JPH0533650U - Microcomputer power supply circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention is intended to simplify a reset circuit of a microcomputer and to effectively use a backup power supply of the microcomputer. According to the present invention, in a power supply circuit of a microcomputer 1 including a switching circuit 2 for switching between a main power supply 4 and a backup power supply 3, by mounting the main power supply 4 when the backup power supply 3 is mounted, the microcomputer is connected via a terminal 1b. Reset 1 In addition, the microcomputer 1 is reset via the terminal 1b by a signal from the terminal f of the microcomputer 1.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a power supply circuit for a microcomputer that operates with either a high-frequency main clock or a low-frequency sub clock according to two types of voltages.

[0002]

[Prior Art]

 Conventional portable electronic devices such as video cameras have the current time as shown in Japanese Utility Model Publication No. 61-169443 (H02J 9/06) even when the main power source such as a battery is not attached. A backup power source such as a lithium battery is indispensable for driving the timer that enables storage.

However, in the above-mentioned conventional technology, when a microcomputer (hereinafter referred to as a microcomputer) is temporarily operated with a high-frequency main clock by power supply from a backup power supply, the power consumption of the backup power supply significantly increases.

Therefore, since the backup power source originally has a small capacity like a lithium battery, the above-mentioned power consumption becomes a serious problem. In addition, operating a high-frequency clock with a low power supply voltage may cause the microcomputer to run out of control.

Therefore, in order to solve this problem, the present applicant has previously proposed in Japanese Patent Application No. 2-122808 (H02J 9/06).

This is the configuration shown in FIG. Reference numeral 1 is a microcomputer that operates with one of two types of clocks having different frequencies according to the power supply voltage applied to the terminals 1a, 1b, and 1c, and 2 is a switching circuit that switches the power supply.

Reference numeral 3 is a backup power source such as a lithium battery, and 4 is a main power source such as a battery. Further, 5 is a first reset circuit for resetting the microcomputer, and 6 is a second reset circuit for similarly resetting the microcomputer.

Reference numeral 11 is an AND circuit, and 12 is a capacitor for having a time constant.

Next, the circuit operation of FIG. 3 will be described.

When the power supply voltage applied is the main power supply 4, the microcomputer 1 operates with a main clock having a high frequency (for example, 12 MHz), and executes various systems when the power is on.

When the power supply voltage is the backup power supply 3, the sub-clock operates at a relatively low frequency (for example, 32 KHz), and the timer operates when the power is off. The operation guarantee voltage of the microcomputer 1 is set to 2.5 to 5V.

The terminal 1 a of the microcomputer 1 is coupled to the fixed contact of the switching circuit 2. One movable contact 2a of the switching circuit 2 is coupled with a logical product circuit 11 having the backup power supply 3 and the second reset circuit 6 as inputs, and the other movable contact 2b is coupled with the output of the main power supply 4. ..

The main power supply 4 is connected to a first reset circuit 5, and the output of the first reset circuit 5 controls the switching of the switching circuit 2 and the control terminal 1 c of the microcomputer 1.

Here, the backup power supply 3 is, for example, a 3V lithium battery, and the main power supply 4 is, for example, a 5V battery.

The first reset circuit 5 outputs a high level when the input voltage is 4.3 V or more, and outputs a low level when the input voltage is less than 4.3 V. The switching circuit 2 outputs the output of the first reset circuit 5. If is low level, it is switched to one movable contact 2a side, and the voltage 3V of the backup power supply 3 is applied to the terminal 1a as the power supply voltage VDD of the microcomputer 1. Conversely, if it is high level, the other movable contact is moved. Switching to the contact 2b side, the voltage 5V of the main power supply 3 is applied to the terminal 1a.

A second reset circuit 6 is connected to the fixed contact of the switching circuit 2.

The second reset circuit 6 outputs a high level when the output voltage of the switching circuit 2 is 2.5 V or more, and outputs a low level when the output voltage is less than 2.5 V. This second reset circuit 6 The output of 6 is input to the reset terminal 1b of the microcomputer 1 and serves as a reset signal. The microcomputer 1 maintains the reset when the output of the first reset circuit 5 is at the low level.

Further, the output of the second reset circuit 6 is also input to the AND circuit 11 described above, the logical operation is performed with the output of the backup power supply 3, and the microcomputer 1 is reset and controlled.

In FIG. 3, when the main power supply 4 and the backup power supply 3 are not mounted, the output of the second reset circuit 6 becomes low level, and the switching circuit 2 switches to the movable contact 2a side. If only the backup power supply 3 is installed in this state, one input 11b of the logical product circuit 11 becomes high level, but the output of the second reset circuit 6 is low level, so the output of the logical product circuit 11 also becomes low level. It becomes a level.

