Display device

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and, more particularly, to a display device having a memory function, e.g., a display device using a ferroelectric liquid crystal element.

2. Related Background Art

A known liquid crystal element using a liquid crystal compound comprises scanning and signal electrodes arranged in a matrix form, and a liquid crystal compound filled between the electrodes to constitute a large number of pixels, thereby displaying image information.

According to a conventional time-divisional method of driving such a display element, voltage signals are sequentially and periodically applied to the scanning electrodes, and predetermined information signals are in parallel applied to the signal electrodes in synchronism with the scanning electrode operations. According to the above-mentioned display element and its driving method, it is difficult to increase both the pixel density and the screen size.

The most popular liquid crystal element is a TN (twisted nematic) element since it has a relatively short response time among the liquid crystal materials and low power consumption. In a state of no electric field applied, twisted nematic liquid crystal molecules having positive dielectric anisotropy have a twisted structure (helical structure) in a direction of thickness of a liquid crystal layer, as shown in FIG.

41

A. The liquid crystal molecules of the respective molecular layers are twisted and parallel to each electrode surface between the upper and lower electrodes. However, as shown in

FIG. 41B

, in an electric field, the nematic liquid crystal molecules having positive dielectric anisotropy are oriented in the direction of the electric field, thereby causing optical modulation. When a display element is arranged in a matrix electrode structure by using such a liquid crystal material, a signal voltage higher than a threshold value required for orienting the liquid crystal molecules in a direction perpendicular to each electrode surface is applied to a selected area (i.e., a selected point) as an intersection between the corresponding scanning and signal electrodes. The signal voltage is not applied to non-selected intersections (non-selected points) between the non-selected scanning and signal electrodes. Therefore, in these points, the liquid crystal molecules are twisted and parallel to each electrode surface. When linear polarizers in a relationship of crossed nicols are arranged on the upper and lower surface of this liquid crystal cell, light is not transmitted at the selected point(s), but light is transmitted at the non-selected point(s) due to the twist structure of the liquid crystal and an optical rotary power, thereby providing an imaging element.

With a matrix electrode structure, a limited electric field is applied to an area (so-called “semi-selected point”) where the scanning electrode is selected and the signal electrode crossing this scanning electrode is not selected, and vice versa. If the difference between the voltage applied to the selected point and the voltage applied to the semi-selected point is sufficiently large, and a voltage threshold required for vertically aligning the liquid crystal molecules with respect to the electrode surface can be set to an intermediate value between the above voltages, the display element can be normally operated.

When the number (N) of scanning lines is increased in the above system, a duration (i.e., a duty ratio) for which an effective electric field is applied to one selected point during scanning of one frame is decreased at a rate of 1/N. For this reson, the difference between voltages, i.e., effective values, applied to the selected and non-selected points upon repetition of the scanning cycle is decreased when the number of scanning lines is increased. As a result, a decrease in image contrast and a crosstalk phenomenon cannot be avoided inevitably.

The above phenomena inevitably occur when a liquid crystal without a bistable state (i.e., liquid crystal molecules are stably oriented in a direction parallel to the electrode surface and their orientation is changed in a direction perpendicular to the electrode surface during an effective application of the electric field) is driven by utilizing an accumulation effect as a function of time (i.e., scanning is repeated). In order to solve this problem, various driving schemes such as a voltage averaging scheme, a 2-frequency driving scheme, and a multiple matrix scheme are proposed. However, none of these conventional schemes are satisfactory. Therefore, a large screen and a high packing density of a display element cannot be obtained since the number of scanning lines cannot be sufficiently increased.

In order to solve the above problem, the present applicant filed a U.S. Ser. No. 598,800 (Apr. 10, 1984) entitled as a “Method of Driving Optical Modulation Device”. In this prior art, the present applicant proposed a method of driving a liquid crystal having a bistable state with respect to an electric field. An example of the liquid crystal which can be used in the above driving method is preferably a chiral smectic liquid crystal, and more preferably a chiral smectic C-phase (SmC*) or H-phase (SmH*).

The SmC* has a structure in which liquid crystal molecular layers are parallel to each other, as shown in FIG.

