JPH11203172A - Watchdog monitoring circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reset a microcomputer and to prevent malfunctions by simultaneously providing the frequency judgement circuit of a watchdog waveform and a duty factor judgement circuit. SOLUTION: The duty factor judgement circuit 13 is added so as to cope with the abnormality of a duty factor not detected by a conventional frequency judgement circuit 7 among pulse waves outputted from a W/D terminal 2 provided in the microcomputer 1. The duty factor judgement circuit 13 is provided with a low-pass filter 10 in an initial stage, only the pulse cycle change of low frequency components is taken out by the low-pass filter 10 and only a part where a pulse width becomes wide in the case that the duty factor becomes abnormal is extracted. Then, the extracted pulse waves are passed through a voltage follower 11 and sent to a differential amplifier circuit 12 and a voltage value intended beforehand is outputted there. The voltage is sent to a buffer amplifier 6, current-amplified there and then, inputted to an RES terminal 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a duty ratio judging circuit in a watchdog monitoring circuit for monitoring a watchdog waveform output during operation of a microcomputer.

[0002]

2. Description of the Related Art In today's automobiles, complicated and various controls are performed by a microcomputer in controlling the operation of an engine and electrical components. The parts to be controlled are roughly classified into a power control system required for driving the automobile and an environment control system for making the environment in the vehicle interior favorable for the occupant.

[0003] In general, the environment in which an automobile is used is very severe for these electrical components. In particular, spiking noise from an ignition system of an engine that generates electric noise constitutes the noise. It is very harmful in terms of the frequency components that are present. In particular, strict measures against noise intrusion are applied to the frequency components in the frequency band in the region where the microcomputer operates.

[0004] In particular, a power control system related to the running of an automobile is required to take stricter measures against noise, such as a brake system, a traction control system, an engine rotation control system, and a transmission control system of an automatic car. , Since it is a part directly related to occupant safety, a mechanical malfunction prevention system has been taken as a countermeasure in addition to electrical noise countermeasures.

[0005] In addition, even for an unintended operation caused by an occupant's manual operation error, for example, in an automobile having an automatic transmission, unless the brake pedal is depressed, the operation of the shift lever becomes impossible. And other safety measures have been implemented, which has had the effect of reducing accidents.

Next, as measures against noise relating to comfortable equipment for occupants in the vehicle cabin, a general noise filter is used to prevent noise from being mixed into car audio, and a noise filter is applied to a temperature control device of an air conditioner for an automobile. Prevention of malfunction due to equipment, electrical shielding to a microcomputer used in a temperature control device, and monitoring of malfunction by a watchdog monitoring circuit have been performed.

FIG. 2 schematically shows an example of a circuit conventionally used for monitoring the W / D waveform 20 of the microcomputer 1.

When a program of the microcomputer 1 is executed, a W / D waveform 20 is always output from the W / D terminal 2, and the operation of the microcomputer 1 is monitored by monitoring the W / D waveform 20. Is determined.
The W / D waveform 20 is input to the frequency determination circuit 7, and the frequency determination circuit 7 outputs a reset signal 21 to the RES terminal of the microcomputer 1 when the W / D waveform 20 is a pulse wave indicating a predetermined cycle. 3 is not output.

However, when the W / D waveform 20 is no longer a pulse wave having a predetermined period, the Schmitt trigger circuit 5
Excites a pulse wave sufficient for resetting, and outputs a reset signal 21 to the RES terminal 3.

The frequency judging circuit 7 is provided with a high-pass filter circuit 4 at the first stage, and the pulse cycle of the W / D waveform becomes longer, or a new unintended pulse wave appears between the pulse waves. In this case, only this component is rectified in the form of a pulse wave to the next stage and output.

At the timing when the rectified pulse wave is at the Lo level, a Schmitt trigger circuit 5 provided in the next stage excites a pulse wave sufficient for resetting, and this pulse wave is current-amplified by the output buffer 6. , RE
The signal is input to the S terminal 3 as a reset signal.

[0012]

In such a conventional noise countermeasure, in particular, in a watchdog monitoring circuit for monitoring the operation of a microcomputer, a W / D signal output during a program operation of the microcomputer is used.
Only the frequency of the D waveform was monitored. Assuming that the operation is normal while the W / D waveform is being output, the microcomputer does not output a reset, and the output of the waveform is interrupted.
The reset signal is output only when the voltage value of the i level or the Lo level becomes unstable.

