buzzer sound here is to notify the user that the time counting in the stopwatch mode is started in response to the depression of the start switch by the user. 
     Next, the control unit  21  determines whether the buzzer  42  stops sounding (step ST 34 ). If the buzzer  42  is still sounding, the process remains in the standby state, and when the buzzer  42  stops, the process proceeds to the next step. 
     Next, the battery information detection circuit  10  sets the timer  11  based on the battery detection control signal P 6 , and outputs the reference voltage V 3  from the reference voltage generating circuit  13 . Further, in the battery information detection circuit  10 , the comparator circuit  14  compares the battery dividing voltage V 2  with the reference voltage V 3  at predetermined intervals of time, and measures the battery voltage Vbt to detect the recovery state of the battery  5  (step ST 35 ). 
     When the battery  5  recovers, and the battery recovery signal P 4  is output, the control circuit  21  stores in the storage circuit  22  the detection conditions (the time intervals at which to measure the battery voltage Vbt, the measurement start time, the reference voltage V 3 , the number of times of the measurement made or the time elapsed until the battery recovers, etc.) newly obtained from the driving of the buzzer  42 . On the other hand, when the battery  5  does not recover even after the measurement has been made the predetermined number of times, the process moves to the battery recovery mode, as in the first embodiment. This operation flow is the same as that in the first embodiment, and therefore will not be described in detail herein. 
     Next, as the stopwatch is started, the control circuit  21 , in preparation for driving the 1/20-second stepping motor  36   a , retrieves the past detection conditions stored in the storage circuit  22 , newly determines the detection conditions for the battery voltage Vbt, and outputs the battery detection control signal P 6  (step ST 36 ). The detection conditions retrieved here from the storage circuit  22  represent the information obtained when the buzzer  42  was driven in the immediately preceding period. However, when driving the 1/20-second stepping motor  36   a  for the first time, the drive instruction for the 1/20-second stepping motor  36   a  and the detection conditions for the battery voltage Vbt are determined based on the detection conditions associated with the buzzer  42  driven in the immediately preceding period. 
     Next, the control circuit  21  outputs the motor control signal P 5 , in response to which the motor driving circuit  33  drives the 1/20-second stepping motor  36   a  thus starting to advance the second hand in 1/20-second increments (step ST 37 ). The stopwatch thus starts counting the time with the second hand moving in 50-mS increments. 
     The control circuit  21  causes the 1/20-second stepping operation of the 1/20-second stepping motor  36   a  to stop at predetermined intervals of time. After the driving of the 1/20-second stepping motor  36   a  is stopped, the battery information detection circuit  10  sets the timer  11  based on the battery detection control signal P 6 , and outputs the reference voltage V 3  from the reference voltage generating circuit  13 . Further, in the battery information detection circuit  10 , the comparator circuit  14  compares the battery dividing voltage V 2  with the reference voltage V 3  at predetermined intervals of time, and measures the battery voltage Vbt to detect the recovery state of the battery (step ST 38 ). 
     When the battery  5  recovers, and the battery recovery signal P 4  is output, the control circuit  21  stores in the storage circuit  22  the detection conditions newly obtained from the driving of the 1/20-second stepping motor  36   a . On the other hand, when the battery  5  does not recover even after the measurement has been made the predetermined number of times, the process moves to the battery recovery mode, as in the first embodiment. This operation flow is the same as that in the first embodiment, and therefore will not be described in detail herein. 
     Next, the control circuit  21  determines whether the start switch not shown is depressed or not (step ST 39 ). If the answer is NO (switch OFF), the process returns to step ST 36 , and the process from step ST 36  to step ST 39  is repeated, thus continuing the 1/20-second stepping operation. On the other hand, if the answer is YES (switch ON), the process proceeds to the next step. 
     Next, if the answer in step ST 39  is YES (switch ON), the control circuit  21 , in preparation for driving the buzzer  42 , retrieves the past detection conditions stored in the storage circuit  22 , newly determines the detection conditions for the battery voltage Vbt, and outputs the battery detection control signal P 6  (step ST 40 ). The detection conditions retrieved here from the storage circuit  22  represent the information obtained when the hand motor  34  was driven in the immediately preceding period. The instruction for driving the buzzer  42  and the detection conditions for the battery voltage Vbt after the driving are determined based on this information. 
     Next, the control circuit  21  outputs the buzzer control signal P 10 , in response to which the buzzer driving circuit  37  drives the buzzer  42  to produce a prescribed buzzer sound (step ST 41 ). The reason for producing the buzzer sound here is to notify the user that the time counting in the stopwatch mode is stopped in response to the depression of the start switch by the user. The control circuit  21  stops the driving of the buzzer  42  after a predetermined time. When driving the buzzer  42 , if it is found from the detection conditions associated with the hand motor  34  driven in the immediately preceding period that the battery  5  is slow to recover, control may be performed to reduce the duty cycle of the buzzer  42  and thereby reduce the load. 