42

. The direction of a major axis of each molecule is inclined with respect to the layer. These liquid crystal molecule layers have different inclination directions and therefore constitute a helical structure.

The SmH* has a structure in which the molecular layers are parallel to each other, as shown in FIG.

43

. The direction of a major axis of each molecule is inclined with respect to the layer, and the molecules constitute a six-direction filled structure on a plane perpendicular to the major axis of the molecule.

The SmC* and SmH* have helical structures produced by the liquid crystal molecules, as illustrated in FIG.

44

.

Referring to

FIG. 44

, each liquid crystal molecule e

3

has electrical bipolar moments e

4

in a direction perpendicular to the direction of the major axis of the molecule e

3

. The molecules e

3

move while maintaining a predetermined angle θ with respect to the Z-axis perpendicular to a layer boundary surface e

5

, thereby constituting a helical structure.

FIG. 44

shows a state when a voltage is not applied to the liquid crystal molecules. If a voltage exceeding a predetermined threshold voltage is applied to the X direction, the liquid crystal molecules e

3

are orientated such that the electrical bipolar moments e

4

are parallel to the X-axis.

The SmC* or SmH* phase is realized as one of the phase transition cycles caused by changes in temperatures. When these liquid crystal compounds are used, a proper element must be selected in accordance with the operating temperature range of the display device.

FIG. 45

shows a cell when a ferroelectric liquid crystal (to be referred to as an FLC hereinafter) is used. Substrates (glass plates) e

1

and e

1

′ are coated with transpatent electrodes comprising In

2

O

2

, SnO

2

or ITO (indium-tin oxide). An SmC*-phase liquid crystal is sealed between the substrates e

1

and e

1

′ such that liquid crystal molecular layers e

2

are oriented in a direction perpendicular to the substrates e

1

and e

1

′. The liquid crystal molecules e

3

represented by thick lines have bipolar moments e

4

in directions perpendicular to the corresponding molecules e

3

. When a voltage exceeding a predetermined threshold is applied between the substrates e

1

and e

1

′, the helical structure of the liquid crystal molecules e

3

is changed such that the directions of orientation of the liquid crystal molecules e

3

are aligned with the direction of the electric field. Each liquid crystal molecule e

3

has an elongated shape and exhibits refractive anisotropy in the major and minor axes. For example, when polarizers having a positional relationship of crossed nicols with the orientation direction are arranged on the upper and lower surfaces of the upper and lower glass plates, it is readily understood that there is provided a liquid crystal optical modulation device having optical characteristics which change in accordance with the polarities of the applied voltage.

When the thickness of the liquid crystal cell is sufficiently small (e.g., 1 μm), the helical structure of liquid crystal molecules cannot be established even if an electric field is not applied thereto, and the bipolar moment P or P′ is directed upward or downward, as shown in FIG.

46

. When an electric field E or E′ (the fields E and E′ having different polarities) exceeding the predetermined threshold value is applied to this cell for a predetermined period of time, the bipolar moment is directed upward or downward so as to correspond to the electric field vector of the electric field E or E′. Therefore, the liquid crystal molecule is oriented in a first stable state f

3

or a second stable state f

3

′.

Use of such an FLC in an optical modulation element has the following two advantages. First, the resultant optical modulation element has a very short response time (1 μsec to 100 μsec), and second, the liquid crystal molecule orientation has a bistable state.

The second point will be described with reference to FIG.

46

. When the electric field E is applied to the liquid crystal molecules e

3

, the liquid crystal molecules e

3

are oriented in the first stable state f

3

. This state is kept stable even if the electric field is withdrawn. When the electric field E′ having a polarity opposite to that of the electric field E is applied, the liquid crystal molecules e

3

are orientated in the second stable state f

3

′. This state is kept unchanged even if the electric field E′ is withdrawn. Therefore, the liquid crystal molecules e

3

have a memory function. If the level of the electric field E does not exceed the predetermined threshold value, the orientation state of the molecule is maintained.

