Abstract:
An on-vehicle computer includes a hardware timer. The hardware timer is started when a vehicle accessory switch changes to its OFF position. A suspending request is transmitted from a BIOS to an application program and a BIOS timer is started when the vehicle accessory switch changes to its OFF position. A suspending permission answer is returned from the application program to the BIOS and an application program timer is started in response to the suspending request. A first turn-OFF command is generated when an elapsed time measured by the application program timer reaches a first predetermined time interval (T 2 ). The BIOS is enabled to generate a suspending command in response to the suspending permission answer. A second turn-OFF command is generated in cases where the suspending permission answer continuously fails to be returned to the BIOS until an elapsed time measured by the BIOS timer reaches a second predetermined time interval (T 1 ). Power supply to the main computer portion is turned off in response to at least one of the first turn-OFF command and the second turn-OFF command. Power supply to the main computer portion is turned off in cases where the BIOS continuously fails to generate the suspending command and the first turn-OFF command and the second turn-OFF command continuously fail to be generated until an elapsed time measured by the hardware timer reaches a third predetermined time interval (T 3 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to an on-vehicle computer. 
     This invention particularly relates to an on-vehicle computer having a function of protecting a vehicular battery, for example, a function of preventing a vehicular battery from being excessively discharged by the occurrence of a problem such as a hang-up in a computer routine. 
     2. Description of the Related Art 
     A typical automotive vehicle has on-vehicle electric apparatuses such as a radio receiver and a stereophonic audio system. The on-vehicle electric apparatuses are powered by DC (direct current) energy from a vehicular battery. The positive side of the DC power is called “+B”. The on-vehicle electric apparatuses are turned on and off by actuating an ACC (accessory) switch of the vehicle. 
     The voltage of a vehicular electric power supply formed by a vehicular battery tends to be unstable when a related vehicle is in operation. Generally, the power supply voltage repetitively drops and rises. In some cases, the power supply voltage drops below an acceptable minimum level required to normally operate on-vehicle electric apparatuses. 
     In the case where an on-vehicle electric apparatus is a radio receiver or a stereophonic audio system, it is good to provide the electric apparatus with a power supply backup which can deal with an excessive power-supply voltage drop for several seconds. If the power supply voltage continues to be excessively low for longer than several seconds before returning to a normal range, operation of the radio receiver or the stereophonic audio system is temporarily interrupted. After the interruption, the radio receiver or the stereophonic audio system is reset and restarted. The reset and restart spend a time interval of a few seconds to about ten seconds. Usually, the interruption and the following restart of the radio receiver or the stereophonic audio system does not cause any serious problem. 
     A computer system using a recording medium disc and a lengthy OS (operating system) spends a long time to start its operation after a power supply switch thereof is changed to an ON position. The starting time of such a computer system is equal to several times or several tens of times of the starting time of a radio receiver or a stereophonic audio system. Therefore, the computer system is unsuited for on-vehicle use since a power supply voltage thereto frequently drops below an acceptable minimum level while a related vehicle is in operation. 
     In the computer system, processes of writing and reading data into and from the recording medium disc include mechanical steps which tend to be adversely affected by mechanical vibration. Also in this regard, the computer system is unsuited for on-vehicle use. It should be noted that the on-vehicle computer is subjected to mechanical vibration while a related vehicle is in operation. 
     A prior-art on-vehicle computer has a casing designed to cut off vibration travelling from a vehicle body toward the inner portion of the computer. The prior-art on-vehicle computer is equipped with an auxiliary battery which maintains operation of the computer when a power supply voltage generated by a vehicular battery drops below an acceptable minimum level. 
     When a power supply switch of the prior-art on-vehicle computer is changed to an OFF position, the computer implements a process of ending a program and then the computer is actually turned off. In the case where a hang-up occurs in the program, the prior-art on-vehicle computer can not be turned off even when the power supply switch is changed to its OFF position. In this case, the computer continues to consume electric power at a significant rate, and there is a chance that the vehicular battery is excessively discharged. The engine of an automotive vehicle may stop if the vehicular battery is excessively discharged. 
     U.S. Pat. No. 5,560,023 corresponding to Japanese published unexamined patent application 8-194561 discloses a desktop computer system having a system suspend/resume capability that causes the system to enter the suspend state when the operating system&#39;s APM driver ceases functioning. The computer system of U.S. Pat. No. 5,560,023 has a CPU, a nonvolatile storage device, volatile registers and memory data, a power management processor, a backup suspend timer and a power supply in circuit communication. The power management processor controls the regulation of power to the CPU by the power supply. The suspend/resume system is controlled by an operating system having power management control. The backup suspend timer executes independently of the power management portion of the operating system. The backup suspend timer causes the system to suspend if the power management portion of the operating system ceases functioning and the system should otherwise be suspended. 
     U.S. Pat. No. 5,862,394 corresponding to Japanese published unexamined patent application 10-27044 discloses a system and method of intelligently terminating power to a computing device. According to the system and method in U.S. Pat. No. 5,862,394, after a software control program starts, a timer circuit gets set. Once the timer circuit gets set, the timer proceeds until timed out. In addition, the software control program initiates an orderly shut down procedure concurrently. The software control program first starts a software shut down process and a hardware shut down process. The software control program has to be able to reset the timer circuit before it times out if additional time is needed to complete the shut down process. Finally, after the timer circuit has timed out, the orderly termination of power to the system begins. In addition, the software control program is implemented to set the timer value to time out instantly if the shut down process is complete. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an improved one vehicle computer. 
