JPS6270923A - Integrated circuit containing oscillating circuit - Google Patents

Abstract

PURPOSE:To decrease the power consumption by using a switching means to supply selectively the oscillation signal of one of two oscillating circuits to a system clock generating circuit. CONSTITUTION:A microcomputer 1 contains two oscillating circuits 5 and 2 for the original oscillation and a timepiece respectively. A switching circuit 11 works to supply selectively the oscillation signal of the circuit 5 and 2 to a system clock generating circuit 12. A control register 14 produces the switching control signal for the circuit 11. Thus a system clock phiC is usually produced based on the slow signal of the circuit 2. Then a system is actuated slowly. While the circuit 11 is switched to produce a fast clock phiC based on the original oscillation signal only when the fast processing is required. In such a way, the power consumption is greatly decreased.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a technology that is particularly effective when applied to oscillation control technology and technology for forming oscillation signals in semiconductor integrated circuits. The present invention also relates to techniques that are effective for use in microcomputers having clock oscillation circuits.

[Background Art] In computers using microcomputers and ICs, an oscillation circuit using an oscillator such as a crystal oscillator is installed in order to generate a clock signal for system operation (hereinafter referred to as a system clock). . In such a data processing system, for example, when the system operates intermittently, power consumption can be reduced by stopping the original oscillation and thereby temporarily stopping the states of the microprocessor, memory, etc. Therefore, a halt function is sometimes provided to stop the clock and stop the system in response to an external control signal or a command from the CPU.

However, in an LSI such as a microcomputer that has a clock function, if the oscillation circuit is shared between the clock and the primary oscillation, the clock cannot be stopped, so it is not possible to realize the low power consumption mode as described above. Can not. Therefore, conventionally, two oscillation methods were used: a 32.768kHz crystal oscillation circuit for watches, and an inexpensive CR oscillation circuit or an oscillation circuit using a ceramic resonator for the original oscillation (approximately 400kHz). Microcomputers with circuits are also provided (for example, the third layer of "Hitachi 4-bit 1-chip Microcomputer System, 8MC840 Series, LCD-m User's Manual" published by Hitachi, Ltd. in June 1980). , 4th
．． 24th. (See page 25).

However, in the above-mentioned microcomputers, when the primary oscillation is stopped and the system is operated by stopping the primary oscillation and moving to a low power consumption mode, and then restarting the primary oscillator side oscillation circuit to operate the system, unstable oscillation of one oscillator circuit occurs. The signal may cause the system to malfunction. Therefore, it is necessary to provide an appropriate oscillation stabilization wait time when oscillation is restarted, and to generate the system clock after oscillation has stabilized. Furthermore, since the frequency of the original oscillation is higher than that for a clock, if the one-oscillation stabilization wait time is longer than necessary, the power consumption increases accordingly.

In particular, in conventional microcomputers having a low power consumption mode, the system is operated intermittently (for example, once every 62.5 ms) by an overflow signal from a timer. In other words, the system only needs to run when it is needed, but if the system clock is stopped, it is impossible to know whether the system needs to run or not. So, with conventional microcomputers.

In addition to starting the system intermittently using a timer, the system also stopped the primary oscillation during that time to reduce power consumption. However, when the system is operated intermittently using a timer, the system is operated even when it is not necessary, making it difficult to keep the power consumption to the necessary minimum.

Additionally, it was made to have a low power consumption mode.
A microcomputer such as the HD44790 manufactured by Hitachi, Ltd. is designed to drive a liquid crystal display device, but data transfer from the microcomputer to the liquid crystal driver is performed using a high-frequency system clock. Therefore, even in a microcomputer system operating in a low power consumption mode, there is an inconvenience that liquid crystal display cannot be performed unless the system clock is constantly operating.

[Object of the Invention] An object of the present invention is to provide an oscillation control technique that can further reduce the power consumption of a microcomputer having a low power consumption mode.

Another object of the present invention is to provide an oscillation control technique that can easily prevent malfunctions due to unstable oscillation when starting the original oscillation.

Still another object of the present invention is to enable liquid crystal display even when the microcomputer is operating in a low power consumption mode.

The above and other objects and novel features of the present invention will become clear from the description of this document and the accompanying drawings.

[Summary of the Invention] Representative inventions disclosed in this application will be summarized as follows.

