JPH08142794A - Diagnosis circuit for runaway detecting circuit - Google Patents

Abstract

PURPOSE: To detect the anomaly of a runaway detecting circuit in the initial stage by diagnosing a runaway detecting circuit for a CPU at the time point when an electric power is detected, by judging that the operation of the runaway detecting circuit is normal when receiving a reset signal from the free running detecting circuit within a prescribed time from the start of a program. CONSTITUTION: The standard time (standard time from the start of the free running of a program to the generation of a reset signal) is set in a comparison register 2 according to the program, and a free running counter 13 for metering this time lapse is operated, and the inside clock pulse is counted, and the counting processing is started. Accordingly, the inside clock pulse is counted up in proportion to the time lapse, and this operation is carried out until the counted value reaches the comparison register set value, and it is judged if a reset signal is supplied from a runaway detecting circuit 15 during this standard time, and if the reset signal is supplied, it is judged that the function of the runaway detecting circuit 15 is normal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diagnostic circuit for a runaway detection circuit such as a watchdog timer which detects, resets and initializes a program runaway of a CPU.

[0002]

2. Description of the Related Art The structure of a conventional runaway detection circuit according to this invention will be described below by taking a vehicle occupant protection device shown in FIG. 4 as an example. That is, in the same figure, the DC / DC converter 3 boosts and outputs the voltage from the battery 1 supplied via the ignition switch 2, and supplies the boosted voltage to the backup capacitor 5 via the resistor 4 to charge it. To do. When the CPU 11 determines that a serious collision has occurred based on the acceleration signal from the acceleration sensor 14, the CPU 11 supplies a trigger signal to the switching transistor 8 so that the charged electric charge is conducted between the collector and the emitter. As a result, the charge stored in the backup capacitor 5 is squeezed through the diode 6,
The mechanical acceleration switch 10 is discharged through direct current, ignited by explosive powder, and the airbag is deployed. Also, DC / D
When the C converter 3 fails, the current from the battery 1 is supplied to the squeeze 9 via the diode 7.

Further, the CPU 11 is supplied with the voltage from the battery 1 through the ignition switch 2 and is supplied with electric power from the circuit system power supply circuit 16 which generates a low voltage, and the program is operated according to a predetermined flowchart in accordance with the supply of electric power. However, when the operation is normal, the runaway detection circuit 1
Although a clock pulse having a predetermined frequency is supplied to 5, the runaway detection circuit 15 supplies a reset signal to the CPU 11 when the operation becomes abnormal by supplying a high level signal to the runaway detection circuit 15 instead of the clock pulse. Supply to initialize program operation.

[0004]

As described above, the conventional runaway detection circuit 15 has a configuration in which when the program of the CPU 11 runs out of control, it is detected and the program operation of the CPU 11 is initialized. If 15 is defective or the electrical connection circuit pattern between the CPU 11 and the runaway detection circuit 15 is broken, the CPU 11
It was thought that there was a possibility that normal operation could not be restored if the program of (1) went out of control.

In particular, for a very important device such as a vehicle occupant protection device for protecting an occupant from an accident, it would have been possible to deal with it by notifying that an abnormal situation had occurred before traveling. However, if a serious accident was caused without noticing an abnormality, it could lead to an irreversible major problem.

Therefore, the present invention has been made in view of the above problems, and makes it possible to detect an abnormality of the runaway detection circuit at the initial stage by diagnosing the runaway detection circuit of the CPU when power is supplied. The purpose is to

[0007]

A diagnostic circuit of a runaway detection circuit according to the present invention has a program built therein, and outputs a clock pulse when the program is operating normally, and a CPU that outputs the clock pulse. Clock pulse is input and the supply of the clock pulse is stopped,
A runaway detection circuit that outputs a reset signal for initializing the CPU, the CPU itself generates a program runaway state immediately after power is supplied, and detects the runaway within a predetermined time when the program is generated. When the reset signal is supplied from the circuit, it is determined that the operation of the runaway detection circuit is normal.

[0008]

According to the present invention, immediately after the power supply voltage is supplied to the CPU, the CPU itself causes the program runaway state, and when the reset signal is supplied from the runaway detection circuit within a predetermined time of the program generation. , It is judged that the operation of the runaway detection circuit is normal, and when the reset signal is not supplied, it is judged as abnormal.