     As described above, even when there are a plurality of loads, such as the buzzer and the motor, that have entirely different characteristics and that are driven alternately, since the detection conditions including the recovery information of the battery  5  (such as the number of times of the measurement made or the time elapsed until the battery  5  recovers) obtained from the driving of the respective loads are stored in the storage circuit  22  for shared use, the drive instruction for driving any one of the loads and the detection conditions for the battery voltage Vbt after driving the load can be determined based on the stored detection conditions. 
     The drive instruction for driving the load and the detection conditions for the battery voltage Vbt after driving the load need not necessarily be determined based on the immediately preceding detection conditions stored in the storage circuit  22 . For example, the detection conditions obtained over a long term period in relation to the driving of the load may be stored, and the drive instruction for driving the load and the detection conditions for the battery voltage Vbt after driving the load may be determined by referring to the thus stored long-term detection conditions. In that case, the driving conditions such as the driving speed of the load and the detection conditions for the battery voltage Vbt can be set meticulously by predicting changes in the state of charge, etc. from the changes in the recovery state of the battery  5  over the long term period. 
       FIG. 13  is a timing chart for explaining the driving operation when the plurality of loads to be driven in the multi-function electronic watch have different characteristics. 
     Referring to the timing chart of  FIG. 13 , the operation will be described below by taking as an example the case where two different loads, the buzzer  42  and the 1/20-second stepping motor  36   a , are driven in succession in the multi-function electronic watch  40 . 
     In  FIG. 13 , the buzzer driving signal P 13  is output for the duration of period from timing T 30  to timing T 31 , and the buzzer  42  is driven to produce a buzzer sound. At this time, since a large drive current flows to the buzzer  42  due to the buzzer driving signal P 13 , the battery voltage Vbt of the battery  5  drops from the no-load voltage Vbt 1  to the voltage Vbt 3  in corresponding relationship to the output of the buzzer driving signal P 13 . 
     Next, when the driving of the buzzer  42  stops at timing T 31 , the control circuit  21  retrieves the past detection conditions from the storage circuit  22 , and determines the detection conditions for the battery voltage Vbt. The battery information detection circuit  10  measures the battery voltage Vbt at predetermined intervals of time (measurement sampling M 31 ). When the battery voltage Vbt becomes higher than the reference voltage V 3 , it is determined that the battery  5  has recovered, and the battery recovery signal P 4  is output to the control circuit  21 . In response to the battery recovery signal P 4 , the control circuit  21  stores the detection conditions newly obtained from the driving of the buzzer  42  into the storage circuit  22  by write timing W 2 . 
     When the battery recovery signal P 4  is received, the control circuit  21  determines that the battery  5  has recovered sufficiently to be able to drive the next load, and outputs the motor driving signal P 7   c  at timing T 32  to perform the 1/20-second stepping operation. 
     The output of the motor driving signal P 7   c  continues until timing T 33 , and the period from timing T 32  to timing T 33  defines one block of the 1/20-second stepping operation. At this time, since a medium amount of drive current flows to the 1/20-second stepping motor  36   a  due to the motor driving signal P 7   c , the battery voltage Vbt of the battery  5  drops from the no-load voltage Vbt 1  to the voltage Vbt 2  in corresponding relationship to the output of the motor driving signal P 7   c . Since the drive current of the buzzer  42  is larger than the drive current of the 1/20-second stepping motor  36   a , the voltage Vbt 3  when the buzzer  42  is driven is lower than the voltage Vbt 2  when the 1/20-second stepping motor  36   a  is driven. 
     One block driving of the 1/20-second stepping operation of the 1/20-second stepping motor  36   a  ends at timing T 33 . After the driving of the 1/20-second stepping motor  36   a  ends, the control circuit  21  retrieves the past detection conditions from the storage circuit  22 , and determines the detection conditions for the battery voltage Vbt. The battery information detection circuit  10  measures the battery voltage Vbt at predetermined intervals of time (measurement sampling M 31 ). When the battery voltage Vbt becomes higher than the reference voltage V 3 , it is determined that the battery  5  has recovered, and the battery recovery signal P 4  is output to the control circuit  21 . In response to the battery recovery signal P 4 , the control circuit  21  stores the detection conditions newly obtained from the driving of the 1/20-second stepping motor  36   a  again into the storage circuit  22  by write timing W 2 . 
