JPH08272768A - Stand-by time adjusting device for microcomputer - Google Patents

Abstract

PURPOSE: To provide a stand-by time adjusting device for microcomputer which can suppress variation in the time constant of a time constant circuit consisting of a resistance and a capacitor. CONSTITUTION: According to the result of a comparison between one level period of a rectangular wave obtained by shaping the waveform of a charging and discharging output and a reference clock, the connection point of one of plural series resistances 25-1 to 25-n is connected to the capacitor 17 to constitute a time constant circuit. Consequently, the time constant of the time constant circuit can be held constant and the stand-by time of a microcomputer 15 can be made constant. Therefore, this device is used for a slave equipment of telephone and then the calling state of the master equipment is surely detected to generate a ring-back tone through the speaker of the slave equipment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer standby time adjusting device suitable for controlling the standby time of a microcomputer used in a cordless telephone handset or the like.

[0002]

2. Description of the Related Art At present, the telephone market has become active by the time a telephone consisting of a master unit and a slave unit is used in a general household. In order to expand the market for this type of telephone, it is inevitable to reduce the cost of the telephone itself. Therefore, recently, a master side connected to the telephone line and a slave side wirelessly communicated with the master side. There is also a low-priced model in which both the provision of a speaker for emitting a ringing sound is stopped and the speaker of the master unit side is omitted and the speaker is provided only on the slave unit side. In this case, the child device periodically determines whether the parent device is ready to accept an external call through the telephone line, and outputs the speaker of the child device only when it is accepted. In addition, it is necessary to configure a system between the master unit and the slave unit. Specifically, the slave unit has a microcomputer built therein, and the microcomputer determines whether or not the master unit is in the calling state of the telephone bell. Since the child device is a cordless type and is driven by a battery, it is necessary to use a microcomputer in consideration of the life of the battery. FIG. 2 is a diagram showing an example of a microcomputer that is built in and used in a child device.

In FIG. 2, (1) is a microcomputer, and outside the microcomputer (1),
A resistor (2) and a capacitor (3) and a speaker (4) connected in series between the power supply Vdd and the ground are provided. In particular, the connection point of the resistor (2) and the capacitor (3) is connected to the microcomputer (1). Connected to terminals (5) and (6),
Moreover, the input of the speaker (4) is connected to the terminal (7) of the microcomputer (1). The resistance (2)
And a capacitor (3) constitutes a time constant circuit having a fixed time constant.

In the inside of the microcomputer (1), reference numeral (8) is a Schmitt inverter having hysteresis, the input of which is connected to the terminal (5) and the terminal voltage of the capacitor (3), that is, the charging voltage of FIG. 3 (a). A discharge voltage (sawtooth voltage) is applied. Here, the Schmitt inverter (8) has two different threshold voltages, one high threshold voltage Vth is shown by a chain line, and the other low threshold voltage Vtl is shown by a chain line in FIG. . The resistance value of the resistor (2) and the capacity of the capacitor (3) are such that the charging / discharging period performed once is 1 sec.
Is set so that the charging / discharging operation is performed in a cycle of 1 sec. More specifically, the output of the Schmitt inverter (8) is 990 mse in one second cycle.
c is at a high level, so that the remaining 10 msec is at a low level, that is, charging is performed for 990 msec and then 1
The values of the resistor (2) and the capacitor (3) are determined so that the discharge is performed at 0 mesc. As a result, as a result, the output of the Schmitt inverter (8) becomes as shown in FIG.
As shown in (1), the level becomes high for 990 msec and low level for 10 msec within 1 sec.
(9) is a hold control unit, which receives this high level output from the Schmitt inverter (8)
When the microcomputer (1) is set to the hold mode (standby state) for msec and the low level output of the Schmitt inverter (8) is received, this 10 m
The microcomputer (1) is brought into a normal operation state only for the sec period. This hold control section (9)
In detail, it is a part that performs software processing, and when the output of the Schmitt inverter (8) is recognized as a high level, an interrupt signal is generated, and at this time, a ROM (not shown)
Based on the result of decoding the program data read from, the microcomputer (1) is set to the hold mode for performing the minimum necessary operation to reduce the current consumed by the microcomputer (1). Further, when the hold control section (9) recognizes the output of the Schmitt inverter (8) as a low level, another hold signal is generated,
At this time, the microcomputer (1) is set to the normal operation state based on the result of decoding the program data read from the ROM.

