JPH0363764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reset circuit for a microcomputer.

BACKGROUND OF THE INVENTION In recent years, microcomputers have been widely used in various consumer devices.

The reset circuit of a conventional microcomputer (hereinafter referred to as microcomputer) will be explained below.

FIG. 1 shows a circuit diagram of a first conventional microcomputer reset circuit.

Reference numeral 1 denotes a first constant voltage source, which supplies power to the microcomputer 3. Reference numeral 2 denotes a second constant voltage source, which supplies power to the first constant voltage source 1. 3 is a microcomputer, 3a is its power supply terminal, and 3b is its reset terminal. 4 is a first transistor constituting a reset circuit. Similarly, 5 is a second transistor. R ₁ to R ₅ are resistors, and C is a capacitor.

FIG. 2 is a timing waveform diagram of voltages at various parts of the conventional microcomputer reset circuit.

11 is the voltage waveform of the second constant voltage source 2 shown in FIG. 12 is a voltage waveform of the first constant voltage source 1 shown in FIG. 13 is the base potential of the transistor 4. 14 is the base voltage of the transistor 5. 15 is the potential of the reset terminal 3b of the microcomputer 3.

The operation of the conventional microcomputer reset circuit configured as described above will be explained below.

First, when the power is turned on, the second constant voltage source 2
As shown in 11, it rises in a certain fixed time. On the other hand, a first constant voltage source 1 that supplies power to the microcomputer
stands up slightly later than 11, like 12. The base potential of the transistor 4 is connected to the second constant voltage source 2
Since the potential of is divided by resistors R ₁ and R ₂ , 13
The voltage rises as shown in FIG. 2, and the transistor 4 is turned on after a certain period of time. Base potential 1 of transistor 5
4 turns on transistor 5 until transistor 4 turns on, but when transistor 4 turns on, it reverses and turns off transistor 5. As shown by 15, the reset terminal 3b of the microcomputer 3 is L when the transistor 5 is on;
When turns off, it rises to H.

In order to reset the microcomputer 3 normally when the power is turned on, the power terminal 3a of the microcomputer 3 must be connected to the microcomputer 3.
After reaching the operating range, a certain period of time (20μsec
degree) It is necessary to maintain the potential of the reset terminal 3b at L. Therefore, in the above case, the time t ₁ from when the power supply 12 of the microcomputer 3 is turned on until the potential 15 of the reset terminal 3b of the microcomputer 3 becomes H is
is the reset time.

When the power is turned off, the operation order is exactly the opposite of when the power is turned on, and the reset terminal 3 of the microcomputer 3
The time t2 from when the potential 15 of b becomes L to when the power supply 12 of the microcomputer 3 drops below the operating range of the microcomputer ₃ becomes the reset time.

However, the conventional configuration described above has the problem of high cost because many circuit parts are required for reset.

Therefore, in order to solve this problem, the circuit configuration shown in FIG. 3 may be used.

FIG. 3 shows a circuit diagram of a microcomputer reset circuit in a second conventional example. In FIG. 3, 21 is a first constant voltage source for the microcomputer power supply. 22 is a second constant voltage source that supplies power to the first constant voltage source 21. 23 is a microcomputer, 23a is a power terminal of the microcomputer 23, 23b
is a reset terminal of the microcomputer 23. Reference numeral 24 denotes a Zener diode constituting the reset circuit, and the Zener potential _VZ is determined so that the voltage at the reset terminal 23b is approximately equal to the power supply voltage of the microcomputer in the operating state. 25 is a resistor constituting a reset circuit.

FIG. 4 shows a timing waveform diagram of the microcomputer reset circuit in FIG. 3.

In FIG. 4, 31 indicates the potential of the second constant voltage source 22. In FIG. 32 is the power terminal 23 of the microcomputer 23
The potential of a is shown. 33 indicates the potential of the reset terminal 23b of the microcomputer 23.

The operation of the second conventional microcomputer reset circuit configured as described above will be described below.

