JPH04291610A - Reset circuit for microcomputer - Google Patents

Abstract

PURPOSE:To obtain a reset circuit capable of quickly and surely inputting a reset signal to plural microcomputers (MCs) even when software runs away or a device power supply is instantaneously disconnected and attaining restoration to normal operation. CONSTITUTION:A low voltage detecting circuit 3 for monitoring a voltage drop is connected to the device power supply 2 for a control device 1 and runaway detecting circuits 5a, 5b for monitoring the runaway of software in respective MCs 4a, 4b are included in the device 1. The MCs 4a, 4b respectively have reset terminals 6a, 6b, and at the time of depressing a reset switch when the device 1 generates abnormality, the whole control device 1 is reset. The circuits 5a, 5b connected to the MCs 4a, 4b through runaway monitoring signals 9a, 9b respectively monitor the runway of software processing in the MCs 4a, 4b and runaway detection signals 10a, 10b from respective circuits 5a, 5b are inputted to an OR circuit 11, which executes the OR operation of the signals 10a, 10b and outputs the OR result to the reset terminals 6a, 6b of the MCs 4a, 4b.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset circuit for a microcomputer, which is used in a control device using a plurality of microcomputers, and includes a low voltage detection circuit for the device power supply and a runaway detection circuit for the microcomputer.

0002

[Prior Art] In recent years, in order to improve reliability and safety, various abnormality detection means have been installed in control devices to automatically reset microcomputers as necessary. Ta.

Conventionally, there has been a reset circuit for this type of microcomputer as shown in FIG. The configuration will be explained below with reference to the drawings. As shown in the figure, a low voltage detection circuit 3 for monitoring a drop in voltage is connected to a device power source 2 of a control device 1 used for equipment or the like. 4 is a microcomputer (hereinafter referred to as a microcomputer);
Reference numeral 5 denotes a runaway detection circuit that monitors software runaway of the microcomputer 4. Also, the reset switch (
(not shown), and when the control device 1 becomes abnormal, the entire control device can be reset by pressing this reset switch. The low voltage detection circuit 3 detects an abnormality (for example, 90% of the reference voltage).
%), a low voltage detection signal 7 is output, and the detection signal is input to a logical sum circuit (OR circuit) 8. In addition, when the runaway detection circuit 5 detects software runaway of the microcomputer 4 based on the runaway monitoring signal 9 (for example, when the reset signal of the runaway detection circuit 5 from the microcomputer 4 is not input within a certain period), the runaway detection signal 10 is output. The output detection signal is input to the OR circuit 8. The low voltage detection signal 7 and the runaway detection signal 10 are logically summed by an OR circuit 8 and input to the reset terminal 6 of the microcomputer 4.

With the above configuration, even if a momentary interruption of the power supply voltage or a runaway of the microcomputer 4 occurs, the abnormality is detected by the low voltage detection circuit 3 and the runaway detection circuit 5, and the output thereof resets the microcomputer 4 to resume normal operation. A return to this is planned.

Furthermore, when using a plurality of microcomputers 5, if one low voltage detection circuit 3 and one runaway detection circuit 5 are used, the runaway detection circuit 5 becomes very complicated.
This increases the burden on the microcomputer 4 (control amount, etc.), increases the scale of the low voltage detection circuit 3, and reduces reliability. As a countermeasure against this problem, as shown in FIG.
Attempts were also made to detect runaway independently of each other.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned conventional configuration, when the control content becomes complicated and a plurality of microcomputers are used, if the control is synchronized between the microcomputers 4a and 4b, the microcontroller 4a The runaway is microcomputer 4b
This causes a problem in that the control becomes unstable and it becomes difficult to return to normal operation.

