JP2001157361A - Circuit device and method of data management - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problems that a large-sized charging and discharging capacitor is needed because it takes much time to detect the voltage of a battery line and processing time is added after detection of a voltage drop, power voltage is maintained during it for preventing reset, the cost of a power supply is high because a low-drop constant-voltage power supply is used, and the time of low voltage is longer, especially in consideration of a possible drop in battery performance at low temperature. SOLUTION: This circuit device is formed out of a first voltage monitoring means 24 for comparing the output voltage of a constant-voltage power supply 7 supplying power to a control circuit 10 and other circuits with guaranteed operation voltage and producing a trigger signal if the output voltage becomes lower than the guaranteed operation voltage, and a second voltage monitoring means 25 for comparing the output voltage of the constant-voltage power supply with operation lower-limit voltage and producing a reset signal if the output voltage becomes lower than the operation lower-limit voltage. The control circuit is provided with an interrupt circuit 14 handling an interrupt on receiving the trigger signal and a processing executing circuit 17 conducting resetting upon receiving the reset signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit device provided with a constant voltage power supply such as a vehicle-mounted data processing device, for example, a control circuit for a meter.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a meter control circuit as a conventional circuit device.
Reference numeral 1 denotes a circuit device, which is a power supply terminal O of the circuit device 101.
A battery (power supply) 102 is connected between 1 and O2, and various sensors 103 such as a vehicle speed sensor, an engine rotation sensor, a fuel remaining amount sensor, and a water temperature sensor are connected to the signal input terminal P. 104 is a starter motor, 105 is an actuator such as a door lock, etc. These are connected to the battery 102 via an ignition (IG) switch 106.

A constant-voltage power supply 107 receives a battery voltage via a backflow prevention diode 108, converts the battery voltage to a constant voltage of, for example, 5 V, and outputs the constant voltage. The charge / discharge capacitors C1 and C2 are connected to the input and output sides. I have. Reference numeral 109 denotes a power supply terminal O1, O2, a signal input terminal P, and a control circuit 110.
An interface circuit 111 is provided between the control circuit 110 and an output side of the constant voltage power supply 107. The control circuit 110 includes an oscillator 112, a memory 113 storing information used by the control circuit during a control operation, an external noise avoidance processing unit 110a, a CPU 114 as a processing execution circuit for inputting a signal from these and executing processing, a movement It has a drive circuit 115, an LCD controller 116, and an LCD drive circuit 117.

The movement drive circuit 115 is a CPU 11
The LCD drive circuit 117 drives the crossed coil movement of the speedometer 118 in response to the output of the CPU 4 and receives the output from the CPU 114 via the LCD controller 116.
An indicator 119 such as an od / trip meter for displaying the traveling distance or a clock for displaying the time is driven. The control circuit 110 and the memory 113 may be implemented by a microcomputer (hereinafter, referred to as a microcomputer). In this case, the reset circuit 111 includes a watchdog reset circuit in addition to a power-on reset.

Next, the operation will be described. Constant voltage power supply 1
Reference numeral 07 converts the battery voltage to a constant voltage (5 V in the illustrated example), and supplies the constant voltage to the CPU 114 and other circuits (not shown) supplied to the reset circuit 111. When the ignition switch 106 is in the IGN ON position, the CPU 11
Reference numeral 4 denotes a signal input to the signal input terminal P, which is input through the interface circuit 109, processes the input signal, stores the result in the memory 113, and displays the time, mileage, and the like at that time. 119 is displayed.

In this state, the ignition switch 106 is turned on to the starter position and the starter motor 10
4. When a load such as the actuator 105 is connected to the battery 102, as shown in FIG.
The voltage supplied to the battery 2 varies from 14 V to 3 to 4 V, for example, and the current consumption of the movement is 120 m
A, the voltage output from the constant voltage power supply 107 also drops, and the CPU 114 malfunctions or
CD display is wrong, movement is wrong,
Inconveniences such as loss of data stored in the memory 113 occur.

Therefore, the voltage of the battery line is monitored by the voltage detecting means 109a (see FIG. 8) provided in the interface circuit 109, and when the voltage drop is detected, the CPU 114 prevents the voltage drop of the constant voltage power supply 107 and prevents the memory voltage from being reduced. In order to prevent data loss and display malfunction, restrict the operation of the CPU 114 after the data backup, the operation of the display OFF processing movement, etc. Mode).