First, when the power is turned on, the second constant voltage source 22
rises at a certain time as shown in 31.
The power supply terminal 23a of the microcomputer 23 rises a little later than the waveform 31 of the second constant voltage source, as shown at 32. Since the reset terminal 23b of the microcomputer 23 is connected to the output terminal of the second constant voltage source 22 via the Zener diode 24, it is always kept lower than the second constant voltage source 22 by the Zener potential _VZ . . Therefore, when the power is turned on, the power starts after a certain period of time. From the above, microcontroller 23
The time from when the voltage 32 at the power supply terminal 23a of the microcomputer 23 rises to the operating range of the microcomputer 23 until the voltage 33 at the reset terminal 23b of the microcomputer 23 becomes H is the reset time.

When the power is turned off, the operating order is exactly opposite to that when the power is turned on, and the reset terminal 23b of the microcomputer 23
The time from when the voltage 33 of the microcomputer 23 becomes L until the voltage 32 of the power supply terminal 23a of the microcomputer 23 falls below the operating range of the microcomputer 23 is the reset time.

As described above, according to this embodiment, by providing a reset circuit with a simple configuration of a combination of the Zener diode 24 and the resistor 25, the reset operation can be ensured and the cost can be significantly reduced.

However, in the configuration of the second conventional example,
As shown in FIG. 4, the Zener potential V _Z has a value close to the potential 31 of the second constant voltage source 22, so the potential difference V _h becomes small, and when a momentary power outage occurs or power supply noise occurs, the Zener potential V Z becomes a value close to the potential 31 of the second constant voltage source 22. The potential 3 of the constant voltage source 22 of
1 has a problem in that the microcomputer is reset by mistake when it becomes less than the Zener potential.

Problems to be Solved by the Invention The present invention solves the above-mentioned conventional problems by significantly reducing the number of circuit components, and not only makes it possible to reliably reset the microcomputer when the power is turned on, but also reduces noise and noise to the power supply. The purpose of this invention is to provide a microcomputer reset circuit that is stable against voltage drops caused by instantaneous power outages.

Means for Solving the Problems In order to solve the above-mentioned conventional problems, the microcomputer reset circuit of the present invention supplies the output of the first constant voltage source to the power terminal of the microcomputer, and supplies the output of the first constant voltage source to the power terminal of the microcomputer. supplying the output of the first constant voltage source to the Zener diode;
The voltage is supplied to a series circuit of two resistors, and the potential at the midpoint between the two resistors in the series circuit is supplied to the reset terminal of the microcomputer.

Effect According to the above configuration, the Zener potential of the Zener diode can be set low by dividing the anode potential of the Zener diode with two resistors, so that the voltage drop of the second constant voltage source caused by momentary power outage, etc. On the other hand, there is no possibility of erroneous reset, and a stable reset circuit can be realized.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 5 is a circuit diagram of a microcomputer reset circuit showing an embodiment of the present invention. In the figure, 21 is a first constant voltage source for the microcomputer power supply. 22 is a second constant voltage source that supplies power to the first constant voltage source 21. 23 is a microcomputer, 23a is a power supply terminal of the microcomputer 23, and 23b is a reset terminal of the microcomputer 23. 24 is a Zener diode, which has the same structure as that shown in FIG. 3. The difference from the configuration shown in FIG. 3 is that the resistor constituting the reset circuit is divided into resistors 41 and 42, and a reset signal is supplied to the reset terminal 23b of the microcomputer 23 from the midpoint between the resistors 41 and 42.

FIG. 6 is a timing waveform diagram of the microcomputer reset circuit of the embodiment shown in FIG. 51 indicates the potential of the second constant voltage source 22. 52 indicates the potential of the first constant voltage source 21. 53 is the anode potential of the Zener diode 24. 54 indicates the potential of the reset terminal 23b of the microcomputer 23.

The operation of the microcomputer reset circuit of the second embodiment configured as described above will be explained.