     A first aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not a vehicle accessory switch changes to its OFF position; a hardware timer; second means for starting the hardware timer when the first means detects that the vehicle accessory switch changes to its OFF position; third means for providing a BIOS timer; fourth means for transmitting a suspending request from a BIOS to an application program and starting the BIOS timer when the first means detects that the vehicle accessory switch changes to its OFF position; fifth means for providing an application program timer; sixth means for returning a suspending permission answer from the application program to the BIOS and starting the application program timer in response to the suspending request; seventh means for generating a first turn-OFF command when an elapsed time measured by the application program timer reaches a first predetermined time interval (T 2 ); eighth means for enabling the BIOS to generate a suspending command in response to the suspending permission answer; ninth means for generating a second turn-OFF command in cases where the sixth means continues to fail to return the suspending permission answer to the BIOS until an elapsed time measured by the BIOS timer reaches a second predetermined time interval (T 1 ); a main computer portion; tenth means for turning off power supply to the main computer portion in response to at least one of the first turn-OFF command and the second turn-OFF command; and eleventh means for turning off power supply to the main computer portion in cases where the BIOS continues to fail to generate the suspending command and the seventh means and the ninth means continue to fail to generate the first turn-OFF command and the second turn-OFF command until an elapsed time measured by the hardware timer reaches a third predetermined time interval (T 3 ); wherein the first predetermined time interval (T 2 ) is longer than the second predetermined time interval (T 1 ), and is shorter than the third predetermined time interval (T 3 ). 
     A second aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not at least one of a vehicular-battery voltage and an internal-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a hardware timer; second means for starting the hardware timer when the first means detects that at least one of the vehicular-battery voltage and the internal-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; third means for providing a BIOS timer; fourth means for transmitting a shutting-down request from a BIOS to an application program and starting the BIOS timer when the first means detects that at least one of the vehicular-battery voltage and the internal-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; fifth means for returning a shutting-down permission answer from the application program to the BIOS; sixth means for enabling the BIOS to generate a shutting-down command in response to the shutting-down permission answer; seventh means for generating a turn-OFF command in cases where the fifth means continues to fail to return the shutting-down permission answer to the BIOS until an elapsed time measured by the BIOS timer reaches a second predetermined time interval (T 1 ); a main computer portion; eighth means for turning off power supply to the main computer portion in response to the turn-OFF command; and ninth means for turning off power supply to the main computer portion in cases where the BIOS continues to fail to generate the shutting-down command and the seventh means continues to fail to generate the turn-OFF command until an elapsed time measured by the hardware timer reaches a third predetermined time interval (T 3 ); wherein the second predetermined time interval (T 1 ) is shorter than the third predetermined time interval (T 3 ). 
     A third aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not the computer is in its suspended state; second means means for, in cases where the first means detects that the computer is in its suspended state, detecting whether or not at least one of a vehicular-battery voltage and an internal-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a hardware timer; third means for starting the hardware timer when the second means detects that at least one of the vehicular-battery voltage and the internal-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; fourth means for providing a BIOS timer; fifth means for transmitting a shutting-down request from a BIOS to an application program and starting the BIOS timer when the second means detects that at least one of the vehicular-battery voltage and the internal-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; sixth means for returning a shutting-down permission answer from the application program to the BIOS; seventh means for enabling the BIOS to generate a shutting-down command in response to the shutting-down permission answer; eighth means for generating a turn-OFF command in cases where the sixth means continues to fail to return the shutting-down permission answer to the BIOS until an elapsed time measured by the BIOS timer reaches a second predetermined time interval (T 1 ); a main computer portion; ninth means for turning off power supply to the main computer portion in response to the turn-OFF command; and tenth means for turning off power supply to the main computer portion in cases where the BIOS continues to fail to generate the shutting-down command and the eighth means continues to fail to generate the turn-OFF command until an elapsed time measured by the hardware timer reaches a third predetermined time interval (T 3 ); wherein the second predetermined time interval (T 1 ) is shorter than the third predetermined time interval (T 3 ). 
     A fourth aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not a vehicle accessory switch changes to its OFF position; a main computer portion including a CPU; second means for enabling the CPU to output a suspending command when the first means detects that the vehicle accessory switch changes to its OFF position; and third means for cutting off power supply to the main computer portion in cases where the CPU continuously fails to output the suspending command during a predetermined time interval after the first means detects that the vehicle accessory switch changes to its OFF position. 
     A fifth aspect of this invention provides an on-vehicle computer comprising a power-supply management portion operating in accordance with a first program; first means provided in the power-supply management portion for detecting whether or not a vehicle accessory switch changes to its OFF position; a main computer portion including a CPU which operates in accordance with a second program different and separate from the first program; second means provided in the power-supply management portion for feeding the CPU with information representing that the vehicle accessory switch changes to its OFF position; third means for enabling the CPU to return a suspending command to the power-supply management portion in response to the information from the second means; a power-supply controller for controlling power supply to the main computer portion; and fourth means provided in the power-supply management portion for controlling the power-supply controller to cut off power supply to the main computer portion in cases where the CPU continuously fails to return the suspending command during a predetermined time interval after the first means detects that the vehicle accessory switch changes to its OFF position. 
     A sixth aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not a vehicular-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a main computer portion including a CPU; second means for enabling the CPU to output a shutting-down command when the first means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; and third means for cutting off power supply to the main computer portion in cases where the CPU continuously fails to output the shutting-down command during a second predetermined time interval after the first means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval. 
     A seventh aspect of this invention provides an on-vehicle computer comprising a power-supply management portion operating in accordance with a first program; first means provided in the power-supply management portion for detecting whether or not a vehicular-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a main computer portion including a CPU which operates in accordance with a second program different and separate from the first program; second means provided in the power-supply management portion for feeding the CPU with information representing that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; third means for enabling the CPU to return a shutting-down command to the power-supply management portion in response to the information from the second means; a power-supply controller for controlling power supply to the main computer portion; and fourth means provided in the power-supply management portion for controlling the power-supply controller to cut off power supply to the main computer portion in cases where the CPU continuously fails to return the shutting-down command during a second predetermined time interval after the first means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval. 
     An eighth aspect of this invention provides an on-vehicle computer comprising first means for detecting whether or not the computer is in its suspended state; second means means for, in cases where the first means detects that the computer is in its suspended state, detecting whether or not a vehicular-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a main computer portion including a CPU; third means for enabling the CPU to output a shutting-down command when the second means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; and fourth means for cutting off power supply to the main computer portion in cases where the CPU continuously fails to output the shutting-down command during a second predetermined time interval after the second means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval. 
