JPS59100958A - Runaway detecting circuit of microcomputer - Google Patents

Abstract

PURPOSE:To decrease the number of component parts by using a frequency selecting circuit, a voltage reduction detecting circuit and a rectangular wave oscillating circuit which produces a signal to reset a microcomputer by the detection signals of said selecting circuit and detecting circuit. CONSTITUTION:The reverse input terminal (-) of an operational amplifier 47 is set ''L'' level of a prescribed cycle as long as a microcomputer has normal working and the output of oscillation is supplied with a prescribed frequency. As a result, the ''H'' level is not raised up to the reference voltage level although it is fed back by the output of the amplifier 47. If the microcomputer has some fault with reduction of oscillating frequency, the potential of the terminal (-) of the amplifier 47 rises up by a feedback resistance 43. This circuit prevents the input of the following signals. Therefore the potential of the terminal (-) becomes higher than the reference voltage V2, and the output of the amplifier 47 is set at ''L'' level. Then a reset signal is produced.

Description

[Detailed Description of the Invention] Among products using microcomputers, products used in automobiles and the like are powered entirely by pantries, so the power supply voltage of the microcomputer may be unstable (for example, if the cell
When the motor starts, the voltage drops suddenly), and external factors such as noise and induction disturbances can cause the microcomputer to malfunction and go out of control.

Conventionally, runaway has been detected by oscillating a rectangular wave signal of a constant frequency from a microcomputer and monitoring all of these signals. In addition, a separate circuit is configured to prevent runaway from fluctuations in the power supply voltage. However, in order to configure these circuits separately and use, for example, an OR circuit as one runaway detection circuit, the number of components is large and the circuit is complicated.

Therefore, the present invention configures the runaway detection circuit with a relatively simple circuit, and reduces the number of parts. The purpose is to reduce iQ.

The basic configuration of the present invention is a rectangular wave oscillation circuit, frequency selection 1
It is a combination of a circuit and one giant circuit for detecting pressure reduction, and if the oscillation signal output from the microcomputer exceeds the frequency determined by the frequency selection circuit, the oscillation signal is not transmitted to the next stage, and a rectangular wave is output. The oscillation circuit generates a reset pulse to reset the microcomputer.

Similarly, if the emitted +a signal is below a certain frequency, this is detected and applied. Furthermore, it is possible to block the transmission of the oscillation signal and perform a reset even when the voltage decreases. Therefore, by combining the above eight circuits, the parts can be made common, and the number of parts can be greatly reduced.

Embodiments will be described below based on the drawings. Terminal 1 is connected to a constant power supply (-1-Vcc), and terminal 2 is the microcomputer's oscillation output K, Q. The terminal 4 is connected to the J-fi, and the terminal 4 is connected to the reset terminal of the microcomputer. First, in the frequency selection circuit 1o, the terminal 2, that is, the oscillation output of the microcomputer, is connected to the resistor 11, the diode 12, and the resistor 13.
It is connected to one end of the capacitor 14 via the inverting input terminal ←) of the operational amplifier 15. In addition, the reference voltage divided by the constant power supply Vcc and the total resistance 16.
Feedbanked via 8'z. The output of this operational amplifier 15 is connected to a capacitor 21, and a resistor 2.
2, 2 sy, (input to the base of the transistor 24 through the collector of the transistor 24.
It is connected to the collector of the transistor 36 of the voltage reduction detection circuit 8o and to the resistor 411 of the rectangular wave q oscillation circuit 40 via. The reduced voltage detection circuit 80 is connected to a battery power source at a terminal 8, and is connected to a resistor 81 and a Zener diode 83 via an nX resistor 82. The other end of the resistor 81 is connected to the constant power supply ■cc, and the Zener diode 8,8
The other ends are connected to the bases of transistors 341 and 84, respectively. The collector of the transistor 86 is grounded by the resistor 35 and the base of the transistor 86 is connected to the ground. Next, the square wave oscillation circuit 4.0 has a resistor 4.1
The other end of σ is input to the inverting input terminal (-2) of the operational amplifier 47, and is also connected to the output terminal of the operational amplifiers 4 and 7 via capacitors 4 and 2.
- A second reference voltage divided by the constant power supply Vcci resistor 441.45 is input to the non-inverting input terminal (G) of 7, and the output is further fed-banked by the resistors 4 and 6.

Next, the operation of each circuit will be explained. Frequency selection circuit 1
Each resistance of 0 is defined here as follows. That is, the resistance value of the resistor 11 is made larger than that of the resistor 13, and each resistor 16, 17, and 18 degrees Celsius are made to have the same resistance value. At this time, the oscillation signal of the microcomputer (for example, 100
When a rectangular wave of Hz) is input, this oscillation signal becomes lH/
When the signal is at l level, the signal is connected to the resistor 11 and capacitor 1.
4, the integral is n\ and when the level is lLl, the resistance l]
1. The diode 18 and capacitor 14 reduce the amount of waste by 7L. Here, each resistance value is set to be sufficiently small compared to 18 resistors and 11 resistors, so the integration time constant is smaller at the time of falling (switching from 〃H〃 level to 〃I,〃 level). It becomes smaller than when starting up.