[0008]

Since the conventional circuit device is configured as described above, for example, when it is detected that the power supply voltage has dropped to 3 to 4 V or less due to cracking and a low voltage state has been detected, With the backup capacitor,
A large backup capacitor is required to drive the IC in the normal mode and perform processing associated with a drop in power supply voltage, such as data backup and display OFF processing.

The detection of the voltage drop is performed by the voltage detecting means 10.
9a, the power supply voltage is directly detected, so that it is easily affected by the external environment. For example, it takes time to detect the voltage of the battery line due to processing time such as avoidance of extraneous noise. Is added, it is necessary to maintain the power supply voltage during that time and prevent resetting. In particular, a clock, a trip meter, and the like reset the drive voltage, that is, the data stored in the memory 113 when the output voltage of the constant-voltage power supply decreases.
Need to backup. For this reason, it is necessary to increase the size of the backup charge / discharge capacitors C1 and C2 of the constant voltage power supply.

Further, a margin U at the time of a battery voltage drop
For P, it is necessary to use a low-drop type low voltage loss constant voltage power supply, which increases the cost of the power supply. In particular, considering the case where the battery performance is lowered at a low temperature, the time of low voltage is also prolonged, which leads to an increase in the size of the charge and discharge capacitors C1 and C2. That is, at low temperatures, the battery voltage decreases and the capacitor capacity also decreases. further,
Since the coil resistance of the starter motor and the like is reduced, the battery voltage is also greatly reduced. Therefore, there is a problem that it is necessary to increase the charge and discharge capacitors C1 and C2 in anticipation thereof.

The present invention has been made in order to solve such a conventional problem, and does not require resetting of data stored in the memory 113 at a voltage drop of about cranking, thereby reducing power consumption. It is an object of the present invention to obtain a circuit device which does not require a low-drop power supply and has small charge / discharge capacitors C1 and C2.

[0012]

A circuit device according to the present invention includes a control circuit for processing various types of input information, a memory for storing information used by the control circuit during control operations, and a constant voltage input voltage. A constant-voltage power supply for supplying power to the control circuit and other circuits, and comparing an output voltage of the constant-voltage power supply with an arbitrary first set voltage within an operable voltage range of the control circuit; A first voltage monitoring means for generating a trigger signal when the voltage becomes lower than a voltage, and an output voltage of the constant voltage power supply being an arbitrary voltage between the first set voltage and a lower limit voltage capable of holding data stored in the memory. A second voltage monitoring means for generating a reset signal when the output voltage becomes lower than the second set voltage as compared with a second set voltage, the control circuit comprising: Receiving and interrupting An interrupt circuit for executing processing, and executes the process according to the interrupt command from the interrupt circuit, in which a processing execution circuit for executing a reset process receiving said reset signal.

A circuit device according to the present invention includes a latch circuit which is set in response to a reset signal and stores that the output voltage of the constant voltage power supply has become equal to or lower than a second set voltage.

The circuit device according to the present invention includes a reset release delay circuit that outputs a reset release signal to the processing execution circuit a predetermined time after the extinction of the trigger signal due to the return of the output voltage of the constant voltage power supply.

The circuit device according to the present invention compares the output voltages of the constant voltage power supplies with different first set voltages, and generates a trigger signal when the output voltage becomes lower than the first set voltage. It is provided with a plurality of first voltage monitoring means for separately supplying trigger signals to the interrupt circuit.

In the circuit device according to the present invention, the interrupt circuit has a memory for storing or determining which first voltage monitoring means the supplied trigger signal is from.

The circuit device according to the present invention supplies power from an auxiliary power supply when the output of a constant voltage circuit that supplies power to an instrument having data that needs to be held falls below a prescribed value, and the output of the constant voltage circuit is When the voltage becomes equal to or lower than a first set voltage equal to or lower than a specified value, the function of the meter is partially stopped, the data is backed up, and the output of the constant voltage circuit is lower than the first set voltage. When the voltage falls below the second set voltage, the data is reset, and when the output of the constant voltage circuit returns to the predetermined value or more,
The backup data is supplied to the meter and displayed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing a meter control circuit as a circuit device according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a circuit device, and a circuit device 1 has a power supply terminal O1, O2. A battery (power supply) 2 is connected, and various sensors 3 such as a vehicle speed sensor, an engine rotation sensor, a fuel remaining amount sensor, and a water temperature sensor are connected to a signal input terminal P.
Is connected. Reference numeral 4 denotes a starter motor, and reference numeral 5 denotes an actuator such as a door lock, which are connected to the battery 2 via an ignition switch 6.