     A ninth aspect of this invention provides an on-vehicle computer comprising a power-supply management portion operating in accordance with a first program; first means provided in the power-supply management portion for detecting whether or not the computer is in its suspended state; second means means provided in the power-supply management portion for, in cases where the first means detects that the computer is in its suspended state, detecting whether or not a vehicular-battery voltage continues to be lower than a predetermined reference voltage for a first predetermined time interval; a main computer portion including a CPU which operates in accordance with a second program different and separate from the first program; third means provided in the power-supply management portion for feeding the CPU with information representing that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval; fourth means for enabling the CPU to return a shutting-down command to the power-supply management portion in response to the information from the third means; a power-supply controller for controlling power supply to the main computer portion; and fifth means provided in the power-supply management portion for controlling the power-supply controller to cut off power supply to the main computer portion in cases where the CPU continuously fails to return the shutting-down command during a second predetermined time interval after the second means detects that the vehicular-battery voltage continues to be lower than the predetermined reference voltage for the first predetermined time interval. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an on-vehicle computer according to a first embodiment of this invention. 
     FIG. 2 is a set of flowcharts of program segments in the on-vehicle computer in FIG.  1 . 
     FIG. 3 is a diagram of a first exemplary sequence of communications among hardware devices, a BIOS, an OS, a driver program, and an application program in the on-vehicle computer in FIG.  1 . 
     FIG. 4 is a diagram of a second exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  1 . 
     FIG. 5 is a diagram of a third exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  1 . 
     FIG. 6 is a diagram of a fourth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  1 . 
     FIG. 7 is a block diagram of an on-vehicle computer according to a second embodiment of this invention. 
     FIG. 8 is a set of flowcharts of program segments in the on-vehicle computer in FIG.  7 . 
     FIG. 9 is a diagram of a first exemplary sequence of communications among hardware devices, a BIOS, an OS, a driver program, and an application program in the on-vehicle computer in FIG.  7 . 
     FIG. 10 is a diagram of a second exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  7 . 
     FIG. 11 is a diagram of a third exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  7 . 
     FIG. 12 is a diagram of a fourth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  7 . 
     FIG. 13 is a diagram of a fifth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  7 . 
     FIG. 14 is a diagram of a sixth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  7 . 
     FIG. 15 is a block diagram of an on-vehicle computer according to a third embodiment of this invention. 
     FIG. 16 is a set of flowcharts of program segments in the on-vehicle computer in FIG.  15 . 
     FIG. 17 is a diagram of a first exemplary sequence of communications among hardware devices, a BIOS, an OS, a driver program, and an application program in the on-vehicle computer in FIG.  15 . 
     FIG. 18 is a diagram of a second exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  15 . 
     FIG. 19 is a diagram of a third exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  15 . 
     FIG. 20 is a diagram of a fourth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  15 . 
     FIG. 21 is a diagram of a fifth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  15 . 
     FIG. 22 is a diagram of a sixth exemplary sequence of communications among the hardware devices, the BIOS, the OS, the driver program, and the application program in the on-vehicle computer in FIG.  15 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     FIG. 1 shows a block diagram of an on-vehicle computer according to a first embodiment of this invention. The on-vehicle computer of FIG. 1 includes a CPU  1 , a main memory  2 , a hard disc drive  3 , a power-supply management portion  4 , and a ROM (a read only memory)  9  which are connected via a bus. 
     The main memory  2  includes a RAM (a random access memory). The ROM  9  stores a program called a BIOS (a basic input/output system). The CPU  1  can refer to the BIOS. The hard disc drive  3  contains a recording disc called a hard disc. An OS (operating system), a driver (a device driver program), and an application program are stored in the recording disc in the hard disc drive  3 . The CPU  1  can refer to the OS, the driver, and the application program via the hard disc drive  3 . The application program is based on the OS and the driver. 
     The power-supply management portion  4  is connected to a vehicle ACC switch  8 . The power-supply management portion  4  includes a register loaded with a signal representing a state of the ACC switch  8 . The power-supply management portion  4  also includes a register loaded with a signal which represents whether or not the computer is in a suspended state (a suspended mode of operation). The ACC-state register and the suspended-state register can be accessed by the CPU  1 . The power-supply management portion  4  further includes a hardware timer formed by a counter. In addition, the power-supply management portion  4  includes a programmable logic device or a processor which operates in accordance with a power-supply management program stored in an internal ROM. The programmable logic device is connected to the ACC switch  8 , the ACC-state register, the suspended-state register, and the hardware timer. 
     A power-supply controller  5  is connected to the power-supply management portion  4 . The power-supply controller  5  is connected to a power feed line in the computer. The power-supply controller  5  is connected to a “+B” line leading from a vehicular battery (not shown). The power-supply controller  5  includes a switch for controlling the supply of electric power to a main portion of the computer. The main portion of the computer contains the CPU  1  and the main memory  2 . 
     The on-vehicle computer of FIG. 1 includes an internal battery (an auxiliary battery)  6  and a voltage monitoring portion  7 . The internal battery  6  is connected to the power-supply controller  5  and the voltage monitoring portion  7 . The voltage monitoring portion  7  is connected to the power-supply management portion  4 . The voltage monitoring portion  7  is connected to the “+B” line. The voltage monitoring portion  7  includes a first sensor for detecting a voltage at the “+B” line. The voltage monitoring portion  7  informs the power-supply management portion  4  of the detected “+B” line voltage. The voltage monitoring portion  7  includes a second sensor for detecting a voltage across the internal battery  6 . The voltage monitoring portion  7  informs the power-supply management portion  4  of the detected internal-battery voltage. 
     The main portion of the on-vehicle computer can be fed with electric power from at least one of the “+B” line and the internal battery  6  via the power-supply controller  5 . The on-vehicle computer is changed among an OFF state, a normal ON state (a normal operation state), and a suspended state in accordance with operation of the power-supply controller  5 . 
     An explanation will be given of a change of the on-vehicle computer from its ON state to its suspended state. The right-hand portion &lt;H/W&gt; of FIG. 2 is a flowchart of a segment of the power-supply management program for controlling the power-supply management portion  4 . As shown in FIG. 2, a first step S 1  of the power-supply management program segment decides whether or not the ACC switch  8  changes to its OFF position. When the ACC switch  8  does not change to its OFF position, the step S 1  is repeated. When the ACC switch  8  changes to its OFF position, the program advances from the step S 1  to a step S 1 A. 
     The step S 1 A loads the ACC-state register with a signal representing an ACC_OFF state. After the step S 1 A, the program advances to a step S 2 . 