Reference numeral (10) is a call determination unit, which is a circuit unit (not shown) in the preceding stage for carrying out communication signal processing with the master unit built in the slave unit, and the master unit now makes a call at the request of the other party. In order to do so, it receives a signal indicating whether or not it is in a calling state, and controls a charge / discharge control unit described later.
The determination operation of the read determination unit (10) is performed during the 10 msec period during which the microcomputer (1) normally operates. (11) is the charge / discharge control unit described above, and first receives the output of the Schmitt inverter (8) and controls the charge / discharge of the capacitor (3). Reference numeral (12) is an N-channel MOS transistor (hereinafter referred to as an NMOS transistor) that forms a discharge path of the terminal voltage of the capacitor (3), the gate is connected to the output of the charge / discharge control unit (11), and the drain is the terminal. It is connected to the non-grounded side of the capacitor (3) via (6), and the source is grounded. When the output of the Schmitt inverter (8) is at a high level, the charge / discharge control unit (11) basically outputs a low level discharge prohibition signal (for example, 0 volt), and the NMO
The S transistor (12) is turned off to continue the charging operation of the capacitor (3). On the other hand, when the output of the Schmitt inverter (8) is at a low level, a high level discharge permission signal (for example, 5 volts) is output to turn on the NMOS transistor (12) to discharge the electric charge of the capacitor (3). Further, when an output indicating "no call" is applied to the charge / discharge control unit (11) from the call determination unit (10), the charge / discharge control unit (11) outputs a signal output based on the output of the Schmitt inverter (8). To do. On the other hand, when the call determination unit (10) obtains an output indicating "calling", the charge / discharge control unit (11) ignores the output of the Schmitt inverter (8) and continues to output only the discharge inhibition signal. That is, the output of the Schmitt inverter (8) is finally fixed to the low level, and the microcomputer (1) continues the normal operation state. Reference numeral (13) is a ringing tone generating section, which receives a "calling present" output from the calling determining section (10) and generates a ringing tone. The ringing tone output from the ringing tone generator (13) is output from the terminal (7) via the buffer (14) and is emitted from the speaker (4).

The microcomputer (1) configured as described above is built in the slave unit, but the signal for making a call sent from the telephone line to the master unit is usually 1
It is intended to ring a ringing sound at intervals of sec. Therefore, if the microcomputer (1) repeatedly executes each cycle consisting of the hold mode and the normal operation mode every 1 sec in accordance with the time constant of the time constant circuit, it will be intermittently performed in the 10 msec period of the normal operation mode. Make sure to determine whether the base unit is in the calling state,
A ringing tone can be emitted from the speaker (4) without fail at the timing of calling.

[0007]

By the way, in the above-mentioned conventional technique, the resistor (2) and the capacitor (3) are external parts to the microcomputer (1), and ideally, they are charged and discharged in a cycle of 1 sec. It is a fixed time constant in which the resistance value and the capacitance are selected to perform. However, in practice,
The time constant changes due to factors such as fluctuations in the power supply Vdd and temperature changes. If this time constant changes,
The charging / discharging cycle deviates from 1 sec, and the high and low level periods of the Schmitt inverter (8) fluctuate accordingly. In particular, when the time constant becomes large and the high level period of the Schmitt inverter (8) continues for 1 sec or more, the main unit is in the calling state for 1 s.
In the ec period, there may be a defective timing in which the microcomputer (1) cannot shift from the hold mode to the normal operation mode, and there is a problem that the speaker (4) cannot emit the ringing tone at this defective timing.

In order to suppress the fluctuation of the time constant, a crystal resonator having a small fluctuation has been conventionally used, but this is not a preferable measure because of the problem of high cost. Therefore, it is an object of the present invention to provide a standby time adjustment device for a microcomputer capable of suppressing fluctuations in the time constant of a time constant circuit composed of resistors and capacitors.

[0009]

The present invention has been made to solve the above problems, and is characterized by a reference clock generation circuit for generating a reference clock based on an oscillation clock. A plurality of series resistors that are connected in series to form a time constant circuit by connecting any one of the connection points to a capacitor, and a charge / discharge control unit that controls charge / discharge of the time constant circuit. A waveform shaping section that shapes the charge / discharge output of the time constant circuit into a rectangular wave, and a rectangle of the waveform shaping section that corresponds to one charge / discharge output when one charge / discharge output of the time constant circuit is one cycle. A comparison unit that compares one level period of the wave output with the reference clock; and a resistance switching unit that connects any one connection point of the series resistors to the capacitor based on the output of the comparison unit. ,, By controlling the cycle of charging and discharging the output of the serial time constant circuit is that the constant standby time of the microcomputer corresponding to the one or the other of level period of the square wave output.