Even if the switching circuit 2 is on the movable contact 2a side, the power supply voltage VDD is 0 V, and the power supply voltage is not applied to the microcomputer 1. Moreover, since the output of the second reset circuit 6 is at a low level, the microcomputer 1 maintains the reset state. As described above, even if only the backup power supply 3 is mounted without mounting the main power supply 4, the microcomputer 1 does not operate, and the power consumption of the backup power supply 3 does not occur.

Next, when the main power supply 4 is attached while the backup power supply 3 is attached, or when the backup power supply 3 is attached after the main power supply 4 is attached, the output of the first reset circuit 5 becomes The level shifts to the high level, and the switching circuit 2 switches to the movable contact 2b side. Along with this, 5 V is applied to the terminal 1a, the output of the second reset circuit 6 shifts to the high level, the reset of the microcomputer 1 is released, and the operation is started by the main clock of 12 MHz.

After that, when the main power supply 4 is removed, the output of the first reset circuit 5 shifts to the low level, the switching circuit 2 switches to the movable contact 2a side, and 3V is applied to the terminal 1a. At this time, since the output of the second reset circuit 6 maintains the high level, the microcomputer 1 executes the timer operation with the sub clock of 32 KHz.

FIG. 4 shows the driving timing of the above-mentioned microcomputer. If only the main power supply 4 is removed after time t2 from the time when the main power supply 4 is installed, the main clock operates at this time t2. After that, when the first reset circuit 5 shifts to the low level, this level shift is detected by the microcomputer 1 via the terminal 1c, and the clock is switched from the main clock to the sub clock by software. It works with Buklock.

This clock switching needs to be performed before the voltage applied to the microcomputer 1 drops from 5 V to the operation guarantee voltage of the main clock, but it is applied by inserting the capacitor 12 between the terminal 1a and the ground. The voltage can be held, the drop of VDD from 5 V to 3 V becomes gentle, and by setting the holding period to several msec, the clock is reliably switched to the sub clock during this period.

Therefore, the driving of the microcomputer by the high-frequency main clock by the backup power supply is prevented, the large power consumption of the backup power supply and the microcomputer runaway can be suppressed, and the practical value is high.

[0026]

However, in the case of the above-mentioned conventional example, the clock of the microcomputer 1 is switched in an extremely short time after the main power supply 4 is turned off and the voltage VDD of the power supply terminal of the microcomputer is switched to the backup power supply 3. Must be switched from the high speed clock (12 MHz) to the low speed clock (32 KHz), and therefore the first reset circuit 5 for detecting that the main power supply is turned off is required.

Further, the second reset circuit 6 for detecting that the voltage of the backup power supply 3 has dropped is also necessary, and the reset circuit becomes large-scaled.

Moreover, from when the power supply voltage VDD of the power supply terminal 1a is detected to be equal to or lower than the reset voltage (4.5V) of the first reset circuit 5 until the reset voltage (2.5V) of the second reset circuit 6 is detected. It is necessary to switch the clock of the microcomputer 1 to the low-speed clock (32 KHz), and if the microcomputer 1 continues to operate at the high-speed clock (12 MHz) for a while after switching to the backup power supply 3, or if the impedance of the backup power supply 3 Is high, the power supply voltage VDD of the power supply terminal 1a becomes equal to or lower than the reset voltage (2.5V) of the second reset circuit 6, and the second reset circuit 6 resets the microcomputer 1.

Further, when the voltage of the backup power supply 3 becomes equal to or lower than the reset voltage (2.5V) of the second reset circuit 6, the microcomputer 1 is reset, so that the microcomputer 1 operates at a low speed of 2.0V or 1.5V. Even if it can operate, the backup power supply 3 cannot be used sufficiently because it stops the clock operation when the voltage reaches 2.5V.

The present invention solves the above problems, and can provide a reset circuit of a microcomputer with a simple circuit configuration.

[0031]

[Means for Solving the Problems]

 The present invention provides a power supply for a microcomputer including a first power supply, a second power supply having a voltage V2 lower than the voltage V1 of the first power supply, and a microcomputer that operates at least with a main clock when the voltage V1 is applied. In the circuit, the microcomputer relates to a power supply circuit of a microcomputer, which performs reset control at least by an output of the microcomputer itself.

[0032]

[Action]

 The present invention can simplify the reset circuit of the microcomputer and can effectively use the backup power supply of the microcomputer.

[0033]

【Example】

 FIG. 1 shows a power supply circuit of a microcomputer according to an embodiment of the present invention. The same parts as those in the conventional example are designated by the same reference numerals and the description thereof will be omitted.

A logical product circuit 11 outputs a logical product of two inputs.

The operation will be described with reference to FIG. First, when the backup power supply 3 and the main power supply 4 are off or disconnected, a low level is input to the terminal 1b of the microcomputer 1.

In this case, the output of the normal microcomputer 1 is often high impedance, and the terminals 1e and 1f have the resistors R3 and R2 grounded and pulled down.

Since the power supply voltage VDD is 0V, the terminals 1e and 1f are at low level.