     The step S 2  implements a counting process. Specifically, the step S 2  starts the hardware timer in the power-supply management portion  4 , or increments the elapsed time (the time-representing number) indicated by the hardware timer. 
     A step S 3  following the step S 2  decides whether or not a suspending command is present. The suspending command is given by the BIOS. When the suspending command is present, the program advances from the step S 3  to a step  34 . When the suspending command is not present, the program advances from the step S 3  to a step S 5 . 
     The step S 4  controls the power-supply controller  5 , and thereby changes the computer to its suspended state. The step S 4  loads the suspended-state register with a signal representing that the computer is in its suspended state. After the step S 4 , the current execution cycle of the power-supply management program segment ends. 
     The step S 5  decides whether or not at least one of two turn-OFF commands (two shut-down commands) is present. The turn-OFF commands are given by the BIOS and the application program. When at least one of the turn-OFF commands is present, the program advances from the step S 5  to a step S 6 . When any turn-OFF command is not present, the program advances from the step S 5  to a step S 7 . 
     The step S 6  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. Then, the step S 6  resets or stops the hardware timer. After the step S 6 , the current execution cycle of the power-supply management program segment ends. 
     The step S 7  compares the elapsed time indicated by the hardware timer with a predetermined time interval T 3 . When the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the program advances from the step S 7  to a step S 8 . Otherwise, the program returns from the step S 7  to the step S 2 . 
     The step S 8  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. After the step S 8 , the current execution cycle of the power-supply management program segment ends. 
     The intermediate portion &lt;BIOS&gt; of FIG. 2 is a flowchart of a segment of the BIOS for controlling the CPU  1 . As shown in FIG. 2, a first step S 11  of the BIOS segment accesses the ACC-state register in the power-supply management portion  4 , and decides whether or not the signal in the ACC-state register represents the ACC_OFF state. When the signal in the ACC-state register represents the ACC_OFF state, the program advances from the step S 11  to a step S 12 . When the signal in the ACC-state register does not represent the ACC_OFF state, the step S 11  is repeated. 
     The step S 12  transmits a suspending-request message to the application program. After the step S 12 , the program advances to a step S 13 . 
     The step S 13  implements a counting process. Specifically, the step S 13  starts a software timer (a BIOS timer or a timer provided by the BIOS), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 14  following the step S 13  decides whether or not a suspending process is permitted. Information of whether or not the suspending process is permitted is given by the application program. When the suspending process is permitted, the program advances from the step S 14  to a step S 15 . When the suspending process is not permitted, the program advances from the step S 14  to a step S 16 . 
     The step S 15  generates a suspending command. The step S 15  transmits the suspending command to the power-supply management portion  4 . Then, the step S 15  resets or stops the software timer. After the step S 15 , the current execution cycle of the BIOS segment ends. 
     The step S 16  compares the elapsed time indicated by the software timer with a predetermined time interval T 1 . Preferably, the predetermined time interval T 1  is shorter than the predetermined time interval T 3 . When the elapsed time indicated by the software timer reaches the predetermined time interval T 1 , the program advances from the step S 16  to a step S 17 . Otherwise, the program returns from the step S 16  to the step S 13 . 
     The step S 17  generates a turn-OFF command. The step S 17  transmits the turn-OFF command to the power-supply management portion  4 . After the step S 17 , the current execution cycle of the BIOS segment ends. 
     The left-hand portion &lt;APPLI/DRIVER/OS&gt; of FIG. 2 is a flowchart of a segment of the OS-driver-based application program for controlling the CPU  1 . The application program segment in FIG. 2 is periodically executed by, for example, an interruption process. As shown in FIG. 2, a first step S 21  of the application program segment decides whether or not a suspending-request message is present. The suspending-request message is transmitted from the BIOS. When the suspending-request message is present, the program advances from the step S 21  to a step S 22 . When the suspending-request message is not present, the step S 21  is repeated. 
     The step S 22  decides whether or not a suspending process is permitted. When the suspending process is permitted, the program advances from the step S 22  to a step S 23 . When the suspending process is not permitted, the step S 22  is repeated. 
     The step S 23  informs the BIOS that the suspending process is permitted. After the step S 23 , the program advances to a step S 24 . 
     The step S 24  implements a counting process. Specifically, the step S 24  starts a software timer (an application program timer or a timer provided by the application program), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 25  following the step S 24  compares the elapsed time indicated by the software timer with a predetermined time interval T 2 . Preferably, the predetermined time interval T 2  is shorter than the predetermined time interval T 3 , and is longer than the predetermined time interval T 1 . When the elapsed time indicated by the software timer reaches the predetermined time interval T 2 , the program advances from the step S 25  to a step S 26 . Otherwise, the program returns from the step S 25  to the step S 24 . 
     The step S 26  generates a turn-OFF command. The step S 26  transmits the turn-OFF command to the power-supply management portion  4 . After the step S 26 , the current execution cycle of the application program segment ends. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4  receives a suspending command from the BIOS, the power-supply management portion  4  controls the power-supply controller  5  and thereby changes the computer to its suspended state. In addition, the power-supply management portion  4  loads the suspended-state register with a signal representing that the computer is in its suspended state. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4  receives at least one of turn-OFF commands (shut-down commands) from the BIOS and the application program, the power-supply management portion  4  controls the power-supply controller  5  and thereby changes the computer to its OFF state. In addition, the power-supply management portion  4  resets or stops the hardware timer. 
     In the case where the power-supply management portion  4  continues to receive neither a suspending command nor a turn-OFF command and then the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the power-supply management portion  4  controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     It is preferable to set the predetermined time intervals T 1 , T 2 , and T 3  as “T 1 &lt;T 2 &lt;T 3 ”. According to this setting, 3-stage fail-safe can be implemented. In the case where the computer operates normally, when the ACC switch  8  is changed to its OFF state, the power-supply management program informs the BIOS of the ACC_OFF state and the BIOS transmits the suspending-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the suspending process is permitted. The BIOS transmits the suspending command to the power-supply management portion  4  in response to the return information from the OS-driver-based application program. The power-supply management portion  4  controls the power-supply controller  5  in response to the suspending command, and thereby changes the computer to its suspended state. When the computer is in its suspended state, the OS is in its stand-by state and the application program is set aboard. The computer being in its suspended state consumes electric power at only a small rate, and the vehicular battery is hardly discharged excessively. When the ACC switch  8  is returned to its ON position, the suspended state of the computer is cancelled and the OS resumes in a short time. 
