JPS5846450A - Detector for abnormal operation of microcomputer - Google Patents

Abstract

PURPOSE:To detect a failure in the operation of a microcomputer and also to evade an increase of the number of memories in the microcomputer and the use of an extra output terminal, by utilizing the output signal of the microcomputer to an element to be driven. CONSTITUTION:A rise detecting circuit 12 is connected to the input side of an element 11 to be driven to generate a pulse signal to a charging and discharging circuit 13 when an output appears at an output terminal 10a, and a voltage detector 14 which discriminates between the levels H and L of the output of the charging and discharging circuit 13 is connected to the output side of the circuit while the output side of the detector is connected to a power source circuit or an output circuit. The rise detecting circuit 12 inputs the signal of a microcomputer 1 directly to one terminal of an AND gate 15 and an input to the other terminal, and a capacitor C1 is connected between the 1st and 2nd resistances R1 and R2. The charging and discharging circuit 13 is equipped with a transistor Tr, and its collector side is connected to a power source VDD through the 4th resistance R4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an abnormal operation detection device that detects abnormal operation when a microcomputer malfunctions for some reason and prevents the output from continuously maintaining an abnormal state. It is.

Conventionally, a device using a monostable multivibrator as shown in FIG. 1 has been known as a device for detecting that a microcomputer (hereinafter referred to as microcomputer) is in an abnormal state.

In other words, a retriggerable monostaple multivibrator (retrigger monostable vibrator) 2t is connected to the output terminal 1a of the microcomputer 1, and a pulse signal R1 is periodically generated at the output terminal of the microcomputer 1. When the microcomputer is operating normally, it is at an H level. When the microcomputer is malfunctioning, an L-level signal is output, and when the L-level signal is output, the microcomputer malfunction is detected, and the power supply voltage of the power supply board that supplies power to the microcomputer is adjusted. 0
(2) Alternatively, the drive is turned off for dangerous loads among the loads being driven.

However, the above-mentioned device has the following drawbacks.

■ It is necessary to create a software process to periodically generate pulse signals at the microcomputer output terminal, which increases the amount of memory on the microcomputer.

■ It is necessary to provide a dedicated output terminal for pulse signal generation, and when using a one-chip microcontroller with a limited number of output terminals, an external output expansion IC must be provided to increase the number of output terminals. becomes complicated and costly.

The present invention has been made in view of the above circumstances, and its purpose is to detect abnormal operation of a microcomputer without increasing the memory of the microcomputer or using extra output terminals. The purpose is to provide equipment.

Embodiments of the present invention will be described below with reference to FIG. 2 and subsequent figures.

A driven element 11 such as a multi-digit display or an input cusp inch incorporated in a matrix is connected to the output terminal IOa of the one-chip microcomputer 10, and a periodically turned on/off signal (pulse signal) outputted from the microcomputer 10 is ) is applied. A rise detection circuit 12 is connected to the input side of the driven element 11, and generates a pulse signal to the charge/discharge circuit 13 when the output rises to the output terminal 10a (when the ON signal rises). In addition, a voltage detector 14 is connected to the output side of the charge/discharge circuit 13 for determining whether the output of the charge/discharge circuit 13 is H or L, and the output side thereof is connected to a power supply circuit or an output circuit. be.

The rise detection circuit 12 directly inputs the signal from the microcomputer 10 to one terminal of the AND gate 15, and inputs the signal to the other terminal to the inverter 16, the first . input via the second resistor R1 + 几2, and the first. A capacitor C1 is connected between the second resistor R1 and the second resistor R1.
A signal is output, an off signal is input, and an L signal is output just in case.

The charge/discharge circuit 13 includes a transistor Tr whose base is connected to the output side of the AND gate 15 via a third resistor RI, and whose collector side is connected to the power supply DD via a fourth resistor R4f. 5 resistance Re, capacitor C2
, CMO8 of the voltage detector 14 via the sixth resistor 'FL6.
When the output of the AND gate 15 is 1, a discharging circuit is formed, and when the output is L, a charging circuit is formed.

The voltage detector 14 determines whether the output of the charging/discharging circuit +3 is H (higher voltage than the determination voltage) or L (lower voltage than the determination voltage), and the threshold voltage for determination is CMO.
0.3 to 0.7 when using S gate 16' VI)
It becomes D.

