JPS61156443A - Runaway monitoring device of microcomputer - Google Patents

Abstract

PURPOSE:To give automatically the reset to a microcomputer and to improve a reliability by constituting a single pulse of a single shot pulse generating circuit which inputs to a resetting terminal, when a pulse detecting circuit, a charging discharging circuit and a microcomputer run away and the output of the charging discharging circuit is the prescribed value or above. CONSTITUTION:When a program is normally operated, a pulse (a) of a constant period t0 is outputted, the fall of the same pulse (a) is detected at a pulse detecting circuit 1, the pulse goes to be a differential waveform pulse and is inputted to an inverter gate element 6. A rectangular wave is outputted from the inverter gate element 6, and inputted to a charging discharging circuit 2. At the charging discharging circuit 2, a pulse (c) is discharged during H, charged during L and the charging and discharging are repeated. When R1, R2, R5, C1 and C2 are determined so that a peak voltage Vp1 of a charging discharging waveform of the charging discharging circuit 2 may not exceed the threshold of an input voltage of a single shot pulse generating circuit 3, for the output of the single shot pulse generating circuit 3, L is continued and the reset is not given to the microcomputer.

Description

[Detailed Description of the Invention] (Industrial Application Field) The microcomputer runaway monitoring device of the present invention detects the abnormality and automatically resets the microcomputer when the microcomputer runs out of control for some reason. Moreover, it is designed to automatically return after being reset.

(Prior Art) A conventional monitoring device of this type is shown in FIG. 3.

This means that when the program is operating normally and pulse a is being output from the microcomputer, rising edge detection circuit A detects the rising edge of pulse a, charging/discharging circuit B is discharged, and the input terminal of comparison circuit C is connected. When the program goes out of control and the output of pulse a stops, charging/discharging circuit B is charged, and the voltage input to the input terminal of comparator circuit C becomes the reference voltage. When the voltage exceeds V ref, the comparator circuit C outputs a runaway detection signal.

(Problem to be Solved by the Invention) In the device shown in Figure 3, the runaway detection signal is a mere level output, so if it is directly connected to the reset terminal of the microcomputer, once runaway occurs, the computer will remain stopped. There was a problem that it could not be automatically restored.

Further, in this device, two gate elements E and F are used in the rising edge detection circuit A, and a comparator IC is used in the comparison circuit C, resulting in a problem of high cost.

(Means for Solving the Problems) An object of the present invention is to detect runaway of a program, automatically reset the microcomputer, and enable automatic recovery to improve reliability.

Therefore, the runaway monitoring device of the present invention, as shown in FIG. When the computer goes out of control and the output of the charging/discharging circuit 2 continuously exceeds a predetermined value for a predetermined period of time or more.

It consists of a single shot pulse generation circuit 3 which generates a single pulse and inputs it to the reset terminal of the microcomputer.

The pulse detection circuit 1 is composed of a capacitor C1, a resistor R1, and an inverter gate element 6.

The charging/discharging circuit 2 includes resistors R2 to R5, a transistor Tr, and a capacitor C2.The single shot pulse generating circuit 3 includes an AND gate element 7, a capacitor C3, and a resistor R6.

(Function) In the device shown in Fig. 1, when the program is operating normally and the microcomputer is outputting a pulse a with a constant period to, the falling edge of the pulse a is detected by the pulse detection circuit l, and the differential This becomes a waveform pulse (FIG. 2b) and is input to the inverter gate element 6.

The inverter gate element 6 outputs a rectangular wave (the width of H is tl and the width of L is tO-tl) as shown in FIG.

tl can be found from the following equation (1), assuming that the threshold value of the inverter gate element 6 is Vsl.

tl=cl-R1-1n((V-Vsl)/VO)
-... (1) In the charging/discharging circuit 2, while pulse C is H (tl
) is discharged and charged for L (to-tl), and this charging and discharging is repeated.

Peak voltage V of charging/discharging waveform of charging/discharging circuit 2 (Fig. 2 d)
From equations (1), (2), and (3), R1,
If R2, R5, CI, and C2 are determined, the output of the single shot pulse generation circuit 3 will continue to be L as shown in FIG. 2e, and the microcomputer will not be reset.

Vs2 <Vp =V(1-e'a(Lf1+1)
*11 @ (2) χO to Vpe- (3) Next, when the program goes out of control and the output signal a from the microcomputer is fixed at H or L, the charging/discharging circuit 2 is not charged. The peak value Vp2 of the discharge waveform
exceeds the threshold value s2 of the AND gate element 7, and a differential waveform pulse (FIG. 2f) is output to the single shot pulse circuit 3, which resets the microcomputer.

At this time, if the threshold value of the reset input of the microcomputer is set to Vs3, the width t2 of the reset pulse f is as follows (
4) Determined from the formula.

t2':: -C3R4In(VS3/V) @”
(4) The reset microcomputer is reset only while the reset pulse f is input, and automatically returns when the pulse becomes L.

In the device shown in Figure 1, automatic reset and runaway are repeated (even if the automatic reset is applied, the runaway starts again).
This results in an oscillating phenomenon. In this case, it is preferable to automatically stop when this occurs more than a predetermined number of times within a predetermined period of time, and to output this state to the outside.

Also, it is a good idea to make sure that it is canceled when the power is turned off and then turned back on.

(Effects of the Invention) Since the present invention is configured as described above, it has the following effects.

(1) Since the microcomputer is automatically reset at the same time as the program runs out of control, the reliability of the system is improved.

(2) Since the reset pulse f is a single shot pulse, the reset microcomputer automatically returns when the reset pulse f becomes L, and the operation of the microcomputer automatically resumes when the runaway ends.

(3) Costs are reduced because it can be constructed using only inexpensive parts without using a comparator.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing an example of the runaway monitoring device of the present invention, FIG. 2 is a waveform diagram explaining the operation of the device shown in FIG. 1, and FIG. 3 is a wiring diagram of a conventional runaway monitoring device. a is pulse 1 is pulse detection circuit 2 is charging/discharging circuit

Claims (1)

[Claims] There is a pulse detection circuit that detects pulses with a constant period output from the microcomputer, a charging/discharging circuit that charges and discharges the detected pulses, and a pulse detection circuit that detects pulses with a constant period that are output from the microcomputer, and a charging/discharging circuit that charges and discharges the detected pulses. A microcomputer runaway monitoring device consisting of a single shot pulse generation circuit that generates a single pulse and inputs it to the reset terminal of the microcomputer when the value exceeds the specified value.