JPH11119870A - Power source voltage detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the battery exchange of a portable electronic appliance surer. SOLUTION: When the power source voltage drops down to a first voltage, the output of a first detection circuit 1 changes from logical value '0' to logical value '1', an interruption processing circuit 5 is supplied with a set signal of logical value '1' of a first flag circuit 3 and executes an interruption processing for an alarm of battery exchange. Moreover, when the power source voltage lowers down to the second voltage, an output of the second detection circuit 2 changes from logical value '0' to logical value '1' and the interruption processing circuit 5 is supplied with the set signal of logical value '1' of a second flag circuit 4 and executes the interruption processing for bringing a microcomputer in to a hold mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply voltage detection circuit suitable for monitoring the consumption of a battery mounted on a portable electronic device or the like.

[0002]

2. Description of the Related Art A portable electronic device (video camera, still camera, etc.) uses a battery as a power supply, and therefore, monitors a falling state of a power supply voltage. A function to monitor whether the voltage is within the guaranteed voltage range must be provided, and measures must be taken to prevent electronic devices from malfunctioning as much as possible. It is not an exaggeration to say that recent electronic devices are configured to execute various operations based on control signals of the microcomputer, and it is no exaggeration to say that the malfunction of the microcomputer is directly related to the malfunction of the electronic device. Is likely to cause Therefore, the microcomputer has a built-in circuit for monitoring a falling state of the power supply voltage, and when detecting a state in which the power supply voltage has dropped to VL near the minimum voltage that guarantees normal operation of the microcomputer, the microcomputer performs the above-described operation. Measures were taken. Specifically, (1) when the power supply voltage drops to VL due to the consumption of the battery, the microcomputer is set to the hold mode (stopping the oscillating operation of the oscillator, stopping the arithmetic processing operation, and holding the data stored in the RAM). By doing so, the time during which the power supply voltage falls to the minimum voltage is extended, and during this time, the user is given an opportunity to replace the battery. (2) The power supply voltage becomes V
When the microcomputer is lowered to L, the microcomputer is set to a halt mode (stopping high-speed operation processing, executing minimum necessary low-speed operation processing, holding RAM stored data while the oscillation operation of the oscillator is continued), A method of outputting a warning signal for prompting battery replacement, and the like have been executed.

[0003]

However, since the methods (1) and (2) detect only one voltage VL near the minimum voltage that guarantees normal operation of the electronic device, there are the following problems. . In the case of the method (1), since the warning to prompt the user to replace the battery is not issued, the user has no way to confirm that the electronic device is about to replace the battery, other than discovering that the key input is prohibited. . Therefore, if the power supply voltage drops to a value lower than the minimum voltage without using the electronic device even though it is time to replace the battery, the data stored in the RAM disappears and the electronic device malfunctions. Yes, not the best solution.

In the case of the method (2), a warning operation for urging battery replacement is added to the halt mode. Therefore, the time during which the power supply voltage falls to the minimum voltage is limited to the time when the power supply voltage reaches the minimum voltage in the normal halt mode. Shorter than the descent time. That is, the warning operation for prompting the battery replacement can be executed only for a short time. Therefore, when the user does not carry the electronic device, or
When the user carries the electronic device but does not use it, the power supply voltage drops to a value lower than the minimum voltage if the warning display or warning sound cannot be confirmed even though the warning operation is being performed. Resulting in. Therefore, similar to (1),
There is a problem that the data stored in the RAM disappears and the electronic device malfunctions, and this is not the best solution.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply voltage detecting circuit which enables a user to more surely confirm the replacement of a battery of a portable electronic device than before.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and detects a state of a power supply voltage of an electronic device which normally operates within a predetermined potential difference range. A power supply voltage detection circuit that detects a first voltage higher than a minimum voltage that guarantees normal operation of the electronic device; and a second detection circuit that detects a second voltage between the first voltage and the minimum voltage. A second detection circuit, a first flag circuit that is set when the first detection circuit detects a state in which the power supply voltage has dropped to the first voltage, and a second detection circuit that determines that the power supply voltage is the second voltage. A second flag circuit which is set when a state of the first flag is detected,
Outputs of the flag circuit and the second flag circuit are supplied;
An interrupt processing circuit that executes an interrupt process according to the state of the first flag circuit in preference to an interrupt process according to the state of the second flag circuit, wherein the power supply voltage has decreased to the first voltage. At this time, by executing an interrupt process according to the state of the first flag circuit, a signal for warning that the power supply voltage has dropped to near the minimum voltage is output.

