GB2260844A - Book type display apparatus - Google Patents

Abstract

The present invention is directed to a book type display apparatus in which two display units are provided as double-spread pages like a book and which includes a random access function and a data acquisition function as an electronic text so that the reader can read this book type display apparatus as a book. Two casings (31), (32) of box type are made foldable at the center and display units such as LCD panels (24L), (24R) are provided on both casings (31)' (32), whereby data or graphic pattern of each page can be simultaneously displayed on the two display units in a double-spread page fashion. <IMAGE>

Description

BOOK TYPE DISPLAY APPARATUS The present invention relates to display apparatus suitable for a portable book type display for electronic texts and, more particularly, is directed to a portable book type display apparatus in which pages can be contrasted with each other as double-spread pages of a book.

Conventional portable display apparatus known as electronic text type display apparatus include a display screen on which only one picture is displayed. Therefore, this electronic text type display apparatus does not resemble a book from which displayed contents are read. Therefore, the use of this apparatus is limited to a dictionary from which necessary information can be retrieved.

FIG. 1 of the accompanying drawings shows a conventional portable display apparatus 1 which is arranged as a portable computer that is composed of two openable units. As shown in FIG. 1, one side 2 serves as a display apparatus 3 and the other side 4 serves as an operation key pad 5. The display screen of this type of apparatus is very small and information displayed thereon are too small to read. Moreover, the amount of data to be displayed at any one time is very small so that this type of display apparatus cannot function as a so-called electronic text type display apparatus.

A portable book type display apparatus has been proposed, in which electronic texts are composed of a CD-ROE'.

(compact disc-read-only memory) or the like so that information or data can be read out.

According to the electronic texts using CO-ROMs, the user or reader must buy and read, every time,information data integrally formed on media known as CD-ROM. Furthermore, since the portable display apparatus includes a single display screen, pages cannot be compared with each other upon display.

In addition, since the picture screen is small, the amount of data that can be displayed is very small and the pages tend to be frequently turned over, which is very difficult to read Therefore, it is an object of the present invention to provide an improved book type display apparatus in which the aforesaid shortcomings and disadvantages encountered with the prior art can be eliminated.

In a first aspect of the present invention, there is provided a display apparatus comprising: a first display unit; a second display unit; a member for coupling said first and second display units in a mutually rotatable relationship in which said first and second display units are closeable together in an opposing relation and openable to an angularly spaced open position; a memory circuit including a first storage area in which a display signal for display on said first display unit is stored and a second storage area in which a display signal for display on said second display unit is stored; a coupling unit for coupling a storage medium from which a display signal is supplied to said memory circuit; and an instruction switch for instructing the writing of said display signal in each of said first and second storage areas to alter the display contents on said first and second display units.

The memory circuit may include a third storage area in which a display signal that is not displayed is stored and a control circuit may be provided for controlling the write and read of the display signal in and from the memory circuit with a selecting circuit for selectively supplying the display signals stored in the respective storage areas to the display unit, so that when reading out the display signals stored in the first and second storage areas and supplying the read-out display signals to the display unit, the control circuit writes the display signal supplied to the display unit in the third storage area.

In a second aspect of the present invention, there is provided a display apparatus which comprises a display unit, a memory circuit including a plurality of storage areas in which a display signal displayed on the display unit is stored at every predetermined unit, a control circuit for controlling the write and read of the display signal in and from the memory circuit, and a selecting circuit for selectively supplying display signals stored in the plurality of storage areas to the display unit, wherein when a display signal stored in one of the plurality of storage areas is read out therefrom and supplied to the display unit, a display signal to be the display unit next is written in other storage area.

Thus the present invention can provide a book type display apparatus which is easy to carry and which includes electronic texts that can be read anywhere like pocket books and in which pages of electronic text can be contrasted with each other regardless of the fact that pages are continuous or discontinuous.

The pages of electronic text may be turned over sequentially and the electronic text can be accessed in a random access fashion.

The display units may display not only character data but also characters, graphic patterns of graphics or the like and the displayed contents, i.e., characters and graphic patterns can be enlarged and reduced in size.

The predetermined data and graphic patterns can be obtained anywhere e.g. from other communication network line in addition to a recording medium such as a CD-ROM or the like.

The number of data used in the display mode can be preserved after a power switch thereof is turned off and the apparatus may include marking and bookmark functions to mark and retrieve pages and words. The apparatus may be adapted to display a page that is displayed last when a power switch thereof is turned on.

The apparatus may have a dictionary function and a word retrieval function.

With the invention the display apparatus can be made compact in size because only data of necessary portion in one text can be retrieved and displayed and displayed pages may be read in the darkness and switched at high speed just as the reader can turn over pages of a book. Also it is possible to reduce the amount of electric power consumed by using a liquid crystal having a memory function as a display apparatus.

The present invention will be further described in the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings, in which like reference numerals are used to identify the same or similar parts in the several views, and in which: FIG. 1 is a plan view of a conventional portable display apparatus; FIG. 2 is a block diagram showing a book type display apparatus according to a first embodiment of the present invention; FIG. 3 is a perspective view of an external appearance of the book type display apparatus according to the first embodiment of the present invention; FIGS. 4A through 4D are respectively diagrams used to explain various kinds of display modes of the display apparatus according to the present invention; ; FIG. 5 is a block diagram used to explain an arrangement which derives data according to the display apparatus of the present invention; FIG. 6 is a flowchart to which references will be made in explaining how to obtain data according to the embodiment of the present invention; FIG. 7 is a diagram showing a memory map of data according to the display apparatus of the present invention; FIG. 8 is a flowchart to which references will be made in explaining how to display discontinuous portions of one text in the display apparatus according to the embodiment of the present invention; FIG. 9 is a diagram used to explain contents of a VRAM that is used in the display apparatus according to the embodiment of the present invention; FIG. 10 is a diagram of a memory map of contrast-type data used in the embodiment of the display apparatus according to the present invention;; FIG. 11 is a flowchart to which references will be made in explaining how to display the contrast-type data used in the embodiment of the display apparatus according to the present invention; FIG. 12 is a block diagram of the display apparatus using an ordinary liquid crystal and illustrating the display apparatus according to a second embodiment of the present invention; FIG. 13 is a diagram of a waveform used to explain the driving condition of the display apparatus shown in the block diagram of FIG. 12; FIG. 14 is a block diagram of the display apparatus using a liquid crystal having a memory function and illustrating the display apparatus according to a third embodiment of the present invention; FIG. 15 is a block diagram similar to the block diagram of FIG. 14 and illustrating the display apparatus according to a fourth embodiment of the present invention;; FIG. 16 is a diagram of a waveform used to explain the driving condition of the display apparatus shown in the block diagrams of FIGS. 14 and 15; FIG. 17 is a hysteresis characteristic graph of a phase change mode liquid crystal used in the display apparatus according to the present invention; FIG. 18 is a block diagram of the display apparatus which can be operated at high speed read-out mode according to a fifth embodiment of the present invention; FIG. 19 is a diagram of a waveform used to explain operation of the display apparatus shown in the block diagram of FIG. 18; FIG. 20 is a diagram used to explain a relationship between picture screens and frame memory used in the display apparatus according to the present invention; FIG. 21 is a block diagram showing the display apparatus according to a sixth embodiment of the present invention;; FIG. 22 is a diagram of a memory map of data used in the display apparatus according to the present invention; FIG. 23 is a block diagram of the display apparatus which can be operated at high speed read-out mode according to a seventh embodiment of the present invention; and FIG. 24 is a diagram of waveform used to explain operation of the display apparatus accordina to the present invention.

