JPH10197850A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the liquid crystal display device which saves energy by making good use of characteristics of TN liquid crystal and ferroelectric liquid crystal. SOLUTION: While a selective display means of a controller 1 judges characteristics of data to be displayed and displays data selectively on a 1st liquid crystal display means 4 of a liquid crystal panel or 2nd liquid crystal display means 5 with memory capability according to the characteristics of the data, a display switching means displays the data displayed selectively on the 1st liquid crystal display means 4 by switching the 1st liquid crystal display means to the 2nd liquid crystal display means 5. Then an operation control means stops the 1st liquid crystal display means 4 and a 1st control means from operating when the data is displayed on only the 2nd liquid crystal display means 5 to reduce the power consumption of the 1st liquid crystal display means 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal device having a liquid crystal panel, and more particularly to display control of a liquid crystal panel.

[0002]

2. Description of the Related Art Some conventional liquid crystal devices include a liquid crystal panel using, for example, a TN liquid crystal or a ferroelectric liquid crystal as a display unit. Here, a general TN liquid crystal performs light switching by utilizing the fact that the direction of molecules changes depending on the presence or absence of an electric field. Here, in order to continue the display, an AC electric field is always applied, or a common electrode is scanned as in a simple matrix drive, data is applied to the segment electrodes, and an electric field is sequentially applied to the elements to be turned on. It is necessary to apply an electric field to. Therefore, the driving operation is always performed during the display time.

On the other hand, the ferroelectric liquid crystal has a property of exhibiting a hysteretic behavior with respect to the application of an electric field due to the ferroelectricity of molecules and having a memory property of retaining the previous operation without applying an electric field. . Recently, a film liquid crystal formed by applying a ferroelectric polymer liquid crystal on a film has been developed.

By the way, considering the actual use scene of the liquid crystal device, there are many overwhelmingly still images on a computer screen including a portable electronic device except when displaying a moving image. For example, in writing a sentence, it is a repetition of thinking and input, and the ratio of the time of actually inputting with the keyboard or pen is smaller than the total display time. Further, in a situation where a document is viewed or a review is performed while looking at the screen, the time ratio increases.

[0005]

However, in the conventional liquid crystal device, for example, a liquid crystal panel using a TN liquid crystal must be constantly driven during a use period even if it is fast in speed, resulting in a power consumption problem. There was a point. On the other hand, a liquid crystal panel using a ferroelectric polymer liquid crystal can reduce power consumption when there is no change if the memory effect is used, but the rewriting time is several milliseconds per line and there is some movement. Had a problem that it could not follow.

Accordingly, the present invention has been made to solve such a conventional problem, and it is an object of the present invention to provide a liquid crystal device capable of saving energy by utilizing the characteristics of a TN liquid crystal and a ferroelectric liquid crystal. It is intended for.

[0007]

According to the present invention, there is provided a liquid crystal panel comprising a first liquid crystal display unit and a second liquid crystal display unit having a memory function, the first and second liquid crystal panels being overlapped with each other.
First and second display control units for controlling the display operation of the liquid crystal display means, and determining the characteristics of the data to be displayed;
Selectively selecting the first data according to a characteristic of the data;
Selection display means for displaying on the second liquid crystal display means, and display switching means for switching and selectively displaying data selectively displayed on the first liquid crystal display means on the second liquid crystal display means. And a control device having operation control means for stopping the operations of the first liquid crystal display means and the first control means when data is displayed only on the second liquid crystal display means. It is characterized by the following.

Further, according to the present invention, the display switching means of the control device performs the display switching and erases the data displayed on the first liquid crystal display means at the predetermined timing according to the characteristics of the data. It is characterized by the following.

Further, according to the present invention, the characteristics of the display data are as follows:
It is characterized by deterministic data that hardly changes, uncertain data that is likely to change, and transient temporary data.

The present invention also provides a liquid crystal panel comprising a first liquid crystal display unit and a second liquid crystal display unit having a memory function, and a display of the first and second liquid crystal display units. First and second display control units for controlling operation;
A display switching unit for switching the data displayed on the first liquid crystal display means to the second liquid crystal display means at a predetermined timing and displaying the data, and a method for displaying data only on the second liquid crystal display means. And an operation control unit for stopping the operations of the first liquid crystal display means and the first control means.

