JPH06149417A - Cpu reset device - Google Patents

Abstract

PURPOSE:To reduce current consumption just after the reduction of a power supply voltage by immediately stopping the operation of a CPU after data are saved, detecting the power supply voltage when it recovers a specified value before the lapse of prescribed time, generating an interruption signal and returning the CPU to the normal operation. CONSTITUTION:An edge detection circuit 4 for detecting the edge of a voltage detection signal (b) is added and when a voltage drop is caused and recovered, an interruption signal (d) is generated. Namely, each time the falling edge and rising edge of the voltage detection signal (b) are respectively detected, the edge detection circuit 4 outputs the pulse of a prescribed short time width. Thus, a CPU 3 stops the operation and turns to a low current consumption state after processing such as saving data in an internal register corresponding to the falling edge of the interruption signal (d) at the time of voltage drop occurrence and when the voltage drop is recovered in a short time and a CPU reset signal is not generated, the CPU 3 is returned to the operating state with the fall edge of the interruption signal (d) at the time of this power supply voltage recovery.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for resetting a CPU that controls an electronic watt-hour meter or the like when the power supply is lost, and particularly to reduce the current consumption of the CPU immediately after the power supply voltage drops at the time of a power supply interruption. The present invention relates to a CPU reset device which prevents loss of continuity of processing due to occurrence of CPU reset as much as possible.

In the following figures, the same reference numerals indicate the same or corresponding parts.

[0003]

2. Description of the Related Art Conventionally, a circuit for multiplying an AC voltage by an AC current and converting it into a pulse train proportional to power, and controlling such as counting the pulses and displaying the amount of power, maximum demand power, etc. on a liquid crystal are performed. There is known an electronic watt-hour meter including a CPU that performs a liquid crystal display with a battery backup even when the AC power supply is interrupted, and a peripheral circuit thereof.

FIG. 3 shows a configuration example of a conventional reset circuit of a CPU of this kind of electronic watt-hour meter, and FIG. 4 shows operation waveforms of respective parts in FIG. In FIG. 3, 3 is a CPU, 1 is a voltage detection circuit that monitors the voltage a of the DC power supply of this circuit, and outputs an L level voltage detection signal b when this voltage a falls below a specified value. Delay signal b, CP
It is a CR delay circuit which is given to U3 as a CPU reset signal c.

Next, the operation of FIG. 3 will be described with reference to FIG. That is, in FIG. 3, the power supply voltage a is monitored and the voltage detection signal b of the voltage detection circuit 1 for detecting a voltage drop is directly C
The voltage detection signal b is given to the PU 3 as an interrupt signal, and the voltage detection signal b is delayed by the CR delay circuit 2 to be given to the CPU 3 as a CPU reset signal c. Voltage detection signal b
Is at "L" level when the power supply voltage a is below the specified value, and is at "H" level when it is above the specified value. The interrupt signal b is valid only at the falling edge. When the voltage drops, this interrupt signal b becomes CP
It is input prior to the generation of the U reset signal c, and the CPU 3
Is a CPU reset signal input (that is, the signal c becomes effective level) after processing such as data saving of the internal register
The loop process is executed at one place while monitoring the interrupt signal b up to. When the voltage drop recovers in a short time as shown in FIG. 4 and the CPU reset signal c is not generated,
When the interrupt signal b is released, the process before the voltage drop occurs is returned to.

[0006]

However, in the case of the circuit of FIG. 3, since the CPU 3 continues to operate as shown in FIG. 4A after the generation of the "L" interrupt signal b, the operation shown in FIG. Its current consumption does not decrease, so the power supply voltage a
Is accelerated and the CPU reset signal is easily generated. If the CPU reset signal is generated, the continuity of the process is lost. Originally, the reset signal generation circuit of FIG. 3 is a circuit provided mainly for coping with the battery voltage drop at the time of battery backup, and originally such generation of the CPU reset signal is not preferable for continuing the processing. Therefore, an object of the present invention is to provide a CPU reset device that solves this problem and can reduce current consumption immediately after the power supply voltage drops.