Reference numeral 7 denotes a backflow prevention diode for reducing the battery voltage.
And a constant voltage power supply that converts the voltage to a constant voltage of, for example, 5 V and outputs the constant voltage.
1 and C2 are connected. Reference numeral 9 denotes an interface circuit provided between the power supply terminal O2 and the signal input terminal P and the control circuit 10. The control circuit 10 includes an oscillator 12, a memory 13 for storing processing data, an interrupt circuit 14, a one-shot circuit 15, an OR circuit 16, a CPU 17 as a processing execution circuit for executing processing based on these signals, a movement drive circuit 18, a CPU 17 LCD drive circuit 20 for inputting the output of FIG.

The movement drive circuit 18 receives the output of the CPU 17 and drives a speedometer 21 and a cross coil movement of an engine tachometer, fuel gauge, and water temperature gauge (not shown). LCD drive circuit 20 outputs the output from CPU 17 to LC
The display unit 22 receives an instruction via the D controller 19 and drives a display 22 such as an od / trip meter for displaying a traveling distance or a clock for displaying time.

Reference numeral 23 denotes an operation mode control circuit connected between the constant voltage power supply 7 and the control circuit 10. The operation mode control circuit 23 controls the output voltage of the constant voltage power supply 7 within the operable voltage range (operation guarantee voltage) of the control circuit. Is compared with an arbitrary set voltage Vref2 (for example, 4.5 V) (first set voltage).
And a comparator 24 (first voltage monitoring means) for generating a trigger signal when the output voltage of the comparator becomes lower than an arbitrary set voltage Vref2 within the operable voltage range (operation guarantee voltage).
The output voltage of the constant voltage power supply 7 is set to an arbitrary set voltage Vref1 (an arbitrary set voltage Vref2 between an arbitrary set voltage Vref2 within the operable voltage range (operation assurance voltage) and an operation lower limit voltage capable of holding data stored in the memory 13). For example, about 2 V) (second
The comparator 25 (second voltage monitoring means) that generates a reset signal when the output voltage of the constant voltage power supply 7 becomes lower than the arbitrary set voltage Vref1 (second set voltage). And a latch circuit 26 for holding that the reset signal is generated from the comparator 25. The trigger signal is sent to the interrupt circuit 14 and the one-shot circuit 15, and the reset signal is sent to the OR circuit 16.
Is supplied to

The CPU 17, the memory 13, the movement drive circuit 18, the LCD controller 19, and the LCD drive circuit 20 may be implemented by a microcomputer.

Next, the operation will be described. Constant voltage power supply 7
Converts the battery voltage into a constant voltage (5 V in the illustrated example), and supplies the constant voltage to the operation mode control circuit 23, the control circuit 10, and each circuit (not shown). When the ignition switch 6 is in the IGN ON position, the CPU 17 inputs the signal input to the signal input terminal P via the interface circuit 9, processes the input signal, and stores the result in the memory 13.
And the time and traveling distance at that time are displayed on the display 22. The operation so far is the same as that of the conventional device shown in FIG.

In this state, when the ignition switch 6 is turned on to the starter position and loads such as the starter motor 4 and the actuator 5 are connected to the battery 2, power is supplied to the power supply terminals O1 and O2 as shown in FIG. The battery voltage fluctuates and drops. Therefore, the constant voltage power supply 7
The output voltage from the power supply also decreases, for example, as shown in FIG.
, The trigger signal S1 is generated in the comparator 24. At the falling edge of the trigger signal S1, the interrupt circuit 14 operates to give an interrupt instruction to the CPU 17 and release the reset of the latch circuit 26. The CPU 17 performs the following processing according to the instruction.

