JPH0313614B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reset circuit for a microcomputer, and particularly to a circuit for detecting an abnormality in a microcomputer and resetting it.

Programs in microcomputers may malfunction due to internal factors such as malfunction or deterioration of internal elements, or external factors such as radio wave interference.
A so-called runaway state may occur.

Therefore, a circuit has been proposed for detecting this runaway state and resetting the microcomputer to restore normal operation when the runaway occurs, and FIG. 1 shows an example of this circuit.

In Fig. 1, 1 is a microcomputer, and this microcomputer 1 is programmed in advance to output a constant frequency pulse P from port A as shown in Fig. 2b when the execution program is normal. . The output from this port A is input to the monostable multivibrator 2, the output of this monostable multivibrator 2 is supplied to the input side of the monostable multivibrator 3, and the output of this monostable multivibrator 3 is input to the OR circuit 4. Supplied to one input side, OR circuit 4
The output of is supplied to the reset terminal of the microcomputer 1. The other input side of the OR circuit 4 is supplied with the output of a power-on reset circuit 9 comprising an inverting circuit 8 for inverting the signal at the connection point between the resistor 6 and the capacitor 7.

According to such a configuration, at time _t9 , a signal of "1" is output from 8 until the capacitor 7 is charged after the power switch (not shown) is turned on, so that the signals shown in FIG. As shown in d, reset signal R ₁ is applied to the reset terminal of microcomputer 1.
is input, and the microcomputer 1 executes a predetermined program.

If the execution program of microcomputer 1 is normal, from time t ₁₁ , from port A to Figure 2b
As shown in , a pulse P with a constant period t ₁ is output,
This period t ₁ is the inversion time t ₂ determined by the resistor 2a and capacitor 2b of the monostable multivibrator 2.
Therefore, the output of the monostable multivibrator 2 does not invert and always continues to output a signal of "1" as shown in FIG. 2c.

The microcomputer 1 goes out of control,
The frequency of the output of port A decreases, and the above reversal time
If the monostable multivibrator 2 is not triggered within t ₂ , the output of the monostable multivibrator 2 reverses to "0" at time t ₁₂ as shown in Figure 2c.
Therefore, monostable multivibrator 3
is triggered to generate a reset signal with a constant pulse width.
_R2 will be output and the microcomputer 5 will be reset.

Next, when the program abnormality is recovered by the reset signal _R2 , the pulse P is outputted from the port A again at the time _t14 when a predetermined period of time has elapsed from the time _t13 when the reset signal _R2 became "0". Therefore, the output of the monostable multivibrator 2 becomes "1", and the output of the monostable multivibrator 3 becomes "0".

However, according to the conventional reset circuit of a microcomputer, if a runaway state occurs immediately after the reset signals R ₁ and R ₂ change from "1" to "0" at points t ₁₀ and t ₁₃ , the port is reset. Since pulse P is not output from A, the output of monostable multivibrator 2 does not change from "0" to "1".
Therefore, the reset signal is not outputted again. In other words, the reset signal is output only when a runaway occurs while the pulse P is being output from port A. Even if the runaway occurs before the pulse P starts being output, the reset signal cannot be output. This case has the disadvantage that it is not possible to recover from an abnormality in the microcomputer 1. In addition, if the microcomputer 1 receives radio wave interference continuously for a long period of time, only the first reset signal, _R2 , is output, so it has the disadvantage that it will not be able to recover normally when the fault is removed. Was.

The purpose of the present invention is to eliminate the above-mentioned drawbacks by providing a circuit that converts the magnitude of the frequency of a pulse signal output during operation of a microcomputer into a voltage value, detects the magnitude of this voltage value, and outputs a reset signal. This will be explained in detail below using examples.

FIG. 3 is a circuit diagram showing an embodiment of the reset circuit for a microcomputer according to the present invention. In the same figure, 10 is a microcomputer, and when the execution program is normal, the reset circuit is as shown in FIG. 4d. It is programmed in advance to output pulses P of a constant period from port A, and to set the output from port A to "0" or "1" when the execution program becomes abnormal due to a runaway state. The output from port A is supplied to a frequency-voltage conversion circuit 11, and the output of this frequency-voltage conversion circuit 11 is supplied to a Schmitt circuit 12 via a capacitor 19 and a resistor 20 connected in parallel with the capacitor 19 to form a discharge circuit. supplied,
A reset signal obtained from the output terminal 13 of the Schmitt circuit 12 is supplied to the reset terminal of the microcomputer 10.

The frequency-voltage conversion circuit 11 has a capacitor 1
4, a circuit consisting of a resistor 15 and a diode 16;
It consists of a circuit consisting of a resistor 17 and a diode 18, and the terminal voltage of the capacitor 19 is connected to port A.
It is proportional to the frequency of the pulse output from the

The Schmitt circuit 12 consists of a transistor 22 and a transistor 23 as switching elements, a capacitor 24, and a resistor 25, as shown in FIG.
As shown in FIG.
When it reaches HTL, it turns on and the output voltage from terminal 13 goes from "1" to "0", and when it drops and reaches the lower threshold voltage LTL, it turns off and the output voltage goes from "0" to "0". 1".

26 is a negative feedback circuit, and Schmitt circuit 12
It consists of a series circuit of a resistor 27 and a diode 28, with one end connected to the output terminal 13 of the Schmitt circuit 12 and the other end connected to the input side of the Schmitt circuit 12.

The operation of the microcomputer reset circuit constructed as above will be explained using the time charts shown in FIGS. 4a, b, c, and d.

