JPH01277915A - Reset circuit for microcomputer - Google Patents

Abstract

PURPOSE:To effectively operate a reset circuit for a microcomputer by providing a time constant circuit between a battery power source and the power detection input of a reset device and slowly raising and quickly lowering the supply voltage given to the reset device. CONSTITUTION:A time constant circuit 3 is provided between a power input terminal 1 and a reset circuit 6. When a supply voltage VD supplied from the battery power source is given to the reset circuit 6 through the time constant circuit 3, the time constant for charging is small but is large for discharging because a diode D2 connected in parallel with a resistance R2 of the time constant circuit 3 is set in the charging direction of a capacitor C2. Consequently, the input voltage of the reset circuit quickly rises at the time of power-on and slowly falls at the time of a momentary interruption of the supply voltage VD. Thus, the reset circuit for the microcomputer is effectively operated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a reset circuit for a microcomputer;
It is particularly suitable for use in portable electronic devices that operate on battery power.

[Summary of the invention]

A time constant circuit is provided between the power supply and the reset means, and by slowing down the fall of the power supply voltage applied to the reset means and making the rise thereof fast, a reset is not applied when the momentary interruption of the power supply voltage is short, and This is a reset circuit for a microcomputer that allows a power-on reset to occur quickly when the power is turned on.

[Conventional technology]

Portable electronic devices are equipped with a battery box, and when carried, a battery is inserted into the battery box and the device is operated using battery power. If vibrations, shocks, etc. are applied to an electronic device when it is operated on battery power, the batteries in the battery box may move and cause the battery electrodes to contact each other, or the battery electrodes and the electrode terminals of the battery box to contact each other. The power supply voltage may be interrupted momentarily.

On the other hand, an electronic device equipped with a microcomputer is provided with a reset means, and when the power supply voltage rises to a specified value, a reset signal is applied from the reset means to start the operation of the microcomputer. Therefore, if a power supply voltage is momentarily cut off while a portable electronic device equipped with a microcomputer is operated on battery power, a reset is required each time. Therefore, even if the power supply voltage is momentarily interrupted, the microcomputer will not go out of control.

[Problem to be solved by the invention]

Frequent resets caused by instantaneous interruptions in the power supply voltage may interrupt operation and cause problems.

That is, for example, in the case of a liquid crystal television that does not have a non-volatile memory that stores operating conditions, the channel returns to the initial setting value every time the television is reset. Therefore, for example, if a reset is applied while watching 6 channels on a liquid crystal television whose initial setting is 1 channel, the 6 channels may change to 1 channel.

Further, in the case of a display device that displays various screen displays (initial displays) when the power is turned on, this display is performed every time there is a momentary power outage, which is troublesome. Also, in the case of devices that require a long initial reset time, frequent resets can make the device difficult to use.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to prevent a reset from being applied when the interruption time is short, and to quickly perform a power-on reset when the power is turned on.

[Means to solve the problem]

The microcomputer reset circuit of the present invention detects the rise of the power supply voltage V0 supplied from the battery power supply 5 and resets the microcomputer 4. The time constant circuit 3 is composed of a resistor R2 and a capacitor C2, and a diode D2 that charges the capacitor C2 is connected to the resistor R2. connected in parallel.

[Effect]

Power supply voltage supplied from battery power supply 5■. is applied to the reset means 6 via the time constant circuit 3. Since the diode D2 connected in parallel to the resistor R2 of the time constant circuit 3 is in the charging direction of the capacitor C2, the charging time constant is small and the discharging time constant is large. Therefore, the input voltage VI of the reset means 6
N rises rapidly when the power is turned on, and the power supply voltage ■. During a momentary power failure, the voltage falls slowly, making it difficult to reset.

〔Example〕

FIG. 1 is a circuit diagram of a microcomputer reset circuit showing one embodiment of the present invention. Power supply voltage supplied to power input terminal 1 ■. is given to the power supply filter 2 and the time constant circuit 3. Power filter 2 is a capacitor Cal,
It consists of C4 and coil L1, and the power supply voltage is ■. is applied to the drive voltage input terminal 4a of the microcomputer 4 after the voltage change is smoothed by the power supply filter 2.

The time constant circuit 3 is composed of a resistor R2 and a capacitor c2, and a diode D2 that charges the capacitor Ct is connected in parallel to the resistor R2. Therefore, the voltage 8 at the output point B of the time constant circuit 3 rises rapidly when the power is turned on.
It falls slowly when the power is turned off.

Voltage at output point B ■3 is reset as input voltage VIN I
Given to C0I. The reset IC0I is provided as a reset means 6, and when the input voltage V+N exceeds the threshold voltage (■TH) of the cent IC0I, the output voltage (■) is derived to the low-pass filter. Set 1 to high level. Also, when the input voltage VIN falls below the threshold voltage VT)l, the output voltage ■. . , inverts to low level.

