JP2001156610A - Watchdog timer control circuit and watchdog timer control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a watchdog timer control circuit that can prevent malfunction of a watchdog timer and to provide a watchdog timer control method. SOLUTION: The watchdog timer control circuit is provided with a 1st control means that includes a charging means that is provided with a pair of charging resistive elements and capacitors, a discharge means that discharges electric charges charged in the charging means, a charging characteristic changeover means that is provided with a pair of differential transistors(TRs) to change the charging characteristic of the charging voltage, a decision means that detects a charging voltage being a charge amounts charged in the charging means and transmits a reset signal when the charging voltage exceeds a specified level, and an output circuit that transmits an output pulse to operate the discharge means for a prescribed period, and with a 2nd control means that includes a voltage monitor means that monitors the charging voltage and a charging characteristic revision means that supplies a signal to change the charging characteristic of the charging voltage to a pair of the differential TRs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a watchdog timer control technique, and more particularly to a watchdog timer using a charging circuit, which can prevent malfunctions caused mainly by fluctuations in charging characteristics due to temperature characteristics and the like. The present invention relates to a watchdog timer control circuit and a watchdog timer control method.

[0002]

2. Description of the Related Art FIG. 2 shows a charging characteristic of a general charging circuit. In FIG. 2, the horizontal axis represents the elapsed time from the start of charging, the vertical axis represents the charging voltage, the curve (a) shows the characteristic at high temperature, the curve (b) shows the characteristic at normal temperature, and the curve (c) shows the characteristic at low temperature. The characteristics are shown. In general, a charging circuit composed of a resistance element and a capacitor changes its charging characteristics as shown in FIG. 2 due to temperature fluctuation of the capacitance of the capacitor. That is,
The charging voltage at the timing of the A / D conversion varies between Vl and Vh.

FIG. 3 shows an example of a conventional watchdog timer P10 having a charging circuit P13 having the temperature characteristic of FIG. In FIG. 3, P10 is a conventional watchdog timer, P11 is a discharging circuit, P13 is a charging circuit, P1
7 denotes a comparator, and P21 denotes a CPU.

The voltage fluctuation at each point from FIG. 3 is shown in FIG. Referring to FIG. 4, during normal operation, like a waveform, the CPU
Since the charge of the charging circuit P13 is discharged at regular intervals by outputting a discharge pulse at regular intervals from P21, the charge voltage Vc periodically repeats a fluctuation like a waveform. At this time, the determination level set by the comparator P17 is set higher than the peak voltage of the waveform, and the comparator P17 does not send out the reset signal as long as the pulse from the CPU P21 is periodically output. If the pulse from the CPU P21 is interrupted due to an abnormality, the periodic discharge of the charging circuit P13 stops,
Since the charging voltage Vc exceeds the determination level set by the comparator P17, the comparator P17
By transmitting a reset signal to the CPU 21, the operation in the abnormal state can be stopped.

[0005]

In the conventional watchdog timer using the charging circuit, as described above, the abnormality determination time from when the pulse output is stopped until the abnormality is determined and the operation is stopped is determined by the watch. Dog timer P
10 is determined in consideration of the safety and the like of the system for making the function of the system 10 work. However, when the charging circuit P13 has a temperature characteristic as shown in FIG.
As shown in the waveforms and waveforms, the charging time increases at low temperatures as compared with that at normal temperature, and the charging voltage Vc does not exceed the determination level of the comparator P17 even though the abnormality determination time has been exceeded. Operation cannot be stopped. Conversely, as shown in the determination level ', waveform', and waveform 'in FIG. 5, the charging time at high temperature is shorter than that at normal temperature, and the charging voltage Vc is higher than the abnormality determination time. Exceeds the determination voltage of the comparator P17, and the normal operation is stopped. In other words, there has been a problem that the charging characteristics fluctuate due to the influence of the temperature characteristics and the like, making it impossible to determine the abnormality, or determining that the abnormality is normal.

The present invention has been made in view of such a problem, and an object of the present invention is to generate a watchdog timer using a charging circuit mainly due to fluctuations in charging characteristics due to temperature characteristics and the like. It is an object of the present invention to provide a watchdog timer control circuit and a watchdog timer control method capable of preventing a malfunction.

