JP2000356556A - Failure-detecting device of sensor circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To securely detect failure regardless of failed parts without increasing costs. SOLUTION: A microcomputer 21 is provided with a pull-up circuit 22 for connecting an input terminal PI that is connected to a sensor circuit 1 in a pull-up state through a resistor RPU. Then, the microcomputer 21 judges whether an A/D conversion value when the pull-up circuit 22 is connected and that when no pull-up circuit 22 is connected are within a specific range or not to detect each failure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a one-chip microcomputer having a built-in A / D conversion function.

[0002]

Conventionally, an analog detection signal from a sensor circuit including a sensor such as a thermistor is subjected to A / D conversion by an A / D converter built in a one-chip microcomputer. Is known to perform signal processing. For example, in FIG. 7, RTH is a thermistor as a sensor whose resistance value changes with temperature, RS is a resistor for voltage division, and the sensor circuit 1 composed of a series circuit of the thermistor RTH and the resistor RS generates a predetermined voltage. It is inserted and connected between the power supply terminal VDD to be supplied and the ground line. The connection point between the thermistor RTH and the resistor RS is connected to the input terminal PI of the microcomputer 2 serving as control means via another resistor RH, and between the connection point between the resistor RH and the input terminal PI and the ground line. Is connected to a polar capacitor CS. The time constant circuit 3 including the resistor RH and the capacitor CS is added to absorb noise and ripples entering the signal line when the signal line input to the A / D converter 4 described later is long. is there.

On the other hand, an A / D converter 4 for digitally converting a detection signal from the sensor circuit 1 is provided inside the microcomputer 2. Also, the input terminals PI and A of the microcomputer 2
A series circuit of a protection resistor R and a switch S that is turned on when performing A / D conversion in response to a command from the microcomputer 2 is provided between the switch S and the / D converter 4. A sample and hold capacitor C is provided between the connection point of the A / D converter 4 and the ground line. A connection point between the switch S and the capacitor C is connected to a comparator inside the A / D converter 4. (Not shown).

[0004] In the above configuration, when the circuit is normal without any disconnection failure or the like, the resistance value fluctuates according to the temperature change of the thermistor RTH, and the voltage of the power supply terminal VDD is divided by the thermistor RTH and the resistance RS. The detection signal of the sensor circuit 1 also changes. Further, the switch S is turned on and off at predetermined time intervals by a command from the microcomputer 2, and during the ON period of the switch S, the detection signal of the sensor circuit 1 passes through the input terminal PI of the microcomputer 2. The signal is applied to the A / D converter 4 and converted into a digital signal by the A / D converter 4. Therefore, when the temperature of the thermistor RTH changes, the digital signal value (A / D conversion value) output from the A / D converter 4 every time the switch S is turned on changes stepwise. recognize.
The change of the A / D conversion value due to the temperature change of the thermistor RTH is designed to be within a predetermined range in advance.

Next, the operation in the case where some disconnection failure occurs in the circuit will be described. The microcomputer 2 determines that the A / D conversion value that is the conversion result of the A / D converter 4 is equal to or less than the predetermined range that is predicted when the A / D converter 4 is normal (for example, 8 bits).
In the case of the A / D converter 4, when the A / D conversion value becomes less than 10 Hex or more than F0 Hex), a circuit failure is detected. For example, when a disconnection occurs in the line A between the connection point of the thermistor RTH and the resistor RS and the thermistor RTH, the electric charge stored in the capacitor CS until that time is discharged via the resistor RH and the resistor RS, and Switch S
Is closed, the electric charge stored in the capacitor C is also released from the resistor R via the resistors RH and RS. As a result, both the voltage VCS between both ends of the capacitor CS and the voltage VC between both ends of the capacitor C become 0 V,
The D-converted value also falls below the predetermined range, and the microcomputer 2 can detect a disconnection failure in the circuit. Further, if the line A 'between the connection point of the thermistor RTH and the resistor RS and the resistor RS breaks, in this case, the electric charge is stored in the capacitor CS from the thermistor RTH via the resistor RH and the switch S Turns on, the capacitor C via the resistor R
Charge is also stored. As a result, the voltage VCS and the voltage VC both have the same voltage value as the power supply terminal VDD, and the A / D conversion value also becomes a predetermined range or more, and the microcomputer 2 can detect a disconnection failure in the circuit.