In order to obtain a short response time and an effective memory function, the thickness of the cell is preferably minimized, generally, to 0.5 μm to 20 μm and, more preferably, to 1 μm to 5 μm.

A method of driving the FLC will be described with reference to

FIGS. 47

to

49

D.

FIG. 47

is a cell arrangement having a matrix electrode structure containing an FLC compound (not shown) therein. The cell arrangement includes scanning electrodes corn and signal electrodes seg. An operation when the scanning electrode com

1

is selected will be described.

FIGS. 48A and 48B

show scanning signals, in which

FIG. 48A

shows an electrical signal applied to the scanning electrode com

1

and

FIG. 48B

shows an electrical signal applied to other scanning signals (i.e., the non-selected scanning electrodes) com

2

, com

3

, com

4

, . . . .

FIGS. 48C and 48D

show information signals, in which

FIG. 48C

shows an electrical signal applied to the selected signal electrodes seg

1

, seg

3

, and seg

5

, and

FIG. 48D

shows an electrical signal applied to the non-selected signal electrodes seg

2

and seg

4

.

Time is plotted along the abscissa in each chart of

FIGS. 48A

to

48

D and

FIGS. 49A

to

49

D and voltage values are plotted along the ordinate in each chart of

FIGS. 48A

to

49

D.

For example, when a motion image is to be displayed, the scanning electrodes com are sequentially and cyclically selected. If a threshold voltage for giving the first stable state in a liquid crystal cell having bistable characteristics with respect to a predetermined applied voltage time Δt

1

or Δt

2

is given as −Vth

1

, and a threshold current voltage for giving the second stable state therein is given as +Vth

2

, the electrode signal applied to the selected scanning electrode com (com

1

) is an alternating voltage which is set at 2 V in a phase (time) Δt

1

and −2 V in a phase (time) Δt

2

as shown in FIG.

48

A. When electrical signals having a plurality of phase intervals and different voltage levels are applied to the selected scanning electrode, an immediate change occurs between the first stable stage corresponding to the optically “dark” (black) state and the second stable state corresponding to the optically “bright” (white) state.

As shown in

FIG. 48B

, the scanning electrodes com

2

to com

5

, . . . are set at an intermediate potential of the cell applied voltage, i.e., a reference potential (e.g., a ground state). The electrical signal applied to the selected signal electrodes seg

1

, seg

3

, and seg

5

is given as V, as shown in FIG.

48

C. The electrical signal applied to the non-selected signal electrodes seg

2

and seg

4

is given as −V, as shown in FIG.

48

D. Therefore, the above voltage values are set to be desired values satisfying the following conditions:

V<V

th

2

<3

V

−3

V<−V

th

1

<−

V

Waveforms of voltages applied to pixels A and B (

FIG. 47

) of the pixels applied with the above electrical signals are shown in

FIGS. 49A and 49B

, respectively. As is apparent from

FIGS. 49A and 49B

, a voltage 3V exceeding the threshold value Vth

2

is applied in the phase Δt

2

to the pixel A located on the selected scanning line. A voltage −3V exceeding the threshold value −Vth

1

is applied in the phase Δt

1

to the pixel B on the same selected scanning line. Therefore, when the signal electrode on the selected scanning line is selected, the liquid crystal molecules are oriented in the first stable state. However, when the signal electrode on the selected scanning line is not selected, the liquid crystal molecules are oriented in the second stable state.

As shown in

FIGS. 49C and 49D

, the voltage applied to all pixels on the non-selected scanning line is V or −V. In either case, the voltage does not exceed the corresponding threshold voltage. The liquid crystal molecules in each pixel excluding the ones on the selected scanning line do not change their orientation state and are kept in the state established by the previous scanning cycle. In other words, when the scanning line is selected, one-line signal write is performed. The signal state is kept unchanged until the next selection is started upon completion of one frame. Therefore, even if the number of scanning electrodes is increased, the selection time/line is not almost changed, and a decrease in contrast does not occur.