The low-pass filter 7 consists of a capacitor C4 and a resistor R1, and the output voltage of the reset IC0I. .

is applied to the reset terminal 4b of the microcomputer 4 after the voltage change is smoothed by the low-pass filter 7. A protection diode D1 is connected between the reset terminal 4b and the drive voltage input terminal 4a, that is, between the output point of the low-pass filter and the output point E of the power filter 2. For example, a germanium diode is used as the protective film diode D, and the resistor R1 of the low-pass filter serves as a load for the protective diode D.

The portable device is provided with a battery box 8 as shown in the plan view of FIG. 2, and when the device is carried, a dry battery 10 is stored in the battery box 8 and the device is driven by the battery power source 5. The battery box 8 is provided with a positive electrode terminal 11 and a negative electrode terminal 12, and four dry batteries 10 are housed between these terminals 11 and 12 when the driving voltage is 6.

The battery output is taken out via a power line 13 connected to the positive electrode terminal 11 and a power line 14 (earth line) connected to the negative electrode terminal 12, and the positive voltage is taken out via a power switch (not shown). ) to the power input terminal 1.

If the device is subjected to vibrations, shocks, etc. while operating on the battery power source 5, the dry battery 10 may move within the battery box 8. During this movement, the contact between the electrodes of the dry battery 10 and the contact between each electrode and the terminals 11 and 12 are momentarily separated, and the power supply voltage ■ is applied to the power input terminal 1. may be interrupted momentarily.

Next, the power supply voltage ■. The operation of the reset circuit when the instantaneous interruption time is short will be explained with reference to the operating waveforms shown in FIG. At time point to in FIG. 3, when the power supply voltage VD applied to the power supply input terminal 1 is momentarily interrupted, the potential at the connection point A in FIG. , falls at a predetermined time constant as shown in FIG. 3A.

Since the polarity of diode D2 connected in parallel with resistor R2 is in the charging direction of capacitor C2, the voltage at connection point A is
, falls, the charge on capacitor Cz increases to resistor R2
is discharged through. Therefore, the voltage Vl at the output point B of the time constant circuit 3, that is, the input voltage VIN of the reset IC0I, slowly drops with a time constant of cz x Rt, as shown in FIG. 3B.

Time 1 when time T1 has elapsed from time to. At the time, the power supply voltage ■ is applied to the power input terminal l. is supplied, the voltage vA at the connection point A increases as shown in FIG. 3A. At the time it, the voltage at the connection point A is the capacitor C2.
When the terminal voltage of capacitor C! will be charged. During charging, the charging current flows through the diode D, so the charging time constant Ctxt, (rt
: Internal resistance of diode D2) is small. Therefore, the input voltage VIN of ICOI rises rapidly as shown in FIG. 3B, and at time t, the voltage vA of the connection point A
, that is, the power supply voltage V.

Since the instantaneous voltage drop is gradual, the instantaneous voltage drop is T.

is short, the input voltage VIN
does not fall below the threshold voltage vT,l of reset IC0I. Therefore, the output voltage V of the reset IC0L.

Since ut remains at a high level and does not change as shown in FIG. 3C, the voltage 2 at the output point of the low-pass filter remains at a high level and does not change.

On the other hand, the voltage ■ at the connection point A changes from time t0 to t.

The output point E of the power supply filter 2 decreases between
The voltage V, is the voltage at the connection point A, as shown in Figure 3.
, changes with a waveform that is a rounded version of the change in . Therefore, when the instantaneous interruption time is short, the voltage drop of the drive voltage vDD applied to the drive voltage input terminal 4a of the microcomputer 4 becomes small.

When the power supply voltage V, is momentarily cut off, the voltage vE at point E decreases, while the voltage vL at point does not change.
The voltage at point ■, becomes higher than the voltage at point E, ■. Therefore, when these voltages VL, V are directly supplied to the reset terminal 4b and the drive voltage input terminal 4a, the potential of the reset terminal 4b becomes higher than that of the drive voltage input terminal 4a. If this potential difference exceeds, for example, 0.4 square meters, the terminal input protection circuit of the microcomputer 4 may be destroyed. In the embodiment, a protection diode D1 is connected between the output point of the low-pass filter and the output point E of the power filter 2. Therefore, the reset terminal 4b of the microcomputer 4
The reset input voltage ■8 applied to is as follows. In this case, since the voltage VL does not change, the reset input voltage ■ is changed from the voltage VE (driving voltage VIlltl) at the output point E to the diode D, as shown in FIG. 3F.
The potential is increased by the forward voltage (2) (the potential indicated by the broken line in FIG. 3E). Therefore, drive voltage input terminal 4a
The drive voltage V input to. Even if V decreases during a momentary interruption, the potential difference between the drive voltage input terminal 4a and the reset terminal 4b can be suppressed to below the forward voltage V of the diode D. In the case of a germanium diode, the forward voltage (2) is 0°3 (2), so the potential of the reset terminal 4b does not become higher than the potential of the drive voltage input terminal 4b by 0.3 V or more. Therefore, the terminal input protection circuit of the microcomputer 4 will not be destroyed even if the potential of the reset terminal input voltage (7) is held at a high level to prevent the reset from occurring during a momentary interruption of the power supply voltage (2). Note that when the instantaneous interruption of the power supply voltage is extremely short like this, the microcomputer 4 does not run out of control, so there is no problem even if the microcomputer 4 is not reset.