That is, in a microcomputer that has two oscillation circuits, one for the primary oscillation and one for the clock, the oscillation signal of either the primary oscillation circuit or the clock oscillation circuit is selectively sent to the system clock generation circuit. By providing a switching circuit that can be supplied and having the switching control signal to the switching circuit formed by a software configurable control register, it is possible to generate a system clock that is normally based on the slow signal of the clock oscillator circuit. The above purpose is achieved by forming a fast system clock based on the original oscillation signal, and then operating the system very slowly, and only when fast processing is required, the switching circuit is switched by software to form a fast system clock based on the original oscillation signal. be.

[Example 1] An example in which the present invention is applied to a single-chip microcomputer having a low power consumption mode with a clock function and a halt function is shown in Figs. 1 and 2.
This will be explained using figures.

In order for the single-chip microcomputer of this embodiment to realize one clock function, as shown in FIG. , 3b, a crystal resonator 4 constituting a crystal oscillator is externally attached. Also,
A pair of external terminals 5a connected to the original oscillation circuit 5 in the chip 1.

A ceramic resonator 7 is connected to 6b.

A CR oscillation circuit may be configured by connecting a crystal oscillator instead of a ceramic oscillator or by connecting a resistive element.

A control/execution unit 10 that executes a system program stored in the built-in ROM 8 is operated by a system clock φC formed by dividing the original oscillation signal supplied from the original oscillation circuit 5. be done.

In the single-chip microcomputer of this embodiment, the oscillation operation of the original oscillation circuit 5 is stopped by the control signal HLT from the external or internal control/execution unit 10, thereby reducing power consumption in the original oscillation circuit 5. The oscillation frequency of the original oscillation circuit 5 is the oscillation frequency 32. of the crystal oscillation circuit 2.
Since the frequency is set to about 400 kHz, which is considerably higher than 768 kHz, power consumption is considerably reduced by stopping the single oscillation circuit 5.

In a conventional single-chip microcomputer, when the oscillation operation of the original oscillation circuit 5 is stopped by a control signal HLT or the like, the supply of the system clock to the control/execution unit 10 itself is stopped, and the control/execution unit 10 is put in a halt state. It was supposed to be moved to the state. In contrast, in this embodiment, the oscillation signal of the original oscillation circuit 5 is supplied via the switching circuit 11 to the clock generation circuit 12 consisting of a frequency dividing circuit, etc., to form the system clock φC. .

The switching circuit 11 is supplied with an oscillation signal from the crystal oscillation circuit 2, and when the oscillation signal from the original oscillation circuit 5 is not supplied to the clock generation circuit 12, the oscillation signal from the crystal oscillation circuit 2 is supplied instead. is provided.

That is, when the oscillation signal of the original oscillation circuit 5 is stopped.

The oscillation signal of the crystal oscillation circuit 2 is supplied to the clock generation circuit 12 to form a very slow system clock φC, which can be supplied to the control/execution unit 10. As a result, even if the oscillation of the original oscillation circuit 5 is stopped by the control signal HLT, the control/execution unit 10 does not stop operating like a conventional microcomputer, but operates at a very slow speed. It is operated by. Therefore,
It is not necessary to restart the original oscillation circuit 5 and operate the control/execution unit 10 intermittently using an overflow signal from the frequency divider circuit 13 that divides the oscillation signal of the crystal oscillation circuit 2 as in the conventional case. do not have. In this embodiment, the control/execution unit 10 is always working, and the only difference in operating speed is when the original oscillation stops and when it starts.

In order to control switching of the oscillation signal to the clock generation circuit 12 by the switching circuit 11, a switching control register 14 is used.
is provided.

In this embodiment, the switching control register 14 can be set by software, that is, by executing a program. That is, by setting (or resetting) the switching control register 14 using software before stopping the original oscillation using the control signal HLT, the oscillation signal from the crystal oscillation circuit 2 is supplied to the clock generation circuit 12. System clock φC
will no longer be stopped. For example, when an external input/output operation button is operated and the microcomputer needs to perform quick processing, the control signal HL
T is released to restart the original oscillation circuit 5, and the switching control register 14 is reset (or set) by software. This makes it possible to supply the original oscillation signal to the clock generation circuit 12 and increase the frequency of the system clock φC.

Moreover, in the above embodiment, the source oscillation circuit 5 is controlled by software.
It is possible to control the activation timing of the oscillation signal and the switching timing of the oscillation signal by the switching circuit 11. Therefore, the supply of unstable oscillation signals immediately after the starting of the original oscillation circuit 5 is cut, and the clock generation circuit 1 waits until the oscillation has stabilized.
It can be supplied to 2.

According to the above embodiment, the original oscillation circuit 5 is operated only when fast operation is required to increase the frequency of the system clock φC, and at other times, the original oscillation circuit 5 is stopped and the crystal oscillation circuit 2 Since the slow system clock φC can be formed based on the oscillation signal from the oscillation signal from the oscillation signal φC to operate slowly, the total power consumption can be significantly reduced.