This will be described with reference to a flowchart shown in FIG. 8. In step S101, when the switch S is turned on in accordance with a command from the microcomputer 2 to perform A / D conversion,
If the A / D conversion value converted by the A / D converter 4 is less than 10 Hex (step S102), the process proceeds to step S103, and the microcomputer 2 determines that the line A is disconnected. Conversely, this A
If the / D conversion value is equal to or more than F0Hex (step S104),
In step S105, the microcomputer 2 determines that the line A 'is disconnected. And the A / D conversion value is 10
When it is within the predetermined range of not less than Hex and less than F0Hex, it is determined that no disconnection has occurred, and the microcomputer 2 performs control based on the A / D converted value (step S106).

On the other hand, if the line B from the connection point of the thermistor RTH and the resistor RS to the resistor RH is broken, or if the line C from the connection point of the resistor RH and the capacitor CS to the input terminal PI of the microcomputer 2 is broken, The microcomputer 2 cannot detect a failure in the circuit. For example, assuming that the line B is disconnected, in this case, the capacitor C or the capacitor C
Since there is no path for discharging S, the voltage VCS immediately before the disconnection is stored in the capacitor CS as it is. Therefore, even if the switch S is turned on, the A / D conversion value from the A / D converter 4 is within a normal predetermined range, and the microcomputer 2 cannot recognize the disconnection in the circuit. Also, track C
When the disconnection occurs, the input terminal PI of the microcomputer 2 is in a state where nothing is connected, so that the input side impedance of the microcomputer 2 increases, and when the switch S is turned on, the voltage VC becomes indefinite. In this case, the voltage VC becomes a specific value depending on the state of the surrounding circuit signal, but the A / D conversion value from the A / D converter 4 is often within a predetermined range and does not become an abnormal value.

As described above, in the conventional circuit configuration, the A / D converter 4 outputs the A / D signal from the A / D converter 4 depending on where the disconnection occurs.
In some cases, the converted value does not fall outside the predetermined range, which causes a problem that the microcomputer 2 cannot reliably detect a failure.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a failure detection device for a sensor circuit capable of performing reliable failure detection regardless of a location where a failure has occurred. I do.

[0010]

In order to achieve the above object, a failure detection device for a sensor circuit according to the present invention converts a detection signal from the sensor circuit into an A / A signal in a microcomputer.
In the failure detection device for a sensor circuit which performs D conversion and detects a failure in the microcomputer when the A / D conversion value is out of a predetermined range, the microcomputer has an input terminal connected to the sensor circuit. A connection circuit for connecting in a pull-up or pull-down state via a resistor, based on an A / D conversion value when the connection circuit is connected and an A / D conversion value when the connection circuit is not connected; Each is configured to perform failure detection.

In a normal state where no disconnection has occurred, even if the connection circuit is connected and the input terminal of the microcomputer is pulled up or pulled down, the voltage of the input terminal changes much as compared with the case where the connection circuit is not connected. However, the A / D conversion value in the microcomputer falls within a predetermined range expected in a normal state regardless of whether or not the connection circuit is connected.

On the other hand, if the line from the sensor circuit to the input terminal of the microcomputer is broken, the input terminal has a high impedance when the connection circuit is not connected, and the A / D conversion value is within a predetermined range and is abnormal. In many cases, it is not a value. However, if the connection circuit is connected and the input terminal of the microcomputer is pulled up or pulled down, the voltage of the input terminal changes greatly compared to the case where the connection circuit is not connected. Is out of the predetermined range, and the failure can be reliably detected.

If a disconnection or the like occurs in the sensor circuit, the voltage at the input terminal of the microcomputer itself becomes an abnormal value.
The D-converted value falls outside the predetermined range, and the failure can be reliably detected in this case as well.

That is, if a microcomputer having a function of pull-up control or pull-down control of the input terminal is used, only a part of the software of the microcomputer is changed, and the cost is not increased.
Irrespective of the location where the failure has occurred, reliable failure detection can be performed.

[0015]

Hereinafter, an embodiment of the present invention will be described.
This will be described with reference to the accompanying drawings. First, the internal configuration of the microcomputer 21 used in the present embodiment will be described. As shown in FIG. 1, an input terminal PI, which is an input port of the microcomputer 21, is connected to a predetermined positive voltage terminal (power supply terminal VDD) via a resistor RPU. ), And a general-purpose input / output circuit 23 for directly inputting / outputting an input port from the microcomputer 21. As described above, in order to increase the added value of the IO (input / output), the microcomputer 21 may provide a port having an A / D conversion function to the general-purpose input / output function or pull-up control (or connect the input port of the microcomputer 21 to a resistor). Many of them are provided with a function of adding a pull-down control (grounding through the ground). The present embodiment focuses on such a pull-up control function and a pull-down control function of the microcomputer 21 in particular.