Data backup processing (memory is not rewritten even if microcomputer accesses memory 13 erroneously, memory disable processing). Turn OFF the display 22. Drive output OFF processing for the speedometer 21 and other engine tachometers, fuel gauges, and water temperature gauges. Sleep processing of the control circuit 10. When the trigger signal S1 is output, that is, when the output voltage of the constant-voltage power supply is instantaneously dropped, the voltage is further reduced without resetting. Performs pre-processing for keeping the power supply for a minimum necessary time (for example, several hundred ms). That is, in order to minimize the current consumption, the operation of the circuit element consuming the current is stopped, and the operation of the CPU 17 itself is stopped or the state is shifted to the current saving mode.

Next, the output voltage of the constant voltage power supply is 4.5V.
When the trigger signal S1 returns to a value larger than 4.5 V from the following, the trigger signal S1 is inverted at 4.5 V to generate a rising edge. Therefore, the one-shot circuit 15 receiving this rising edge generates a pulse of several tens of ms, for example. . This pulse becomes a reset signal of the CPU 17 via the OR circuit 16. Therefore, this one-shot circuit 15 has a role of a reset release delay circuit for stabilizing oscillation at power-on. Further, the latch circuit 26 is reset in response to the S1 "H" level, and the Q output becomes "L".

As shown in FIG. 3, when the output voltage of the constant voltage power supply 7 drops to 2 V or less, a trigger signal S1 is first generated in the comparator 24 in the course of the voltage drop.
At the falling edge of the trigger signal S1, the interrupt circuit 14 operates to perform the above-described interrupt processing. Thereafter, a reset signal is generated in the comparator 25 by the voltage drop below 2 V, and the reset signal
Is held in a set state, and this reset signal is supplied to the OR circuit 1
6 to the CPU 17.

Then, a reset process (hardware reset, reset of the entire circuit) is performed by the CPU 17 using the charging voltage of the charging / discharging capacitor C2 as a power supply voltage. In other words, if the voltage is lower than the voltage at which data cannot be logically held even when the power is held, the state is regulated by reset (the unstable voltage region for memory holding is eliminated).

When the output voltage of the constant voltage power supply 7 returns from 2 V or less to 4.5 V or more, the reset signal from the comparator 25 and the trigger signal S1 from the comparator 24 disappear, and the rising edge of the trigger signal S1 occurs. Then
One-shot circuit 15 receiving this rising edge
Generates a pulse of several tens of ms, for example. This pulse is supplied to the CPU 17 via the OR circuit 16 as a reset signal. The reset state of the CPU 17 continues from an internal reset generation state by the reset signal Q to an internal reset release by a pulse of the one-shot circuit (power-on reset state: FIG. 4 is a timing chart for explaining the operation at this time. ).

The one-shot circuit 15 delays the reset release timing of the CPU 17 by the output pulse,
It has a role of a reset release delay circuit for stabilizing the circuit operation when the power supply rises.

According to the first embodiment, the reset signal is not output when the voltage drops by about the cranking. Data backup and display OFF processing are performed by the trigger signal S1 from the comparator 24. b. Set the control circuit to the low power consumption mode. In the case of a microcomputer, the mode shifts from the normal mode to the slow mode, the standby mode, or the stop mode.

Then, when the output voltage of the constant voltage power supply 7 becomes 2 V or less (operating lower limit voltage of the control circuit, memory storable voltage), a reset signal is output for the first time. At this time,
Since the backup and display OFF processing have already been completed, at least the capacity of the backup capacitor can be reduced.

Further, since the output voltage of the constant voltage power supply is monitored, it is hardly affected by the external environment. A process for avoiding external noise and the like is not necessary, and chattering avoidance (several tens of milliseconds) which has been conventionally performed is unnecessary, and an IC including a reset circuit capable of reducing the capacity of a backup capacitor can be realized. It can be integrated into a circuit and the circuit configuration can be simplified.

Embodiment 2 FIG. 5 is a block diagram showing a main part of a meter control circuit as a circuit device according to a second embodiment of the present invention. The same parts as those in the first embodiment shown in FIG. Description is omitted. In FIG. 5, reference numerals 24a to 24n compare an arbitrary set voltage within a different operable voltage range (operation guarantee voltage) with the output voltage of the constant voltage power supply 7 as a comparison voltage, and the output voltage is within the operable voltage range. This is a comparator (first voltage monitoring means) that generates a trigger signal when the voltage becomes lower than an arbitrary set voltage. The trigger signals from the comparators 24a to 24n are supplied to the interrupt circuit 14 independently and separately.
Reference numeral 14a denotes a memory provided in the interrupt circuit 14, which stores which comparator the supplied trigger signal is from.

