JPS61224019A - Resetting circuit of microprocessor - Google Patents

Abstract

PURPOSE:To prevent the malfunctions of a device and a system in which a microprocessor is used by continuing a resetting signal covering the period when power source voltage becomes lower temporarily than specified voltage. CONSTITUTION:A power source voltage monitoring circuit 110 supervises power source voltage 1 of a microprocessor 200 and an alarm signal 2 is sent out from the circuit 110 to a resetting signal generating circuit 120. When power source voltage is lower than a specified value, the signal 2 becomes low level. Clock signals 3 having continuous specified time interval are sent out from a clock circuit 120a of the circuit 120. A resetting signal 4 is generated in the circuit 120b making the signal 3 a base and sent to the microprocessor 200. The signal 4 is sent while the signal 2 is low level and for a specified time from the point of time when the signal 2 changes from low level to high level.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reset circuit that prevents malfunctions of a microprocessor that occur during transient changes in the voltage applied to the microprocessor.

〔overview〕

When the power supply to the microprocessor is turned on, after the voltage reaches a predetermined level that allows the microprocessor to operate,
In a circuit that continuously supplies a reset signal to this microprocessor until the operation of this microprocessor stabilizes, when the power supply voltage temporarily falls below the predetermined voltage while this microprocessor is operating, By continuing the reset signal during the period when the power supply voltage is below the predetermined voltage, operations performed during the period when the power supply voltage is below the predetermined voltage will not become effective.

[Conventional technology]

Conventional circuits used to reset microprocessors are shown in FIGS. 4 and 5. First, in the circuit shown in FIG. 4, a method is adopted in which a lift signal having a time width necessary for the microprocessor is obtained using a time constant determined by a resistive element 101 and a capacitor 102. That is, since no charge is accumulated in the capacitor 102 when the power is first turned on, the output of the Schmitt input buffer 104 becomes low level and the microprocessor 200 is reset. As time passes, the capacitor 102 is charged via the resistive element 101, and when the input threshold voltage V of the buffer 104 is exceeded, the output becomes high level and the reset of the microprocessor 200 is released. Furthermore, the diode 103 causes the capacitor 102 to rapidly discharge when the power is cut off or momentarily interrupted. In this conventional circuit, when the power supply voltage rises rapidly as shown in FIG. However, if the power supply voltage rises slowly as shown in Figure 5), the voltage of the capacitor 102 will exceed the input threshold voltage Vth of the buffer 104 before the power supply voltage reaches the guaranteed operation voltage of the microprocessor. The reset will be canceled. This reset should be released after a predetermined time has elapsed after the power supply voltage was determined. Furthermore, even in the case of a momentary power interruption as shown in FIG. 5(C), that is, when the power supply voltage once drops to Ov and immediately recovers, the operation of the microprocessor 200 after the time when the voltage drops below the guaranteed operating voltage is Since this is not guaranteed, it is necessary to reset the microprocessor 200 when the power supply voltage is restored. However, if the instantaneous interruption time is short, the voltage of the capacitor 102 will not drop until the input threshold voltage V of the buffer 104, so no reset signal will be output.

A conventional circuit shown in FIG. 6 is known as a circuit for solving such problems at the time of power-on and instantaneous power-off. In this circuit, the comparison circuit 108 compares the reference voltage source 107 with the power supply voltage divided by the resistive elements 105 and 106, and when the voltage is below the specified value, the transistor 109 turns on. Even if the rise is slow, the transistor 109 is turned off when the voltage exceeds the specified voltage, and from this point on, a predetermined reset is performed by the time constant determined by the resistive element 101 and the capacitor 102, so that the microprocessor 100 does not malfunction. .

[Problem that the invention seeks to solve]

However, in the case of instantaneous power interruption or voltage drop, as shown in Fig. 7 (b)
There is no problem if the voltage of the capacitor 102 drops to the input threshold voltage V of the buffer 104 while the transistor 109 is on, as shown in FIG. If the voltage of the capacitor 102 does not drop sufficiently even if the transistor 109 is turned on due to a momentary interruption or voltage drop, the microprocessor 200 may malfunction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reset circuit for a microprocessor that can prevent malfunctions of the microprocessor that occur when a power supply abnormality such as a momentary power interruption, voltage drop, or power outage occurs and when the power is turned on.