According to the present invention, the characteristics of the data to be displayed are determined by the selection display means of the control device.
The data is selectively displayed on the first liquid crystal display means of the liquid crystal panel or the second liquid crystal display means having a memory function according to the characteristics of the data, and selectively displayed on the first liquid crystal display means by the display switching means. The displayed data is switched and displayed on the second liquid crystal display means at a predetermined timing. When the data is displayed only on the second liquid crystal display means by the operation control means, the operations of the first liquid crystal display means and the first control means are stopped, so that the operation of the first liquid crystal display means is stopped. Reduce power consumption.

Further, as in the present invention, the data displayed on the first liquid crystal display means is switched and displayed on the second liquid crystal display means at a predetermined timing by the display switching section, while the data is displayed on the second liquid crystal display means. When only data is displayed, the operation control section stops the operations of the first liquid crystal display means and the first control means, thereby reducing the power consumption of the first liquid crystal display means.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a plan view of a liquid crystal device according to a first embodiment of the present invention. This liquid crystal device 1A has a pen computer provided with a PHS (wireless communication). Here, the liquid crystal device 1A is provided with a liquid crystal panel 2A having a double structure having a TN liquid crystal display element and a memory type liquid crystal display element, and information input to the liquid crystal device 1A is performed by a pen 3A and a PHS. It is supposed to do. In FIG. 1, reference numeral 4A denotes a PHS antenna.

FIG. 2 is a control block diagram of the liquid crystal device 1A. In FIG. 2, 1 is a CPU of about 16 bits, and 2 is a TN liquid crystal display element which is a first liquid crystal display means of the liquid crystal panel 2A. (Hereinafter, referred to as a TN element) 4 and a memory liquid crystal display element (hereinafter, referred to as a memory element) 5 using a ferroelectric polymer liquid crystal or the like, which is a second liquid crystal display means having a memory function, to perform two-screen display. Display control unit 3 is a VR that stores data of two screens of the liquid crystal panel 2A.
AM.

The CPU 1 performs calculation and control of the liquid crystal device 1A and, as will be described later, a selection display means for judging attributes of display data and selectively displaying the data on the TN element 4 or the memory element 5. Display switching means for switching the data selectively displayed on the TN element 4 to the memory element 5 at a predetermined timing for display, and stopping the operation of the TN element 4 and the like when displaying data only on the memory element 5 And a control device for controlling the operation. In addition,
In the present embodiment, the CPU 1 performs these processes by software.

Here, the TN element 4 and the memory element 5
As shown in FIG. 3, the relationship between
The N element 4 is overlaid, and a polarizing plate (not shown) is attached to the upper surface of the TN element 4 and the lower surface of the memory element 5. Further, a digitizer 7 as input means is disposed above the TN element 4. A typical input system of the digitizer 7 is a resistive film system.
There are an electromagnetic induction method, an ultrasonic method, and the like. As a control method, for example, in a resistive film or the like, a voltage change caused by a pen input is periodically checked by A / D conversion and coordinate conversion is performed in a software manner. There is something.

In FIG. 2, reference numeral 6 denotes a digitizer control unit for controlling a digitizer 7, and 8 denotes a PHS control unit for controlling, for example, a PHS which is a wireless digital communication means. The wireless digital communication means may be communication means such as light such as IrDA. Reference numeral 9 denotes a peripheral control unit, which is a standard I / O (eg, RS-232C, PCMCI).
A) is controlled. Reference numeral 10 denotes a memory control unit, which is a DRAM
It controls the main memory 11 composed of the above. 12
Is a power control unit, which performs a power saving operation including a partial power supply.

Next, the display control operation of the display control unit 2 will be described with reference to FIG. The display control unit 2 separately inputs display data and a display control signal to the TN element 4 and the memory element 5. Here, since the TN element 4 drives whenever necessary, the common driver 13 is activated from the upper line by using the H-sync signal as a clock.

The segment driver 14 drives display data of each line. Here, the display data is input from the display control unit 2 to a shift register inside a segment driver (not shown) in synchronization with a clock, and is loaded to each driver of the segment driver 14 at each H-sync. Then, one screen ends with V-sync, and the processing is repeated from the first line.

When only the memory element 5 displays data, the display control section 2 stops these control clocks, so that the display is turned off and the power is reduced. Further, by stopping the liquid crystal drive power supply 15a by turning off the switch 15 by the display control unit 2, the energy saving effect can be improved.

