JPH0453452B2 - - Google Patents

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a reset circuit for equipment using a microcomputer. This invention relates to a circuit for obtaining a long reset signal.

``Prior art'' In devices that use microcomputers, it is important to detect drops, instantaneous interruptions, or loss of power supply voltage and to reliably stop and restart the microcomputer, and a reset circuit is added for this purpose. ing.

FIG. 2 shows an example of a conventional reset circuit, and the conventional system will be explained using this figure. This reset circuit is mainly composed of two elements, a power supply voltage drop detection element 7 and a power supply cutoff detection element 8, and a reset signal is obtained by calculating the logical sum of the outputs of both elements using an OR circuit 6.

The power supply voltage drop detection element 7 includes a voltage dividing circuit 1 that detects the power supply voltage, a reference voltage generation circuit 2 that generates a reference voltage corresponding to the minimum power supply voltage level that guarantees operation of a microcomputer (not shown), and a voltage dividing circuit 1 that detects the power supply voltage. It is composed of a comparator 3 that compares and determines the output. When the power supply voltage drops continuously due to an abnormality in the power supply unit, a reset signal is generated by the output of the comparator 3, and the microcomputer is stopped to prevent malfunction.

In addition, the power failure detection element 8 has a power supply 10 and a ground 1.
The CR integrating circuit 4 is composed of a resistor 41 and a capacitor 42 connected between each other, and a diode 12. When the power is turned on, a reset signal with a constant pulse length determined by the time constant of the CR integration circuit 4 is obtained, and when the power is turned off, the charge in the capacitor 42 is rapidly discharged by the diode 12 connected to the power supply 10, thereby reducing the power supply voltage. The configuration is such that a reset signal with a constant pulse length can be obtained even in the event of a momentary power outage.

FIGS. 3a, b, and c show waveforms of various parts of the conventional circuit with time t plotted on the horizontal axis. From T1 to T in Figure 3a
2, if a power supply voltage drop A occurs such that the output voltage of the voltage divider circuit 1 falls below the reference voltage G,
The power supply voltage drop detection element 7 generates a continuous reset signal B from T1 to T2. T3 to T
If the power is cut off between C and D between 4 or between T5 and T6, the charge in the capacitor 42 will be rapidly discharged at T3 or T5, so when the power is restored at T4 or T6, the state shown in Fig. 3b will occur. As shown, charging of the capacitor 42 is started from ground potential, and a constant pulse length T as shown in FIG.
Reset signals E and F are generated. Here S
is the threshold voltage of the OR circuit 6. In this way, when the power supply voltage drops, a continuous reset signal is obtained by the power supply voltage drop detection element 7, and when the power supply is cut off, the power cutoff detection element 8 obtains reset signals E and F with a constant pulse length T regardless of the length of the cutoff time. It will be done.

"Problems to be Solved by the Invention" In large and medium-sized equipment that uses microcomputers, it is common practice to divide the equipment into functional units and configure the equipment with multiple functional units and a common power supply. . The example shown in FIG. 4 is composed of two functional units #1 and #2 and a common power supply 20. In this case, while functional unit #1 is in operation, the power supply is removed by replacing functional unit #2, etc.
When the SWS 2 is turned on again, the common power supply 20 will experience a momentary voltage drop due to the rush current to the functional unit #2, which may cause the microcomputer in the functional unit #1 to malfunction, such as runaway.

The time for this voltage drop may be shorter than the time required for the reset signal of the microcomputer, and in this case, the power supply voltage drop detection element 7 and power-off detection element 8 of the conventional circuit described above do not provide a reset signal of sufficient length. The problem was that I couldn't get a signal.

For example, between T11 and T12 in FIG. 5a showing the output voltage of voltage divider circuit 1, or between T13 and T1
Consider the case where instantaneous drops P and H in the power supply voltage occur between 4 and 4.

Even if power supply voltage drops P and H occur, the voltage of the capacitor 42 does not drop to the ground potential as shown in FIG. 5b, and the charge in the capacitor 42 is not sufficiently discharged. Therefore T12 and T14
Even if the power is restored, the time from the start of charging the capacitor 42 to the threshold voltage of the OR circuit 6 is shorter than the constant pulse length T shown in FIG. 3c, and the pulse lengths of the reset signals I and J are as follows. Third
The pulse length is shorter than the pulse length of reset signals E and F shown in the figure.