Next, this integrated waveform is input to the inverting input terminal of the operational amplifier 15, but since the output of the operational amplifier 15 is fed back to the non-inverting input terminal by the resistor 18, the reference voltage k ■As 1, resistance 16.17.1
If all resistance values of 8 are set equal, the output of the operational amplifier will be at iHl level (considered as constant power supply voltage Vcc).
When , vl:4'd・VCC becomes 〃L〃level (
(considered to be ground level), ■l=1/8.
vcc, and the output of the operational amplifier 1.5 has a waveform with hysteresis.

Next, this output signal is differentiated by a capacitor 21 and a resistor 28, tn, and inverted by a transistor 24, and is input to a rectangular wave oscillation circuit 4 (1).

Therefore, every time this waveform signal is input, the inverting input terminal (-) of the operational amplifier 47 outputs lLo L/L according to the frequency of the oscillation output of the microcomputer.
Will it be hell? Op amp 47 output 411Hl
maintains the level. Here, since the inverting input terminal (-) G of the operational amplifier 47 is feedbanked from the output terminal by resistors 4 and 8, once it reaches the //L level, the time is determined by the capacitor 42. The potential gradually increases at a constant rate. In addition, the reference voltage of the non-inverting input terminal (G) of the operational amplifier 47 is 72, and the resistance values of the resistors 44, 45, and 46 are all the same as in the operational amplifier 15. Therefore, the output terminal of the operational amplifier 47 is Hl level (V
When c c ), V2:2/3-Vcc, lL
i L/H/l/(7) time Niha, v2=1/3,
Vcc is turned on.

When the microcomputer is operating normally and the oscillation output is input at a predetermined frequency, the operational amplifier 4
Since the inverting input terminal ←) of 7 is set at lLl level at a predetermined period, /z)i// is output from the operational amplifier 47.
Even if the level is fed banked, it does not rise to the reference voltage (η=2/8.vcc in this case), and the output of the operational amplifier 47 is maintained at the oHtt level.

Next, when an abnormality occurs in the microcomputer and the oscillation frequency becomes low, the potential of the inverting input terminal (-) of the operational amplifier 47 increases due to the feedback resistor 48, but the next signal is not input. , becomes higher than the reference voltage (2), the output of the operational amplifier 47 becomes L level, and a reset signal is generated. On the other hand, when the oscillation frequency of the microcomputer becomes higher, the rise time constant of the frequency selection circuit IO (the resistor 11 and the capacitor 14
As mentioned above, the H7l level (here, the reference voltage vl of the operational amplifier 15 = Al
1・Vcc), the next falling signal is input, and the output of the operational amplifier 15 becomes ItL.
The iHl level is maintained without switching to the l level. Therefore, the potential of the inverting input terminal ←) of the operational amplifier 47 also continues to rise from the feedback resistor 4.31F- after changing the L// level, and the reference voltage v2: 2.
/3 ・Vcc cannot be tracked and a reset is required.

In this manner, if the microcomputer goes out of control and an abnormality occurs in its oscillation frequency, it is possible to detect and reset the oscillation frequency regardless of whether the frequency changes to high or low.

Next, the operation of the voltage reduction detection circuit 80 will be explained.

Normally, the battery power supply voltage is high enough, so the resistor 31.
The voltage divided by 32 causes the transistor 841 to
is conducting, so transistor 86 is cut off. However, the battery power supply dropped and transistor 84
When hf is shut off, the transistor 36 becomes conductive and the constant power supply voltage Vcc is input to the inverting input terminal of the operational amplifier 47 via the resistor 41 ←), so the output of the operational amplifier 47 becomes Well, it takes a reset.

Incidentally, when the power supply of the microcomputer is turned off, the capacitor 4.2 of the square wave oscillation circuit 40 changes the level of the inverting input terminal (-) of the operational amplifier Φ7 to the output of the operational amplifier 47. It also has the function of resetting the micro computer as ILL/L/HELL.

[Brief explanation of drawings]

The figure is a circuit diagram showing an example of a runaway detection circuit for a microcomputer according to the invention. IO...Frequency selection circuit, 80...Low voltage detection circuit, 4.0...Square wave oscillation circuit Patent applicant Reio Nakai, Representative of Aisin Seiki Co., Ltd.

Claims (1)

[Claims] A frequency selection circuit detects that the oscillation signal output from the microcomputer is higher than a predetermined frequency and lower than a second predetermined frequency, and a reduced voltage detection circuit detects that the power supply voltage is lower than a predetermined voltage. A runaway detection circuit for a microcomputer, comprising a circuit and a rectangular wave oscillation circuit that emits a signal that the microcomputer detects based on the detection signals of the respective circuits.