As has been described above, in order to solve the problems posed by the conventional display elements using a TN liquid crystal, an FLC which has a bistable effect with respect to an electric field and allows an arrangement of a display element for maintaining the stable state is proposed. Regarding drive control of a display element using an FLC, some problems concerning its characteristics still remain unsolved.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a display control unit for performing optimal drive control while effectively utilizing characteristics of an optical modulation element, e.g., a ferroelectric liquid crystal element (FLC element) having a bistable function for an electric field when the optical modulation element is used to arrange a display device.

It is another object of the present invention to provide a display control unit combined with a display device including X and Y side electrodes and a display element sandwiched between the X and Y side electrodes, the display control unit comprising a plurality of lines for supplying voltages having different values to the X and Y side electrodes, a switch for connecting the lines with the electrodes or disconnecting the lines from the electrodes, and a means for controlling the switch within a selection period of the X or Y side electrodes.

It is still another object of the present invention to provide a display control unit which can properly determine drive waveform data to optimally drive the display element with various waveforms within one selection period in accordance with a content of the drive waveform data.

According to the present invention as described above, there are provided a plurality of lines for supplying voltages having different values to the electrodes in the display unit, a switch for connecting the lines with the electrodes or disconnecting the lines from electrodes, and the means for controlling the switch within a selection period. Therefore, the electrodes of the display element such as an FLC element requiring voltage polarity driving can be optimally driven with various waveforms in accordance with contents of the waveform data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a block diagram showing an arrangement of a display device and a control system according to an embodiment of the present invention;

FIGS. 2 and 3

are an exploded perspective view and a sectional view, respectively, showing an arrangement of the display unit of the device shown in

FIG. 3

;

FIG. 4

is a graph for explaining the relationship between the drive voltage and an applied time;

FIGS. 5A and 5B

and

FIG. 6

are timing charts for explaining drive waveforms of an FLC element;

FIGS. 7A and 7B

are charts for explaining the relationship between the drive voltage and the transmittance of the FLC element;

FIG. 8

is a graph showing the relationship between the temperature and drive voltage of the FLC element;

FIG. 9

is a graph showing the relationship between the temperature data, drive voltage data, and the frequency data, all of which are stored in a memory area in a controller in the device shown in

FIG. 1

;

FIG. 10

is a view showing blocks as effective display areas according to the embodiment shown in

FIG. 1

;

FIG. 11

is a block diagram showing an arrangement of the controller of the embodiment shown in

FIG. 1

;

FIG. 12

is a memory map of a memory space in the controller shown in

FIG. 11

;

FIG. 13

is a view for explaining an address change in the embodiment shown in

FIG. 1

;

FIG. 14

is a view for explaining a one-to-one correspondence between a line number and a jumping table in the embodiment shown in

FIG. 1

;

FIG. 15

is a block diagram for explaining a method of selecting scanning lines in the embodiment shown in

FIG. 1

;

FIG. 16

is a block diagram showing an arrangement of a data output unit in the embodiment shown in

FIG. 1

;

FIG. 17

is a timing chart showing singals for setting drive waveform generation in the data output unit shown in

FIG. 16

;

FIG. 18

is a block diagram showing an arrangement of an A/D conversion unit in the embodiment shown in

FIG. 1

;

FIG. 19

is a block diagram showing an arrangement of a D/A conversion unit and a power controller in the embodiment shown in

FIG. 1

;

FIG. 20

is a block diagram showing an arrangement of a frame drive unit in the embodiment shown in

FIG. 1

;

FIG. 21

is a block diagram showing a schematic arrangement of a segment drive element in the embodiment shown in

FIG. 1

;

FIG. 22

is a circuit diagram showing a detailed arrangement of the segment drive element shown in

FIG. 21

;

FIG. 23

is a block diagram showing a schematic arrangement of a common drive element in the embodiment shown in

FIG. 1

;

FIG. 24

is a circuit diagram showing a detailed arrangement of the common drive element shown in

FIG. 23

;

FIG. 25

is a schematic view for explaining a driving operation of a display unit;

FIGS. 26A and 26B

are timing charts of drive signals of the common and segment lines in a block erase mode;

FIG. 27

is a chart showing a waveform obtained by combining the common and segment line drive waveforms shown in

FIGS. 26A and 26B

;