     In the case where a hang-up occurs in the application program or the OS, the OS-driver-based application program fails to respond to the suspending-request message from the BIOS and does not return the information to the BIOS which indicates that the suspending process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 . The power-supply management portion  4  controls the power-supply controller in response to the turn-OFF command, and thereby changes the computer to its OFF state. Accordingly, in this case, the power supply to the computer is forced to be cut off. In the event that a hang-up occurs also in the BIOS, when the elapsed time indicated by the hardware timer in the power-supply management portion  4  reaches the predetermined time interval T 3 , the power-supply management portion  4  controls the power-supply controller  5  and thereby changes the computer to its OFF state. Therefore, also in this case, the power supply to the computer is forced to be cut off. 
     Thus, in the case where the occurrence of a hang-up in the OS, the application program, or the BIOS hinders the computer from falling into its suspended state when the ACC switch is changed to its OFF position, the power supply to the computer is forced to be cut off. Accordingly, it is possible to prevent the vehicular battery from being excessively discharged. 
     With reference to FIG. 3, in the case where the computer operates normally, when the ACC switch  8  is changed to its OFF state, the power-supply management program informs the BIOS of the ACC_OFF state and the BIOS transmits the suspending-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the suspending process is permitted. The BIOS transmits the suspending command to the power-supply management portion  4  in response to the return information from the OS-driver-based application program. The power-supply management portion  4  controls the power-supply controller  5  in response to the suspending command, and thereby changes the computer to its suspended state. 
     With reference to FIG. 4, when the ACC switch  8  is changed to its OFF state, the power-supply management program informs the BIOS of the ACC_OFF state and the BIOS transmits the suspending-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the suspending process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 . The power-supply management portion  4  controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 5, when the ACC switch  8  is changed to its OFF state, the power-supply management program informs the BIOS of the ACC_OFF state and the BIOS transmits the suspending-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the suspending process is permitted. It is assumed that a hang-up occurs in the BIOS, and hence the BIOS does not transmit the suspending command to the power-supply management portion  4  in response to the return information from the OS-driver-based application program. In this case, when the elapsed time indicated by the software timer in the application program reaches the predetermined time interval T 2 , the application program transmits the turn-OFF command to the power-supply management portion  4 . The power-supply management portion  4  controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 6, when the ACC switch  8  is changed to its OFF state, the power-supply management program informs the BIOS of the ACC_OFF state and the BIOS transmits the suspending-request message to the OS-driver-based application program. It is assumed that hang-ups occur in both the OS-driver-based application program and the BIOS, and hence the OS-driver-based application program and the BIOS do not transmit the suspending command and the turn-OFF commands to the power-supply management portion  4 . In this case, when the elapsed time indicated by the hardware timer in the power-supply management portion  4  reaches the predetermined time interval T 3 , the power-supply management portion  4  controls the power-supply controller and thereby changes the computer to its OFF state. 
     Second Embodiment 
     FIG. 7 shows a block diagram of an on-vehicle computer according to a second embodiment of this invention. The on-vehicle computer of FIG. 7 is similar to the on-vehicle computer of FIG. 1 except for design changes indicated hereinafter. 
     The on-vehicle computer of FIG. 7 includes a power-supply management portion  4 A instead of the power-supply management portion  4  (see FIG.  1 ). The power-supply management portion  4 A has a power-state register for storing a signal representing that a power voltage is in a predetermined low range. 
     The on-vehicle computer of FIG. 7 is changed among an OFF state, a normal ON state (a normal operation state), and a shut-down state in accordance with operation of the power-supply controller  5 . 
     An explanation will be given of a change of the on-vehicle computer from its ON state to its shut-down state. The right-hand portion &lt;H/W&gt; of FIG. 8 is a flowchart of a segment of a power-supply management program for controlling the power-supply management portion  4 A. As shown in FIG. 8, a first step S 31  of the power-supply management program segment derives a current voltage at the “+B” line and a current voltage of the internal battery  6  from the information generated by the voltage monitoring portion  7 . The step S 31  compares the current “+B” line voltage with a first predetermined reference voltage. The step S 31  compares the current internal-battery voltage with a second predetermined reference voltage. When the current “+B” line voltage is lower than the first predetermined reference voltage or when the current internal-battery voltage is lower than the second predetermined reference voltage, the program advances from the step S 31  to a step S 32 . When the current “+B” line voltage is equal to or higher than the first predetermined reference voltage and also the current internal-battery voltage is equal to or higher than the second predetermined reference voltage, the step S 31  is repeated. Generally, the first and second predetermined reference voltages are different from each other. The first and second predetermined reference voltages may be equal to each other. 
     The step S 32  implements a counting process. Specifically, the step S 32  starts a software timer (a timer provided by the power-supply management program), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 33  following the step S 32  compares the elapsed time indicated by the software timer with a time interval of one second. When the elapsed time indicated by the software timer reaches a time interval of one second, the program advances from the step S 33  to a step S 34 . Otherwise, the program returns from the step S 33  to the step S 32 . 
     The step S 34  derives a current voltage at the “+B” line and a current voltage of the internal battery  6  from the information generated by the voltage monitoring portion  7 . The step S 34  compares the current “+B” line voltage with the first predetermined reference voltage. The step S 34  compares the current internal-battery voltage with the second predetermined reference voltage. When the current “+B” line voltage is lower than the first predetermined reference voltage or when the current internal-battery voltage is lower than the second predetermined reference voltage, the program advances from the step S 34  to a step S 35 . When the current “+B” line voltage is equal to or higher than the first predetermined reference voltage and also the current internal-battery voltage is equal to or higher than the second predetermined reference voltage, the program returns from the step S 34  to the step S 31 . 
     The step S 35  loads the power-state register with a signal representing a low power-voltage state. After the step S 35 , the program advances to a step S 36 . 
     The step S 36  implements a counting process. Specifically, the step S 36  starts the hardware timer in the power-supply management portion  4 A, or increments the elapsed time (the time-representing number) indicated by the hardware timer. 