Next, the operation will be described. Since the entire operation is the same as that of the first embodiment shown in FIG. 1, different points will be described. A state in which the output voltage of the constant voltage power supply 7 changes within the range of the operation guarantee voltage is detected by a plurality of comparators 24a to 24n having different comparison voltages. Now, when the output voltage of the constant voltage power supply 7 drops to 4.5 V or less, a trigger signal is supplied from the comparator 24a to the interrupt circuit 14. The interrupt circuit 14 determines that the supplied trigger signal is output from the comparator 24a, and gives an interrupt instruction corresponding to the trigger signal to the CPU 17. C
Based on this instruction, the PU 17 executes the movement driving circuit 1
The process of step 8 is interrupted, and the speedometer 21 is stopped.

Further, when the output voltage of the constant voltage power supply 7 continues to drop and becomes 3.5 V or less, a trigger signal is also output from the comparator 24n and supplied to the interrupt circuit 14. The interrupt circuit 14 outputs the trigger signal to the comparator 24.
n is output, and an interrupt instruction corresponding to the trigger signal is given to the CPU 17. Based on this instruction, the CPU 17 sets the movement drive circuit 18 and L
The processing of the CD controller 19 and the LCD drive circuit 20 is interrupted, the speedometer 21 and the display 22 are stopped, the current consumption is reduced, and the voltage drop is suppressed. When power is supplied to an external sensor 30 such as a vehicle speed sensor, for example, C
The power supply to the external sensor 30 can be controlled by controlling the switching circuit 31 based on the output of the PU 17.

At the time of the above-described arithmetic processing, the interrupt circuit 14 can determine to which extent the output voltage of the constant voltage power supply 7 has dropped by judging which comparator is the trigger signal. Therefore, this is stored in the memory 14a.
At the start of the process based on the voltage return, only necessary processes are performed based on the stored contents.

According to the second embodiment, the constant voltage power supply 7
The state in which the output voltage changes within the guaranteed operating voltage range
Since the detection is performed in a plurality of stages by the plurality of comparators 24a to 24n having different comparison voltages, it is possible to perform processing management suitable for the change state of the voltage. In addition, by storing the voltage change state in the memory 13 or the like, it is possible to appropriately perform processing management at the time of voltage return.

[0039]

As described above, according to the present invention, the output voltage of the constant voltage power supply for supplying power to the control circuit and other circuits is set to an arbitrary first set voltage within the operable voltage range of the control circuit. A first voltage monitoring means for generating a trigger signal when the output voltage becomes lower than the operation assurance voltage, and capable of holding the output voltage of the constant voltage power supply as the first set voltage and the data stored in the memory. A second voltage monitoring means for generating a reset signal when the output voltage becomes lower than the second set voltage as compared with an arbitrary second set voltage between the second set voltage and the control circuit; An interrupt circuit that executes an interrupt process in response to the trigger signal, and a process execution circuit that executes a process in accordance with an interrupt command from the interrupt circuit and performs a reset process in response to the reset signal. Since it is configured as obtain, in the voltage drop of about cranking, without outputting a reset signal, it is possible to perform an operation restricted by interrupt processing. As a result, even if the output voltage of the constant-voltage power supply has large fluctuations, malfunction of the circuit and downsizing of the charge / discharge capacitor can be realized, and each circuit element can be simplified. Further, there is an effect that loss of data stored in the memory can be prevented even in a long-term low voltage state of the output voltage of the constant voltage power supply.

According to the present invention, the control circuit is provided with the latch circuit which is set in response to the reset signal and stores the fact that the output voltage of the constant voltage power supply becomes equal to or lower than the second set voltage. There is an effect that regulation of the mode and regulation of the reset state can be stably performed.

According to the present invention, the processing execution circuit is provided with the reset release delay circuit for generating the reset release signal after a predetermined time from the extinction of the trigger signal due to the return of the output voltage of the constant voltage power supply. This has the effect of stabilizing the circuit operation and enabling the stable operation of the control circuit.