[0007]

The gist of the present invention is as follows: a charging means having a charging resistor and a capacitor; a discharging means for discharging charges charged in the charging means; A charging characteristic switching unit including a transistor for changing a charging characteristic of a charging voltage, and detecting the charging voltage, which is an amount of charge charged in the charging unit, and when the charging voltage exceeds a specified level. Determining means for transmitting a reset signal to the first control means, first control means including an output circuit for transmitting an output pulse for operating the discharging means at a constant period, and voltage monitoring means for monitoring the charging voltage. A watchdog comprising: a second control unit including a charging characteristic changing unit that supplies a signal for changing a charging characteristic of the charging voltage to the transistor. It resides in the timer control circuit. According to another aspect of the present invention, in order to monitor the charging voltage, the charging voltage is input to a voltage monitoring means of the second control means different from the first control means, 2. The watchdog timer control circuit according to claim 1, wherein the watchdog timer control circuit has a configuration for periodically monitoring a charging characteristic of the charging unit. According to another aspect of the present invention, a circuit is provided for changing the charging characteristic of the charging unit by the second control unit, so that the charging characteristic is appropriate regardless of the fluctuation of the charging voltage. 3. The watchdog timer control circuit according to claim 2, further comprising a circuit for controlling the circuit. The gist of the invention described in claim 4 is to determine whether the A / D conversion value of the charging voltage at a predetermined timing after the start of charging is within a certain range, and determine whether the value is outside the range. 4. The watchdog according to claim 1, wherein in the case, the transistor is controlled to change the charging characteristic by switching the charging resistance element of the charging unit. 5. It resides in the timer control circuit. According to another aspect of the present invention, a charging unit including a charging resistance element and a capacitor, a discharging unit for discharging a charge charged in the charging unit, and a charging characteristic of a charging voltage are changed. Charging characteristic switching means including a transistor for detecting the charging voltage, which is the amount of charge charged in the charging means, and transmitting a reset signal when the charging voltage exceeds a specified level. Determining means, a first control means having an output circuit for sending an output pulse for operating the discharging means at a constant cycle, a voltage monitoring means for monitoring the charging voltage, and a charging characteristic of the charging voltage. A watchdog timer control circuit having a second control means including a charge characteristic changing means for supplying a signal for changing the charge voltage to the transistor. Watch for inputting the charging voltage to a voltage monitoring means of the second control means different from the first control means to periodically monitor a charging characteristic of the charging means. It lies in the dog timer control method. The gist of the invention described in claim 6 is that a circuit for changing the charging characteristic of the charging means by the second control means is provided so that the charging characteristic is appropriate regardless of the fluctuation of the charging voltage. 6. The watchdog timer control method according to claim 5, wherein the circuit is controlled in the following manner. The gist of the invention described in claim 7 is that it is determined whether the A / D conversion value of the charging voltage at a predetermined timing after the start of charging is within a certain range and is out of the range. 7. The watchdog timer control method according to claim 5, wherein in the case, the transistor is controlled to change the charging characteristic by switching the charging resistance element of the charging unit.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A feature of the present invention is that in a watchdog timer using a charging circuit, the charging characteristics are monitored and switching of the charging characteristics is performed. This is to prevent malfunction due to the change of. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram for explaining a watchdog timer control circuit 10 according to one embodiment of the present invention. In FIG. 1, 10 is a watchdog timer control circuit, 11 is a discharge circuit (discharge means), 13 is a charge circuit (charge means), 15 is a charge characteristic switching means, 17 is a comparator (judgment means), and 19 is a CPU (No. 2, 21 is a CPU (first control means), 131 is a charging capacitor, 171 and 173 are voltage dividing resistance elements, 191
Is an A / D conversion circuit (voltage monitoring means), 193 is an output circuit (charging characteristic changing means), 211 is an output circuit, A and B are differential transistors (a pair of differential transistors), Ra and R
b indicates a charging resistance element, and Vc indicates a charging voltage.

Referring to FIG. 1, a watchdog timer control circuit 10 of the present embodiment includes a charging circuit 13 (charging means), a discharging circuit 11 (discharging means), a charging characteristic switching means 15, a comparator 17 ( Determining means), a CPU 21 (first control means) having an output circuit 211,
A CPU 19 (second control means) is provided.

The charging circuit 13 (charging means) includes a pair of charging resistance elements Ra and Rb and a charging capacitor 131. The discharging circuit 11 (discharging means) includes a charging circuit 13
(Charging means) is provided with a structure for discharging the charged electric charge. The charging characteristic switching means 15 includes differential transistors A and B (a pair of differential transistors) for changing the charging characteristic of the charging voltage Vc. Comparator 17
The (determination means) detects the amount of charge charged in the charging circuit 13 (charging means), that is, the charging voltage Vc, and detects the charging voltage Vc.
Is greater than a prescribed level (a voltage value determined by a voltage division ratio of the voltage dividing resistance elements 171 and 173), a reset signal is transmitted. The CPU 21 (first control means) includes an output circuit 211 for transmitting an output pulse for operating the discharge circuit 11 (discharge means) at a constant cycle. The CPU 19 (second control means) includes an A / D conversion circuit 191 (voltage monitoring means) for monitoring the charging voltage Vc and a signal for changing the charging characteristics of the charging voltage Vc by the differential transistors A and B ( An output circuit 193 (charging characteristic changing means) for supplying a pair of differential transistors) is provided.