On the other hand, when the 1-chip micron 10 is used to control a copying machine, it almost always has a signal that periodically turns ON and 01i'F at its output.

This is to perform time-sharing input or output in order to make effective use of the limited number of input and output terminals, and a typical example is the use of a dynamic lighting device to display multi-digit numbers. This is an example.

Next, the operation of detecting abnormal operation of the microcomputer using the signal for driving the gate driver of the dynamic lighting device will be explained based on the timing factors shown in FIG.

First, it is assumed that the period of the digit drive signal (microcomputer output) is τ8, and the time when the signal is in the H state is τON.

Then, the rise detection circuit 12 receives the microcomputer output signal and receives the pulse width τpt determined by the first resistor R1, the capacitor C1, and the threshold voltage of the (7MO8 gate).
- Outputs the pulse (H signal) at 9 o'clock when the input rises. However, if the time τOH is smaller than the pulse width τp, the pulse width τ becomes ton regardless of the above.

In the charge/discharge circuit 13, when the output of the rising edge detection circuit 12 is L, the transistor T is turned off (R4+Rs), and the output becomes 0.
Since a charging circuit having a time constant of 2 is formed, the output voltage VjI of the charging/discharging circuit 13 at that time can be expressed as when t-p t τθ.

Also, when the output of the rising edge detection circuit 12 is L, R'+
Assuming that the discharge circuit has a time constant of Ct, the output voltage V+i at that time is 0<:t.When tp, V+i -V'・e''''
It can be expressed as 1”0 ・1・(2).

In equations (1) and (2), v' is the voltage when discharging starts from a charged state, and the collector-emitter voltage Vom' of the transistor Tr is:
Assume that ov, e−g%2.

In other words, it is easy to actually make the voltage between the collector and emitter of the transistor Tr less than αOIV by using a 28CI8150R etc. as the transistor, and if a film capacitor of about 4700 PF is used as the capacitor Cz, R6 can be 0Ωfp, There is no problem even if it is approximated by vam -0, eR5c2-Q.

Note that the above-mentioned equations (1) and (2) express Vu at 0 < 1 ≦ τB, but since it is sufficient to take periodicity into consideration for lifting a heavy platform per day, here it is expressed as 0 Let us consider the range t≦τB.

Therefore, v+s-V'e-stone 7 at l-r day
As long as G does not exceed the voltage detector 140 input voltage Vtb, the output of the voltage detector will not become H. That is, 1 day V th >V' e - one side (4)
If each constant is selected so as to satisfy the following, the output of the limit voltage detector 4, where the output of the microcomputer 10 changes with a period of TB, will not become H and no abnormal signal will be generated.

Furthermore, when the microcomputer 10 malfunctions and the periodic change in output stops, the output voltage v11 of the charge/discharge circuit 13 exceeds the input threshold voltage Vth, the output of the voltage detector 14 becomes I(, and the microcomputer 10 malfunctions. can be detected.

As described above, the present invention can detect abnormal operation of the microcomputer by using the output signal of the microcomputer 10 sent to the driven element 11.

Therefore, there is no need to provide the microcomputer 10 with a command function for outputting a signal for detecting abnormal operation, so there is no need to increase the number of memories of the microcomputer or use an extra output terminal.

[Brief explanation of the drawing]

Fig. 2 is an explanatory diagram of a conventional example, Fig. 2 is an explanatory diagram of an embodiment of the present invention, and Fig. 3 is a diagram showing a different operation timing. 10 is a microcomputer, 10a is an output terminal, 11
12 is a driven element, 12 is a rising detection circuit, 13 is a charging/discharging circuit, and 14 is a voltage detector. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Masaaki Yonehara Patent Attorney Tadashi Hamamoto Figure 2

Claims (1)

[Claims] A rise detection circuit 12 connected to the output terminal 10a of the microcomputer 10 that periodically sends a signal to the driven element 11, a charge/discharge circuit 13 connected to the rise detection circuit 12, and an output voltage of the charge/discharge circuit 13. 1. An abnormal operation detection device for a microcomputer, characterized in that a voltage detector 14 outputs an abnormal operation signal when the voltage reaches a predetermined voltage.