FIG. 2 shows the configuration of the failure detection device according to the present embodiment. The same parts as those in FIG. 7 shown in the conventional example are denoted by the same reference numerals, and detailed description of common parts will be omitted because they are duplicated. As described above, a pull-up circuit 22 in which a series circuit including a resistor RPU and a switch SPU is connected between the power supply terminal VDD and the input terminal PI is added inside the microcomputer 21. Switch SPU
Is turned on / off independently of the switch S in response to a command from the microcomputer 21, and its timing is controlled by software of the microcomputer 21. When the switch SPU is turned on, the input terminal PI is connected to the resistor RP
The state is connected to the power supply terminal VDD via U. Each element inside the microcomputer 21 including these pull-up circuits 22
Each of them has a sealed structure packaged by the exterior of the microcomputer 21.

In FIG. 2, the resistance value of the resistor RPU is 10
0 kΩ, resistance value of resistance R and resistance RH is 10 kΩ, resistance value of resistance R
The resistance value of H is 18 kΩ, and the resistance value of the thermistor RTH varies between 4.5 and 300 kΩ depending on the temperature. The capacitor CS has a large capacitance (1 μF) with respect to the capacitance of the capacitor C (10 pF). Other configurations are the same as those in FIG.

Next, the operation of the above embodiment will be described with reference to waveform diagrams of FIGS. 3 to 5 and a flowchart of FIG.
The upper waveform diagram of FIG. 3 shows the voltage VCS between both ends of the capacitor CS with the lapse of time t in the normal state, and the lower waveform diagram of the pull-up control and the A / D conversion shows the voltage VCS. The timing of whether or not each operation is performed is shown with the elapse of time t. further,
The upper waveform diagram of FIG. 4 shows the voltage VCS when the line B is disconnected in FIG. 2 with the elapse of time t, and the upper waveform diagram of FIG. The voltage VAD at the terminal PI is shown over time t.
4 and 5 are the same as those in FIG.

The failure determination in this embodiment is performed according to the procedure shown in the flowchart of FIG. First, step S
In step 1, the switch SPU of the pull-up circuit is turned on in response to a command from the microcomputer 21 to connect the input terminal PI to the power supply terminal VDD via the resistor RPU (pull-up control is on). Then, in step S2, a wait of, for example, 100 μs is performed in this state. After waiting for a predetermined time, the microcomputer 21 turns on the switch S for a predetermined time and executes A / D conversion by the A / D converter 4 (step S3). The operations in steps S1 to S3 correspond to the ON period of the pull-up control in FIGS.

At this time, if the A / D conversion value converted by the A / D converter 4 is out of a predetermined range, for example, F8Hex or more (step S4), the process immediately proceeds to step S5, where the thermistor RTH and the resistance RS are set. Resistance RH from connection point
The microcomputer 21 determines that the line B reaching the input terminal PI of the microcomputer 2 from the connection point of the resistor RH and the capacitor CS to the input terminal PI of the microcomputer 2 is disconnected. If the A / D converted value is less than F8Hex in step S4, the process proceeds to step S6, where the microcomputer 21 turns off the switch SPU of the pull-up circuit 22 and sets the input terminal PI via the resistor RPU.
Connection between the power supply terminal VDD and the power supply terminal VDD (pull-up control off). Then, in step S7, a wait of, for example, 400 μs is performed in this state.

Since the pull-up circuit 22 is disconnected during the period in which the pull-up control shown in FIGS. 3 to 5 is off, the circuit configuration is the same as that of the conventional example shown in FIG.
In the meantime, a failure determination is performed in the same procedure as in the conventional steps S101 to S107. That is, step S101
After the switch S is turned on and A / D conversion is performed,
If the A / D conversion value is less than 10 Hex (step S10
2), the process proceeds to step S103, and the microcomputer 21 determines that the line A is disconnected. If the A / D conversion value is equal to or larger than F0Hex (step S104), the process proceeds to step S105, and the microcomputer 21 determines that the line A ′ is disconnected. When the A / D conversion value is within the predetermined range of 10 Hex or more and less than F0 Hex, the microcomputer 21 performs the original control (for example, cooking control (not shown) based on the A / D conversion value) at step S1. Return to the procedure (step S106). As described above, in this embodiment, the A / A
Not only the A / D converted value when the D conversion is performed (a portion shown in FIGS. 3 to 5) but also when the A / D conversion is performed by connecting the pull-up circuit 22 (FIGS. 3 to 5). The A / D conversion value of (b) shown in FIG.