An arrangement of a book type display apparatus according to a first embodiment of the present invention, which is utilized as an electronic text, will be described with reference to FIGS. 2 and 3.

FIG. 2 of the accompanying drawings shows an overall blocs diagram of the embodiment of the book type display apparatus and FIG. 3 of the accompanying drawings shows the external appearance of this book type display apparatus of the present invention in a perspective view fashion.

As shown in FIG. 2, a display apparatus generally depicted by reference numeral 10 comprises a main system unit 11, a liquid crystal display (LCD) driver unit 12 and an input unit 13.

The main system unit 11 comprises a microcomputer 14, an ordinary system read-only memory (ROM) 15, a system random access memory (RAM) 16 and a font ROM 17. The microcomputer 14 will hereinafter be referred to as a central processing unit (CPU) 14.

The CPU 14, the system ROM 15, the system RAM 16 and the font ROM 17 are interconnected by means of a data bus 18 and a control bus 19.

The key input unit 13 includes input terminals Tl, T2 to which there are supplied key inputs from various keys, input terminals T31 TA to which there are input data (electronic text data) from a recording medium such as an IC memory card or the like and input terminals Ts, T6 to which there are input data, etc., from a communication network line (telephone line network) and data stored in a compact disc (CD).

The key input signals from the input terminals T1 , Th are connected through a key controller 20 to an LCD controller 22 in the LCD driver unit 12. The data from the recording medium such as the IC memory card or the like and applied to the input terminals T3 , T are directly connected to the LCD controller 22 and the communication data from the input terminals T5, T6 are connected through an RC-232C controller 21 to the data bus 18 and control bus 19 and to the LCD controller 22 of the LCD driver unit 12.

The LCD controller 22 is connected to a video RAM (VRAM) 23 and also connected through the data bus 18 and the control bus 19 to a first LCD panel 24L forming a left display portion and a second LCD panel 24R forming a right display portion. The first and second LCD panels 24L, 24R include Y-axis driver units 25LI, 25L2, 25R1, 25R2 and X-axis driver units 26L, 26R, respectively.

While the display panels are formed of the LCD panels 24L, 24R as described above, the present invention is not limited thereto and thin display panels such as plasma display, electroluminescence (EL) display or the like may be used. At that time, of course, the LCD controller 22 may be replaced with a plasma display controller and an EL display controller.

FIG. 3 of the accompanying drawings shows an entire external appearance of the book type display apparatus according to the present invention.

As shown in FIG. 3, the display apparatus 10 comprises a first casing 31 and a second casing 32. The first and second casings 31 and 32 are made of metal or synthetic resin and are substantially box in shape. The first and second casings 31, 32 are 153 mm long, 106.8 mm wide and 15 mm high (the second casing is 22 mm high). The LCD panels 24L, 24R are 105 mm long and 72 mm wide, The first and second casings 31 and 32 are coupled at their left and right side surfaces. Under the condition such that the first and second casings 31 and 32 are closed by means of an inside hinge 33, the first and second LCD panels 24L, 24R are opposed to each other. On the other hand, under the condition that the first and second casings 31 and 32 are opened, the first and second LCD panels 24L, 24R are extended at an angular distance of 180 degrees, i.e., the first and second LCD panels 24L, 24R are disposed in parallel to each other similarly to the case that an ordinary book is opened.

The first and second casings 31 and 32 incorporate therein the electronic circuits which were described in detail with reference to FIG. 2.

A first operation key pad 34 is disposed on the lower surface of the first LCD panel 24L of the first casing 31.

Similarly, a second operation key pad 35 also is disposed on the lower surface of the second LCD panel 24R of the second casing 32.

Reference numeral 34a in the first operation key pad 34 depicts a bookmark key, 34b depicts the next bookmark key and 34c depicts a preceding bookmark key. When the bookmark key 34a is pressed once, a bookmark function is effected similarly to the case that a bookmark is put between the pages of a book. When the bookmark key 34a is pressed next, the page marked by the bookmark is read. When the next bookmark key 34b and the preceding bookmark key 34c are pressed, the portions marked with these keys 34b, 34c are displayed.

Each time a backward picture key 34e on the first operation key pad 34 is pressed, a picture of succeeding page, if it is 10 pages after, then pictures of 10 pages after, 20 pages after, are aresequentially displayed on the first and second LCD panels 24L, 24R. When a next picture key 34f is pressed, the next pictures of pages 32, 33 are displayed on the first and second LCD panels 24L, 24R, for example, if now pages 30 and 31 are displayed on the first and second LCD panels 24L, 24R.

Similarly, when a forward picture key 35a on the second operation key pad 35 is pressed, pages 28 and 29 are displayed if now pages 30 and 31 are being displayed on the first and second LCD panels 24L, 24R.

If the forward picture key 35b is pressed once, then a page of 10 pages before is displayed. If the forward picture key 35b is pressed twice, then a page of 20 pages before is displayed.

If a menu key 35c is pressed, then a predetermined menu and a cursor are displayed on the second LCD panel 24R. The cursor on the display screen is moved in the upper or lower direction by pressing an upward key 35d or downward key 35e and moved to the position of the predetermined menu. Then, if a selection key 35f is depressed, a menu on the cursor position is selected.

While various operations are effected by the keys on the first and second key pads 34, 35 according to the above arrangement, if the first and second LCD panels 24, 25 are formed astouch-sensitive panels, then the first and second key pads 34, 35 may be omitted.

Engagement members 36A, 36B are disposed on the first and second casings 31, 32 and locked to each other when the first and second casings 31, 32 are closed.