On the other hand, since the memory element 5 has a memory effect, it is not necessary to drive the memory element 5 at all times, and it is only necessary to rewrite a changed portion. From this relation, the common driver 16 is not activated sequentially from the top, but the display control unit 2 sends the specified line data of the display data to the decoder 18 and activates the common driver so that a specific line is activated. 16 is controlled. Here, the number of lines to be rewritten is not limited to one, and a plurality of lines may be used as one unit. The display data is input by a shift register (not shown), and is loaded into each of the segment drivers 17 by a display control signal.

FIG. 5 is a memory map of the VRAM 3. The VRAM 3 stores data of the TN element 4 in the first area 3a and data of the memory element 5 in the second area 3b. .

FIG. 6 is a diagram showing a block configuration of the display control unit 2. In FIG. 6, reference numeral 19 denotes a CPU I / F which is an interface with the CPU bus B.
The CPU I / F 19 mediates I / O access from the CPU 1 to the control registers 22 and 25 and memory access to the VRAM 3.

Reference numeral 20 denotes a bus control unit, which controls access to the VRAM 3. Here, an access request to the VRAM 3 is made from the CPU 1, the TN element 4, and the memory element 5, but the TN element 4 is accessing cyclically.
Since the data cannot be delayed the most, the priority order is the access from the TN element 4 and the second is the CPU.
Since the access is from 1, the memory element 5 is set to the last rank because the input itself has no premature acuteness.

Reference numeral 21 denotes a memory control unit which controls access to the VRAM 3. Note that the memory control unit 21 determines that the VRAM 3
In the case of AM, timing and the like are adjusted including refresh control.

Reference numeral 22 denotes a TN which is a first display control unit.
The control register 22 is a control register of the element control unit 4A. The control register 22 includes a stop signal of the internal clock of the TN element control unit 4A and a switch 15 of the liquid crystal drive power supply 15a for driving the TN element 4 shown in FIG. It generates a display off signal for performing the on / off operation in a soft manner. Note that the control register 22 can also be configured so that the start address of the VRAM 3 can be set. 23 is a timing control unit, and this timing control unit 23
Data synchronization clock for driving TN liquid crystal, Hs
This is for generating display control signals such as sync, V-sync, and the like.

Reference numeral 24 denotes a VRAM access control unit. The VRAM access control unit 24 sends an access request to the bus control unit 20 so as to obtain data from the VRAM 3 in response to generation of a control signal from the timing control unit 23. When the permission is granted, an address is issued to obtain data, and the timing control unit 23 sends the data to the segment driver 14 as display data.

On the other hand, reference numeral 25 denotes a control register of the memory element control unit 5A as a second display control unit. The control register 25 includes a VRAM start address, a rewrite line number, the number of lines, a write end flag, a control ON / OFF flag. It is for setting off and the like. When the display data to be rewritten occurs, the control is set to ON, and accordingly, the timing control unit 26 starts operating and the VRA
The M access control unit 27 sets 1 from the VRAM head address.
Line number data is obtained via the bus control unit 20. As described above, the bus acquisition order is the lowest.

The timing control section 26 outputs the head line number together with the display control signal and sends it to the decoder 18, and then sends the display data to the segment driver 17. Hereinafter, this operation is repeated for the number of lines to be rewritten, and when it is completed, the write end flag is turned on. Upon seeing this, the system side (CPU 1) determines that the writing has been completed.

Next, transition of the display state of the liquid crystal device 1A having such a configuration will be described with reference to FIG.

If the input information S3 from the pen or the keyboard is uncertain, or is uncertain information that disappears immediately, such as the locus of a gesture command of the pen, the information is first displayed on the TN element 4. Further, the change blinking information S4 in which data is constantly rewritten, such as blinking of a cursor or blinking of a clock, is continuously displayed on the TN element 4.

On the other hand, when an area such as a new window S5 is written, the contents of the memory element 5 written below are erased, and the information of the window is written to the TN element 4. Forms such as personal information (PIM) and an application (application) S6 having a business format have the same form. In many cases, data exists over a plurality of pages, and the form is divided into a memory element 5 and data is divided into a TN element 4. indicate. When a page turn occurs, the data part,
That is, only the TN element 4 needs to be rewritten.