     The 1/20-second stepping operation of the 1/20-second stepping motor  36   a  is repeatedly performed on a block-by-block basis, as described above; accordingly, the 1/20-second stepping operation is started at timings T 32 , T 34 , T 36 , etc. and is stopped at timings T 33 , T 35 , T 37 , etc. as shown in the figure. 
     In the measurement sampling M 31  after the end (timing T 33 ) of the first 1/20-second stepping operation of the 1/20-second stepping motor  36   a , the detection conditions for the battery voltage Vbt are determined based on the past detection conditions stored after the driving of the buzzer  42  performed in the immediately preceding period (as indicated by arrow A 8 ). The buzzer  42  and the 1/20-second stepping motor  36   a  are loads having entirely different characteristics, and their drive currents are different in both magnitude and waveform. Accordingly, the past detection conditions stored in relation to the driving of the buzzer  42  do not perfectly match the driving of the 1/20-second stepping motor  36   a.    
     However, since the detection information stored after the driving of the buzzer  42  represents the recovery information of the battery  5  immediately before driving the /20-second hand motor  36   a , the information can provide sufficient information as to the state of charge of the battery  5 , the ambient temperature, etc. when driving the 1/20-second stepping motor  36   a . Therefore, the instruction for driving the 1/20-second stepping motor  36   a  and the detection conditions for the battery voltage Vbt after the driving can be determined using the detection conditions for the battery  5  obtained from the driving of the buzzer  42 , and this has a great effect in achieving highly reliable load driving. Furthermore, since the battery state detection circuit  10  quickly detects the recovery of the battery  5  after driving the buzzer  42 , the 1/20-second stepping operation can be quickly performed upon recovery of the battery  5  after driving the buzzer  42 . This achieves smoother stopwatch operation with the buzzer sound immediately followed by the 1/20-second stepping operation. 
     On the other hand, in the measurement sampling M 31  after the end (timing T 35 ) of the second 1/20-second stepping operation of the 1/20-second stepping motor  36   a , the detection conditions are determined based on the past detection conditions stored after the driving of the 1/20-second stepping motor  36   a  performed in the immediately preceding period (as indicated by arrow A 9 ). In other words, for the second and subsequent 1/20-second stepping operations of the 1/20-second stepping motor  36   a , the drive instruction and the detection conditions for the battery voltage Vbt are determined based on the immediately preceding 1/20-second stepping operation of the 1/20-second stepping motor  36   a . Since the detection conditions can be dynamically varied based on the past detection conditions obtained for the same load under the same driving conditions and representing the state of charge of the battery  5  in the immediately preceding period, optimum load driving and battery state detection can be achieved. The new detection conditions may be determined by also using other information such as the ambient temperature. 
     In the measurement sampling M 31  after timing T 35  in  FIG. 13 , for example, the measurement of the battery voltage Vbt is started by setting the measurement time intervals shorter than those employed in the measurement sampling after timing T 33 . This is because the control circuit  21  has changed the detection conditions (measurement time intervals) at timing T 35  by determining that the battery  5  recovers quickly, based on the detection information stored after the immediately preceding driving. 
     As described above, in the electronic apparatus according to the present invention, when there are a plurality of loads, such as the buzzer and the motor, that have entirely different characteristics and that are driven alternately, the detection conditions obtained from the driving of the respective loads can be stored in the storage means for shared use. As a result, using the detection conditions stored for shared use, the drive instruction for driving any load having a different characteristic and the detection conditions for the battery voltage after driving such a load can be determined. Accordingly, in an electronic apparatus that implements its functions by driving in a complex manner a plurality of loads having different characteristics, it becomes possible to drive the plurality of loads quickly in a highly reliable manner. 
     The loads having different characteristics are not limited to the motor and the buzzer, but they may be the LED  43  and the sensor  44  mounted in the multi-function electronic watch  40  of the second embodiment. The electronic apparatus according to the present invention can be applied to a variety of electronic apparatuses, including mobile phones and digital cameras, that are equipped with various kinds of loads such as a vibrator, an LCD or other display device, a communication device, an imaging device, etc. though not shown here. 
     Further, in the electronic apparatus according to the present invention, the conditions for detecting the battery recovery after driving the load can be varied as desired by changing the setting of the timer  11  in the battery recovery detection circuit  10  or the setting of the reference voltage generating circuit  13  constructed from a D/A conversion circuit. As a result, if the kind of the battery or the characteristic of the load changes as a result of changing the specification of the electronic apparatus, the detection conditions can be easily corrected by making necessary corrections to the firmware contained in the control means. Accordingly, the electronic apparatus according to the present invention can flexibly accommodate any change in the specification or design.