Next, the overall operation of the present embodiment will be described in detail with reference to FIGS. FIG. 2 shows the charging characteristics of a general charging circuit P13. In FIG.
The horizontal axis is the elapsed time from the start of charging, the vertical axis is the charging voltage, the curve (a) is the characteristic at high temperature, the curve (b) is the characteristic at room temperature, the curve (c) is the characteristic at low temperature, and ThL is The specified lower limit of the A / D conversion value, ThH, indicates the specified upper limit of the A / D conversion value. Generally, the charging characteristic of the charging circuit P13 including the resistance element and the capacitor changes as shown in FIG. 2 due to the temperature fluctuation of the capacitance of the capacitor. That is, the charging voltage at the timing of A / D conversion is Vl to
Vh.

FIG. 3 shows an example of a conventional watchdog timer P10 having a charging circuit P13 having the temperature characteristic of FIG. The voltage fluctuation at each point from FIG. 3 is shown in FIG. Referring to FIG. 4, during normal operation, the CPUP
Since a discharge pulse is output at a constant interval from 21, the charge of the charging circuit P13 is discharged at a constant interval, so that the charging voltage Vc periodically repeats a fluctuation like a waveform. At this time, the determination level set by the comparator P17 is set higher than the peak voltage of the waveform, and the comparator P17 does not send out the reset signal as long as the pulse from the CPU P21 is periodically output. If the pulse from the CPU P21 is interrupted due to an abnormality, the periodic discharge of the charging circuit P13 stops,
Since the charging voltage Vc exceeds the determination level set by the comparator P17, the comparator P17
By transmitting a reset signal to the CPU 21, the operation in the abnormal state can be stopped.

As described above, the abnormality determination time from when the pulse output stops to when the abnormality is determined and the operation is stopped is determined in consideration of the safety of the system in which the watchdog timer P10 functions, and the like. However, the charging circuit P
13 has the temperature characteristic as shown in FIG.
As shown in the determination levels, waveforms, and waveforms of FIG. 7, the charging time increases at low temperatures as compared with that at normal temperature, and the charging voltage Vc does not exceed the determination level of the comparator P17 even though the abnormality determination time has been exceeded. However, there is a problem that the operation in the abnormal state cannot be stopped.

Conversely, as shown in the determination level ', waveform', and waveform 'in FIG. 5, the charging time at high temperature is shorter than at normal temperature, and although the abnormality determination time is not exceeded, The charging voltage Vc exceeds the determination voltage of the comparator P17, which causes a problem that normal operation is stopped.

Therefore, in this embodiment, as shown in FIG. 1, in order to monitor the charging voltage Vc, the charging voltage Vc
It is input to the A / D conversion circuit 191 (voltage monitoring means) of the CPU 19 (second control means) different from U21 (first control means), and the charging characteristics of the charging circuit 13 (charging means) are periodically changed. Monitor. Further, a circuit for changing the charging characteristics of the charging circuit 13 (charging means) is prepared by the CPU 19 (second control means), and the circuit is controlled so as to obtain appropriate charging characteristics irrespective of the fluctuation of the charging voltage Vc. .

That is, in FIG. 2, it is determined whether or not the A / D converted value of the charging voltage Vc at a certain timing after the start of charging is within a certain range. The pair of charging resistance elements Ra and Rb of the charging circuit 13 (charging means) are switched by the differential transistors A and B (a pair of differential transistors) to change the charging characteristics.

For example, in FIG. 1, the charging resistor Ra is supplied by the differential transistor A, the charging resistor Rb is supplied by the differential transistor B, and the resistance value of the charging resistor Ra <the charging resistor. The resistance value of Rb is set.

First, at normal temperature, only the differential transistor A is turned on, and a charging circuit 13 (charging means) is constituted by the charging resistor Ra and the charging capacitor 131, and the A / D conversion value of the charging voltage Vc is obtained. Are set within the specified range (between ThH and ThL) shown in FIG. 2.

Now, the charging characteristics change at low temperatures,
Assuming that the A / D conversion value of the charging voltage Vc becomes Vl which is equal to or less than a specified lower limit ThL as shown by a curve (b) in FIG.
By turning on the differential transistor B at
The circuit configuration is configured by connecting the charging resistance element Ra and the charging resistance element Rb in parallel, thereby lowering the combined resistance value and changing the charging characteristic from the curve (c) to the curve (b) in FIG.

Conversely, when the temperature is high, the A / D conversion value of the charging voltage Vc is equal to the specified upper limit (Th) as shown by the curve (a) in FIG.
H) If Vh is not less than Vh, the differential transistor A is turned off and only the differential transistor B is turned on in FIG.
By doing so, the resistance value of the charging circuit 13 (charging means) is increased, and the charging characteristics are changed from the curve (a) to the curve (b).