[0010]

According to the present invention, based on the result of comparison between one level period of a rectangular wave obtained by shaping the waveform of the charging / discharging output and the reference clock, any one of the plurality of series resistors is connected to a capacitor. The time constant circuit is configured by connecting them. As a result, the time constant of the time constant circuit can be kept constant, and the standby time of the microcomputer can be kept constant. Therefore, if the device of the present invention is used in a slave unit of a telephone, the calling state of the master unit can be reliably detected and a ringing tone can be emitted from the speaker of the slave unit.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a diagram showing a standby time adjusting device for a microcomputer according to the present invention. In addition, in FIG.
The same numbers are given to the same configurations as those and the description thereof is omitted.

In FIG. 1, reference numeral (15) is a microcomputer, and a vibrator (16) such as ceramic and a capacitor (1) are provided outside the microcomputer (15).
7) is provided. Both ends of the vibrator (16) are connected to terminals (18) and (19), and one end of the capacitor (17) on the non-grounded side is connected to terminals (20) and (21). Now, inside the microcomputer (15), (22) and (23) are respectively inverters and resistors connected in parallel, and both ends are connected to terminals (18) and (19). An oscillator is composed of the external vibrator (16), the internal inverter (22) and the resistor (23). For example, if the oscillation frequency of the oscillator (16) is 4 MHz, a rectangular original clock of 4 MHz is generated from the output of the inverter (22). (24) is a reference clock generator, which divides an original clock of 4 MHz by, for example, 4
A reference clock having a cycle of 1 MHz, that is, 1 μsec is generated.

On the other hand, (25-1) to (25-n) are resistors connected in series, and one end of the resistor (25-1) is connected to the power supply Vdd. The resistors (25-1) to (2
The resistance values of 5-n) are equal in this embodiment. The transmission gates (26-1) to (26-) are connected to the connection points of the resistors (25-1) to (25-n), respectively.
-N) is connected to one end, and the other ends of the transmission gates (26-1) to (26-n) are commonly connected to each other and connected to the non-grounded side of the capacitor (17) via the terminal (21). There is. That is, by selecting any one of the transmission gates (26-1) to (26-n) by the resistance switching unit described later, the resistances (25-1) to (2-1) are selected.
N by any one of 5-n) and the capacitor (17)
This makes it possible to configure various types of time constant circuits. The drain of the NMOS transistor (12) forming the discharge path is connected to the terminal (21).

(27) is a Schmitt inverter (waveform shaping section) having two different threshold voltages, and generates a rectangular wave SO which becomes a high or low level according to the charge / discharge voltage of the time constant circuit. It should be noted that the charging / discharging time of the time constant circuit once is 1 sec (charging time is 990 m
sec, the discharge time is 10 msec), one of the transmission gates (26-1) to (26-n) is turned on, that is, from the Schmitt inverter (27), the time constant circuit With one charging / discharging operation, as shown in FIG. 3B, a rectangular wave SO is obtained which has a high level for 990 msec and a low level for the remaining 10 msec. This rectangular wave SO is applied to the charge / discharge control unit (11).

A hold controller (28) receives the high level output from the Schmitt inverter (27), puts the microcomputer (15) in the hold mode for 990 msec, and sets the Schmitt inverter (27) at the low level. When you receive the output, this 1
The microcomputer (15) is set to the normal operation mode only for a period of 0 msec. This hold control section (28) is, in detail, a section that performs software processing, and when it recognizes the output of the Schmitt inverter (27) as a high level, it generates an interrupt signal, and at this time the ROM
Based on the decoding result of the program data read from (not shown), the current consumed by the microcomputer (15) is reduced by setting the hold mode in which the microcomputer (15) performs only the minimum necessary operation. Further, when the hold controller (28) recognizes the output of the Schmitt inverter (27) as a low level, another hold signal is generated, and at this time, the microcomputer (15) is generated based on the decoding result of the program data read from the ROM. ) Is the normal operation mode. However, the hold control unit (28) uses the Schmitt inverter (27).
When the high-level output of is received a predetermined number of times (for example, 10 times), only the last one is sent to the microcomputer (15).
For a 990 msec period to generate a different interrupt signal.