If there is no change in the display data of the TN element 4 even after a certain period of time, the data is transferred to the display data of the memory element 5. Furthermore, if a part of the data is selected (selected) S7 and becomes an object of editing, the possibility of changing the display contents increases, so the data is returned to the TN element 4 again.
Side, and during the editing operation (for example, movement) S8, the TN
Only the data of the element 4 corresponds, and if the determination is determined S9, the data is transferred to the memory element 5.

As described above, the CPU 1 switches the elements 4 and 5 to be displayed via the display control unit 2 in accordance with the possibility of data change or the fixed time.
Then, when all data is transferred to the memory element 5,
The TN element 4 is turned off, and the display data is maintained only by the memory effect of the memory element 5.

This is shown in FIG. The horizontal axis is time. First, when something is input or the display changes, it is immediately reflected on the display of the TN element 4.
Then, the data is rewritten to the memory element 5 after a certain period of time has elapsed or a trigger for determining data is applied, and the TN element 4 and the memory element 5 stop driving as shown in FIG. With such a configuration, the power consumption can be suppressed lower than in the case where the conventional TN element 4 is continuously driven as shown in FIG. This is more effective as the driver's stop time is longer.

Next, the division will be described by taking an application as an example. FIG. 9A shows an example in which a business form is selected. Characters and check boxes are displayed in the memory element 5 in advance, and options indicated by A, B, and C are displayed in the TN element 4. Like that.

When one of the options A, B, and C is touched with the pen 3A, the check box is inverted to indicate that this check box is about to be selected. Further, when the pen is pulled up at the inverted position, the selection is determined, and the inverted data is transferred from the TN element 4 to the memory element 5. When the pen 3A is dragged to another place, the selection action is stopped, and the inverted portion of the TN element 4 is erased.

FIG. 9B shows an example of a telephone directory, in which forms and data are displayed on the memory element 5 and a call is made by a built-in dialer. The bold frame indicating the user is displayed using the TN element 4. Further, even when a switch for instructing a dial is pressed, a bold frame for clarifying the instruction is displayed using the TN element 4.

FIG. 9C shows an example of character recognition, in which handwriting written with the pen 3A is displayed using the TN element 4, and
When the recognition result is determined, it is displayed using the memory element 5. Note that a form such as a character input board is the memory element 5 as a matter of course.

In the present embodiment, the resolutions of the two liquid crystals 4 and 5 may be the same or different. However, the data displayed on the TN element 4 is often transient, and setting the resolution of the TN element 4 lower than that of the memory element 5 is not a problem in practical use due to the necessity of constantly driving. It is rather recommended because it is advantageous in terms of power consumption.

Next, a display control flowchart on the system side is shown in FIG. Note that, in this flowchart, the display is started from the point where the display data is generated.

When display data is generated (process 101),
First, the CPU 1 determines the attribute of the display data (decision 10
2). Here, there are three types of attributes: fixed information, uncertain information, and temporary information. The fixed information is the one that should be displayed with little change, or the one that has been fixed, is a business form, and even after a certain period of time. Those that have not changed, those for which the user has indicated confirmation, and those for the memory element 5
Attached when erasing a part of.

The uncertain information is display data such as information being input or a candidate for handwriting recognition, which may be changed by the user at any time. In addition, temporary information is transient and disappears quickly. It is like the trajectory of a pen gesture command, which is unnecessary display information when the command is recognized and it starts executing.

Here, when the attribute of the display data is determined to be the definite information based on the above-described conditions, the CPU 1 first transmits the display data to the second area 3b (see FIG. 5) of the VRAM 3 via the display control unit 2. After writing (processing 103), the timing control unit 26 including the driver is set to ON in the control register 25 of the memory element 5 (memory element driver active) (processing 104), and other information such as the number of lines is stored in the segment driver 14. (Step 105).

Further, after this, rewriting is instructed (process 1).
06), hardware-based writing is performed by the timing controller 26. The CPU 1 determines whether or not the writing has been completed based on the flag of the register, and after this determination, determines whether or not a certain time has elapsed (determination 10).
7) When a certain period of time has elapsed (Y in decision 107), the control of the memory element 5 and its surroundings is turned off (processing 10).
8).

If the CPU 1 determines that the attribute of the display data is indefinite information based on the above-described conditions, and if the TN element 4 is not operating when the data is generated, the control register via the display control unit 2. By setting 22, the drivers 13 and 14 of the TN element 4 are turned on (TN element driver active) (step 110), and data is written to the first area 3 a of the VRAM 3 (see FIG. 5) (step 1).
11). Here, the display of the data is automatically started.
This display is continued until a certain trigger is applied (decision 112).