FIG. 2 is a diagram showing the waveform of each part in each state.

The state A is a case where only the lithium battery of the backup power supply 3 is installed. Since the terminal 1e is at the low level as described above, the voltage output of the backup power supply 3 is output by the AND circuit 11 to the switching circuit 2. It is not output to one movable contact 2a.

State B is a case where the lithium battery of the backup power source 3 and the battery of the main power source 4 are mounted, and the power source voltage VDD is 5V. Further, since the power supply voltage VDD becomes 5 V and the capacitor C1 is charged, and the point h becomes high level, the reset is released via the diode D3 and the program of the microcomputer 1 starts.

Therefore, the microcomputer 1 detects from the terminal 1g of the microcomputer 1 whether or not the backup power supply 3 is installed, and if the backup power supply 3 is installed, the timer of the microcomputer 1 is not cleared.

However, although not shown, if the data is abnormal as a timepiece, it is determined that the microcomputer 1 was in a runaway state before power-on, and the timepiece mechanism is reset.

The state C is a state in which the lithium battery of the backup power supply circuit 3 is attached and the main power supply 4 is removed, and the terminals 1e and 1f continue to output a high level. As a result, since the microcomputer 1 is not reset, the timepiece mechanism continues to operate until the voltage of the lithium battery of the backup power source 3 drops below the inoperable voltage of the microcomputer 1.

State D is a state in which the backup power source 3 is attached and the main power source 4 is attached. When the main power source 4 is attached, the microcomputer 1 detects from the terminal 1d of the microcomputer 1 and the terminal 1f Outputs a low level.

This signal is input to the reset terminal 1b of the microcomputer 1 through the diode D2 and resets the microcomputer 1 (hereinafter referred to as self reset). Due to this self-reset, the terminals 1e and 1f become high impedance, so that the resistor R2 is pulled down to the low level.

Then, due to 5V passing through the filter composed of the resistor R1, the diode D1, and the capacitor C1, the point h becomes high level after a while, so that the reset is released and the program of the microcomputer 1 is started.

By this processing, the terminals 1e and 1f output a high level.

The state E is a case where the main power supply 4 is turned off or removed after the backup power supply 3 is turned off or removed. Since the power supply voltage VDD becomes 0 V, the terminals 1e and 1f output a low level. Therefore, the microcomputer 1 is in the reset state.

The state F is a case where the main power source 4 is attached in the state E. Since the main power source 4 is in the reset state before being attached, the terminals 1e and 1f output a low level. Due to this, the reset is released (that is, point h is at high level) some time after the main power supply is installed, and the program starts.

As described above, when the main power supply 4 is attached, the microcomputer 1 is reset regardless of whether the backup power supply 3 has been attached until then.

Especially when the main power supply 4 is attached with the backup power supply 3 attached, the microcomputer 1 is self-reset by the signal output from the terminal.

When the counter of the timepiece mechanism is in 0.5 second increments, when the microcomputer 1 is reset, the timepiece data is reset by adding 0.25 seconds, which is the average of the clocks of the timepiece mechanism. Correct the clock error caused by.

Further, in the above description of the configuration, the method in which the power source is attached is used, but the power supply of the mycon 1 is controlled by switching the power switch or the like on and off with the power source attached. The effect of the present invention will not be impaired if other methods are used as long as the circuit can be used.

The switching circuit 2 may use a switching element such as a diode.

[0055]

[Effect of the device]

 The present invention can simplify the reset circuit of the microcomputer. Also, even if the backup power supply becomes 2.5V or less, it will not be reset, and if the clock mechanism continues to operate with only the backup power supply when the main power supply is disconnected, the reset operation will not occur and the microcomputer's operating capability Since the backup power is consumed up to the limit of the above and the operation of the clock mechanism is continued, it is possible to effectively use the backup power of the microcomputer.

Further, when the microcomputer becomes large-scale, the consumption current becomes large even in the operation of the low speed clock, and the use of such a backup power supply becomes effective.

[Brief description of drawings]

FIG. 1 is a diagram showing a power supply circuit of a microcomputer according to an embodiment of the present invention.

FIG. 2 is a waveform of each part in each state of one embodiment of the present invention.

FIG. 3 is a diagram showing a power supply circuit of a conventional microcomputer.

FIG. 4 is an explanatory diagram of power switching of a conventional example.

[Explanation of symbols]

 1 Microcomputer 2 Switching circuit 3 Backup power supply 4 Main power supply 11 AND circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G06F 1/04 301 C 7368-5B

Claims (1)

[Scope of utility model registration request] 1. A first power source, a second power source having V2 lower than a voltage value V1 of the first power source, and at least a voltage value V.
A power supply circuit for a microcomputer comprising a microcomputer that operates with a main clock when 1 is applied, wherein the microcomputer performs reset control at least by the output of the microcomputer itself.