The present invention solves the above-mentioned conventional problems, and aims to quickly and reliably input a reset signal to the microcomputer to restore normal operation even when software runs out of control or when the device power is momentarily cut off. The purpose is to provide a microcomputer reset circuit that can perform

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a reset circuit for a microcomputer that has a plurality of microcomputers and performs control while synchronizing each microcomputer. A low voltage detection circuit that monitors voltage drops in the microcomputer and a runaway detection circuit that monitors software runaway are provided for each microcomputer, and a low voltage detection signal from the low voltage detection circuit and all of the runaway detection circuits are provided. The runaway detection signal is ORed and input to the reset terminal of all the microcomputers, and the runaway detection circuit is reset by the low voltage detection signal from all the low voltage detection circuits.

[0009]

[Operation] With the above configuration, even if one microcontroller goes out of control, the low voltage detection signal from the low voltage detection circuit and the runaway detection signals from all the runaway detection circuits are ORed, so all the microcontrollers are reset at the same time. , it is possible to start synchronously from the initial state again, and to prevent disturbances in synchronous control. In addition, even when the microcomputer is reset due to a momentary power interruption of the device, all the runaway detection circuits are also reset, so it is possible to prevent erroneous detection of runaway due to the state of the runaway detection circuits after the reset is released.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the same components as those shown in the above-mentioned conventional example are given the same reference numerals, and the explanation thereof will be omitted. FIG. 1 shows a block diagram of a microcomputer reset circuit. That is, two microcomputers 4a,
Runaway of software processing is monitored by runaway detection circuits 5a and 5b provided respectively through runaway monitoring signals 9a and 9b, and the respective runaway detection circuits 5a and 5b
The runaway detection signals 10a and 10b from the
, 4b are input to reset terminals 6a, 6b. Also,
The voltage drop in the device power supply 2 is monitored by a low voltage detection circuit 3, and the low voltage detection signal 7 from this low voltage detection circuit 3 is
The R circuits 12a and 12b perform a logical sum and the microcomputer 4a
, 4b are input to the reset terminals 6a, 6b, and the runaway monitoring signals 9a, 9 are inputted by the OR circuits 12a, 12b.
b is also logically summed and input to the runaway detection circuits 5a and 5b.

FIG. 2 shows an example of the configuration of the runaway detection circuit 5a, and when the runaway monitoring signal 9a is input, the capacitor C
Since the charge of 1 is discharged through the transistor TR1, the - terminal voltage V- of the comparator 13 becomes 0V, and the runaway detection circuit 5a is reset. On the other hand, comparator 1
3's + terminal voltage V+ is the comparator output VO and resistor R2
, R3, and R4. When the comparator output VO is 0V, a certain low voltage VLv is obtained, and when the comparator output VO is 5V, a certain high voltage VHv is obtained. Therefore, when the discharge of the charge in the capacitor C1 is finished, the comparator output VO becomes 5V (+ terminal voltage V+ is VHv), and the capacitor C1 is charged again through the resistor R1.
The negative terminal voltage V- of the comparator 13 increases. This-
When the terminal voltage V- becomes higher than the + terminal voltage V+, which is VHv, the comparator output VO is inverted and becomes 0v (+ terminal voltage V
+ becomes VLv), and conversely, the charge of the capacitor C1 is discharged through the resistor R1, and the - terminal voltage V- of the comparator 13 decreases. When this negative terminal voltage V- becomes lower than VLv, which is a certain positive terminal voltage V+, the comparator output VO is inverted again and becomes 5V. Thereafter, this operation is repeated until the runaway monitoring signal 9a is input, and an intermittent pulse (comparator output VO) is output as the runaway detection signal 10a.

FIG. 3 shows the voltage waveform of the operation of the runaway detection circuit 5a. That is, when the runaway monitoring signal 9a is input during the runaway detection period T1 determined by the charging time of the capacitor C1, the comparator output VO is not inverted and the runaway detection signal 10a is not output. but,
Runaway monitoring signal 9a is no longer input and runaway detection cycle T1
When , the comparator output VO is inverted and an intermittent pulse for resetting the microcomputer 4a as shown in the figure is output. For this reason, the software of the microcomputer 4a is configured to output at least one pulse of the runaway monitoring signal 9a within the runaway detection period T1 during normal operation.

