JPH0535367A - Reset signal generator for electronic circuit - Google Patents

Abstract

PURPOSE:To prevent circuit malfunction or CPU run-away caused by external noise. CONSTITUTION:This is a device to generate reset signals for resetting an electronic circuit 60 such as a microprocessor applied circuit or a digital logic circuit, etc., in the manner of a hardware, and the reset signal generator for the electronic equipment is composed of an external noise detector 21 composed of a linear electric conductor arranged so as to surround the electronic circuit 60, waveform shaping circuit 31 to shape the waveform of a spike noise detected by this external noise detector 21, and reset signal generating circuit 41 to generate a reset signal NRST having a set time length based on the output signal of this waveform shaping circuit 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset signal generator for an electronic circuit.

[0002]

2. Description of the Related Art In an electronic circuit such as a microprocessor application circuit or a digital logic circuit, as an initialization process for executing a predetermined function accurately and stably,
It is reset by hardware.

A typical conventional configuration and operation of the reset signal generating circuit (10) are shown in FIGS. In FIG. 3, resistors R1 and R2 are voltage dividing resistors for the power supply voltage Vcc (V1, V2), and COMP.A is a detection voltage Vd1 and a reference voltage V.
ref. It is a comparator for comparing with and has hysteris characteristics. That is, it is obtained by feeding back the output voltage Vo1 to the input. The internal feedback voltage is Vret. Then, Formula 1 is materialized. Vref. = (V1 · R2 / R1 + R2) −Vret. = (V2 · R2 / R1 + R2) + Vret. … (1)

Therefore, when the power supply voltage becomes higher than V1, the comparator COMP.multidot.A changes from "H" to "L" and the transistor Tr.multidot.A changes from "ON" to "OFF". Then, the capacitor C is charged through the constant current power source CI · A, and the voltage Vd2 increases. When this voltage Vd2 becomes higher than the detection voltage of the output comparator COMP • B, the output signal of the output comparator COMP • B becomes “H” →
It changes to "L" and the transistors Tr and B are turned off. Therefore, the reset signal RST is as shown in FIG.
It is canceled at time t1. The time constant T is determined by the current of the constant current power source CI · A, the capacitance of the capacitor C and the value of the detected voltage.

On the other hand, when the power supply voltage becomes lower than V2, the transistor Tr.A is turned on, so that the electric charge of the capacitor C is discharged through the transistor Tr.A and the voltage Vd2 is lowered. Then, when it becomes lower than the detection voltage, the output signal of the output comparator COMP • B becomes “L” →
It changes to “H” and the transistor Tr · B turns “ON”. Therefore, at time t2 in FIG. 4, the reset signal RS
T is valid.

Thus, if the reset signal generating circuit 10 of the voltage monitoring system is used, if the power supply voltage Vcc is equal to or lower than the predetermined value (V2) shown in FIG. 4, the electronic circuit is initialized by the reset signal RST, and the predetermined value (V1)
In the above case, the reset signal RST is released after the delay time T has elapsed, and the malfunction due to the low voltage can be avoided.

On the other hand, even if this inializing process is performed, it is meaningless if the CPU may run away for some reason. For this reason, a so-called watchdog timer for monitoring is provided, and if the watchdog timer is not initialized within a certain time, the CPU is reset by software.

[0008]

However, in the above-mentioned conventional reset signal generating circuit 10, if external noise is present, it is not possible to prevent hardware malfunction due to the spike noise. Further, even if a watchdog timer is provided, if the CPU runs away before the reset by the watchdog timer, the stored data in the memory is destroyed, resulting in a malfunction in terms of hardware.

An object of the present invention is to provide an electronic circuit reset signal generator capable of preventing circuit malfunction and CPU runaway due to external noise.

[0010]

SUMMARY OF THE INVENTION The present invention is a device for generating a reset signal for hardware resetting an electronic circuit such as a microprocessor application circuit or a digital logic circuit, the device surrounding the electronic circuit. An external noise detector made of a linear electric conductor arranged as
An electronic device including a waveform shaping circuit for shaping the spike noise detected by the external noise detector and a reset signal generating circuit for generating a reset signal for a predetermined time based on the output signal of the waveform shaping circuit. It is a circuit reset signal generator.

[0011]

According to the present invention having such a structure, when external noise such as electrostatic noise is applied to the electronic circuit, the external noise detector detects the external noise and the waveform shaping circuit shapes the spike noise. Here, the reset signal generation circuit outputs the reset signal of the set time length from the output signal of the waveform shaping circuit.
Therefore, external noise can be automatically detected and the electronic circuit can be quickly reset.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) A reset signal generation device (2
0), as shown in FIG. 1, is provided with an external noise detector 21, a waveform shaping circuit 31, and a reset signal generation circuit 41, and is configured to automatically detect external noise and generate a reset signal NRST. ..

Further, in this embodiment, the conventional reset signal generating circuit 10 and the OR circuit 50 are provided, and a substantial reset signal TRST is output when either of the reset signals NRST and RST is generated. It is formed so as to reset the electronic circuit.

First, as shown in FIG. 1, the external noise detector 21 is composed of a linear electric conductor arranged so as to surround the electronic circuit (60). For example, it is formed so as to loop around the printed circuit board 60 on which electronic components are mounted. That is, external noise is caught by using this as an antenna. The resistance voltage dividing circuit 32 (resistors R1, R
2) serves as a power source for the external noise detector 21.