On the right side surface of the second casing 32, there are disposed an RS-232-C coupling connector 37, an AC-DC adaptor connector 38, an adjustment variable resistor knob 39 that adjusts contrast of the first and second LCD panels 24, 25, a power change-over switch 40 and a power connector 41, etc.

Through an upper side surface of the second casing 32, there is formed a slot 42 into and from which an IC memory card or the like is inserted and ejected. On the rear surface of the second casing 32, there is provided an IC card eject button 43 as shown by a phantom block. If this button 43 is depressed, then the IC card (not shown) is ejected from the slot 42.

Display modes in the display apparatus thus arranged will be described with reference to FIGS. 4A through 4D of the accompanying drawings.

FIG. 4A shows the state that the LCD panels 24L, 24R are placed in the opened state by opening the first and second casings 31, 32 at an angle of 180-. In use, the display apparatus 10 is 153 mm long and 106 mm wide so as to become easy to carry. Completely independent data are displayed on display screens 100 and 200.

More specifically, if continuous data of page n and page n + 1 are displayed on the first and second LCD panels 24L, 24R similarly to ordinary books and then the next picture key 34f is depressed, as shown in FIG. 4B, pages n + 2 and n + 3 are displayed. Therefore, the continuous pages of the electronictext can be read as if the user were turning off the pages of the ordinary book.

FIG. 4C shows the state that pages, which are not continuous, are displayed on the first and second LCD panels 24L, 24R. For example, a page n is displayed on the display screen 100 and a page m is displayed on the display screen 200. In this case, a display of the page m relating to the page n can be easily displayed on the page n in a random-access fashion.

Further, the page n is displayed on the display screen 100 and graphic patterns, graphs and figures of drawings relating to the page n can be displayed on the display screen 200.

As an example of application, English (or Japanese) words or sentences are displayed on the display screen 100 and Japanese (or English) words or sentences are displayed on the display screen 200 in the form of a translation. In use, one of the English and Japanese words or sentences are displayed and then words or sentences of the other language are displayed if necessary. Thus, the book type display apparatus of the present invention is suitable for the study of both the Japanese and English languages. Further, a map can be displayed on the display screen 100 and guide information sentences of the displayed map can be displayed on the display screen 200.In this case, when the reader wants to know more about the map displayed on the display screen 100, if the guide information sentences of the position are displayed on the display screen 200 by pointing a predetermined position on the map, then the book type display apparatus of this invention becomes very useful as the guide book.

FIG. 4D shows an example of the displayed condition such that two different kinds of texts A and B are displayed side by side for the comparison.

Operation in which continuous or discontinuous data are displayed on the display screens 100 and 200 of the first and second LCD panels 24, 25 as described above will be described with reference to FIGS. 2 to 8 of the accompanying drawings.

As shown in FIG. 2, the CPU 14 in the main system unit 11 operates similarly to ordinary computers. The system ROM 15 and the system RAM 16 are ordinary storage means included in the CPU 14. The font ROM 17 is a ROM for characters and controls the entirety of the LCD driver unit 12.

While the LCD controller 22 in the LCD driver unit 12 is controlled by the CPU 14, the LCD controller 22 accesses the VRAM 23 in a data prefetch fashion because the screens of the LCD panels 24L and 24R are high in resolution.

The first and second LCD panels 24L, 24R, which are controlled via the LCD controller 22, are made perfectly independent as shown in FIG. 3 and can be opened just like the book of pocket edition. The first and second LCD panels 24L, 24R are driven by the X-axis driver units 26L, 26R and the Y-axis driver units 25L1, 25L2 to effect the display.

The input terminals Tl, T2 of the input unit 13 are connected with the first and second key pads 34. 35 and the power change-over switch 40 or the like shown in FIG. 3 and also connected to the CPU 14 via the key controller 20, whereby #processings corresponding to various key operations are effected by the CPU 14.

Similarly, the input terminals T3, 4 of the input unit 13 are connected to the IC memory card output terminals by loading the IC memory card 44 into the slot 42 formed through the upper side surface of the second casing 32 shown in FIG. 2. As will be described later on with reference to FIG. 5, recorded information on the IC memory card 44 is stored in the VRAM 23 through the CPU 14 and the LCD controller 22, thereby being independently displayed on the LCD panels 24L, 24R at every page.

Further, the RS-232C connector 37 is connected to the input terminals Ts, T6 of the input unit 13. Various information data are supplied from a communication network (described later on), for example, through the RS-232C controller 21, the CPU 14 and the LCD controller 22 to the IC memory card 44 and the VAAM 23, in which these data are stored, thus data being independently displayed on the LCD panels 24L, 24R at every page.

An example of an arrangement in which data is obtained via the communication network or by means of the IC memory card 44 will be described with reference to FIG. 5 of the accompanying drawings.

Referring to FIG. 5, the display apparatus 10 includes a communication function, such as the above RS-232C and so on. The above RS-232C connector 37 is connected to a communication network 45. This communication network 45 is used when data from a computer 47 or from other external storage medium 46, e.g., optical disc or data from an electronic text publishing company 48 is supplied from a public communication network such as a telephone line network or the like. If a telephone line network 49 is used as this public communication network, data is transmitted and received via a MODEM (modulator and demodulator) 50. This MODEM 50 may of course be incorporated within the display apparatus 10, if necessary. Furthermore, necessary data may be obtained from the IC memory card 44.

When the telephone line network 49 is used, the reader calls the electronic text publishing company 48 and obtains data by means of the communication network of the RS-232C, for example.

It is needless to say that data may be transmitted and received via an integrated services digital network (ISDN) by which data can be transmitted and received at high speed.

A procedure for obtaining data from the electronic text publishing company 48 as described above will be described with reference to a flowchart forming FIG. 6 of the accompanying drawings.

Referring to FIG. 6, a user ID is transmitted to the electronic text publishing company 48 via the telephone line network 49 at step S1. The user ID is necessary for the user to pay a data acquisition charge to the electronic text publishing company 48. The charge may of course be included in a channel charge just like some special telephone services or paid according to the telephone subscriber system.

In the second step S2, data retrieval lists such as book title list, a publisher list, an author list or the like are transmitted from the electronic text publishing company side to the display apparatus 10 side and then received.

In the third step S3, by using the menu key 35c, the down and up keys 35d, 35e, the selection key 35f or the like within the second operation key pad 35, the title of the book that the user wants to read and an identifying number, if the book is designated by the identifying number on the electronic text publishing company side, are transmitted to the electronic text publishing company.