FIG. 4 shows an operation flowchart in the above configuration, and the microcomputer 4a will be explained. That is, when started, initial processing is performed in SA1, and processing 1 (SA3) of the main routine is started after waiting for the initial processing (SB1) of the microcomputer 4a to be completed in judgment 1 (SA2). Also, in the main routine, the microcomputer 4b processes 1 (SB3) in judgment 2 (SA4).
) is completed, and then processing 2 (SA5) is started. In addition, interrupt processing (SA6) and output of the runaway monitoring signal 9a (SA7) are performed. The microcomputer 4b also performs the same processing as the microcomputer 4a. During normal operation, the runaway monitoring signal 9a is sent from the microcomputer 4a to the runaway detection circuit 5a, and the runaway monitoring signal 9 is sent from the microcomputer 4b to the runaway detection circuit 5b.
b is output, and each runaway detection circuit 5a is reset. If a software runaway occurs in the microcomputer 4a or the microcomputer 4b, the corresponding runaway detection circuit 5b detects this abnormality by circuit operation, and the runaway detection signal 10a simultaneously resets the microcomputer 4a and the microcomputer 4b. 4a and 4b simultaneously start processing from initial processing, and return to normal operation is attempted. On the other hand, the low voltage detection circuit 3 monitors the device power supply 2 of the control device 1, and when a low voltage is detected due to a momentary power outage, etc., the low voltage detection signal 7 is used to simultaneously reset the microcomputers 4a and 4b, as described above. A return to normal operation is attempted. Further, the low voltage detection signal 7 is simultaneously applied to each runaway detection circuit 5a, and resets each runaway detection circuit 5a, 5b in the same manner as the operation of the runaway monitoring signal 9a. In this manner, at the time when low voltage detection is canceled by resetting the runaway detection circuits 5a and 5b, runaway detection and microcomputer processing can be started simultaneously. In addition, if the runaway detection circuits 5a and 5b are not reset, software runaway may be erroneously detected depending on the state of the runaway detection circuits 5a and 5b (the charging state of the internal capacitor C1) at the time when low voltage detection is canceled. This causes a delay in returning to normal.

[0014]

As is clear from the above embodiments, the microcomputer reset circuit of the present invention includes a low voltage detection circuit that monitors voltage drops in the device power supply, and a runaway detection circuit that monitors software runaway for each microcomputer. A detection circuit is provided, and the low voltage detection signal from the low voltage detection circuit and the runaway detection signal from all the runaway detection circuits are logically summed and inputted to the reset terminals of all the microcomputers, and The runaway detection circuit is reset by the low voltage detection signal from the low voltage detection circuit, and with this configuration, even in the event of software runaway or momentary power failure of the device, the microcomputer can be quickly and reliably reset. A reset signal can be input to restore normal operation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a reset circuit of a microcomputer in an embodiment of the present invention.

[Figure 2] Circuit diagram of the runaway detection circuit of the reset circuit of the same microcomputer

[Figure 3] Waveform diagram of input and output signals of the runaway detection circuit of the reset circuit of the same microcomputer

[Figure 4] Operation flowchart of the reset circuit of the same microcomputer

[Figure 5] Block diagram of a conventional microcomputer reset circuit

[Figure 6] Block diagram of another conventional microcomputer reset circuit

[Explanation of symbols]

2 Device power supply 3 Low voltage detection circuit 4a, 4b Microcomputer 5a
, 5b Runaway detection circuit 6a, 6b Reset terminal 7 Low voltage detection signal 10a, 10b Runaway detection signal

Claims (1)

[Claims] 1. A reset circuit for a microcomputer that has a plurality of microcomputers and performs control while synchronizing each microcomputer,
A low voltage detection circuit that monitors the voltage drop of the device power supply and a runaway detection circuit that monitors software runaway for each microcomputer are provided, and the low voltage detection signal from the low voltage detection circuit and all of the runaway detection circuits are provided. A microcomputer reset circuit that ORs runaway detection signals from the circuit and inputs the result to reset terminals of all the microcomputers, and resets the runaway detection circuit with the low voltage detection signals from all the low voltage detection circuits. .