The operations in steps S1 to S3 correspond to the ON period of the pull-up control in FIGS.
If there is no abnormality in the sensor circuit 1 outside the microcomputer 21 including the time constant circuit 3, even if the switch SPU is turned on in step S1, the voltage VCS between both ends of the capacitor CS hardly changes, and pull-up control is performed. It only increases by about 5 mV at the maximum as compared with the state without the power. Then, when the pull-up control is turned off, a part of the charge stored in the capacitor CS is released via the resistors RH and RS, and returns to the original state. Therefore, when the switch S is turned on in step S3, the voltage VC immediately before the A / D converter 4 becomes equal to the voltage VCS, but the A / D converted value converted by the A / D converter 4 is calculated in steps S1 to S1. Even if each procedure of S106 is repeated many times, it is within the predetermined range and hardly changes.

On the other hand, from the sensor circuit 1 to the microcomputer
If the line to the input terminal PI of FIG. 21, specifically the line B shown in FIG. 2 is disconnected, when the switch SPU is turned on in step S1, the capacitor CS is connected via the resistor RPU.
Is charged, and the voltage VCS rises by 5 mV. However, even if the pull-up control is switched off in step S6 thereafter, unlike the normal state, there is no path for discharging the capacitor CS, so that the voltage VCS keeps increasing by 5 mV, and the procedures in steps S1 to S106 are repeated. It rises gradually with each repetition. Finally, in step S4, the A / D conversion value reaches, for example, F8Hex or more, and the microcomputer 21 determines whether the line B is disconnected. In this embodiment, steps S1 to S10
If the repetition time of each procedure up to 6 is set to 1 ms, a failure can be determined approximately 3.4 seconds after the line B is disconnected.

When the line C shown in FIG. 2 is disconnected, the voltage VAD of the input terminal PI becomes indefinite as described in the conventional example and the pull-up control is turned off, as described in the conventional example.
Even if the switch S is turned on at 01, the A / D conversion value often falls within a predetermined range. However, when the pull-up control is turned on, the voltage VAD of the input terminal PI becomes equal to the voltage of the power supply terminal VDD because nothing is connected to the input terminal PI. Therefore, in step S4,
The A / D converted value reaches F8Hex or more, for example, FFHex, and the microcomputer 21 can determine the disconnection in the line C. In this embodiment, the voltage VAD of the input terminal PI becomes equal to the power supply terminal VDD 3.7 μs after the switch SPU is turned on.

As described above, in this embodiment, the detection signal from the sensor circuit 1 is A / D-converted in the microcomputer 21, and when the A / D conversion value is out of the predetermined range, the microcomputer 21 outputs the signal. In the failure detection device for the sensor circuit 1 that detects a failure by using the microcomputer 21, the microcomputer 21 includes a pull-up circuit 22 as a connection circuit that connects the input terminal PI connected to the sensor circuit 1 to a pull-up state via a resistor RPU. Fault detection is performed based on the A / D conversion value when the pull-up circuit 22 is connected and the A / D conversion value when the pull-up circuit 22 is not connected.

In this case, when there is no disconnection outside the microcomputer 21, the switch SPU connects the pull-up circuit 22 in a normal state and the input terminal PI of the microcomputer 21 is pulled up (predetermined via the resistor RPU). The voltage VAD of the input terminal PI does not change much as compared with the case where the pull-up circuit 22 is not connected (in the present embodiment, a change of about 5 mV) even when the power supply terminal VDD which is a voltage terminal is connected. The A / D conversion value in the microcomputer 21 falls within a predetermined range expected in a normal state regardless of whether the pull-up circuit 22 is connected or not.

On the other hand, when the line C from the sensor circuit 1 to the input terminal of the microcomputer 21 is broken, the input terminal PI has a high impedance when the pull-up circuit 22 is not connected, and the A / D conversion value is within a predetermined range. Often, there is no abnormal value. However, if the pull-up circuit 22 is connected and the input terminal of the microcomputer 21 is pulled up,
Since the voltage of the input terminal PI greatly changes as compared with the case where the pull-up circuit 22 is not connected, the A / D conversion value is out of the predetermined range, and the failure can be reliably detected.

When a disconnection or the like occurs in the sensor circuit 1, the voltage VAD of the input terminal PI of the microcomputer 21 becomes 0 V or the same voltage value as the power supply terminal VDD, resulting in an abnormal value. Therefore, the A / D conversion value is out of the predetermined range in a state where the pull-up circuit 22 is not connected. In this case, the failure can be reliably detected.

That is, if the microcomputer 21 having the function of pulling up the input terminal PI is used,
By only partially changing the software of No. 21, it is possible to perform reliable failure detection regardless of the location where the failure has occurred, without increasing the cost.