As described above, according to the present embodiment, it is possible to prevent a malfunction caused in the watchdog timer using the charging circuit 13 (charging means) mainly due to a change in charging characteristics due to a temperature characteristic or the like. It has the effect of being able to do so.

It should be noted that the present invention is not limited to the above-described embodiments, and it is clear that each embodiment can be appropriately modified within the scope of the technical idea of the present invention. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment, and can be set to numbers, positions, shapes, and the like suitable for carrying out the present invention. In each drawing, the same components are denoted by the same reference numerals.

[0024]

According to the present invention, it is possible to prevent an erroneous operation of a watchdog timer using a charging circuit, which is mainly caused by fluctuations in charging characteristics due to temperature characteristics and the like.

[Brief description of the drawings]

FIG. 1 is a circuit diagram for explaining a watchdog timer control circuit according to one embodiment of the present invention.

FIG. 2 shows a charging characteristic of a general charging circuit.

FIG. 3 is an example of a conventional watchdog timer having a charging circuit having a temperature characteristic shown in FIG. 2;

FIG. 4 shows voltage fluctuations at respective points from the watchdog timer of FIG. 3;

FIG. 5 shows a case where the device has temperature characteristics as shown in FIG. 2;
3 shows the voltage fluctuation at each point.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Watchdog timer control circuit 11 ... Discharge circuit (discharge means) 13 ... Charge circuit (charge means) 15 ... Charge characteristic switching means 17 ... Comparator (judgment means) 19 ... CPU (second control means) 21 ... CPU ( First control means) 131: charging capacitors 171, 173: voltage-dividing resistance elements 191: A / D conversion circuit (voltage monitoring means) 193: output circuit (charging characteristic changing means) 211: output circuits A, B: difference Active transistors (a pair of differential transistors) Ra, Rb: charging resistance element ThL: lower limit of A / D conversion value ThH: upper limit of A / D conversion value Vc: charging voltage

Claims (7)

[Claims] A charging unit including a charging resistor and a capacitor; a discharging unit configured to release a charge stored in the charging unit; and a charging unit including a transistor configured to change a charging characteristic of a charging voltage. A characteristic switching unit, a determination unit for detecting the charging voltage, which is an amount of charge charged in the charging unit, and transmitting a reset signal when the charging voltage exceeds a prescribed level; and the discharging unit. First control means having an output circuit for sending an output pulse for causing the transistor to operate at a constant cycle; voltage monitoring means for monitoring the charging voltage; and a signal for changing a charging characteristic of the charging voltage to the transistor. A watchdog timer control circuit, comprising: a second control unit including a charging characteristic changing unit that supplies a charge characteristic to the watchdog timer. 2. In order to monitor the charging voltage, the charging voltage is input to a voltage monitoring means of the second control means different from the first control means, and a charging characteristic of the charging means is periodically changed. 2. The apparatus according to claim 1, further comprising:
2. The watchdog timer control circuit according to 1. 3. A circuit for changing a charging characteristic of the charging means by the second control means is provided, and the circuit is controlled so as to have an appropriate charging characteristic irrespective of the fluctuation of the charging voltage. 3. The watchdog timer control circuit according to claim 2, wherein: 4. After the start of charging, it is determined whether an A / D conversion value of the charging voltage at a predetermined timing is within a certain range, and if not, the transistor is controlled. The watchdog timer control circuit according to any one of claims 1 to 3, further comprising a configuration for changing a charging characteristic by switching the charging resistance element of the charging unit. 5. A charging device comprising: a charging device having a charging resistor and a capacitor; a discharging device for discharging a charge stored in the charging device; and a transistor having a transistor for changing a charging characteristic of a charging voltage. Characteristic switching means, determination means for detecting the charging voltage, which is the amount of charge charged in the charging means, and transmitting a reset signal when the charging voltage exceeds a prescribed level; and discharging means A first control means having an output circuit for sending an output pulse for causing the transistor to operate at a constant period; a voltage monitoring means for monitoring the charging voltage; and a signal for changing a charging characteristic of the charging voltage to the transistor. A watchdog timer control circuit having a second control means provided with a charge characteristic changing means for supplying the charging voltage to the charge characteristic monitoring means; Wherein the pressure first
A watchdog timer control method comprising: inputting a voltage to a voltage monitoring means of the second control means, which is different from the control means, and periodically monitoring a charging characteristic of the charging means. 6. A circuit for changing a charging characteristic of the charging means by the second control means, and controlling the circuit so as to obtain an appropriate charging characteristic irrespective of the fluctuation of the charging voltage. The watchdog timer control method according to claim 5, wherein 7. After the start of charging, it is determined whether an A / D conversion value of the charging voltage at a predetermined timing is within a certain range, and if not, the transistor is controlled. 7. The watchdog timer control method according to claim 5, wherein the charging characteristic is changed by switching the charging resistance element of the charging unit.