JPS5840637A - Resetting circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction due to a momentary break of power supply by supplying a voltage lower than a resetting voltage to a reset terminal when a power voltage drops below a limit voltage for the normal operation of a computer, and performing resetting operation once the computer operates abnormally. CONSTITUTION:When a power voltage Vcc drops below the operation limit voltage of a microcomputer 1, a voltage lower than the limit voltage is supplied to a reset terminal 2 by a level shifting circuit 7 composed of a diode, etc. Consequently, if the power voltage Vcc drops to a voltage at which the microcomputer 1 does not operate normally, resetting operation is started immediately.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reset circuit used in a microcomputer.

A conventional circuit of this type was constructed as shown in FIG.

1 is a microcomputer, 2 is a reset signal (negative logic) input terminal, 3 is a power supply terminal, 4 is a resistor, 5 is a diode, and 6 is a capacitor.

In this circuit, the voltage at terminal 2 rises later than the voltage at terminal 3 when the power is turned on, and the reset is canceled after the power supply voltage applied to the microcomputer becomes stable.

This delay time is determined by the values of resistor 4 and capacitor 6. In the event of a momentary power interruption, capacitor 6
The electric charge accumulated in the circuit is discharged through the diode 5, and the voltage at the reset terminal 2 decreases, causing a reset. However, the reset voltage Vmr of a general microcomputer is about 1.3V, and the diode 5. Since the forward voltage VD of
If the voltage does not drop to this level, the reset will not work. On the other hand, a microcomputer does not operate normally at a voltage much higher than 0.4V (generally about 4V). Gatte, VTR color VRESET-VD
(7) If the power supply voltage momentarily drops within the range (4V to 0.4V) and then recovers to normal, the microcomputer is not reset and remains in abnormal operation.

In order to eliminate these drawbacks, the present invention is designed to immediately reset the microcomputer when the power supply voltage drops below the voltage at which the microcomputer starts to operate abnormally.The present invention will be described in detail with reference to the drawings below.

FIG. 2 shows an embodiment of the present invention, in which 7 is a level shift circuit. In the 70 circuit, when the power supply voltage Vcc becomes lower than the VTR, that is, the 70 input voltage becomes VTH-VD.
= 3.3V, this is a level shift circuit that supplies a voltage lower than VRESET to the reset terminal 2.

By using such a circuit, if the microcomputer does not operate normally and the power supply voltage Vcc drops to the voltage VTH, the reset operation can be started immediately.The level shift circuit uses a diode, etc. This can be achieved using

FIG. 3 shows another embodiment of the present invention, in which 8 is a comparison circuit;
Reference numeral 9 denotes a reference voltage generation circuit, and the reference voltage generation circuit is realized using a Zener diode or the like, and the comparison circuit is realized using a comparator or a transistor switch or the like. One of the input terminals of the comparison circuit is connected to Vcc, and the other is connected to a reference voltage generation circuit 9 that generates a voltage corresponding to a VTR. Comparison circuit °8 generates an output voltage sufficiently higher than VRESET when Vcc is higher than reference voltage VTR, and generates an output voltage sufficiently lower than VRESET in the opposite case.

By supplying this output voltage to reset terminal 2,
The computer is reset as soon as the power supply voltage drops below the reference voltage (VTH). Further, circuits 4 to 6 are the same circuits as those used in the conventional circuit, and perform an operation to delay reset cancellation when the power is turned on. When the power supply voltage is equal to or higher than VccIJ''-VTH, the output voltage of the comparator circuit 8 becomes sufficiently higher than VRESET.

Therefore, the capacitor 6 is charged via the resistor 4, and the voltage at the reset terminal 2 is delayed by a certain period of time to VRESET.
becomes higher, and the reset of the conbeater is released.

Conversely, when Vcc becomes lower than VTR, the comparator circuit output voltage becomes sufficiently smaller than VRESET, and capacitor 6
The accumulated charges are discharged through the diode 5 in a short time, and the reset terminal voltage becomes less than VRE8ET, and the converter is reset. Further, in FIG. 4, the arrangement of the comparator circuit and the circuits 4.5.6 is reversed, and the same operation as in FIG. 3 can be realized.

FIG. 5 shows another embodiment of the present invention, in which the output of the comparator circuit 8 is an oven collector as shown in the figure, and is used to discharge the charge of the capacitor 5 in FIG. The diode 5 used in the circuit is replaced by a transistor for the output of the comparator circuit.The transistor switch circuit shown in FIG. 5 is a type of comparator circuit using transistors.

In the embodiments shown in FIGS. 3 and 5, the comparison circuit 8 and the reference voltage generation circuit 9 can be replaced with the level shift circuit 7 shown in FIG. 2 or the one-resistance voltage divider circuits 10 and 11 shown in FIG. It is possible.

FIG. 6 shows another embodiment of the invention, 10 and 11.
is resistance. Resistors IO and 11 are connected when Vcc is VT
It is adjusted so that the voltage at terminal 2 becomes VRESET when it becomes H. Therefore, when Vcc becomes lower than VT)I, it is immediately set by the computer.

Resistance 4. As in FIG. 1, the capacitor 6 is used to delay release of low voltage when the power is turned on, and the diode 5 is also used to rapidly discharge the charge accumulated in the capacitor 6 when Vcc drops.

As explained above, when the power supply voltage drops below the limit voltage VTR for normal computer operation, by supplying a voltage lower than the reset voltage VRESET to the reset terminal, the converter is reset at the same time as the converter starts abnormal operation. This makes it possible to prevent malfunctions caused by instantaneous power interruptions.

Figure 7 is an example of actually measuring the effect of the reset circuit, (a
) shows an example of the conventional circuit (b) shown in FIG. 6 using resistance division, and (C) shows an example shown in FIG. 4 using a comparison circuit. As can be seen from the figure, the characteristics can be significantly improved compared to the conventional circuit. In Figures 7 (al to (C)), region A is a region where no reset is applied and abnormal operation occurs, region B is a region where no reset is applied and normal operation continues, and region C is a region where reset is applied and normal operation begins. Indicates the area to be used.

[Brief explanation of the drawing]

FIG. 1 shows a conventional reset circuit, FIG. 2 shows an embodiment of the reset circuit according to the present invention, and FIGS. FIGS. 7A to 7C are diagrams showing the characteristics of the reset circuit in this embodiment. 1... Microcomputer, 2... Reset input terminal, 3... Power supply voltage terminal, 4
．． 10.11...Resistor, 5...Diode, 6
...Capacitor, 7.Level shift circuit, 8.Comparison circuit, 9.Reference voltage generation circuit. Patent applicant Nippon Telegraph and Telephone Public Corporation Patent application agent Megumi Yamamoto −

Claims (4)

[Claims] (1) Detecting means for detecting that the power supply voltage used for the converter has fallen to the limit for normal operation of the computer, and an input terminal provided for resetting the converter; 1. A reset circuit comprising a voltage sending circuit that sends out a voltage for executing reset according to the output of the means. (2) The reset circuit according to claim 1, wherein the voltage sending circuit is one circuit selected from a level shift circuit, a resistance divider circuit, a transistor switch circuit, and a comparison circuit. (3) The reset circuit according to claim 1, wherein a parallel circuit of a resistor and a diode, and a capacitor inserted between the output and the ground point are provided at the output of the voltage output path. (4) The reset circuit according to claim 1, wherein the output of the voltage sending circuit is grounded via a capacitor and connected to a power supply terminal via a resistor.