Next, the waveform shaping circuit 31 shapes the spike noise from the external noise detector 21 as a trigger pulse signal Tp of the reset signal generation circuit 41 described later in detail.

In the case of this embodiment, the waveform shaping circuit 31 includes a current limiting resistor Rs for limiting the current against high voltage spike noise induced by static electricity, and a surge absorber 33 (diode D1, diode D1, for clipping the potential level).
D2), reference voltage setting device 34 (resistors R3, R4, R5)
And a comparison circuit 35 (comparators CO1, CO2), and O
A trigger pulse signal (output signal) Tp is generated when an external noise that may cause a malfunction is input to the electronic circuit (60).

The reset signal generation circuit 41 outputs a single pulse having a preset time length by the trigger pulse signal Tp, that is, a reset signal NRST. In this embodiment, a monostable multivibrator (SN74LS122 manufactured by TI) is used. 42 is used. The set time is determined by the resistance value of the resistor Rt and the capacitance of the capacitor Ct.

In the first embodiment having such a configuration, the electronic circuit (60) monitors the power supply voltage by the same reset signal generating circuit 10 as in the conventional example, and the reset signal RST (TR
It is reset at ST). Further, if there is external noise after this initialization processing, the reset signal NRST (T
It can also be reset by RST).

According to this embodiment, however, the external noise detector 21, the waveform shaping circuit 31, and the reset signal generating circuit 41 are included, so that the external noise causes the electronic circuit (60) to malfunction. In the case of a feared magnitude, the reset signal NRST can be quickly generated. Therefore, malfunction of the circuit and runaway of the CPU can be prevented.

Further, since the reset signal generation circuit 41 can change the setting of the output time length of the reset signal NRST, it can be widely applied and operated properly.

Further, the same reset signal generating circuit 10 and OR circuit 50 as those of the conventional example are provided, and the reset signal NRST by the present device 20 and the reset signal R by monitoring the power supply voltage are provided.
Since ST and OR are connected by OR, it is possible to further prevent a complete malfunction.

(Second Embodiment) As shown in FIG. 2, this second embodiment is introduced into a keyboard (electronic circuit) 62 connected to an electronic device main body 61 with a curl cord 63 (core wire 64, shield 65). This is the case.

That is, the keyboard 62 (key 67) incorporates a controller (electronic circuit) in order to reduce the load on the main body (CPU) 61 and reduce the number of core wires 64 of the curl cord 63. .. However, the frame ground of the keyboard 62 is the main body 61 and the shield 65.
Since it is connected only by itself, the impedance of the frame ground is very high, and there is a strong possibility of malfunction due to external noise (static electricity).

Here, the external noise detector 21 is formed of a loop-shaped electric conductor indicated by hatching on the keyboard 62, and is connected to the waveform shaping circuit 31 via the resistor R6. Further, the shield 65 is connected to the waveform shaping circuit 31 via the capacitor C7 and the resistor R7 in order to prevent the shield 65 from being induced to the frame guide side.

Therefore, if the reset signal NRST is set to be output with an external noise that is lower than the noise level that causes each LDC in the keyboard 62 to malfunction, for example, an incorrect code will be output from the keyboard 62. It is possible to prevent the keyboard 62 from hanging up or hanging up.

In the above first and second embodiments,
The reset signal NRST from the device 20 and the reset signal RST by voltage monitoring are input to the OR circuit 50 to output the final reset signal TRST, but the use of the reset signal NRST is not limited to this. For example, as a high-level interrupt input such as a non-maskable interrupt, it can be used for re-execution of an instruction currently being executed, task re-execution, data cancellation or retransmission, and the like.

[0027]

As described above, according to the present invention, an external noise detector made of a linear electric conductor arranged so as to surround an electronic circuit and a spike noise detected by the external noise detector are provided. Since the waveform shaping circuit for shaping the waveform and the reset signal generation circuit for generating the reset signal of the set time length based on the output signal of the waveform shaping circuit are configured, malfunction of the circuit due to external noise can be prevented, and Abnormalities such as CPU runaway can be quickly resolved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment.

FIG. 3 is a circuit diagram for explaining a conventional reset signal generation circuit.

FIG. 4 is also a timing chart for explaining the operation.

[Explanation of symbols]

 10 Voltage Monitoring Type Reset Signal Generation Circuit 20 Reset Signal Generation Device 21 External Noise Detector 31 Waveform Shaping Circuit 33 Surge Absorber 34 Reference Voltage Setting Device 35 Comparison Circuit 36 OR Circuit 41 Reset Signal Generation Circuit 42 Single Multivibrator 50 OR Circuit 60 Electronic circuit 62 Keyboard (electronic circuit) 63 Curl code 64 Core wire 65 Shield 67 key

Claims (1)

Claim: What is claimed is: 1. A device for generating a reset signal for hardware-resetting an electronic circuit such as a microprocessor application circuit or a digital logic circuit, the device being configured to surround the electronic circuit. An external noise detector made of a linear electric conductor arranged, a waveform shaping circuit for shaping the spike noise detected by the external noise detector, and a preset based on the output signal of the waveform shaping circuit. A reset signal generation device for an electronic circuit, comprising: a reset signal generation circuit that generates a reset signal for a predetermined time.