The present invention has been devised in view of these points, and provides a microcomputer reset method that allows a reset signal of a constant pulse length to be obtained even in the event of a momentary voltage drop simply by partially changing the configuration of the conventional circuit. The purpose is to provide circuits.

"Means for solving the problem" As shown in the block diagram in Figure 1, 1 is a voltage divider circuit that detects the power supply voltage, 2 is a reference voltage generation circuit, and the output voltage of voltage divider circuit 1 and the reference voltage are The output voltage of the voltage generating circuit 2 is compared and determined by a comparator 3. The output terminal of comparator 3 is 1 of OR circuit 6.
It is connected to two input terminals 6a. Also, power supply 10
A CR integrating circuit 4 consisting of a resistor 41 and a capacitor 42 connected between the output terminal 11 and the ground 11 is connected to another input terminal 6b of the OR circuit 6, and a reset signal is obtained from the output terminal 6c of the OR circuit 6. The diode 5 is for discharging the charge in the capacitor 42 and is connected to the output terminal of the comparator 3.

"Function" When the power supply voltage drops, comparator 3
While the power supply voltage is below the reference voltage G, the output terminal of
It becomes low level without time delay, and capacitor 4
The charging charge of 2 is the diode 5 and comparator 3.
is rapidly discharged through the output terminal of the Therefore, even in the event of a momentary drop in power supply voltage, the capacitor 42
becomes the ground potential, and a reset signal of a constant pulse length is obtained after the power supply voltage returns to the normal level, regardless of the drop level of the power supply voltage.

"Embodiment" FIG. 6 shows an embodiment of the present invention. The voltage dividing circuit 1 includes resistors 31 and 32, and the reference voltage generating circuit 2 includes a Zener diode 21 and resistors 22 and 2.
It consists of 3,24.

The voltage dividing ratio of the voltage dividing circuit 1 is determined from the ratio between the threshold value of the power supply voltage that generates the reset signal and the value of the reference voltage.

FIGS. 7a, b, and c are waveform explanatory diagrams of this embodiment. When an instantaneous drop in the power supply voltage K and L occurs between T21 and T22 or between T23 and T24 in FIG. 7a, which shows the voltage of the voltage divider circuit 1,
During that time, the output of the comparator 3 becomes low level, and the charge in the capacitor 42 shown in FIG.
The capacitor 42 is charged with a time constant of
Reset signals M and N of constant pulse length T as shown in FIG. Therefore, regardless of the drop level of the power supply voltage, a reset signal with a constant pulse length can be obtained after the power supply voltage returns to the normal level.

Note that the operation when the power supply voltage continuously decreases and the operation when the power supply is cut off are the same as those of the conventional circuit, so a description thereof will be omitted.

"Effects of the Invention" As described above, according to the present invention, a reset signal of a constant pulse length can be generated even in response to a momentary drop in power supply voltage by simply changing the connection destination of the diode in the conventional circuit. can be obtained, and is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the reset circuit of the present invention.
Figure 2 is a block diagram of the conventional circuit, Figure 3 a, b,
c and FIGS. 5a, b, and c are explanatory diagrams of waveforms of conventional circuits, FIG. 4 is an example of a device configuration of a device to which a microcomputer is applied, FIG. 6 is a circuit diagram showing an embodiment of the present invention, and FIG. a, b, and c are waveform explanatory diagrams in an embodiment of the present invention. In the figure, 1 is a voltage divider circuit, 2 is a reference voltage generation circuit, 3 is a comparator, 4 is a CR integration circuit, and 5
is a diode, 6 is an OR circuit, 10 is a power supply, 11
is earth.

Claims (1)

[Claims] 1 A voltage dividing circuit 1 that detects a power supply voltage, a reference voltage generating circuit 2, a comparator 3 that compares the output voltage of the voltage dividing circuit 1 and the output voltage of the reference voltage generating circuit 2, a power source 10, and a ground 11. It consists of a CR integration circuit 4 connected between, a diode 5 that discharges the charge of the CR integration circuit 4, and an OR circuit 6 that takes the logical sum of the output of the comparator 3 and the output of the CR integration circuit 4. A reset circuit for a microcomputer, characterized in that by connecting the diode 5 to the output terminal of the comparator 3, a reset signal of a constant pulse length is always obtained even in the event of a momentary drop in power supply voltage. .