In the fourth step S4, the electronic text publishing company retrieves data from the title of the book and the identifying number received and data representative of the content of the book is transmitted to and received by the display apparatus 10 side.

In the fifth step S5, the display apparatus 10 side writes and stores the data of the content of the book thus received in the data buffer within the system such as the IC memory card 44 or the like. At the completion of the data acquisition, a completion signal is transmitted to the electronic text publishing company and then the communication is ended.

According to the above mentioned sequence of operation, the reader can obtain information data of the book that the reader wants to read with ease in other places than the home.

A data format and a procedure for displaying various data on the first and second LCD panels 24L, 24R will be described with reference to FIGS. 7 to 10.

FIG. 7 of the accompanying drawings shows a conceptual diagram of a memory map of data according to this embodiment. As shown in FIG. 7, the data map comprises a data ID area 51 in which informations concerting data such as data format, title of book, author, etc., are written, a page memory address conversion data area 52 in which a memory address corresponding to a page is written and a data area 53 in which display data is stored.

If the data displayed on the display apparatus of the electronic text is arranged as described above, then a book of predetermined author and title can be retrieved from the data ID area 51. Also, since the address corresponding to each page of the book is made corresponding to the area 52 so that the CPU 14 can retrieve a predetermined page from the data area 53 with ease.

The CPU 14 can sequentially and independently display continuous pages such as a predetermined novel on the display screens 100 and 200 of the display apparatus 10 very easily as shown in FIGS. 4A and 4B.

That is, in the case of the continuous pages, the data may be displayed in the sequential order of the pages.

The case that the pages are not continuous is roughly classified into the following two cases (a) and (b), i.e., the case that a page distant from a series of sentences in a novel or the like is selected. e.g., when a page 10 and a page 100 are selected and the case such that sentences of two different novels, original text and its translation, map and guide book, etc., are selected. The respective cases (a) and (b) will be described more fully below.

(a) To select discontinuous pages in one text: Initially, a continuous or discontinuous display menu is displayed on the LCD panels 24L and 24R by pressing the selection key 35f or the like. Then, if the discontinuous display menu is selected by the cursor, then the CPU 14 issues a display menu instructing that the reader inputs the page number of the left page and causes the page number to be displayed on the LCD panel 24L.

Under this condition, as shown in FIG. 8, the page number of the left page displayed on the first LCD panel 24L is selected by the cursor, for example, by operating the keys 35c to 35f at step STl.

Similarly, if the CPU 14 issues the display menu instructing that the reader inputs the page number of the right page and displays the page number on the LCD panel 24R, then in the second step ST2, the page number of the right page to be displayed on the second LCD panel 24R is selected by the cursor, for example, by operating the keys 35c to 35f.

In the third step ST3, a memory address of the designated page is obtained from the page e memory address conversion data.

Then, in the fourth step ST4, the CPU 14 writes and displays data corresponding to the right and left pages in the VRAM 23 on the basis of the memory address.

The above-mentioned VRAM 23 includes independent memory areas of six pages in total of left and right page frame memories 23Lb, 23Rb which are used to display data of present one page on the first and second LCD panels 24L, 24R, left and right preceding page frame memories 23La, 23Ra and left and right next page frame memories 23Lc, 23Rc as shown in FIG. 9. Therefore, when the menus are displayed on the left and right present page frame memories 23Lb, 23Rb, for example, if the data, which is written and displayed in accordance with the flowchart of FIG. 8, is written in the left and right next page frame memories 23Lc, 23Rc and moved to the left and right present page areas at the completion of the menu instruction, then data can be displayed without a noise on the display screens.

(b) Different sentences such as two kinds of sentences, text - translation and map - guide book: A contrast type data includes, as shown in FIG. 10, a data ID area 51, a page e address conversion data area 52 and data areas 53a, 53b. In the case of the two different kinds of sentences, memory addresses corresponding to respective pages are written in the page e memory address conversion data area 52. In other cases, memory addresses of the compared pages corresponding to the displayed pages of original text and map are written in the page 4 memory address conversion data area 52. Then, the data area is divided into the two data areas 53a and 53b.A first sentence, a text and a map are written in advance in the data area 53a of the data 1 and a second sentence, a translation and a guide for map are written in advance in the data area 53b of the data 2. Therefore, when the page is switched, data of the page to be switched can be immediately accessed from the page e memory address conversion data.

FIG. 11 of the accompanying drawings shows a flowchart to which references will be made in explaining the way of how to display the contrast type data.

As shown in FIG. 11, a page to be displayed is obtained at a first step STEW. Then, after the address data of the contrast page is obtained from the page e memory address conversion data at a second step STE2, the data is written in the frame memory of the VRAM 23 and then displayed at a third step STE3.

According to the above-mentioned arrangement, in the case of the first and second LCD panels 24L and 24R, if a small back light of a fluorescent type, which is bent in an M-letter configuration, is mounted on the lower surface of the panel or a self light emission type element such as a plasma display and an EL display is used, then this book type display apparatus can be made compact in size and can become easy to carry. Also, according to this book type display apparatus, the reader can read the displayed page in the darkness.

Further, if two small and large character sizes are prepared as the font ROM 17 or the font ROM 17 is arranged so as to include vector fonts, then characters and graphic patterns can be enlarged and reduced in size very easily so that old people can read the display page in large characters. Data of the graphic pattern can be reduced in size with ease by selecting necessary data and throwing away other unnecessary data. Therefore, the graphic pattern can be enlarged n times by increasing data of one dot to data of n dots.

Furthermore, if each frame memory of the VRAM 23 has a power supply back-up function, then a page displayed last can be displayed when the power switch of the apparatus is turned on.

The bookmark and marking are attached and removed as follows: The bookmark is attached to a non-display area of the frame memory of the VRAM 23. The contents of data necessary for attaching the bookmark is composed of a page number, a marking starting line, a marking starting character position and the number of characters. In this case, since the frame memory has the back-up function as described above, bookmark data can be left even when the power switch of the apparatus is switched.

This book type display apparatus can achieve a dictionary function and a word retrieval function. That is, the word retrieval is realized by retrieving a coincidence of character codes. When the dictionary function is realized, word - page conversion data is written in advance in the page e memory address conversion area 52 and data can be obtained therefrom.

The above-mentioned LCD panels 24L, 24R are formed of TN (twisted nematic) type liquid crystal or the like. If the LCD panels 24L, 24R are formed of ferroelectric liquid crystal or phase change mode liquid crystal, then the circuit scale of the liquid crystal controller 22 can be reduced and the number of assembly parts of the apparatus can be reduced, which can reduce an amount of electric power consumption of the display apparatus 10 on the whole. This display apparatus will be described more fully with reference to FIGS. 12 to 16 of the accompanying drawings.