Reference numeral (29) is a measuring unit for comparing the reference clock from the reference clock generating unit (24) with the high level output period from the Schmitt inverter (27). Ideally, the high-level period of the Schmitt inverter (27) is 990 msec, so 1 μm during this period.
The basic condition is that there are 990000 reference clocks with a sec cycle. The measurement unit (29) counts the number of reference clocks that fall within the high level output period of the Schmitt inverter (27). (30) is a determination unit, and the reference clock number measured by the measurement unit (29) is 99000.
It is determined whether there are more or less than zero. And 9900
The n-bit table data read from the ROM is set in a resistance switching unit, which will be described later, which is composed of an n-bit register, depending on how much or less the number of reference clocks is for 00. . Here, the measurement unit (29) and the determination unit (30) are software-processed based on the program data from the ROM within the above-mentioned 990 msec period in the normal operation mode.

Reference numeral (31) is the resistance switching unit described above, in which n-bit table data from the ROM is set. Each bit of this table data is connected to each control terminal of the transmission gates (26-1) to (26-n). That is, of n bits of table data,
Only one bit becomes "1", only the transmission gate suitable for setting the charging / discharging cycle of the time constant circuit to 1 sec is opened, and the connection point of the plurality of series resistors corresponding to the transmission gate is the terminal (21 ) To the non-grounded side of the capacitor (17).

From the above, a plurality of series resistors (25-1) to (25-1) connected to the capacitor (17) to form a time constant circuit
Since (25-n) can be switched, the charge / discharge cycle of the time constant circuit is always 1 sec even when the power supply Vdd changes, the ambient temperature changes, and the threshold voltage characteristics of the Schmitt inverter (27) vary. Can be From this, if the microcomputer (15) of the present embodiment is built in the slave unit of the telephone and is operated intermittently, it can be surely detected whether or not the master unit is in the calling state without making a detection error, and the master unit. This is very suitable because the ringing tone can be emitted from the speaker (4) of the child device in synchronization with the calling of the.

[0019]

According to the present invention, the connection point of any one of the plurality of series resistors is determined based on the result of comparison between one level period of a rectangular wave obtained by shaping the charge / discharge output and the reference clock. A time constant circuit is configured by connecting with a capacitor. As a result, the time constant of the time constant circuit can be kept constant, and the standby time of the microcomputer can be kept constant. Therefore, if the device of the present invention is used in a slave unit of a telephone, there is an advantage that the calling state of the master unit can be reliably detected and a ringing tone can be emitted from the speaker of the slave unit.

[Brief description of drawings]

FIG. 1 is a diagram showing a device of the present invention.

FIG. 2 is a diagram showing a conventional device.

FIG. 3 is a waveform diagram showing a charge / discharge waveform and a rectangular waveform in FIGS. 1 and 2.

[Explanation of symbols]

 (11) Charge / discharge control section (12) NMOS transistor (15) Microcomputer (17) Capacitor (24) Reference clock generation section (25-1) to (25-n) Series resistance (27) Schmitt inverter (28) Hold Control part (29) Measuring part (30) Judgment part (31) Resistance switching part

Claims (2)

[Claims] 1. A reference clock generation circuit for generating a reference clock based on an oscillation clock, and a plurality of units constituting a time constant circuit by connecting in series any one of the connection points and a capacitor. Series resistance, a charge / discharge control unit that controls charge / discharge of the time constant circuit, a waveform shaping unit that shapes the charge / discharge output of the time constant circuit into a rectangular wave, and one charge / discharge output of the time constant circuit. When 1 is defined as one cycle,
A comparison unit that compares one level period of the rectangular wave output of the waveform shaping unit corresponding to charge / discharge output with the reference clock; and based on the output of the comparison unit, any one of the series resistors. A resistance switching unit that connects the connection point to the capacitor, and controls the cycle of the charge / discharge output of the time constant circuit, and the standby time of the microcomputer corresponding to one or the other level period of the rectangular wave output. A standby time adjustment device for a microcomputer, which is characterized by a constant value. 2. The standby time adjustment device for a microcomputer according to claim 1, wherein the comparison unit performs a comparison operation only for a predetermined one cycle of a plurality of cycles of charge / discharge output of the time constant circuit. .