[Means for solving problems]

The present invention is connected to a power supply circuit of a microprocessor,
A power supply voltage monitoring circuit that sends out an output when the voltage of this power supply circuit is equal to or higher than a predetermined value at which this microprocessor can operate; and a reset signal generation circuit that supplies a reset signal to the microprocessor for a sufficient period of time to stabilize the microprocessor, and as a means for solving the aforementioned problem, the reset signal generation circuit includes:
The present invention is characterized by comprising means for starting supply of the reset signal when the output of the power supply voltage monitoring circuit stops.

[Effect]

The reset signal generating means generates a reset signal when the power supply voltage falls below the dark value by the signal generated by the power supply voltage start circuit, and continues to reset for a predetermined length from the time when the power supply voltage exceeds the dark value again. Generate a signal. The length of this reset signal corresponds to the time value during which the operating state of the microprocessor becomes stable by continuously applying a voltage equal to or higher than the lower limit voltage that guarantees normal operation of the microprocessor.

Due to this effect, a reset signal of sufficient length can be reliably generated no matter what kind of change occurs in the power supply voltage value.

〔Example〕

Hereinafter, a circuit according to an embodiment of the present invention will be explained based on the drawings.

FIG. 1 is a block configuration diagram showing the configuration of a circuit according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of the block shown in FIG. 1, and FIG. 3 is a block diagram showing the configuration of the block shown in FIG. FIG. 3 is a waveform diagram showing waveforms.

First, the configuration of this embodiment circuit will be explained based on FIG. This circuit connects the power supply voltage 1 to the power supply voltage input terminal 150.
a power supply voltage monitoring circuit 110 that inputs the alarm signal 2 and generates the alarm signal 2; a reset signal generation circuit 120 that inputs the alarm signal 2 and generates the reset signal 4; and a reset signal generator that outputs the reset signal 4 to the microprocessor 200. A signal output terminal 151 is provided. Here, the reset signal generation circuit 120 includes a reset clock circuit 120a that generates the clock signal 3, and a counting circuit 120 that generates the reset signal 4 by manually inputting the clock signal 3 and the alarm signal 2.
b.

Next, the operation of this example ml path will be explained based on FIGS. 1 to 3.

First, in FIG. 1, a power supply voltage monitoring circuit 110 monitors a power supply voltage l of a microprocessor 200, for example, +5V, and an alarm signal 2 is sent from this circuit to a reset signal generation circuit 120.

The alarm signal 2 is an active low signal and becomes low level when the power supply voltage is, for example, 4.5V or less. A clock signal 3 having continuous predetermined time intervals is sent from the clock circuit 120a of the reset signal generating circuit 120 to the counting circuit 120b. The counting circuit 120b generates an active low reset signal 4 based on the clock signal 3 and sends it to the microprocessor 200. Reset signal 4
The transmission is performed (1) while the alarm signal 2 is at a low level and (2) within a predetermined time from the time when the alarm signal 2 changes from a low level to a high level.

Next, in FIG. 2, a clock circuit 120a is an oscillation circuit using CMOS IC buffers 124, 125 and 126, and a continuous clock signal 3 is generated at a period determined by a resistor element 121 and a capacitor 122. Furthermore, the input of the CMOS rc buffer 124 is protected by the resistive element 123. This oscillation period is determined by the microprocessor 200.
The reset time is set to approximately 1/10 of the required reset time. A reference voltage generation source consisting of a resistance element 113 and a voltage regulator diode 114 is connected to a non-inverting input of the comparison circuit 115 of the power supply voltage monitoring circuit 110.
1 and 112 is connected to its inverting input. The reference voltage generation source generates a constant reference voltage in a region where the power supply voltage drops to a voltage at which the microprocessor 200 completely stops operating.

The comparator circuit 115 has a minimum operating power supply voltage of about 1 V, and its output is connected to the base of the transistor 116. A pull-up resistor 117 is connected to the collector of the transistor 116, and the alarm signal 2 is output from this connection point.
is output to the counting circuit 120b. The counting circuit 120b is composed of a 4-bit binary counter 127 equipped with a clear terminal CL and an enable terminal EN, and when the outputs are A, BSC, and D in order from the 1st bit, the D output is sent to the microprocessor 200 as a reset signal 4. Both are also connected to the active low clock input terminal CK, and this signal causes the 4-bit binary counter 1 to
27 operations are controlled. The clock signal 3 from the clock circuit 120a is controlled to the enable terminal EN, and the alarm signal 2 from the power supply voltage monitoring circuit 110 is controlled to the active low clear terminal CL. While the alarm signal 2 is at a high level, the 4-bit binary counter 127 operates, but
Since the D output is connected to the clock input terminal CK,
The counting operation stops when the D output becomes high level. Therefore, if the power supply voltage is normal, the reset signal 4 is maintained at a high level. When the alarm signal 2 goes low, the output of the 4-bit binary counter 127 is cleared, so the reset signal 4 goes low. Further, when the alarm signal 2 changes from a low level to a high level, the counting operation starts from that point and stops at the 8th count. Therefore, if the period of the clock signal 3 is set to 2 milliseconds, an active low pulse of 16 milliseconds can be obtained as the reset signal 4.