In this embodiment, on the way from the sensor circuit 1 to the input terminal PI of the microcomputer 21, a time constant circuit 3 comprising an L-shaped circuit of a resistor RH and a capacitor CS is added to absorb noise and ripples. But in this case,
By repeating the operation of detecting a failure based on the A / D conversion value when the pull-up circuit 22 is connected and the operation of detecting the failure based on the A / D conversion value when the pull-up circuit 22 is not connected, Disconnection of not only the line C from the constant circuit 3 to the input terminal of the microcomputer 21 but also the line B from the sensor circuit 1 to the time constant circuit 3 can be reliably detected.

That is, when the line B is disconnected, when the pull-up circuit 22 is connected, the capacitor CS is charged via the resistor RPU, and the voltage VCS slightly changes (increases in the case of pull-up control). I do. However, when the pull-up circuit 22 is not connected, since the path for discharging the capacitor CS does not exist, the operation of connecting the pull-up circuit 22 and the operation of not connecting the pull-up circuit 22 are repeated. The A / D conversion value within the range goes out of the predetermined range. Therefore, disconnection of the line B can be reliably detected only by adding the function of such a repetitive operation to the microcomputer 21.

In this embodiment, when the pull-up circuit 22 is connected, A which is a condition for judging failure detection is used.
Predetermined range of / D conversion value (condition of step S4 in FIG. 6)
However, it is set to be narrower than a predetermined range of the A / D conversion value (the condition of step S104 in FIG. 6) for determining the failure detection when the pull-up circuit 22 is not connected. In this way, if the A / D conversion value when the pull-up circuit 22 is connected reaches F8Hex or more under the condition of step S4 when the line B is disconnected, the microcomputer 21 fails at that point. Is determined, the failure is not determined under the condition of step S102 in which the pull-up circuit 22 is not connected. Therefore, it is possible to distinguish at which point the disconnection has occurred without confusing with the determination of the disconnection of the line A ′ in the sensor circuit 1.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, although the present embodiment has been described using the pull-up circuit 22 in the microcomputer 21, a series circuit of the resistor RPU and the switch SPU may be realized by a pull-down circuit connected between the input terminal PI and the ground line. Good. In this case, when a disconnection occurs in the line B, the voltage VCS and the voltage VC gradually decrease and finally reach 0 V, and when a disconnection occurs in the line C, the switch SPU turns on and becomes 0 V at the same time as the pull-up. The same failure detection as in the up control can be performed.

[0034]

According to the sensor circuit failure detection apparatus of the present invention, the detection signal from the sensor circuit is A / D converted in a microcomputer, and when the A / D conversion value is out of a predetermined range, the microcontroller is activated. In the failure detection device for a sensor circuit that detects a failure in a computer, the microcomputer includes a connection circuit that connects an input terminal connected to the sensor circuit to a pull-up or pull-down state via a resistor, and the connection circuit includes: A / when connected
D / D conversion value and A / when the connection circuit is not connected
In this configuration, failure detection is performed on the basis of the D-converted value, so that reliable failure detection can be performed irrespective of the location where the failure has occurred without increasing the cost.

[Brief description of the drawings]

FIG. 1 is a circuit diagram inside a microcomputer showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a failure detection device for the sensor circuit according to the first embodiment;

FIG. 3 is a waveform chart showing signal voltages of various parts in the same normal operation.

FIG. 4 is a waveform chart showing signal voltages at various parts when the line B is disconnected.

FIG. 5 is a waveform diagram showing signal voltages at various parts when the line C is disconnected.

FIG. 6 is a flowchart showing an operation procedure at the time of the failure determination.

FIG. 7 is a circuit diagram illustrating a failure detection device for a sensor circuit in a conventional example.

FIG. 8 is a flowchart showing an operation procedure at the time of the failure determination.

[Explanation of symbols]

 1 sensor circuit 21 microcomputer (microcomputer) 22 pull-up circuit (connection circuit) RPU resistor PI input terminal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G014 AA02 AB25 AB34 AC18 2G033 AA07 AB02 AC01 AD21 AG09 AG12 2G036 AA25 AA27 BA35 BB01 BB20 BB22 CA06

Claims (1)

[Claims] 1. A malfunction of a sensor circuit which A / D converts a detection signal from a sensor circuit in a microcomputer and detects a malfunction in the microcomputer when the A / D conversion value falls outside a predetermined range. In the detection device, the microcomputer includes a connection circuit that connects an input terminal connected to the sensor circuit to a pull-up or pull-down state via a resistor, and an A / D conversion value when the connection circuit is connected; A fault detecting device for a sensor circuit, wherein faults are detected based on A / D converted values when the connection circuit is not connected.