     A step S 37  following the step S 36  decides whether or not a shutting-down command is present. The shutting-down command is given by a BIOS. When the shutting-down command is present, the program advances from the step S 37  to a step S 38 . When the shutting-down command is not present, the program advances from the step S 37  to a step S 39 . 
     The step S 38  controls the power-supply controller  5 , and thereby changes the computer to its shut-down state. After the step S 38 , the current execution cycle of the power-supply management program segment ends. 
     The step S 39  decides whether or not a turn-OFF command is present. The turn-OFF command is given by the BIOS. When the turn-OFF command is present, the program advances from the step S 39  to a step S 40 . When the turn-OFF command is not present, the program advances from the step S 39  to a step S 41 . 
     The step S 40  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. Then, the step S 40  resets or stops the hardware timer. After the step S 40 , the current execution cycle of the power-supply management program segment ends. 
     The step S 41  compares the elapsed time indicated by the hardware timer with a predetermined time interval T 3 . When the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the program advances from the step S 41  to a step S 42 . Otherwise, the program returns from the step S 41  to the step S 36 . 
     The step S 42  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. After the step S 42 , the current execution cycle of the power-supply management program segment ends. 
     The intermediate portion &lt;BIOS&gt; of FIG. 8 is a flowchart of a segment of the BIOS for controlling the CPU  1 . As shown in FIG. 8, a first step S 51  of the BIOS segment accesses the power-state register in the power-supply management portion  4 A, and decides whether or not the signal in the power-state register represents the low power-voltage state. When the signal in the power-state register represents the low power-voltage state, the program advances from the step S 51  to a step S 52 . When the signal in the power-state register does not represent the low power-voltage state, the step S 51  is repeated. 
     The step S 52  transmits a shutting-down-request message to an application program. After the step S 52 , the program advances to a step S 53 . 
     The step S 53  implements a counting process. Specifically, the step S 53  starts a software timer (a BIOS timer or a timer provided by the BIOS), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 54  following the step S 53  decides whether or not a shutting-down process is permitted. Information of whether or not the shutting-down process is permitted is given by the application program. When the shutting-down process is permitted, the program advances from the step S 54  to a step S 55 . When the shutting-down process is not permitted, the program advances from the step S 54  to a step S 56 . 
     The step S 55  generates a shutting-down command. The step S 55  transmits the shutting-down command to the power-supply management portion  4 A. Then, the step S 55  resets or stops the software timer. After the step S 55 , the current execution cycle of the BIOS segment ends. 
     The step S 56  compares the elapsed time indicated by the software timer with a predetermined time interval T 1 . Preferably, the predetermined time interval T 1  is shorter than the predetermined time interval T 3 . When the elapsed time indicated by the software timer reaches the predetermined time interval T 1 , the program advances from the step S 56  to a step S 57 . Otherwise, the program returns from the step S 56  to the step S 53 . 
     The step S 57  generates a turn-OFF command. The step S 57  transmits the turn-OFF command to the power-supply management portion  4 A. After the step S 57 , the current execution cycle of the BIOS segment ends. 
     The left-hand portion &lt;APPLI/DRIVER/OS&gt; of FIG. 8 is a flowchart of a segment of the OS-driver-based application program for controlling the CPU  1 . The application program segment in FIG. 8 is periodically executed by, for example, an interruption process. As shown in FIG. 8, a first step S 61  of the application program segment decides whether or not a shutting-down-request message is present. The shutting-down-request message is transmitted from the BIOS. When the shutting-down-request message is present, the program advances from the step S 61  to a step S 62 . When the shutting-down-request message is not present, the step S 61  is repeated. 
     The step S 62  decides whether or not a shutting-down process is permitted. When the shutting-down process is permitted, the program advances from the step S 62  to a step S 63 . When the shutting-down process is not permitted, the step S 62  is repeated. 
     The step S 63  informs the BIOS that the shutting-down process is permitted. After the step S 63 , the current execution cycle of the application program segment ends and then the program returns to a main routine. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4 A receives a shutting-down command from the BIOS, the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its shut-down state. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4 A receives a turn-OFF command from the BIOS, the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its OFF state. In addition, the power-supply management portion  4 A resets or stops the hardware timer. 
     In the case where the power-supply management portion  4 A continues to receive neither a shutting-down command nor a turn-OFF command and then the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     It is preferable to set the predetermined time intervals T 1  and T 3  as “T 1 &lt;T 3 ”. According to this setting, 2-stage fail-safe can be implemented. In the case where the computer operates normally, when the power-supply management portion  4 A detects that the low power-voltage state lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 A in response to the return information from the OS-driver-based application program. The power-supply management portion  4 A controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shut-down state. When the computer is in its shut-down state, the vehicular battery or the internal battery  6  is hardly discharged excessively. 
     In the case where a hang-up occurs in the application program or the OS, the OS-driver-based application program fails to respond to the shutting-down-request message from the BIOS and does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 A. The power-supply management portion  4 A controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. Accordingly, in this case, the power supply to the computer is forced to be cut off. In the event that a hang-up occurs also in the BIOS, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 A reaches the predetermined time interval T 3 , the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its OFF state. Therefore, also in this case, the power supply to the computer is forced to be cut off. 
     Thus, in the case where the occurrence of a hang-up in the OS, the application program, or the BIOS hinders the computer from falling into its shut-down state when the low power-voltage state continues to be detected for at least one second, the power supply to the computer is forced to be cut off. Accordingly, it is possible to prevent the vehicular battery or the internal battery  6  from being excessively discharged. 
     With reference to FIG. 9, in the case where the computer operates normally, when the power-supply management portion  4 A detects that the low “+B” line voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 A in response to the return information from the OS-driver-based application program. The power-supply management portion  4 A controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shut-down state. 
     With reference to FIG. 10, when the power-supply management portion  4 A detects that the low “+B” line voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 A. The power-supply management portion  4 A controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 11, when the power-supply management portion  4 A detects that the low “+B” line voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. Furthermore, it is assumed that a hang-up occurs in the BIOS. Accordingly, the BIOS does not transmit the turn-OFF command to the power-supply management portion  4 A even when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 . In this case, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 A reaches the predetermined time interval T 3 , the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     With reference to FIG. 12, in the case where the computer operates normally, when the power-supply management portion  4 A detects that the low internal-battery voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 A in response to the return information from the OS-driver-based application program. The power-supply management portion  4 A controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shut-down state. 