FIGS. 28A and 28B

are timing charts of drive signals of the common and segment lines during line write in a block access mode;

FIGS. 29A and 29B

are charts showing waveforms obtained by combining the common and segment line drive waveforms shown in

FIGS. 28A and 28B

;

FIGS. 30A and 30B

are views for explaining common and segment line drive waveforms during line write in the line access mode;

FIGS. 31A and 31B

are charts showing waveforms obtained by combining the common and segment line drive waveforms shown in

FIGS. 30A and 30B

;

FIG. 32

is a flow chart showing a display control sequence in the embodiment shown in

FIG. 1

;

FIG. 33

is a flow chart showing an initialization processing sequence in the display control sequence of this embodiment;

FIG. 34

is a timing chart for explaining the operation of this embodiment during initialization processing and power-off processing;

FIG. 35

is a view for explaining an algorithm for converting the temperature data into drive voltage data and time data in this embodiment;

FIGS. 36A

to

36

D and

FIGS. 37A

to

37

C are flow charts showing detailed display control sequences in the block and line access modes of this embodiment, respectively;

FIG. 38

is a flow chart showing a detailed display control sequence in the power-off mode in this embodiment;

FIGS. 39A and 39B

and

FIGS. 40A and 40B

are timing charts for explaining the operation of this embodiment according to the display control sequences shown in

FIGS. 36A

to

36

D and

FIGS. 37A

to

37

C, respectively;

FIGS. 41A and 41B

are views for explaining a TN liquid crystal, respectively;

FIG. 42

is a view for explaining an SmC* liquid crystal;

FIG. 43

is a view for explaining an SmH* liquid crystal;

FIG. 44

is a view for explaining the structure of FLC molecules;

FIG. 45

is a view for explaining a display element using an FLC;

FIG. 46

is a view showing an FLC display element which is applicable to the present invention;

FIG. 47

is a view showing a cell arrangement having a matrix electrode structure, which is applicable to the present invention; and

FIGS. 48A

to

48

D and

FIGS. 49A

to

49

D are charts showing waveforms of voltages applied to the FLC element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention will now be described in detail with reference to the accompanying drawings.

The present invention will be described in the following order:

(1) General Description of Device

(2) Arrangement of Display Unit

(3) General Description of Display Control

(3.1) Frame of Display Unit

(3.2) Drive Waveform of Display Element

(3.3) Drive Voltage of Display Element

(3.4) Temperature Compensation

(3.5) Drive Method of Display Unit

(3.6) Display Screen Clearing

(4) Arrangement of Respective Components in Display Control Unit

(4.1) Main Symbols

(4.2) Controller

(4.3) Memory Space

(4.4) Data Output Unit

(4.5) A/D Conversion Unit

(4.6) D/A Conversion Unit and Power Controller

(4.7) Frame Drive Unit

(4.8) Display Drive Unit

(4.8.1) Segment Drive Unit

(4.8.2) Common Drive Unit

(4.9) Drive Waveform

(5) Display Control

(5.1) General Description of Control Sequence

(5.2) Detailed Description of Control Sequence

(5.2.1) Power-ON (Initialization)

(5.2.2) Block Access

(5.2.3) Line Access

(5.2.4) Power-OFF

(6) Effect of Embodiment

(6.1) Effect of Frame Formation

(6.2) Effect of Temperature Compensation

(6.3) Effect of Control in Response to Image Data Input

(6.4) Effect of Display Drive Unit Arrangement

(6.5) Effect of Screen Forcible Clearing

(6.6) Effect of Power Controller Arrangement

(7) Modification

(7.1) Frame Arrangement

(7.2) Temperature Compensation Timing and Partial Rewrite

(7.3) One-Horizontal Scanning Period and Drive Voltage Value

(7.4) Waveform Setting

(7.5) Selection of Block Access or Line Access

(7.6) Number of Scanning Lines

(7.7) Erasure of Effective Display Area

(7.8) Position of Temperature Sensor

(7.9) Display Unit, Display Control Unit, and Wordprocessor

(1) General Description of Device

FIG. 1

shows an embodiment of the present invention. A wordprocessor

1

serves as a host device and supplies image data to a dislay unit of this embodiment. A display control unit

50

receives display data supplied from the wordprocessor

1

and controls driving of a display unit

100

in accordance with various conditions (to be described later). The display unit

100

is arranged using an FLC. Segment and common drive units

200

and

300

respectively drive signal and segment electrodes arranged in the display unit

100

in accordance with drive data supplied from the display control unit

50

. A temperature sensor

400

is arranged at a proper position (e.g., a portion at an average temperature) of the display unit

100

.