Next, the operation when the instantaneous interruption time is long will be explained with reference to the operation waveforms shown in FIG. When a momentary interruption occurs at time t0 in FIG. 4, the voltage 4 at output point A decreases as shown in FIG. 4A, and reaches OV at time t1. Then, at time t, when time T2 has elapsed from time t0, the power input terminal 1
■Power supply voltage.

When is supplied, the voltage (2) at the connection point A rises from OV, and rises to the power supply voltage V at time t6.

On the other hand, as shown in FIG. 4B, the voltage ■ at the output point B and the input voltage VIN of the reset IC01 decrease with the discharging time constant C2XR2 from the time t0 when the instantaneous interruption occurs. Since the time T2 is long, the input voltage VIN is reset at the time t2) below the threshold voltage TH of ICOI, and the voltage at the output point A is the capacitor C2.
The voltage continues to drop until time t4, when it becomes higher than the terminal voltage of . Then, at time t4, when the capacitor C2 starts to be discharged, the input voltage becomes the power supply voltage ■. At time t, it exceeds the threshold voltage V7H, and at time t6 it becomes the same potential as the connection point A. Since the input voltage 1N of the reset IC0I rises quickly in this manner, a power-on reset can be applied quickly when the power is turned on.

Since the input voltage VIN falls below the threshold voltage VTH between time 1t and time t4, the output voltage of the reset IC is ■. □ is from time t2 to time t as shown in Figure 4C.
, the level is low between . Therefore, from the low-pass filter 7, as shown in the fourth diagram, an output voltage ■1 having a waveform in which the voltage change of the output voltage V out of the reset IC0I is smoothed is obtained.

On the other hand, the output voltage at the output point E of the power filter 2 is ■.

begins to decrease from time t0 as shown in FIG. 4E. In this case, since the instantaneous interruption time T2 is long, the voltage drop at the output point E becomes large. However, since the protective diode D1 is provided, even if the voltage drop at the output point E becomes large, the reset input voltage (2) 8 will not become higher than the voltage (2) at the output point E by more than 0.3 V as described above. Further, during a period in which the output voltage (1) of the low-pass filter is lower than the output voltage (2) of the power supply filter 2, the output voltage (2) of the low-pass filter is applied to the reset terminal 4b as shown in equation (1). Therefore, as shown in Fig. 4F, the reset input voltage ■8 falls smoothly following the voltage at the output point E, and when ■, ≦■□+■□, the output voltage ■ , it drops rapidly when the voltage changes. Also, when rising to a high level, ■.

≦V, +Vl! The voltage rises rapidly during the period , and then rises slowly following the voltage at point E.

When the instantaneous interruption time T2 is long as described above, it is possible to prevent the microcomputer 4 from running out of control by setting the reset terminal input voltage vR to a low level and applying a reset.

If the microcomputer 4 is equipped with a reset means 6, a load resistor RL may be connected in place of the reset IC0I and low-pass filter shown in FIG. 1, as shown in the circuit diagram of FIG.

〔Effect of the invention〕

As described above, in the present invention, a time constant circuit is provided between the battery power supply and the power supply detection input of the reset means, and the fall of the power supply voltage applied to the reset means is delayed, so that the battery is moved by vibration etc. The microcomputer can be made less likely to be reset when the voltage is momentarily cut off. Therefore, stable operation can be achieved because no reset is applied in the event of a short instantaneous interruption that prevents the microcomputer from running out of control. In addition, since the power supply voltage rises quickly, even if the reset is not applied when the power is momentarily cut off, the time required until the power-on reset is applied when the power is turned on can be prevented from becoming long.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a reset circuit showing an embodiment of the present invention, Fig. 2 is a plan view of the battery box, Fig. 3 is an operating waveform diagram when the instantaneous interruption time is short, and Fig. 4 is an instantaneous interruption time. FIG. 5 is a circuit diagram of a reset circuit showing an embodiment different from that in FIG. 1. In addition, in the symbols used in the drawings, 2.--.--.--..--power filter 3.
−−−−−・・−・−・−・・・−Time constant circuit 4−・
・−・・−・・−・・Microcomputer 5−・
・−・・−−−m−・・−Battery power supply 6・−・・−・
・−・−・−−−−− It is a reset means.

Claims (1)

[Scope of Claims] Reset means for detecting a rise in power supply voltage applied from a battery power source to reset the microcomputer, and a time constant circuit provided between the battery power source and a power detection input terminal of the reset means. A reset circuit for a microcomputer, comprising: the time constant circuit comprising a resistor and a capacitor; and a diode for charging the capacitor connected in parallel with the resistor.