     With reference to FIG. 13, when the power-supply management portion  4 A detects that the low internal-battery voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 A. The power-supply management portion  4 A controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 14, when the power-supply management portion  4 A detects that the low internal-battery voltage lasts for at least one second, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. Furthermore, it is assumed that a hang-up occurs in the BIOS. Accordingly, the BIOS does not transmit the turn-OFF command to the power-supply management portion  4 A even when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 . In this case, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 A reaches the predetermined time interval T 3 , the power-supply management portion  4 A controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     Third Embodiment 
     FIG. 15 shows a block diagram of an on-vehicle computer according to a third embodiment of this invention. The on-vehicle computer of FIG. 15 is similar to the on-vehicle computer of FIG. 7 except for design changes indicated hereinafter. 
     The on-vehicle computer of FIG. 15 includes a power-supply management portion  4 B instead of the power-supply management portion  4 A (see FIG.  7 ). The power-supply management portion  4 B has a function of deciding whether or not the computer is in a suspended state. 
     The on-vehicle computer of FIG. 15 is changed among an OFF state, a normal ON state (a normal operation state), a shut-down state, and a suspended state in accordance with operation of the power-supply controller  5 . 
     An explanation will be given of a change of the on-vehicle computer from its suspended state to its shut-down state. The right-hand portion &lt;H/W&gt; of FIG. 16 is a flowchart of a segment of a power-supply management program for controlling the power-supply management portion  4 B. As shown in FIG. 16, a first step S 70  of the power-supply management program segment decides whether or not the computer is in its suspended state. When the computer is in its suspended state, the program advances from the step S 70  to a step S 71 . When the computer is not in its suspended state, the step S 70  is repeated. 
     The step S 71  derives a current voltage at the “+B” line and a current voltage of the internal battery  6  from the information generated by the voltage monitoring portion  7 . The step S 71  compares the current “+B” line voltage with a first predetermined reference voltage. The step S 71  compares the current internal-battery voltage with a second predetermined reference voltage. When the current “+B” line voltage is lower than the first predetermined reference voltage or when the current internal-battery voltage is lower than the second predetermined reference voltage, the program advances from the step S 71  to a step S 72 . When the current “+B” line voltage is equal to or higher than the first predetermined reference voltage and also the current internal-battery voltage is equal to or higher than the second predetermined reference voltage, the step S 71  is repeated. Generally, the first and second predetermined reference voltages are different from each other. The first and second predetermined reference voltages may be equal to each other. 
     The step S 72  implements a counting process. Specifically, the step S 72  starts a software timer (a timer provided by the power-supply management program), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 73  following the step S 72  compares the elapsed time indicated by the software timer with a time interval of one second. When the elapsed time indicated by the software timer reaches a time interval of one second, the program advances from the step S 73  to a step S 74 . Otherwise, the program returns from the step S 73  to the step S 72 . 
     The step S 74  derives a current voltage at the “+B” line and a current voltage of the internal battery  6  from the information generated by the voltage monitoring portion  7 . The step S 74  compares the current “+B” line voltage with the first predetermined reference voltage. The step S 74  compares the current internal-battery voltage with the second predetermined reference voltage. When the current “+B” line voltage is lower than the first predetermined reference voltage or when the current internal-battery voltage is lower than the second predetermined reference voltage, the program advances from the step S 74  to a step S 75 . When the current “+B” line voltage is equal to or higher than the first predetermined reference voltage and also the current internal-battery voltage is equal to or higher than the second predetermined reference voltage, the program returns from the step S 74  to the step S 71 . 
     The step S 75  loads the power-state register with a signal representing a low power-voltage state. The step S 75  controls the power-supply controller  5 , and thereby changes the computer to its ON state. After the step S 75 , the program advances to a step S 76 . 
     The step S 76  implements a counting process. Specifically, the step S 76  starts the hardware timer in the power-supply management portion  4 B, or increments the elapsed time (the time-representing number) indicated by the hardware timer. 
     A step S 77  following the step S 76  decides whether or not a shutting-down command is present. The shutting-down command is given by a BIOS. When the shutting-down command is present, the program advances from the step S 77  to a step S 78 . When the shutting-down command is not present, the program advances from the step S 77  to a step S 79 . 
     The step S 78  controls the power-supply controller  5 , and thereby changes the computer to its shut-down state. After the step S 78 , the current execution cycle of the power-supply management program segment ends. 
     The step S 79  decides whether or not a turn-OFF command is present. The turn-OFF command is given by the BIOS. When the turn-OFF command is present, the program advances from the step S 79  to a step S 80 . When the turn-OFF command is not present, the program advances from the step S 79  to a step S 81 . 
     The step S 80  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. Then, the step S 80  resets or stops the hardware timer. After the step S 80 , the current execution cycle of the power-supply management program segment ends. 
     The step S 81  compares the elapsed time indicated by the hardware timer with a predetermined time interval T 3 . When the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the program advances from the step S 81  to a step S 82 . Otherwise, the program returns from the step S 81  to the step S 76 . 
     The step S 82  controls the power-supply controller  5 , and thereby changes the computer to its OFF state. After the step S 82 , the current execution cycle of the power-supply management program segment ends. 
     The intermediate portion &lt;BIOS&gt; of FIG. 16 is a flowchart of a segment of the BIOS for controlling the CPU  1 . As shown in FIG. 16, a first step S 91  of the BIOS segment accesses the power-state register in the power-supply management portion  4 B, and decides whether or not the signal in the power-state register represents the low power-voltage state. When the signal in the power-state register represents the low power-voltage state, the program advances from the step S 91  to a step S 92 . When the signal in the power-state register does not represent the low power-voltage state, the step S 91  is repeated. 
     The step S 92  transmits a shutting-down-request message to an application program. After the step S 92 , the program advances to a step S 93 . 
     The step S 93  implements a counting process. Specifically, the step S 93  starts a software timer (a BIOS timer or a timer provided by the BIOS), or increments the elapsed time (the time-representing number) indicated by the software timer. 