Further, the power supply voltage detection circuit is integrated inside a microcomputer. When the power supply voltage drops to the second voltage after passing the first voltage, the microcomputer is set to a hold mode by executing an interrupt process according to a state of the second flag circuit. It is characterized by.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a block diagram for explaining a power supply voltage detection circuit according to the present invention. The power supply voltage detection circuit is
It is integrated on the same chip as the microcomputer and monitors whether the power supply voltage of the microcomputer is within a voltage range that guarantees normal operation of the microcomputer.

(1) is a first detection circuit, which detects that the power supply voltage has dropped to a first voltage higher than the minimum voltage that guarantees normal operation of the microcomputer due to the consumption of the battery, and has a logical value "1". Is output. (2) is a second detection circuit, in which the power supply voltage passes the first voltage and the second detection circuit
When detecting that the voltage has dropped to the voltage, a logical value "1" is output. Note that there is a relationship of “first voltage> second voltage> minimum voltage”, where the first voltage is higher than the conventional detection voltage VL, and the second voltage is equivalent to the conventional detection voltage VL.

[0010] (3) is a first flag circuit, to which a logical value "1" output when the first detection circuit (1) detects the first voltage is set. (4) is a second flag circuit, to which a logical value "1" output when the second detection circuit (2) detects the second voltage is set. Of course, if the power supply voltage decreases as the battery is consumed, the first flag circuit (3) is set earlier than the second flag circuit (4). The set signals of the first flag circuit (3) and the second flag circuit (4) function as an interrupt request signal for interrupting the current program processing and executing another program processing. An interrupt processing circuit (5) is supplied with a set signal of the first flag circuit (3) and the second flag circuit (4), and executes an interrupt process corresponding to the set signal of the first flag circuit (3) in the second. This is executed prior to the interrupt processing according to the set signal of the flag circuit (4).

A ROM (6) stores program data for controlling various operations of the microcomputer in advance. ROM (6) has a mask RO
Any of M, EPROM, and EEPROM may be used.
(7) is an instruction register, ROM
The program data read from (6) is set. An instruction decoder (8) decodes program data set in the instruction register (7) and outputs a control signal for executing arithmetic processing. (9) is a program counter for addressing the ROM (6).

When the set signal of the first flag circuit (3) is supplied to the interrupt processing circuit (5), the program counter (9) stores the ROM (6) in which program data for warning of battery replacement of the electronic device is stored. The address value of the program counter (9) is changed so that the address of ()) can be specified. When the set signal of the second flag circuit (4) is supplied to the interrupt processing circuit (5), the program counter (9) stores the program data for setting the microcomputer in the hold mode in the ROM (6). The address value of the program counter (9) is changed so that the address can be specified.

The operation of FIG. 1 will be described below with reference to the flowchart of FIG. When a main program for normally operating a portable electronic device is executed, the power supply voltage gradually decreases as the battery is consumed. When the power supply voltage drops to the first voltage, the detection output of the first detection circuit (1) changes from the logical value “0” to the logical value “1”, and the value of the first flag circuit (3) changes to the logical value “1”. Is set to The interrupt processing circuit (5) outputs the logical value “1” of the first flag circuit (3).
When the set signal of the first flag circuit (3) is supplied, it is determined that the set signal of the first flag circuit (3) is an interrupt request signal for warning of battery replacement, the current address data of the ROM (6) is saved, and the main signal is saved. The execution of the program is interrupted, and the value of the program counter (9) is changed to the address value of the ROM (6) in which the program data for warning of battery replacement is stored. Then, when the address of the ROM (6) is designated and the program data read from the ROM (6) is decoded by the instruction decoder (8), a control signal for warning of battery replacement is output. As a warning method for prompting battery replacement, a method of displaying a warning on a liquid crystal screen provided in the electronic device, a method of generating a warning sound from a speaker provided in the electronic device, and the like can be considered. The remaining battery power when the power supply voltage drops to the first voltage,
Comparing the remaining battery level at the time when the power supply voltage drops to the second voltage (conventional voltage VL), the former has a longer remaining battery level, so that the warning operation is longer while the microcomputer remains in the high-speed arithmetic processing state. It can be executed over time (step 1).

When the battery replacement is performed and a specific key input is made during the warning operation of the battery replacement (YES in step 2), the first flag circuit (3) is set to the logical value "0" according to the specific key input. (Step 3). If the first flag circuit (3) has not been reset, the process returns to step 2 (step 3: NO), but if the first flag circuit (3) has been reset, the interrupt processing for warning of battery replacement is terminated, The saved address data is set in the program counter (9), and the interrupted main program processing is restored (step 3Y).
ES). Since the electronic device has a built-in capacitor for power supply backup, the operation of the microcomputer is guaranteed even during the period when the user removes the battery from the electronic device for battery replacement.

