JPH08161203A - Fault diagnostic system for ic for watchdog - Google Patents

Abstract

PURPOSE: To provide the fault diagnostic system of an IC for a watchdog for improving the reliability of a circuit, saving a base area and reducing a cost by mutually monitoring faults on the other side by at least one MPU and at least one IC for the watchdog. CONSTITUTION: The circuit is composed of at least one MPU and at least one IC for the watchdog and reset signals from the IC for the watchdog are inputted to the NMI terminal of the MPU. Also, after the MPU is reset, abnormality signals are outputted from the MPU to the IC for the watchdog and the MPU stops operations until input is performed from the IC for the watchdog to the NMI terminal of the MPU.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
trol unit) failure diagnosis system. More specifically, in electronic circuits, MPU (Mi
The present invention relates to a failure diagnosis system for monitoring a failure of a cro processing unit) and confirming that a so-called watchdog IC normally functions.

[0002]

2. Description of the Related Art In recent years, the quality of electronic products has improved considerably due to the development of electronic technology, but failure always occurs in electronic circuits.
There is a need for a system in which an electronic circuit self-diagnoses whether or not a failure has occurred, assuming that a failure has occurred.

For that purpose, an MPU for monitoring the peripheral circuits is provided, and in particular, many methods have conventionally been adopted as a method for detecting a failure of the MPU itself.

For example, FIG.
3 shows the configuration and operation of a circuit in which MPUs mutually monitor the failure of the other. In this case, since the cost is increased due to the use of two MPUs, an M for monitoring peripheral circuits is used by using a watchdog IC (hereinafter referred to as a watchdog IC) which is an IC having only a monitoring function.
A simpler method of monitoring the PU (hereinafter referred to as MPU) is often used.

[0005]

In the MPU monitoring method using such a watchdog IC, the watchdog IC does not run away because there is no program inside, but a failure such as a disconnection of the signal line for transmitting the reset signal. Therefore, it may not function as a watchdog IC. Therefore, it is necessary to confirm that the watchdog IC functions normally at least when the ignition is on.

However, as shown in FIG. 5, when the ignition is turned on, an abnormal signal is intentionally output from the MPU to the watchdog IC, and the reset signal input from the watchdog IC receiving the abnormal signal is input to the MP.
When the circuit is configured so that U stands by, when the watchdog IC is functioning normally, the MPU is naturally reset and returns to the state when the ignition is turned on again. As a result, since the MPU is repeatedly reset, there is a problem that it cannot be confirmed that the function of the watchdog IC is normal.

In view of the above circumstances, the present invention has been made to solve the above problems, and in a circuit including at least one MPU and at least one watchdog IC, It is an object of the present invention to provide a failure diagnosis system for a watchdog IC, which can confirm that the watchdog IC functions normally.

[0008]

A failure diagnosis system of the present invention is a circuit composed of at least one MPU and at least one watchdog IC, and a reset signal from the watchdog IC is provided as a conventional circuit. It is characterized in that the input is made not to the reset terminal of the MPU but to the NMI terminal of the MPU.

Further, in the failure diagnosis system of the present invention, after resetting the MPU, the MPU outputs an abnormal signal to the watchdog IC, and the watchdog IC causes the NMI (Non Maskable Interru) of the MPU.
The feature is that the MPU stops operating until there is an input at the (pt) terminal.

Further, the failure diagnosis system of the present invention is characterized in that a warning lamp warns of the failure of the watchdog IC.

[0011]

According to the failure diagnosis system of the present invention, at least one MPU and at least one watchdog IC.
In the circuit consisting of, the mutual failures can be monitored mutually.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the configuration of the failure diagnosis system of the present invention and the operation of the failure diagnosis system will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram showing the configuration and operation of a circuit which is an embodiment of the failure diagnosis system of the present invention, and FIG. 2 is a diagram showing a flowchart of the operation of the MPU in the embodiment of the failure diagnosis system of the present invention. FIG. 3 is a diagram showing a flowchart of the operation of the MPU in one embodiment of the circuit including the failure diagnosis system and the warning lamp of the present invention.