[0007]

In order to solve the above problems, a reset device according to a first aspect of the present invention detects that a voltage (a, etc.) of a backup power supply is below a specified value, and
Generates an interrupt signal (such as a voltage detection signal b) of the CPU, and supplies the interrupt signal to a CPU (3 or the like) operating on the power source to save necessary data, and When the falling state has passed a predetermined time (such as the time constant of the CR delay circuit 2) (due to the CPU reset signal c, etc.)
In the CPU reset device for resetting the CPU, immediately after the data is saved, the operation of the CPU is stopped, and when the power supply voltage recovers the specified value before the elapse of the predetermined time, this recovery is detected. Generates a second interrupt signal (d, etc.) and sends this interrupt signal to the CPU.
To allow the CPU to return to normal operation.

Further, in the CPU reset device of claim 2,
The CPU reset device according to claim 1, wherein a means (a voltage detection circuit 1 and the like) for inverting a binary signal at a time point when the power supply voltage is below and above the specified value, and for each inversion of the binary signal. And a means for generating a pulse which becomes the first and second interrupt signals (edge detection circuit 4 etc.).

According to the CPU reset device of claim 3,
The CPU reset device according to claim 1 or 2, wherein the CPU controls an electronic watt hour meter.

[0010]

When the voltage drop of the voltage detection signal b is detected (at the falling edge) and when the voltage recovery is detected (at the rising edge), an interrupt signal is generated through the edge detection circuit 4, and the former interrupt signal is used to send data to the CPU 3. Immediately after evacuation, etc., CPU
The operation of No. 3 is stopped to reduce the current consumption, and the latter interrupt signal causes the CPU 3 to return to the normal operation.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a CPU reset circuit as an embodiment of the present invention and corresponds to FIG. Further, FIG. 2 shows operation waveforms of each part of FIG. In FIG. 1, the voltage detection signal b
Is given to the CPU 3 as an interrupt signal d via the edge detection circuit 4. Here, the edge detection circuit 4 detects the falling edge and the rising edge of the voltage detection signal b as shown by the interrupt signal d in FIG.
Output level pulse.

As described above, in the present invention, the circuit 4 for detecting the edge of the voltage detection signal b is added to make the falling edge of the interrupt signal d both at the time of occurrence of voltage drop and at the time of recovery. As a result, at the falling edge of the interrupt signal d when a voltage drop occurs, the CPU
After processing such as data saving in the internal register 3, the operation 3 is stopped and brought into a low current consumption state as shown in FIG. When the voltage drop is recovered in a short time and the CPU reset signal is not generated, the CPU 3 returns to the operating state at the falling edge of the interrupt signal d when the power supply voltage is recovered.

[0013]

According to the present invention, an interrupt signal is generated via the edge detection circuit 4 at the time of detecting the voltage drop of the voltage detection signal b (at the time of falling) and at the time of the voltage recovery detection (at the time of rising). Since the CPU 3 is caused to save data etc. by the interrupt signal of No. 3, the operation of the CPU 3 is immediately stopped to reduce the current consumption, and the latter interrupt signal is used to restore the CPU 3 to the normal operation. It can be completed in a short time and the processing can be continued.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a main part configuration as one embodiment of the present invention.

FIG. 2 is an operation waveform diagram of each part in FIG.

FIG. 3 is a conventional circuit diagram corresponding to FIG.

FIG. 4 is an operation waveform diagram of each part of FIG.

[Explanation of symbols]

 1 voltage detection circuit 2 CR delay circuit 3 CPU 4 edge detection circuit a power supply voltage b voltage detection signal c CPU reset signal d interrupt signal

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Claims (3)

[Claims] 1. A first interrupt signal is generated by detecting that the voltage of a backup power supply falls below a specified value, and the CPU operating on the power supply is provided with this interrupt signal to save necessary data. And resets the CPU when a predetermined time has passed while the power supply voltage is below the specified value C
In the PU reset device, when the CPU operation is immediately stopped after the data is saved and the power supply voltage has recovered to the specified value before the elapse of the predetermined time, this recovery is detected and a second interrupt is detected. CP for generating an interrupt signal and giving the interrupt signal to the CPU to restore the normal operation of the CPU.
U reset device. 2. The CPU reset device according to claim 1,
Means for inverting the binary signal at the time when the power supply voltage falls below and above the specified value, and means for generating a pulse that becomes the first and second interrupt signals at each inversion of the binary signal. A CPU reset device comprising: 3. The CPU reset device according to claim 1 or 2, wherein the CPU controls an electronic watt hour meter.