The display apparatus generally using a liquid crystal as shown in FIG. 2 is constructed as shown in FIG. 12. In FIG. 12, like parts corresponding to those of FIG. 2 are marked with the same references and therefore need not be described in detail.

In FIG. 12, electronic text data corresponds to the IC memory card 44 that has been described with reference to FIG. 5. That is, the LCD controller 22 needs a bus gate circuit 55 which adjusts the utilization of the bus 18 (19) among the CPU 14, the VRAM 23 and the LCD panels 24L, 24R.

According to the arrangement of the display apparatus shown in FIG. 12, the timing waveforms of the LCD controller 22 and the CPU 14 (i.e., system controller including the system ROM 15 and the system RAM 16) are presented as shown in FIG. 13. In this case, data from the VRAM 23 must constantly be written in the liquid crystal at a constant cycle Tc during a period Tm as shown in FIG. 13. Accordingly, the LCD controller 22 has an initiative of the data bus 19 so that the system controller and other circuit elements can be operated only during a period Ts in which the LCD controller 22 frees the bus of the VRAM 23. Further, since the LCD controller 22 is constantly operated, much more electric power is consumed.

As described above, in the case of the ordinary LCD panels 24L and 24R, the data must constantly be written during the display period so that the LCD controller 22 must be operated even when the displayed contents on the LCD panels 24L, 24R are not changed. Thus, the bus gate circuit 55 that switches the common bus for the portion controlled by the system is required, thus causing a problem of electric power consumption in the display apparatus such as the electronic text. Consequently, since the bus gate circuit 55 is provided, the display apparatus becomes more expensive. Further, since the LCD controller 22 and the CPU 14 (system controller) commonly utilize the data bus 18 and the control bus 19, there is then the problem such that the period during which the system controller uses the bus is reduced.

If the LCD panel 24L (24R) is formed of the ferroelectric liquid crystal or phase change mode liquid crystal in order to solve the above problems, then the drive period of the LCD controller 22 can be reduced and hence the operating period of the CPU 14 (main system) can be reduced. Moreover, since the bus gate circuit 55 that is used to switch the data bus 18 and the control bus 19 is not needed, the display apparatus can become inexpensive and consume a small amount of electric power.

The arrangement of the above display apparatus will be described with reference to FIGS. 14 to 17 of the accompanying drawings.

As a liquid crystal having a memory function, there can be utilized a ferroelectric liquid crystal and a phase change mode liquid crystal, for example.

In the ferroelectric liquid crystal, a dielectric has a spontaneous pole Ps and a liquid crystal is inverted by 180 by the application of the external electric field so that Ps can be inverted to - Ps. A chiral smectic C phase (Smc) or the like, for example, presents a ferroelectricity.

Further, the phase change mode liquid crystal presents the phase transition from a cholesteric phase having a molecular arrangement of spiral structure to a nematic phase having a homeotropic molecular arrangement or conversely the phase transition from the nematic phase to the cholesteric phase by the application of a voltage. By using a hysteresis characteristic presented when the phase transition in the cholesteric phase and the nematic phase occur, the LCD panels 24L, 24R can be given a memory function.

FIG. 17 of the accompanying drawings shows a hysteresis characteristic of the phase change mode liquid crystal having such memory function. An abscissa on the graph of FIG. 17 indicates an applied voltage and an ordinate thereof indicates a transmittance (%). In this case, an elasticity of liquid crystal molecule is increased and a gap between the panels is selected to be about 9 ssm. As shown in FIG. 17, in the H state that indicates the transparent state, the phase change mode liquid crystal has the nematic phase, whereas under the state F, the phase change mode liquid crystal has a cholesteric phase and is in the scattered state. A voltage Vd of about 37V is applied to pixels on the LCD panels 24L, 24R. A voltage of 2vd is applied to the pixels in order to change the phase of the phase change mode liquid crystal from the state F to the state H.After the phase transition was made, the voltage Vd is applied to the pixels to hold the liquid crystal in this state and the voltage applied is changed to 0V in order to change the state of the liquid crystal to the state F.

FIGS. 14 and 15 of the accompanying drawings show block diagrams of electronic text provided as a portable display apparatus in which the LCD panels 24L , 24R are formed of the liquid crystal having such memory function. In FIGS. 14 and 15, like parts corresponding to those of FIG. 12 are marked with the same references and therefore need not be described in detail.

In FIGS. 14 and 15, the bus gate circuit 55 shown in FIG, 12 need not be provided within the LCD controller 22. In the case of FIG. 14, the LCD controller 22 controls the LCD panels 24L, 24R and the VRAM 23 in such a fashion that the LCD panels 24L, 24R and data read out from the VRAM 23 are connected together only one time on one picture screen.

In the case of FIG. 15, the memory function of the liquid crystal is utilized and the VRAM 23 is removed so that data from the IC memory card 44 or the like is directly written in the LCD panels 24L, 24R from the CPU 14. In this case, however, this display apparatus includes no VRAM 23 so that, when displayed data is written by the CPU 14, original data such as data from the IC memory card 44 or the like must be written.

FIG. 16 of the accompanying drawings shows an example of timing waveform of the LCD controller 22 and the CPU 14 (system controller) which are arranged as shown in FIGS. 14 and 15.

As is clear from FIG. 16, considering the timing waveforms of the LCD controller 22 and the system controller, the system controller side (CPU 14 side) has an initiative as in the periods Ts - a and Ts - b. When some data is written in the liquid crystal in order to switch the displayed page, for example, or data must be read out from and written in the VRAM 23, if the LCD controller 22 requests the system controller to free the bus, then the system controller is continuously operated until a satisfactory punctuation of the executable instruction, thereby putting the bus under the control of the LCD controller 22.

Therefore, the LCD controller 22 must be operated during a minimum operation period Tn and the amount of electric power consumption can be reduced as compared with the ordinary liquid crystal. The reduction of electric power consumption can be similarly effected not only in the LCD controller 22 but also in other systems. That is, other control system and signal system may be treated at the same level under the control of the system controller. Therefore, the arrangement of the system can be simplified and the control operation can be carried out at higher speed.

In particular, when a picture is displayed during a certain period (i.e., period in which the reader reads out the electronic text), it is sufficient that the LCD controller 22 requests the CPU 14 to free the bus. As a result, the bus gate circuit 55 is not required, which can make the display apparatus low in electric power consumption and inexpensive.