That is, there is no rewriting for a certain period of time, or until the user indicates that this data is determined. In the meantime, it is natural that the user can perform operations such as erasing and changing the display data.

On the other hand, when a trigger is activated at a predetermined timing (Y in decision 112), the attribute of the display data is changed to fixed information (process 113), and the routine proceeds to the routine for the memory element 5. Then, the writing to the memory element 5 is confirmed, and when the writing is completed (Y in decision 114),
The data in the first area 3a is erased (step 115), the display information on the TN side is lost, and if there is no other data display, the CP is deleted.
U1 turns off the control of the TN element 4 and its surroundings including the TN element control section 4A (step 116). After writing the data to the memory element 5 in this manner, the control of the TN element 4 and its surroundings including the TN element control section 4A is turned off, so that the driving time can be reduced, and the energy can be saved. Can also increase the effect of CP
When determining that the attribute of the display data is temporary information, U1 sets the control registers 22 via the display control unit 2 to turn on the drivers 13 and 14 of the TN element 4 (TN element driver active). (Process 120) Further, data is written to the first area 3a of the VRAM 3 (Process 121). Here, the display of the data is automatically started. This display is continued until a certain trigger is applied (decision 122). Then, when a trigger is input for a short period of time or at a predetermined timing based on the determination of the gesture command (Y in decision 122), the data in the first area 3a is deleted (process 123).
If there is no other data, the CPU 1 turns off the control of the TN element 4 and the peripherals including the TN element control unit 4A (step 124).

As described above, the liquid crystal panel 2A is constructed by overlapping the TN element 4 and the memory element 5 and selecting the elements 4 and 5 to be displayed according to the characteristics of the data to be displayed. You can reduce the time you are actually driving. Thereby, the effect of energy saving of the portable information device and the like can be improved. Note that the liquid crystal panel 2A having the dual structure described in the present embodiment does not limit the type of model from an electronic organizer to a large format display.

In the first embodiment described above, display elements are selected by assigning attributes to display data by software. However, the present invention is not limited to this. The display elements can be divided in hardware based on the above.

Next, such a second embodiment of the present invention will be described.

FIG. 11 is a block diagram of the display control unit according to the present embodiment. 6, the same reference numerals as those in FIG. 6 indicate the same or corresponding parts.

In the figure, 28 is a rewrite timing control unit, and 29 is a logical operation unit. Here, the rewrite timing control unit 28 controls the VRA as shown in FIG.
The M3 TN liquid crystal first area 3a (see FIG. 5) is further divided into a plurality of areas, each of which has an access monitoring counter 3
0 is assigned.

It should be noted that the access monitoring counter 30
A counter such as a watchdog that is reset every time a castle is accessed. The count does not count up as long as rewriting is performed repeatedly in that area. Conversely, a signal is generated when a certain time has elapsed after the rewriting, a flag 31 corresponding to the area is set, the memory transfer control unit 32 is operated, and the data of the castle is transferred to the first area 3a. To the second region 3b (see FIG. 5)
Transfer to

As a result, the timing control section 26 starts operating and is written into the memory element 5. Note that the flag 3
If it can be confirmed that all the data written to the TN element 4 have been set to 1 and all the data written to the TN element 4 have been transferred to the memory element 5, the TN element 4 is turned off as in the previous case.

On the other hand, the logical operation unit 29 converts the display data into V
A logical operation can be performed between TN liquid crystal data and memory liquid crystal data in the RAM 3. The logical operation unit 29 and the rewrite timing control unit 28 constitute a display switching unit that switches the data displayed on the TN element 4 to the memory element 5 for display.

Next, hardware processing by the logical operation unit 29 will be described with reference to the flowchart shown in FIG.

In the present embodiment, reading and writing are all performed in the first area from the viewpoint of the CPU. Actually, when a predetermined time elapses and a read request comes at a predetermined timing, T
The TN liquid crystal data Dtn (processing 131) of the N element 4 and the memory liquid crystal Dm (processing 132) of the memory element 5 are read,
The logical sum is calculated (step 133) and returned to the CPU 1 (step 134).