Next, the operation when the power supply voltage changes will be explained based on FIG. 3.

First, the waveform diagram on the left side of the figure shows the case when the power is turned on. Since the power supply voltage monitoring circuit 110 is also operated at +5V, there is no guarantee of operation until it rises to about +1V, but this does not pose a problem since the microprocessor 200 does not operate at this stage. The power supply voltage rises slowly until it reaches 4.5V, and the power supply voltage start circuit 110 outputs a low-level alarm signal 2, so the reset signal 4 also becomes low level and the microprocessor 20 outputs a low-level alarm signal 2.
0 is continuously reset. At the point when the alarm signal 2 exceeds 4.5■, the alarm signal 2 changes from low level to high level, and from this point on, the low level reset signal 4 is continuously output for, for example, 16 milliseconds. The length of this time is determined based on the reset time required after the power supply voltage of the microprocessor 200 reaches the guaranteed operation voltage.
No malfunctions will occur.

Next, the case of instantaneous power interruption will be explained using the waveform diagram on the right side of FIG. When the power supply voltage decreases to 4.5V or less, the alarm signal 2 from the power supply voltage monitoring circuit 110 becomes low level, and the reset signal 4 also changes to low level, so that the microprocessor 200 is reset. This state is maintained until the power supply voltage exceeds 4.5V again. When the voltage exceeds 4.5V, the reset signal generation circuit 120 operates from that point on and continues to reset the microprocessor 200 for a period of, for example, 16 milliseconds. Therefore, no malfunction occurs in the microprocessor 200 after a momentary interruption.

〔Effect of the invention〕

As explained above, in the event of an abnormality such as a momentary power outage, instantaneous drop, or power outage in the power supply of a microprocessor, the present invention can reset the microprocessor at a voltage higher than the guaranteed operating voltage for a sufficient period of time. This has the effect of preventing malfunctions of devices and systems that have been used, and improving reliability.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram showing the configuration of a circuit according to an embodiment of the present invention. FIG. 2 is a circuit configuration diagram showing the configuration of each block shown in FIG. 1. FIG. 3 is a waveform diagram showing signal waveforms of various parts of the circuit according to the embodiment of the present invention. FIG. 4 is a circuit configuration diagram showing the configuration of the first conventional example circuit. FIG. 5 is a waveform diagram showing signal waveforms of the first conventional circuit. FIG. 6 is a circuit configuration diagram showing the configuration of a second conventional example circuit. FIG. 7 is a waveform diagram showing signal waveforms at various parts of the second conventional circuit. 1... Power supply voltage, 2... Alarm signal, 3... Clock signal, 4... Reset signal, 100... Reset circuit, 101105.106.111.112.113
．． 117.121.123...Resistance element, 102.1
22... Capacitor, 103... Diode, 10
4...Buffer, 107...Reference voltage source, 10B
, 115... Comparison circuit, 109.116... Transistor, 110... Power supply voltage monitoring circuit, 114...
Constant voltage diode, 120... Reset signal generation circuit, 120a... Clock circuit, 120b... Counting circuit,
124.125.126 ・C0M5IC buffer, 1
27...4-bit binary counter, 150...power supply voltage input terminal, 151...reset signal output terminal,
200... Microprocessor, 300... Power supply terminal. Block configuration diagram of the embodiment M 1 Block diagram of the embodiment from Figure y Figure 3 Waveform diagram of each part of the embodiment;! i'1iIi3 Figure 5 - Configuration diagram of the conventional example (a) (b) (c) Waveform diagrams of various parts of the first conventional example

Claims (1)

[Claims] (1) A power supply voltage monitoring circuit that is connected to the power supply circuit of the microprocessor and sends out an output when the voltage of this power supply circuit is equal to or higher than a predetermined value at which the microprocessor can operate; and a reset signal generation circuit that supplies a reset signal to the microprocessor for a sufficient period of time to stabilize the operation of the microprocessor from the time when transmission is started, the reset signal generation circuit comprising: A reset circuit for a microprocessor, comprising means for starting supply of the reset signal when the output of the power supply voltage monitoring circuit stops.