While the frame memories 23La, 23Lb, 23Lc, 23Ra, 23Rb and 23Rc corresponding to respective pages are provided within the VRAM 23 as described above with reference to FIG. 9, let us now explain an arrangement' using these frame memories 23La, 23Lb, 23Lc, 23Ra, 23Rb and 23Rc in which pages can be sequentially turned over like ordinary books and pages can be turned over rapidly.

Embodiments of the book type display apparatus which can read out and display data at high speed according to the present invention will be described with reference to FIGS. 18 to 24. In FIG. 18 and the following drawings, like parts corresponding to those of FIG. 2 are marked with the same references and therefore need not be described in detail.

The display apparatus 24L (24R) is formed of LCD panel.

This display apparatus 24L (24R) is not limited to the LCD panel and a flat CRT (cathode ray tube), a plasma display or the like may be applied thereto. The VRAM 23 is composed of frame memories 23La, 23Lb and 23Lc (only one side in the double-spread pages is shown) which store data of characters, graphic patterns, etc., of one page amount displayed on the LCD panel 24L so as to map the images displayed on the picture screen as a bit pattern of the pixel unit. Display data signals read out from these frame memories 23La, 23Lb and 23Lc are supplied through a changeover switch 56 to the LCD panel 24L in which characters, graphic patterns, etc., of one page amount are displayed on its picture screen. The change-over switch 56 is changed in position by a control signal from the CPU 14.

In FIG. 18, reference numeral 44 designates the IC memory card which is provided as a data base. In actual practice, data is written in the VRAM 23 through the LCD controller 22 that is controlled by the CPU 14. In this case, for simplicity, the IC memory card 44 is controlled by the CPU 14 so that data is directly written in the VRAM 23. Characters of novels and informations such as graphic patterns and so on are stored in the IC memory card 44 as code data signals. Incidentally, the IC memory card 44 is not limited to the semiconductor ROM and disc ROMs such as an optical disc, a magnetic disc or the like may be utilized. If the IC memory card 44 is formed of the disc ROM, a reproducing apparatus is needed of course-.The code data signal from the IC memory card 44 is converted into bit map data by using the font ROM 17 or the like on the basis of the read-out control signal and the address signal from the CPU 14 and then supplied through a change-over switch 60 to the frame memories 23La, 23Lb and 23Lc as a data signal 64, in which it is written.

This change-over switch 60 is changed in position in response to a control signal 61 from the CPU 14.

The read and/or write operation of the frame memories 23La, 23Lb and 23Lc is controlled by a read/write (R/W) control and address signal 63 from the CPU 14 and the address thereof also is thereby designated. In FIG. 18, reference numeral 62 designates a keyboard which comprises the first and second key pads 34, 35 which had been described with reference to FIG. 2.

Operation of the arrangement shown in FIG. 18 will be described below with reference to FIG. 19 of the accompanying drawings. In this case, the display units of this display apparatus are not operated as the double-spread pages and the LCD panel 24 of one page amount will be described.

In FIG. 19 of the accompanying drawings, reference numeral 1 through 25 designate periods and reference symbol R/W depicts read-out and write timings of the frame memories 23La, 23Lb and 23Lc provided within the VRAM 23 under the control of the CPU 14.

Respective read-out and write cycles are equal to each other.

This cycle is equal to a line cycle of the LCD panel 24L, for example, and synchronized with a line synchronizing signal. Oddnumbered periods depict read-out periods and even-numbered periods depict write periods, respectively. Numerals in the read-out (R) in 23La, 23Lb, 23Lc in the frame memories 1, 2 and 3 represent page numbers of one page amount of contents of a book stored in the frame memories 23La, 23Lb, 23Lc of the frame memories 1, 2 and 3.When the above-mentioned numerals are encircled by open squares, the frame memories in which the bit pattern signals of the contents of the book of the pages are stored are connected through the change-over switch 56 to the LCD panel 24L. Further, numerals encircled by open circles in the columns of the frame memories 1 to 3 represent the number of pages of the contents of the book which is being written in the frame memories 1 to 3 from the IC memory card 44 upon reading.

Of data contents of respective pages stored in the frame memory 23La of the frame memory 1 during the periods 1, 3, 5, 7, in the frame memory 23Lb of the frame memory 2 during the periods 1, 3, 5, 7, 9, 11, 13, 15, 17, 19 and in the frame memory 23Lc of the frame memory 3 during the periods 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, the content of the first page of the electronic text stored in the frame memory 23La of the frame memory 1 is displayed on the LCD panel 24L during the periods 1, 3 and 5.

If the next picture key 34f of the first operation key pad 34 in the keyboard 62 is depressed during the next period 7, then the content of the page 2 (or the next page) of the electronic text stored in the frame memory 23Lb of the frame memory 3 is displayed on the LCD panel 24L.

In the next period 8, the writing of the content of the page 4 of the electronic text in the frame memory 23La of the frame memory 1 is started. During the periods 7, 9, 11, 14, 15 and 17, the content of the page 2 of the electronic text stored in the frame memory 23Lb of the frame memory 2 is displayed on the LCD panel 24L. During the next periods 8, 10 and 12, the content of the page 4 of the electronic text is being written in the frame memory 23La of the frame memory 1.

If the next picture key 34f on the keyboard 62 is pressed during the next period 19, then the content of the page 3 of the electronic text stored in the frame memory 23Lc of the frame memory 3 is displayed on the LCD panel 24L. In the next period 20, the writing of the page 5 of the electronic text corresponding to the frame memory 23Lb of the frame memory 2 is started. During the periods 21, 23 and 25, the content of the page 3 of the electronic text stored in the frame memory 23Lc of the frame memory 3 is displayed on the LCD panel 24L, while during the periods 20, 22 and 24, the content of the page 5 of the electronic text stored in the frame memory 23Lb of the frame memory 2 is being written.

The three frame memories 1, 2 and 3 are used for one picture (one page) so that, each time the next picture key 34f is depressed, then the areas 23La, 23Lb and 23Lc of the frame memories 1, 2 and 3 are switched to thereby turn over and display the pages readily.

While the LCD panel 24L that displays one page is described so far, when six areas 23La, 23Lb and 23Lc of the frame memories l to 3 are utilized similarly to FIG. 9, the LCD panels 23L and 23R are set in the ordinary double-spread page fashion and data of two pages are sequentially accessed at each depression of the next picture key 34f similarly to the ordinary book, if six frame memories are prepared as shown in FIG. 20 where the areas 23La, 23Ra of the frame memory 1 are prepared for the preceding page, the areas 23Lb, 23Rb of the frame memory 2 are prepared for the present page and the areas 23Lc, 23Rc of the frame memory 3 are prepared for the next picture, then the present two pages of the present pages are simultaneously displayed and switched after the two pages of the preceding pages were simultaneously displayed and switched by the depression of the next picture key 34f. Further, the two pages of the next pages can be displayed and switched by the depression of the next picture key 34f.