[0009]

EXAMPLES Examples according to the present invention will be described below.
The configuration is the same as that of the conventional configuration shown in FIG. 4, except for a part of the function of the CPU 11 ', that is, a function of diagnosing the malfunction of the runaway detection circuit 15, and the other parts have the same functions. Are denoted by the same reference numerals and omitted, and the functions of different parts will be described.

That is, since the program function of the CPU 11 'in FIG. 1 is added with the diagnostic function of the runaway detection circuit 15 in addition to the program function of the CPU 11 in FIG. Then, the difference in operation will be described with reference to FIG.

The CPU 11 'has a compare register 12 and a free running counter 1 as compared with the CPU 11 of FIG.
3 and 3 have been added for the infinite loop processing described in FIG. 2 (these only work for a given time when power is applied). The program sets the reference time (reference time from the start of program runaway to the generation of the reset signal) in the compare register 12,
In addition, the free-running counter 13 is operated to count the elapsed time, counts the internal clock pulse, and starts the timing process. That is, as shown in FIG. 3, this is performed by counting up the internal clock pulse in proportion to the passage of time, until the count value (free running count value) reaches the compare register set value, and up to this reference time. In the meantime, it is judged whether or not the reset signal is supplied from the runaway detection circuit 15, and when it is supplied, it is judged that the function of the runaway detection circuit 15 is normal.

Next, the program will be described. The CPU 1
When the power is turned on to 1 ', the program proceeds to step ST
After the initial setting in 100, the process proceeds to step ST101, and it is read from the stored contents of the RAM of the CPU 11 'whether or not the failure diagnosis function has already been activated. Here, when it is determined from the stored contents that the failure diagnosis has already been completed, the process proceeds to step ST107, and the normal collision determination function program is activated.

On the other hand, if it is determined in step ST101 that the failure diagnosis is not completed yet, it is recorded in the RAM that the failure diagnosis is completed in the sense that the failure diagnosis will be completed, and the infinite loop of the next step ST103. Get into the process. This infinite loop processing is to artificially create the same state as program runaway and supply a high level signal to the runaway detection circuit 15.

After that, the CPU 11 'makes a step ST10.
4, it is determined whether or not the reset signal is supplied from the runaway detection circuit 15, and if the reset signal is supplied, the process returns to step ST101 and step ST101.
Proceed to 107. If the reset signal is not supplied, the process proceeds to step ST105.

In step ST105, it is determined whether or not the count value of the free running counter 13 (free running count value) has reached the compare register setting value. If it is determined that the count value has not yet reached, the process proceeds to step ST103. Return. If the count value has reached the compare register setting value, the process proceeds to step ST106,
It is determined that the runaway detection circuit 15 is out of order, and the CPU 1
A signal indicating an alarm is supplied from 1'to an alarm circuit (not shown).

That is, when the power is turned on, the CPU 11 'creates a pseudo runaway state and supplies a high level signal to the runaway detection circuit 15, and the runaway detection circuit 15 sends the high level signal to the CPU 11 within a predetermined time from the start of the supply. When the reset signal is not supplied to'the CPU 11 ', the runaway detection circuit 1
A signal for instructing an alarm is output to an alarm circuit (not shown) that 5 is out of order.

[0017]

As described above, according to the present invention, the runaway detection circuit is diagnosed when the power is turned on, so that the device using this function can be used with peace of mind.

[Brief description of drawings]

FIG. 1 is a circuit block diagram for explaining a configuration of an occupant protection system, which is an application example of the present invention.

FIG. 2 is an explanatory diagram of a program for diagnosing a runaway detection circuit according to the present invention.

FIG. 3 is a diagram illustrating an operation of a free running counter.

FIG. 4 is a circuit block diagram of an occupant protection device in which a conventional runaway detection circuit is used.

[Explanation of symbols]

 11, 11 'Microcomputer 12 Compare register 13 Free running counter 15 Runaway detection circuit

Claims (1)

[Claims] 1. A CP which contains a program and outputs a clock pulse when the program is operating normally.
When U and the clock pulse output from the CPU are input and the supply of the clock pulse is stopped, the C
And a runaway detection circuit for outputting a reset signal for initializing the PU. The CPU itself generates a program runaway state immediately after power is supplied, and the runaway detection circuit within a predetermined time when the program is generated. A diagnostic circuit for a runaway detection circuit, which is characterized by determining that the operation of the runaway detection circuit is normal when a reset signal is supplied from the.