On the other hand, when the battery replacement is not performed during the warning operation of the battery replacement, the determination of the battery replacement is repeated (NO in step 2). When the voltage drops to the second voltage, the detection output of the second detection circuit (2) changes from the logical value “0” to the logical value “1”, and the value of the second flag circuit (4) changes to the logical value “1”. Is set to The interrupt processing circuit (5) outputs the logical value “1” of the second flag circuit (4).
Is supplied, the set signal of the second flag circuit (4) is determined to be an interrupt request signal for setting the microcomputer to the hold mode.
The current address data of the OM (6) is saved, interrupt processing for warning of battery replacement is interrupted, and the program data for setting the microcomputer to the hold mode with the value of the program counter (9) is stored. RO
The address value is changed to M (6). And ROM
When the address in (6) is designated and the program data read from the ROM (6) is decoded by the instruction decoder (8), the microcomputer enters the hold mode and power is saved (step 4). .

In the hold mode, the oscillation operation of the oscillator and the arithmetic processing operation of the CPU are stopped only by holding the data stored in the RAM. However, hold release by a specific key input is in a permitted state. Therefore, after the hold mode is set, it is determined whether or not a specific key input has been made during the time from when the power supply voltage reaches the minimum voltage to the second voltage (step 5). If the key input is permitted (YES in step 5), it is determined that the battery has been replaced, and the second flag circuit (4) is reset to a logical value "0" (step 6). If the second flag circuit (4) has not been reset, the process returns to step 5 (step 6N).
O) If the second flag circuit (4) is reset, the process returns to step 3 to end the interrupt processing for setting the microcomputer to the hold mode and store the saved address data in the program counter (9). The interrupt processing for warning that the battery replacement has been set is executed again (step 6 YES). This is to determine whether the voltage of the battery after replacement is higher or lower than the first voltage.

If the key input is not accepted during the time from when the power supply voltage reaches the minimum voltage to the second voltage after the hold mode is set (step 5: NO),
It is determined that the battery has not been replaced. in this case,
Since the power supply voltage becomes lower than the minimum voltage that guarantees the normal operation of the microcomputer, the electronic device does not operate normally again unless the battery is replaced and the microcomputer is reset (step 7).

As described above, as a method of detecting the falling state of the power supply voltage of the microcomputer, two voltages (first voltage> second voltage) which are close to the lowest voltage within the guaranteed voltage range for normal operation of the microcomputer are selected. When the power supply voltage drops to the first voltage, a warning of battery replacement is issued, and when the power supply voltage drops to the second voltage, the microcomputer is set to the hold mode. In particular, since the warning operation can be executed for a long time in the high-speed arithmetic processing, the possibility that the battery can be replaced while the microcomputer is operating normally increases.

[0019]

According to the present invention, as a method for detecting a falling state of the power supply voltage of the microcomputer, two voltages (first voltage> second voltage) close to the lowest voltage within the guaranteed voltage range of the normal operation of the microcomputer are used. Voltage), a warning is issued to replace the battery when the power supply voltage drops to the first voltage, and the microcomputer is set to the hold mode when the power supply voltage drops to the second voltage. Therefore, since the warning operation can be performed for a long time in the high-speed arithmetic processing, there is a high possibility that the battery can be replaced before the power supply voltage reaches the minimum voltage that guarantees the normal operation of the microcomputer.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining a power supply voltage detection circuit according to the present invention.

FIG. 2 is a flowchart illustrating the operation of FIG. 1;

[Explanation of symbols]

 (1) First detection circuit (2) Second detection circuit (3) First flag circuit (4) Second flag circuit (5) Interrupt processing circuit

Claims (3)

[Claims] 1. A power supply voltage detecting circuit for detecting a state of a power supply voltage of an electronic device that normally operates within a predetermined potential difference range, wherein a first voltage higher than a minimum voltage that guarantees normal operation of the electronic device is provided. A first detection circuit for detecting, a second detection circuit for detecting a second voltage between the first voltage and the lowest voltage, and a state in which the first detection circuit reduces the power supply voltage to the first voltage A first flag circuit that is set when detecting the power supply voltage; a second flag circuit that is set when the second detection circuit detects a state in which the power supply voltage has decreased to the second voltage; An interrupt processing circuit to which an output of the second flag circuit is supplied and which executes an interrupt process according to a state of the first flag circuit in preference to an interrupt process according to a state of the second flag circuit; For example, when the power supply voltage decreases to the first voltage, the first
A power supply voltage detection circuit for outputting a signal for warning that the power supply voltage has dropped to near the minimum voltage by executing an interrupt process according to a state of a flag circuit. 2. The power supply voltage detection circuit according to claim 1, wherein said power supply voltage detection circuit is integrated inside a microcomputer. 3. When the power supply voltage drops to the second voltage after passing the first voltage, the microcomputer executes an interrupt process according to a state of the second flag circuit, thereby holding the microcomputer in a hold mode. 3. The power supply voltage detection circuit according to claim 2, wherein