Therefore, for example, if the Hi level and Lo level of the W / D waveform are correct and the number of rectangular waves per unit time, that is, the pulse period is correct, even if the duty ratio of the rectangular wave is abnormal, The watchdog monitoring circuit cannot detect abnormalities, and prevents runaway of the microcomputer, which leads to abnormal operation such as poor temperature control of the air conditioner, abnormal switching of cooling and heating, and inability to control the rotation of the blower fan. Could not.

An object of the present invention is to provide a watchdog monitoring circuit capable of monitoring a duty ratio of a rectangular wave in addition to monitoring a frequency abnormality of a W / D waveform to detect an abnormality.

[0015]

In order to solve the above-mentioned problems, the present invention is combined with a microcomputer which outputs a watchdog waveform during the operation of a program, and monitors the watchdog waveform to detect an abnormality. In a watchdog monitoring circuit that sometimes outputs a reset waveform, a watchdog monitoring circuit characterized in that the watchdog waveform frequency determination circuit and the duty ratio determination circuit are simultaneously provided is a solution.

In this way, the microcomputer can be reliably reset even when an abnormality in the duty ratio occurs in addition to an abnormality in the frequency of the W / D waveform, thereby preventing a malfunction. Become.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments for explaining the present invention will be described.

FIG. 1 is a schematic circuit diagram for explaining a watchdog monitoring circuit according to the present invention. FIG. 3 is a schematic diagram for explaining the W / D waveform 20.

FIG. 1 shows, in addition to the conventional frequency determination circuit 7 shown in FIG.
The tee ratio determination circuit 13 is added in parallel.

In the pulse wave output from the W / D terminal 2 provided in the microcomputer 1, the abnormality of the duty ratio which is not detected by the conventional frequency judgment circuit 7 is judged by the circuit of FIG. Circuit 1
3 is added. The duty ratio determination circuit 13 is provided with a low-pass filter 10 at an initial stage. The low-pass filter 10 extracts only a pulse cycle change of a low-frequency component, and a portion where the pulse width is widened when the duty ratio becomes abnormal. Only those are extracted.

Next, the extracted pulse wave is sent to a differential amplifier circuit 12 via a voltage follower 11,
Here, the intended voltage value is output in advance. This voltage is sent to the buffer amplifier 6, where it is input to the RES terminal 3 after current amplification.

In this manner, it is possible to detect an abnormality in the duty ratio, which cannot be detected conventionally.

FIG. 3 shows W / D output from the W / D terminal 2.
This is a comparison of the pulse widths of the D waveform 20 in the normal state and the abnormal state. When attention is paid to the widths a and b in the figure, the widths a and b are equal in the normal state. However, for some reason, the operation of the microcomputer 1 becomes unstable, and if a runaway state occurs, a state occurs in which the widths of a and b are not equal.

This so-called abnormality of the duty ratio falls into a state in which the width of “a” is larger than the width of “b”, for example, as shown in FIG. As described above, when the width of “a” is widened, when the pulse wave is observed in the dimension of the frequency distribution by Fourier transform, the low frequency component increases as compared with the case of the normal pulse wave. The characteristic low-frequency component is extracted by the first-stage low-pass filter 10 so that an abnormality in the duty ratio can be detected.

The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

[0026]

As described above, according to the first aspect of the present invention, the microcomputer can be reliably reset even when the duty ratio abnormality occurs in addition to the W / D waveform frequency abnormality. It is possible to provide a watchdog monitoring circuit capable of preventing a malfunction from occurring.

[Brief description of the drawings]

FIG. 1 shows an overall circuit diagram of a watchdog monitoring circuit according to the present invention.

FIG. 2 shows an overall circuit diagram of a watchdog monitoring circuit according to the prior art.

FIG. 3 shows the W of the microcomputer.
FIG. 4 is a diagram for explaining a pulse wave output from a / D terminal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Microcomputer 2 ... W / D terminal 3 ... RES terminal 4 ... High pass filter 5 ... Schmitt trigger circuit 6 ... Buffer amplifier 7 ... Frequency judgment circuit 10 ... Low pass filter 11 ... Voltage follower 12 ... Differential amplifier 13 ... Duty Ratio judgment circuit

Claims (1)

[Claims] 1. A watchdog monitoring circuit combined with a microcomputer (1) that outputs a watchdog waveform during operation of a program, monitors the watchdog waveform, and outputs a reset waveform when an abnormality is detected. A watchdog monitoring circuit characterized by having a frequency judgment circuit (7) and a duty ratio judgment circuit (13) at the same time.