The configuration and operation of a circuit which is an embodiment of the fault diagnosis system of the present invention will be described with reference to FIGS. 1 and 2. The circuit is, as shown in FIG. 1, one MPU.
And a single watchdog IC, the MPU outputs an abnormal signal or a normal signal to the watchdog IC, receives an NMI signal as a reset signal from the watchdog IC, and further Power on reset IC not included in the circuit
Is configured to receive a reset signal at the RESET terminal. The MPU executes the following series of operations as shown in the flowchart of FIG.
Confirm that the watchdog IC is functioning normally.

(1) A reset signal is first received from a power-on reset IC not included in the circuit, and initial setting is performed.

(2) An abnormal signal is output to the watchdog IC, the operation is stopped, and the process waits to confirm whether the watchdog IC is normal.

(3) NM from the watchdog IC, which indicates that the watchdog IC has detected the abnormal signal
It receives the I signal and confirms that the watchdog IC is functioning normally.

(4) A normal signal is output to the watchdog IC so that the watchdog IC does not output the NMI signal again.

Next, an embodiment of a failure diagnosis system for warning the user whether or not the watchdog IC is functioning normally by the ECU using the above circuit and further combined with a warning lamp will be described. FIG. 3 shows the E
The flowchart of the operation | movement of MPU in CU is shown, and MPU performs operation | movement according to the following procedures.

(1) First, a reset signal is input from a power-on reset IC not included in the circuit, and then the operation is started from the start address of the start program.

(2) After the initial setting, an abnormal signal is output to the watchdog IC.

(3) After the warning lamp is turned on, an infinite loop is entered to stop the operation.

If the function of the watchdog IC is normal, the watchdog IC outputs the NMI signal to the MPU.

(4) When receiving an NMI signal input, NM
The I program is started and the warning lamp is always turned on regardless of whether or not the warning lamp is turned on at that time.

(5) A normal signal is output to the watchdog IC to stop the output of the NMI signal again from the watchdog IC.

(6) After a certain period of time, the warning lamp is turned off by an appropriate timer, and the main program processing, which is the original function, is started.

In this case, if the watchdog IC is not functioning normally, the watchdog IC does not output the NMI signal to the MPU, so the operation (4) is not executed. That is, since the MPU does not receive the input of the NMI signal, it does not execute the NMI program and continues to execute the infinite loop with the warning lamp lit. As a result, the user can recognize the failure.

When an abnormality occurs in the execution of the NMI program (the supply voltage to the MPU fluctuates, the power-on reset to the MPU does not enter,
It is possible that the program may run out of control due to the operating clock being stopped to the MPU, or the program may stop due to a momentary power failure and restart from the beginning). Upon receiving the input of the NMI signal from the IC, the MPU always turns on the warning lamp for a certain period of time, so that the user can recognize the failure.

[0029]

According to the failure diagnosis system of the present invention, in a circuit composed of at least one MPU and at least one watchdog IC, it is possible to mutually monitor the failure of the other party, so that the reliability of the circuit is improved. Since a watchdog IC having high performance and having only the monitoring function of the MPU can be used, the board area can be saved and the cost can be reduced as compared with the conventional one.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration and an operation of a circuit which is an embodiment of a failure diagnosis system of the present invention.

FIG. 2 is a diagram showing a flowchart of the operation of the MPU in the embodiment of the failure diagnosis system of the present invention.

FIG. 3 is a diagram showing a flowchart of the operation of the MPU in one embodiment of the circuit including the failure diagnosis system and the warning lamp of the present invention.

FIG. 4 is an explanatory diagram showing a configuration and an operation of a conventional circuit in which two MPUs monitor each other.

FIG. 5 is an explanatory diagram showing an operation in which normality of a watchdog IC cannot be confirmed in a circuit including one MPU and one watchdog IC.

Claims (3)

[Claims] 1. At least one MPU and at least one
And a reset signal from the watchdog IC.
A failure diagnosis system for a watchdog IC, which is characterized in that an input is made to a U NMI terminal. 2. After resetting the MPU, the MPU outputs an abnormal signal to the watchdog IC, and the watchdog IC outputs the NMI of the MPU.
The watchdog IC failure diagnosis system according to claim 1, wherein the MPU stops operating until an input is applied to the terminal. 3. A failure diagnosis system for a watchdog IC according to claim 1, wherein a warning lamp warns of the abnormality.