In other words, in a conventional microcomputer having a low power consumption mode, the microcomputer is operated intermittently, for example, once every 62.5 ms by an overflow signal from a timer. Therefore, the current consumption changes as shown by the broken line B in Figure 2',
Also. On the other hand, in the microcomputer of this embodiment, the current consumption changes as shown by the solid line A in the figure.

In the low power consumption mode, the microcomputer of this embodiment does not stop the system tally, so the current consumption increases somewhat compared to the conventional one. However, since the clock frequency is very low, the increase in current consumption is negligible. However, since the microcomputer of this embodiment operates at high speed only when necessary,
The number of operations performed at kHz is significantly reduced compared to the conventional method.

As a result, the total power consumption of the microcomputer of this embodiment is significantly lower.

Furthermore, according to this embodiment, even if the mode shifts to a low power consumption mode in which the original oscillation is stopped, the supply of oscillation signals to the system clock generation circuit 12 is not interrupted, so data transfer to the liquid crystal driver etc. using the system clock is not interrupted. By performing this, the liquid crystal display device can be driven.

[Effects] (1) In a microcomputer that has two oscillation circuits, one for the original oscillation and one for the clock, the oscillation signal of either the original oscillation circuit or the clock oscillation circuit is sent to the system clock generation circuit. Normally, the system clock is formed based on the slow signal of the clock oscillation circuit to operate the system very slowly, and when fast processing is required, The ability to generate a faster system clock based on the original oscillation signal by simply switching the switching circuit using software has the effect of significantly reducing total power consumption.

(2) In a microcomputer that has two oscillation circuits, one for the primary oscillator and one for the clock, the oscillation signal of either the primary oscillator or the clock oscillator is selectively sent to the system clock generation circuit. Since it is equipped with a switching circuit that can supply power, the system clock is not stopped even in low power consumption mode, which has the effect of allowing liquid crystal display even when the microcomputer is operating in low power consumption mode. .

(3) In a microcomputer that has two oscillation circuits, one for M oscillation and one for clock, the oscillation signal of either the original oscillator or the clock oscillator is selectively sent to the system clock generation circuit. A switching circuit that can supply the clock signal is provided, and a switching control signal to this switching circuit is formed by a control register that can be set by software.This function allows software to control the timing at which the original oscillation signal is supplied to the clock generation circuit. This has the effect of easily preventing malfunctions due to unstable oscillation when starting up the original oscillation circuit.

Although the invention made by the present inventor has been specifically explained above based on examples, it goes without saying that the present invention is not limited to the above-mentioned examples and can be modified in various ways without departing from the gist thereof. not. For example, in the above embodiment, the microcomputer is operated using both the original oscillation circuit 5 and the crystal oscillation circuit 2. It is also possible to configure the system clock φC from the clock generation circuit 12 to be supplied to the clock frequency dividing circuit 13 instead of the oscillation signal from the crystal oscillation circuit side.

[Field of Application] In the above explanation, the invention made by the present inventor has mainly been applied to a single-chip microcomputer having a clock function and a low power consumption mode, which is the field of application to which the invention is based. The invention is not limited to this, and can be used in general integrated circuits having two oscillation circuits with different oscillation frequencies.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the configuration of an embodiment in which the present invention is applied to a single-chip microcomputer with a clock function. Fig. 2 is an explanatory diagram showing the difference in current consumption between the present invention and a conventional microcomputer. be. 1... Semiconductor chip (microcomputer), 2
...Crystal oscillation circuit, 3a, 3b, 6a, 6b...
・External terminal, 4...Crystal resonator, 5...Original oscillation circuit, 7...Ceramic resonator, 8...ROM
, 10...control/execution unit, 11...switching circuit,
12... Clock generation circuit, 13... Frequency dividing circuit, 14... Switching control register.

Claims (1)

[Claims] 1. An integrated circuit comprising two oscillation circuits with different oscillation frequencies, and for a clock generation circuit that divides an oscillation signal to form a clock signal necessary for system operation,
An integrated circuit equipped with an oscillation circuit, comprising switching means for selectively supplying an oscillation signal from one of the two oscillation circuits. 2. The switching means includes the oscillation circuit according to claim 1, the operation of which is controlled according to the setting state of a control register that can be set by software. integrated circuit. 3. A logic integrated circuit equipped with an oscillation circuit according to claim 1 or 2, wherein one of the oscillation circuits is configured such that oscillation can be stopped or started by a control signal. .