When the write data Dnw comes from the CPU 1, first, the exclusive logical product of Dm and Dnw is calculated to determine whether or not the data on the memory element side should be changed.
If the data does not need to be changed, the data that has not been written to the memory element 5 but has been sent this time is written to the first area 2a. On the other hand, when it is necessary to rewrite the memory element 5, the memory liquid crystal data is erased and Dnw is written as it is (process 136).

When data is transferred by the memory transfer control 32, the data originally in the memory element 5 is not erased.
The logical operation unit calculates the logical sum Dm (processing 13
7), the data Dtn on the TN element side is erased (Process 13)
8) The result Dm is written to the memory element 5 (process 139).

When data is displayed only on the memory element 5 in this manner, in the present embodiment, the CPU 1 serving as the operation control unit controls the TN element 4 and the T
The operation of the N element 4A is stopped to reduce power consumption.

Instead of assigning attributes to data as in the present embodiment, it is also possible to achieve an energy saving effect by selectively using two liquid crystals on a hardware basis only on a temporal basis.

[0064]

As described above, according to the present invention, TN
A liquid crystal element and a ferroelectric liquid crystal element are overlapped to form a display panel, and the actual driving time of the liquid crystal element is reduced by selecting the liquid crystal element to be displayed according to the characteristics of the data to be displayed. Will be able to do that. As a result, it is possible to obtain the effect of energy saving of portable information devices and the like by utilizing the characteristics of the TN liquid crystal and the ferroelectric liquid crystal.
Further, by switching the display according to the time in hardware, the same energy saving effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a liquid crystal device according to a first embodiment of the present invention.

FIG. 2 is a control block configuration diagram of the liquid crystal device.

FIG. 3 is a diagram showing a structure of a liquid crystal panel of the liquid crystal device.

FIG. 4 is a diagram illustrating a display control operation of a display control unit of the liquid crystal device.

FIG. 5 is a diagram showing a memory area of a VRAM of the liquid crystal device.

FIG. 6 is a block diagram of the display control unit.

FIG. 7 is a diagram illustrating transition of a display state of the liquid crystal device.

FIG. 8 is a diagram showing a drive time of the liquid crystal device.

FIG. 9 is a view showing an example of display on the liquid crystal panel.

FIG. 10 is a display control flowchart of the liquid crystal device.

FIG. 11 is a block diagram of a display control unit of a liquid crystal device according to a second embodiment of the present invention.

FIG. 12 is a block diagram of a rewrite timing control unit of the display control unit.

FIG. 13 is a display control flowchart of the liquid crystal device.

[Explanation of symbols]

 Reference Signs List 1A liquid crystal device 2A liquid crystal panel 1 CPU 2 display controller 3 VRAM 4 TN liquid crystal display element 4A TN element controller 5 memory liquid crystal display element 5A memory element controller 22, 25 control register 23, 26 timing controller 24, 27 VRAM Access control unit 28 Rewrite timing control 29 Logical operation unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G09G 3/36 G09G 3/36

Claims (4)

[Claims] 1. A liquid crystal panel comprising a first liquid crystal display unit and a second liquid crystal display unit having a memory function overlapped with each other, and controlling a display operation of the first and second liquid crystal display units. A first and a second display control unit for determining the characteristics of data to be displayed, and a selective display for selectively displaying the data on the first and second liquid crystal display means according to the characteristics of the data. Means, display switching means for switching and selectively displaying data selectively displayed on the first liquid crystal display means on the second liquid crystal display means at a predetermined timing, and data switching only on the second liquid crystal display means. And a control device having an operation control means for stopping the operations of the first liquid crystal display means and the first control means when displaying is performed. 2. The display switching means of the control device performs the display switching and erases the data displayed on the first liquid crystal display at the predetermined timing according to the characteristics of the data. The liquid crystal device according to claim 1. 3. The characteristic of the display data is deterministic data having little change, uncertain data having a high possibility of change, and transient temporary data. Or the liquid crystal device according to 2. 4. A liquid crystal panel comprising a first liquid crystal display unit and a second liquid crystal display unit having a memory function overlapped with each other, and controlling a display operation of the first and second liquid crystal display units. A first and a second display control unit, a display switching unit for switching and displaying data displayed on the first liquid crystal display unit at a predetermined timing on the second liquid crystal display unit, A liquid crystal display device comprising: an operation control unit that stops operations of the first liquid crystal display unit and the first control unit when data is displayed only on the liquid crystal display unit.