First, when the power is turned on, the second constant voltage source 22
As shown at 51, the potential rises in a certain period of time. The potential of the power supply terminal 23a of the microcomputer 23 rises with a little delay from the second constant voltage source 22, as shown at 52. Since the anode potential of the Zener diode 24 is kept lower than the second constant voltage source 22 by the Zener potential V _Z ', the rise after the power is turned on is delayed by a certain period of time as shown at 53. Since the potential at the reset terminal 23b of the microcomputer 23 is a value obtained by dividing the anode voltage of the Zener diode 24 by the resistors 41 and 42, it has a rise characteristic as shown at 54. After the potential 52 of the first constant voltage source 21 rises to the operating range of the microcomputer 23, the reset terminal 2 of the microcomputer 23 is
The time it takes for the voltage 54 of 3b to become H is the reset time.

When the power is turned off, the order of operation is exactly opposite to that when the power is turned on, and the voltage 54 at the reset terminal 23b goes low.
The time from when the voltage 52 of the power supply terminal 23a of the microcomputer 23 drops below the operating range of the microcomputer 23 becomes the reset time.

Incidentally, during the operation of the microcomputer, the division ratio between the Zener potential V _Z ' and the resistors 41 and 42 is determined so that the voltage 54 at the reset terminal 23b of the microcomputer 23 is approximately equal to the voltage 52 at the power supply terminal 23a of the microcomputer 23. It is necessary to keep it.

With the above configuration, by dividing the anode voltage of the Zener diode 24 by the resistors 41 and 42, the rise and fall of the voltage 54 at the reset terminal 23b of the microcomputer 23 will be the same as in the conventional case shown in FIG. Since the reset time is longer than that of , a stable and reliable reset circuit can be realized. Moreover, by dividing the anode voltage of the Zener diode 24 by the resistors 41 and 42, the Zener potential V _Z ′ of the Zener diode 24 can be set low, so the potential difference V _h ′ becomes large and the second constant due to instantaneous power outage or noise, etc. Erroneous resets due to voltage drops in the voltage source 22 are less likely to occur, and a reset circuit with stable operation can be realized.

Effects of the Invention As described above, according to the microcomputer reset circuit of the present invention, the output of the first constant voltage source is supplied to the power supply terminal of the microcomputer,
The output of the second constant voltage source is supplied to the first constant voltage source and also to a Zener diode and a series circuit of two resistors, and the potential at the midpoint of the two resistors of the series circuit is applied to the microcomputer. Since the voltage is supplied to the reset terminal of the second constant voltage source, erroneous resets due to voltage drops of the second constant voltage source due to instantaneous power outages, noise, etc. are reduced, and a stable reset circuit can be realized.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a microcomputer reset circuit of the first conventional example, FIG. 2 is a timing waveform diagram of a conventional microcomputer reset circuit, FIG. 3 is a circuit diagram of a microcomputer reset circuit of a second conventional example, and FIG. 5 is a timing waveform diagram thereof, FIG. 5 is a circuit diagram of a microcomputer reset circuit in an embodiment of the present invention, and FIG. 6 is a timing waveform diagram thereof. 21...First constant voltage source for microcomputer power supply, 2
2...Second constant voltage source, 23...Microcomputer, 23
a... Power supply terminal of the microcomputer 23, 23b... Reset terminal of the microcomputer 23, 24... Zener diode, 25... Resistor, 31... Potential of the second constant voltage source 22, 32... First constant voltage Potential of source 21, 33...reset terminal 23b of microcomputer 23
potential, 41...resistance, 42...resistance, 51...
Potential of second constant voltage source 22, 52... Potential of first constant voltage source 21, 53... Zener diode 2
4, the anode potential of 54, and the potential of the reset terminal 23b of the microcomputer 23.

Claims (1)

[Claims] 1. The output of the first constant voltage source is supplied to the power supply terminal of the microcomputer, and the output of the second constant voltage source is supplied to the first constant voltage source and connected to a Zener diode and a series circuit of two resistors. A reset circuit for a microcomputer, characterized in that the potential at the midpoint between the two resistors of the series circuit is supplied to the reset terminal of the microcomputer.