According to the present invention, the state in which the output voltage of the constant voltage power supply changes within the range of the first set voltage is detected in a plurality of stages by a plurality of comparators having different reference voltages. With the configuration, there is an effect that processing management suitable for the voltage change state can be performed.

According to the present invention, the state in which the output voltage of the constant voltage power supply changes within the range of the first set voltage is detected in a plurality of stages by a plurality of comparators having different reference voltages, and is detected. Since the voltage change state is configured to be stored, at the time of voltage recovery, there is an effect that processing management can be appropriately performed by reading and using the stored content.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a meter control circuit as a circuit device according to a first embodiment of the present invention.

FIG. 2 is a timing chart for explaining an operation when an output voltage of a constant voltage power supply falls below an operation guarantee voltage.

FIG. 3 is a timing chart for explaining an operation when an output voltage of a constant voltage power supply falls below an operation lower limit voltage.

FIG. 4 is a timing chart for explaining an operation at the time of a power-on reset.

FIG. 5 is a block diagram showing a main part of a meter control circuit as a circuit device according to a second embodiment of the present invention.

FIG. 6 is a block diagram showing a meter control circuit as a conventional circuit device.

FIG. 7 is a diagram illustrating a change in battery voltage.

FIG. 8 is a specific circuit configuration diagram of the voltage detection means.

[Explanation of symbols]

 O1, O2 Power supply terminal 1 Circuit device 2 Battery (power supply) 3 Various sensors 4 Starter motor 5 Actuator such as door lock 6 Ignition switch 7 Constant voltage power supply 8 Backflow prevention diode 9 Interface circuit 10 Control circuit 12 Oscillator 13 Memory 14 Interrupt circuit 14a memory 15 one-shot circuit 16 OR circuit 17 CPU (processing execution circuit) 18 movement drive circuit 19 LCD controller 20 LCD drive circuit 21 speedometer 22 display 23 operation mode control circuit 24, 24a to 24n comparator (first voltage) Monitoring means) 25 comparator (second voltage monitoring means) 26 latch circuit

Claims (6)

[Claims] 1. A control circuit for processing various types of input information, a memory storing information used by the control circuit during a control operation, and a constant voltage for converting an input voltage to a constant voltage and supplying power to the control circuit and other circuits. A power supply, and comparing the output voltage of the constant voltage power supply with an arbitrary first set voltage within an operable voltage range of the control circuit, and generating a trigger signal when the output voltage becomes lower than the set voltage. Voltage monitoring means, and compares the output voltage of the constant voltage power supply with an arbitrary second set voltage between the first set voltage and a lower limit voltage capable of holding stored data in the memory. And a second voltage monitoring means for generating a reset signal when the voltage becomes lower than a second set voltage, wherein the control circuit receives the trigger signal and executes an interrupt process; and of A circuit device comprising: a process execution circuit that executes a process according to an interrupt command and performs a reset process in response to the reset signal. 2. The circuit device according to claim 1, further comprising a latch circuit which is set in response to the reset signal and stores the fact that the output voltage of the constant voltage power supply has become equal to or lower than the second set voltage. 3. A reset release delay circuit for outputting a reset release signal to a processing execution circuit a predetermined time after a trigger signal disappears due to return of an output voltage of a constant voltage power supply.
The circuit device as described. 4. An output voltage of a constant voltage power supply is compared with different first set voltages, and a trigger signal is generated when the output voltage becomes lower than the first set voltage. 2. The circuit device according to claim 1, further comprising a plurality of first voltage monitoring means for supplying the first voltage monitoring means to the interruption circuit. 5. The circuit device according to claim 4, wherein the interrupt circuit includes a memory for storing or determining which of the first voltage monitoring means the supplied trigger signal is from. 6. An auxiliary power supply supplies power from an auxiliary power supply when an output of a constant voltage circuit that supplies power to an instrument having data that needs to be held falls below a specified value. When the voltage falls below the set voltage, the function of the meter is partially stopped and the data is backed up. The output of the constant voltage circuit is lower than the second set voltage lower than the first set voltage. Resetting the data, and when the output of the constant voltage circuit returns to the specified value or more, supplying the backed-up data to the meter for display. .