When the power switch is off, the capacitor 19 is in a discharged state, but when the power switch is turned on at time _t21 and the power supply voltage is applied to the input terminal 29, the terminal voltage of the capacitor 19 is zero, so the transistor 22 is turned off, and therefore the voltage appearing at the output terminal 13 (the voltage on the collector side (power supply side terminal) of the transistor 22) becomes "1". Since this voltage charges the capacitor 19 via the negative feedback circuit 26, the terminal voltage of the capacitor 19 gradually increases, the transistor 22 is thereby turned on, and the voltage at the terminal 13 becomes "0". In this way, a reset signal _R1 is obtained when the power switch is turned on, and this reset signal _R1 is supplied to the reset terminal of the microcomputer 10. In addition,
When the transistor 22 is turned on, the capacitor 19 is discharged through the transistor 22.

If the microcomputer 10 is normal, a pulse P of a constant frequency is output from the port A at a certain time point _t22 based on the reset signal _R1 , and the capacitor 1 that differentiates this pulse P is output.
4, the resistor 17, and the diode 16 charge the capacitor 19, and the terminal voltage of the capacitor 19 increases, so the transistor 22 continues to be turned on. In this way, port A
When a pulse P of a constant frequency is output from
Transistor 22 is turned on, and no reset signal is output from terminal 13.

Here, if the execution program goes out of control due to some reason at time _t23 , the output of port A becomes "1".
Or, since it is held at "0", the capacitor 19 is not charged and its charge is mainly discharged through the resistor 20, and when the terminal voltage of this capacitor 19 drops and reaches the threshold voltage LTL, at time t. _{twenty four}
The transistor 22 is turned off, and the voltage at the terminal 13 becomes "1". Then, since the capacitor 19 is charged via the negative feedback circuit 26, the transistor 22 is turned on at time _t25 , and in this way, a reset signal _R2 is obtained, and the microcomputer 10 is reset by this reset signal _R2 . and run the program for the first time.

Here, if the runaway state continues without normal recovery even though the reset signal _R2 is supplied, the capacitor 19 is discharged through the resistor 20 at time _t25 , and the terminal of the capacitor 19 is When the voltage gradually drops and reaches the threshold voltage LTL, the transistor 22 is turned off at time _t26 , and then the capacitor 19 is charged through the negative feedback circuit 26, so the transistor 22 is turned on at time _t27 .
In this way, the reset signal _R3 can be obtained, and the microcomputer can be normalized using this reset signal _R3 . In this case, if the microcomputer 10 continues to run out of control despite the supply of the reset signal _R3 , the reset signal _R3 is supplied over a predetermined period.

Therefore, according to the invention, the reset signals R ₁ , R ₂
Even if the microcomputer 10 goes into a runaway state immediately after the pulse is supplied and no pulse is output from port A, the reset signal can be output again, so the degree of normal recovery can be increased. Furthermore, even if radio interference occurs for a long time, the reset signal is supplied at regular intervals, so that the microcomputer 10 can be automatically restored quickly after the disturbance is removed.

Also, when the power switch is turned on, the reset signal _R1
Since it has a function for supplying , there is no need for a special circuit for that purpose, and the configuration is simple.

Note that in the present invention, the frequency-voltage conversion circuit 1
Figure 5 shows the input/output characteristics of 1 when the frequency is _0.
By setting the characteristics such that the output voltage decreases when the output voltage becomes abnormally large beyond the limit, even if the frequency of the output pulse from port A becomes abnormally high due to the runaway of the microcomputer 10, the runaway state will not occur. It is possible to supply a reset signal by assuming that the

[Brief explanation of the drawing]

FIGS. 1 and 2 a to d are circuit diagrams and operating waveform diagrams showing an example of a reset circuit of a conventional microcomputer, and FIGS. 3 and 4 a, b, c, and d are diagrams of a microcomputer according to the present invention. A circuit diagram and a waveform diagram of one embodiment of the reset circuit are shown, and FIG. 5 is a characteristic diagram showing another embodiment of the microcomputer according to the present invention. 1, 10... microcomputer, 11...
Frequency-voltage conversion circuit, 12...Schmitt circuit,
13... Output terminal, 14, 19, 24... Capacitor, 22, 23... Transistor, 26... Negative feedback circuit.

Claims (1)

[Claims] 1 In a microcomputer reset circuit having a reset terminal and a port that outputs pulses of a constant frequency during normal operation, a frequency-voltage conversion circuit 11 that converts the output pulse from the port into a voltage, and an output of this frequency-voltage conversion circuit 11. A capacitor 19 that charges voltage and this capacitor 1
a resistor 20 connected in parallel to 9 to form a discharge circuit;
is connected between the power supply and ground, and the charging voltage of the capacitor 19 is at a high predetermined level.
Turns on when HTL is reached, lower predetermined level
It is equipped with a switching element 22 that turns off when the voltage drops to LTL, and a negative feedback circuit 26 that supplies the voltage appearing at the power supply side terminal of this switching element 22 to the capacitor 19, and connects the power supply side terminal of the switching element 22 to the microcomputer. When the microcomputer goes out of control and output pulses are no longer generated, the charging voltage of the capacitor 19 is discharged and the switching element 22 is turned off, the power supply of the switching element 22 is connected to the reset terminal of the switching element 22. The power supply voltage is made to appear at the side terminal, and this power supply voltage is supplied to the capacitor 19 through the negative feedback circuit 26, so that this power supply voltage is supplied to the reset terminal as the reset signal _R2 . In addition, when the power is turned on, the power supply voltage appears at the power supply side terminal of the switching element 22, which is set to OFF, and this generates a reset signal.
A reset circuit for a microcomputer, characterized in that the reset circuit is configured to be supplied to a reset terminal as _R1 .