Thus, the pages can be turned over similarly to the ordinary book.

It is sufficient that the book type display apparatus is constructed as shown in FIG. 21. As shown in FIG. 21, the CPU 14 supplies electronic text data, which is supplied to the IC memory card 44 or the communication network data input unit 13, to the frame memories 23La, 23Lb, 23Lc, 23Ra, 23Rb, 23Rc. Also, the control operation such as the display page control or the like is carried out on the basis of a display controller 22a and a page controller 22b both of which are provided within the LCD controller 22.

The display controller 22a is adapted to control fundamental functions such as forming an address within one page and setting the number of characters per line and lines per page in order to effect the display on the LCD panels 24L, 24R. The page controller 22b is adapted to determine the page to be displayed.

As described above, the respective frame memories are accessed by using two kinds of means, i.e., the address of the memory within one page amount and the output signal of the display page switching page controller 22b which is used to determine the page to be displayed. Accordingly, when the display picture is switched, it is sufficient only to switch the frame memories and hence, the pages can be turned over at high speed.

The switching timing of the signal lines when the read-out and the writing of each frame memory is effected will be described below. Data representative of picture, which is being displayed, is constantly read out from each frame memory at a constant timing. However, when the data bus of the CPU 14 is made free, data of the page displayed next is written in advance in each frame memory. Also, data representative of the next picture is written in each frame memory when the picture is being displayed. Since data to be displayed next is written in advance in each frame memory as described above, data of the next page can be written in each frame memory within a duration in which the reader can confirm the information displayed on the picture screen. Therefore, the pages can be switched at high speed only by the display page switching signal.Also, a noise that takes place when the display page is switched can be reduced. Although a vacant area is sometimes produced in the memory because the frame memory is provided at every page, the resultant vacant memory space can be utilized as ordinary RAM.

An arrangement of the book type display apparatus according to a further embodiment of the present invention will hereinafter be described with reference to FIG. 23. While the change-over switches 56, 60 are respectively interposed between the areaa 23La, 23Lb, 23Lc of the frame memories 1 to 3 and the LCD panel 24L and between the IC memory card 44 and the frame memories 23La, 23Lb, 23Lc forming the VRAM 23 as described above with reference to FIG. 18, according to this embodiment, the VRAM 23 is formed of a RAM composed of three frame banks 23La, 23Lb, 23Lc and the change-over switches 56, 60 are omitted as shown in FIG. 23.

In this case, the read-out and writing of the frame banks 23La, 23Lb, 23Lc and the addressing are controlled on the basis of the read/write (R/W) control and address signal from the CPU 14 and the write and read of the bit pattern signal are effected on the basis of the code data signal from the IC memory card 44.

The address map of the above frame memories 23La, 23Lb and 23Lc is illustrated in FIG. 22. Let it now be assumed that data is displayed on the LCD panel 24L of page n and that addresses are assigned to X00 to YOO. Further, addresses of preceding page (page n-l) are assigned to 000 to X00 and addresses of the next page (page n+l) are assigned to Y00 to ZOO. In this case, each frame memory corresponds to one picture. Accordingly, in order to make the addresses corresponding to respective pages, the setting of the address is made such that only the higher order elements of the addresses such as O, r X, y, Z must be varied (i.e., bank switching system). That is, data within the display screen of the LCD panel 24L are set such that all relative addresses from the display starting point can be accessed.If the page is switched, then the higher-order address is used as the display page signal to switch the page. According to this system, since the page can be switched only by incrementing or decrementing the high-order address of the frame memory 23La of the picture now displayed by "l", a program also can be simplified (except the memory of the lowest-order address and the memory of the highest-order address).

Operation of the embodiment shown in FIG. 23 is similar to that of the embodiment shown in FIG. 18 and therefore need not be described.

While the VRAM 23 is composed of the three frame memories as described above with reference to FIG, 18, the number of the frame memories is no limited thereto and two frame memories or more may be possible. Operation of the embodiment shown in FIG.

18 where the frame memories of the VRM! 23 are composed of two frame memories 23La and 23Lc will be described with reference to FIG. 24 of the accompanying drawings.

As shown in FIG. 24, during the periods 1, 3 and 5, the content of the first page of the electronic text stored in the frame memory 23La is displayed on the LCD panel 24L, and the content of the second page of the electronic text is stored in the frame memory 23Lc. If the next picture key 34f on the keyboard 62 is depressed during the period 7, then the content of the second page of the electronic text stored in the frame memory 23Lc is this time displayed on the LCD panel 24L. During the next period 8, the writing of the content of the third page of the electronic text is started in the frame memory 23La in which the content of the first page is stored.During the periods 7, 9, 11, 13, 15 and 17, the content of the second page of the electronic text stored in the frame memory 23Lc is displayed on the LCD panel 24L. During the periods 8, 10 and 12, the content of the third page of the electronic text is being written in the frame memory 23La. During the periods 13, 15 and 17, the content of the second page of the electronic text stored in the frame memory 23Lc is displayed on the LCD panel 24L.

If the next picture key 34f on the keyboard 62 is depressed during the period 19, then this time, the content of the third page of the electronic text stored in the frame memory 23La is displayed on the LCD panel 24L. During the next period 20, the writing of the content of the fourth page of the electronic text is started in the frame memory 23Lc. During the periods 21, 23 and 25, the content of the third page of the electronic text stored in the frame memory 23La is displayed on the LCD panel 24L. During the periods 20, 22 and 24, the content of the fourth page of the electronic text is being written in the frame memory 23Lb.

According to the above-mentioned respective embodiments shown in FIGS. 18 to 24, the display on the LCD panels 24L and 24R can be switched at extremely high speed and the pages can be turned over similarly to the ordinary book.

While the portable book type display apparatus of pocketbook size has been described so far, the present invention is not limited thereto and the following variants are also possible.

That is, a so-called pocket bell function device is disposed within the first and second casings 31, 32 so that message data can be displayed on the LCD panel 24L or 24R through the RS-23C connector and that an alarm sound can be emanated from the pocket bell. In this case, when the reader reads the electronic text, if the pocket bell information has a priority, then this book type display apparatus can be served as a device for communication in emergency.