     A step S 94  following the step S 93  decides whether or not a shutting-down process is permitted. Information of whether or not the shutting-down process is permitted is given by the application program. When the shutting-down process is permitted, the program advances from the step S 94  to a step S 95 . When the shutting-down process is not permitted, the program advances from the step S 94  to a step S 96 . 
     The step S 95  generates a shutting-down command. The step S 95  transmits the shutting-down command to the power-supply management portion  4 B. Then, the step S 95  resets or stops the software timer. After the step S 95 , the current execution cycle of the BIOS segment ends. 
     The step S 96  compares the elapsed time indicated by the software timer with a predetermined time interval T 1 . Preferably, the predetermined time interval T 1  is shorter than the predetermined time interval T 3 . When the elapsed time indicated by the software timer reaches the predetermined time interval T 1 , the program advances from the step S 96  to a step S 97 . Otherwise, the program returns from the step S 96  to the step S 93 . 
     The step S 97  generates a turn-OFF command. The step S 97  transmits the turn-OFF command to the power-supply management portion  4 B. After the step S 97 , the current execution cycle of the BIOS segment ends. 
     The left-hand portion &lt;APPLI/DRIVER/OS&gt; of FIG. 16 is a flowchart of a segment of the OS-driver-based application program for controlling the CPU  1 . The application program segment in FIG. 16 is periodically executed by, for example, an interruption process. As shown in FIG. 16, a first step S 101  of the application program segment decides whether or not a shutting-down-request message is present. The shutting-down-request message is transmitted from the BIOS. When the shutting-down-request message is present, the program advances from the step S 101  to a step S 102 . When the shutting-down-request message is not present, the step S 101  is repeated. 
     The step S 102  decides whether or not a shutting-down process is permitted. When the shutting-down process is permitted, the program advances from the step S 102  to a step S 103 . When the shutting-down process is not permitted, the step S 102  is repeated. 
     The step S 103  informs the BIOS that the shutting-down process is permitted. After the step S 103 , the current execution cycle of the application program segment ends and then the program returns to a main routine. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4 B receives a shutting-down command from the BIOS, the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its shut-down state. 
     During the period of time between the moment of start of the hardware timer and the moment at which the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , when the power-supply management portion  4 B receives a turn-OFF command from the BIOS, the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its OFF state. In addition, the power-supply management portion  4 B resets or stops the hardware timer. 
     In the case where the power-supply management portion  4 B continues to receive neither a shutting-down command nor a turn-OFF command and then the elapsed time indicated by the hardware timer reaches the predetermined time interval T 3 , the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     It is preferable to set the predetermined time intervals T 1  and T 3  as “T 1 &lt;T 3 ”. According to this setting, 2-stage fail-safe can be implemented. In the case where the computer operates normally in its suspended state, when the power-supply management portion  4 B detects that the low power-voltage state lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 B in response to the return information from the OS-driver-based application program. The power-supply management portion  4 B controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shut-down state. When the computer is in its shut-down state, the vehicular battery or the internal battery  6  is hardly discharged excessively. 
     In the case where a hang-up occurs in the application program or the OS, the OS-driver-based application program fails to respond to the shutting-down-request message from the BIOS and does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 B. The power-supply management portion  4 B controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. Accordingly, in this case, the power supply to the computer is forced to be cut off. In the event that a hang-up occurs also in the BIOS, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 B reaches the predetermined time interval T 3 , the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its OFF state. Therefore, also in this case, the power supply to the computer is forced to be cut off. 
     Thus, in the case where the occurrence of a hang-up in the OS, the application program, or the BIOS hinders the computer from falling into its shut-down state when the low power-voltage state continues to be detected for at least one second, the power supply to the computer is forced to be cut off. Accordingly, it is possible to prevent the vehicular battery or the internal battery  6  from being excessively discharged. 
     With reference to FIG. 17, in the case where the computer operates normally in its suspended state, when the power-supply management portion  4 B detects that the low “+B” line voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 B in response to the return information from the OS-driver-based application program. The power-supply management portion  4 B controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shut-down state. 
     With reference to FIG. 18, when the power-supply management portion  4 B detects that the low “+B” line voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 B. The power-supply management portion  4 B controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 19, when the power-supply management portion  4 B detects that the low “+B” line voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. Furthermore, it is assumed that a hang-up occurs in the BIOS. Accordingly, the BIOS does not transmit the turn-OFF command to the power-supply management portion  4 B even when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 . In this case, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 B reaches the predetermined time interval T 3 , the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its OFF state. 
     With reference to FIG. 20, in the case where the computer operates normally, when the power-supply management portion  4 B detects that the low internal-battery voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. Then, the OS-driver-based application program returns the information to the BIOS which indicates that the shutting-down process is permitted. The BIOS transmits the shutting-down command to the power-supply management portion  4 B in response to the return information from the OS-driver-based application program. The power-supply management portion  4 B controls the power-supply controller  5  in response to the shutting-down command, and thereby changes the computer to its shutdown state. 
     With reference to FIG. 21, when the power-supply management portion  4 B detects that the low internal-battery voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. In this case, when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 , the BIOS transmits the turn-OFF command to the power-supply management portion  4 B. The power-supply management portion  4 B controls the power-supply controller  5  in response to the turn-OFF command, and thereby changes the computer to its OFF state. 
     With reference to FIG. 22, when the power-supply management portion  4 B detects that the low internal-battery voltage lasts for at least one second, the power-supply management program controls the power-supply controller  5  and thereby changes the computer to its ON state. In addition, the power-supply management program informs the BIOS of the low power-voltage state and the BIOS transmits the shutting-down-request message to the OS-driver-based application program. It is assumed that a hang-up occurs in the application program or the driver, and hence the OS-driver-based application program does not return the information to the BIOS which indicates that the shutting-down process is permitted. Furthermore, it is assumed that a hang-up occurs in the BIOS. Accordingly, the BIOS does not transmit the turn-OFF command to the power-supply management portion  4 B even when the elapsed time indicated by the software timer in the BIOS reaches the predetermined time interval T 1 . In this case, when the elapsed time indicated by the hardware timer in the power-supply management portion  4 B reaches the predetermined time interval T 3 , the power-supply management portion  4 B controls the power-supply controller  5  and thereby changes the computer to its OFF state.