Further, if a facsimile receiving function is disposed within the casings 31, 32 and facsimile data is received through the RS-232C connector or the like, then this book type display apparatus can be functioned as a facsimile and book type display apparatus. In this case, facsimile information data is not only displayed on the LCD panels 24L, 24R but also this facsimile information data is stored in the IC memory card of the data medium loaded into the display apparatus. If so, necessary facsimile data can be printed out by using a printer or the like.

Further, a television receiving function, a teletext receiving function and a portable computer function can also be mounted within the casings 31, 32 with ease. If these functions are mounted, e.g., the television receiving function is mounted within the casings 31, 32, this book type display apparatus can be effectively utilized as a television receiver with an interactive function. That is, for deaf people, a television picture can be displayed on the LCD panel 24L and teletext contents can be displayed on the LCD panel 24R. Furthermore, in the case of the teletext broadcasting, the teletext broadcasting can be displayed on the display screen. In the case of the portable computer, the LCD panels 24L, 24R are formed as the touch-sensitive panels which are served as input unit and display apparatus.Thus, the book type display apparatus can be arranged as the double-spread page type display apparatus.

According to the above-mentioned embodiments of the present invention, it is possible to obtain a book type display apparatus formed of electronic texts which is easy to carry and handy to read just like a book of pocket edition. According to this book type display apparatus of the present invention, the display pages can be turned over like a ordinary book and the displayed pages can be compared with each other regardless of the continuous or discontinuous pages. In this portable book type display apparatus, the pages can be sequentially turned over and also accessed in a random access fashion.

Further, it is possible to provide a book type display apparatus which can display on its display units not only character data but also characters and graphic patterns such as graphics as informations displayed on the display units. Also, characters and graphic patterns displayed on the display units can be enlarged and reduced in size.

Further, according to the book type display apparatus of the present invention, predetermined data and graphic patterns can be accessed from a recording medium such as CD-ROM and from other communication network.

According to the present invention, it is possible to obtain a book type display apparatus in which the number of data used in the display mode can be preserved after a power switch thereof is turned off and which includes a bookmark function to mark and retrieve pages and words.

Further, according to the present invention, it is possible to obtain a book type display apparatus which can be made compact in size because only data of necessary portion in one text can be retrieved and displayed and in which data displayed can be read in the darkness.

Furthermore, it is possible to obtain a book type display apparatus in which pictures can be switched at high speed just as the reader can turn over pages of a book and which can reduce an amount of electric power consumption by using a liquid crystal having a memory function as a display device.

As described above, according to the present invention, it is possible to obtain a book type display apparatus which can achieve the following effects: (A) Pages can be displayed in a double-spread page fashion like an ordinary book and this book type display apparatus is suitable for portable use; (B) Pages (regardless of continuous or discontinuous pages) can be compared with each other; (C) Data can be obtained anywhere by using a communication network; (D) Pages can be accessed in a random access fashion; (E) Pages can be read in the darkness; (F) The book type display apparatus can be made compact in size (data of only necessary portion can be accessed regardless of the fact that the electronic text is a complete work or book); (G) Bookmark or marking can be attached or removed freely; (H) Characters and graphic patterns can be enlarged and reduced in size; ; (I) Page displayed last can be displayed when the power switch of the apparatus is turned on; and (J) Pages or words can be marked and checked.

Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments and that various changes and modifications could be effected therein by one skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims (17)

1. A display apparatus comprising: a first display unit; a second display unit; a member for coupling said first and second display units in a mutually rotatable relationship in which said first and second display units are closeable together in an opposing relation and openable to an angularly spaced open position; a memory circuit including a first storage area in which a display signal for display on said first display unit is stored and a second storage area in which a display signal for display on said second display unit is stored; a coupling unit for coupling a storage medium from which a display signal is supplied to said memory circuit; and an instruction switch for instructing the writing of said display signal in each of said first and second storage areas to alter the display contents on said first and second display units.

2. The display apparatus according to claim 1, wherein when images to be displayed on said first and second display units are switched, display signals supplied to said first and second display units are selected as related information in response to an operation of said instruction switch and then supplied to said first and second storage areas.

3. The display apparatus according to claim 2, wherein said related information are images of adjacent pages of a book whose pages are opened.

4. The display apparatus according to claim 2 or 3, wherein said related information are an image signal and a signal which is used to explain said image signal.

5. The display apparatus according to claim 1, 2, 3 or 4 further comprising a connection terminal for connecting said display apparatus to an external communication network line, wherein information input from said connection terminal is stored in said storage medium.

6. The display apparatus according to claim 5, wherein said communication network line is connected to said storage medium.

7. The display apparatus according to claim 5 or 6, wherein said communication network line is a telephone network line.

8. The display apparatus according to any one of the preceding claims, wherein said storage medium is an IC card.

9. A display apparatus according to any one of the preceding claims wherein the member is a rotating member.

10. A display apparatus according to any one of the preceding claims wherein the memory circuit includes a third storage area in which a display signal that is not displayed is stored; and the apparatus further comprises a control circuit for controlling the write and read of said display signal in and from said memory circuit and a selecting circuit for selectively supplying the display signals stored in said respective storage areas to said display unit, wherein when reading out the display signals stored in said first and second storage areas and supplying said read-out display signals to said display unit, said control circuit writes said display signal supplied to said display unit in said third storage area.

11. The display apparatus according to claim 10, wherein said display signal is a page information, a page information of the page next to the next page is stored in said third storage area, display signals corresponding to opened two pages are stored in other remaining storage areas and said instruction switch functions as a button which is used to turn over pages.

12. A display apparatus comprising: a display unit; a memory circuit including a plurality of storage areas in which a display signal displayed on said display unit is stored at every predetermined unit; a control circuit for controlling the write and read of said display signal in and from said memory circuit; and a selecting circuit for selectively supplying display signals stored in said plurality of storage areas to said display unit, wherein when a display signal stored in one of said plurality of storage areas is read out therefrom and supplied to said display unit, a display signal to be on said display unit next is written in other storage area.

13. The display apparatus according to any one of the preceding claims, wherein said display apparatus is a pocket book-size display apparatus.

14. The display apparatus according to any one of the preceding claims, wherein each display unit of said display apparatus is formed of a liquid crystal having a memory function.

15. The display apparatus according to claim 14, wherein said liquid crystal having a memory function used in each said display unit is a ferroelectric liquid crystal.

16. The display apparatus according to claim 14, wherein said liquid crystal having a memory function used in each said display unit is a phase change mode liquid crystal.

17. A display apparatus constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in Figures 2 to 24 of the accompanying drawings.