The display unit

100

includes a display screen

102

, an effective display area

104

in the display screen, and a frame unit

106

defining the effective display area

104

in the display screen

102

. In this embodiment, an electrode corresponding to the frame unit

106

is arranged on the display unit

100

and is driven to form a frame on the display screen

102

.

The display control unit

50

includes a controller

500

(to be described later with reference to

FIG. 11

) for controlling exchange of various data with the display unit

100

and the wordprocessor

1

. A data output unit

600

initializes driving of the drive units

200

and

300

on the basis of data from the controller

500

in accordance with the display data supplied from the wordprocessor

1

and data setting of the controller

500

. The data output unit

600

will be described later with reference to

FIG. 16. A

frame drive unit

700

generates the frame unit

106

on the display screen

102

on the basis of data output from the data output section

600

.

A power controller

800

properly transforms a voltage signal from the wordprocessor

1

and generates a voltage applied to the electrodes through the drive units

200

and

300

under the control of the controller

500

. A D/A conversion unit

900

is arranged between the controller

500

and the power controller

900

and converts digital data from the controller

500

into analog data which is then supplied to the power controller

800

. An A/D conversion unit

950

is arranged between the temperature sensor

400

and the controller

500

. The A/D conversion unit

950

converts analog temperature data from the display unit

100

into digital data. This digital data is supplied to the controller

500

.

The wordprocessor

1

has a host device function serving as a source for supplying display data to the display unit

100

and the display control unit

50

. The wordprocessor

1

can be replaced with any other host device such as a computer or an image reading apparatus. In this embodiment, the wordprocessor

1

can exchange various data. The data to be supplied to the display control unit

50

are as follows:

D: A signal including address data and a horizontal sync signal for designating display positions of image data and other data. The address data for accessing a display address (corresponding to the display device on the effective display area

104

) of the image data can be output as address data without modifications if the host device is the one having a VRAM corresponding to the effective display area

104

. In this embodiment, the wordprocessor

1

superposes the signal D on the horizontal sync singal or a retrace (flyback) erase signal and supplies the composite signal to the data output unit

600

.

CLK: A transfer clock for image data PD

0

to PD

3

, which is supplied to the data output unit

600

.

PDOWN: A signal for acknowledging a system power-off state, which is supplied as a nonmaskable interrupt signal (NMI) to the controller

500

.

Data supplied from the display control unit

50

to the wordprocessor

1

are as follows:

PON/OFF: A status signal for acknowledging the end of rising/falling of the display control unit

50

in the system power-on/-off operation, which status signal is output from the controller

500

.

Light: A signal for designating an ON/OFF operation of a light source FL combined with the display unit

100

, which is output from the controller

500

.

Busy: A sync signal for instructing the wordprocessor

1

so as to wait for transfer of the signal D or the like in order to perform various setting operations in the initialization and display operation of the display control unit

50

. That is, the signal Busy is received by the wordprocessor

1

and is output from the controller

500

through the data output unit

600

.

(2) Arrangement of Display Unit

FIGS. 2 and 3

are an exploded perspective view and a sectional view, respectively, showing an arrangement of the display unit

100

using an FLC. Referring to

FIGS. 2 and 3

, the display unit

100

includes upper and lower glass plates or substrates

110

and

120

. Polarizers are arranged in a relationship of crossed nicols with respect to the orientation of the FLC element. A wiring unit

122

is arranged on the inner surface of the lower glass substrate

120

and comprises transparent electrodes

124

of, e.g., ITO and an insulating film

126

. A metal layer

128

is formed on the transparent electrodes

124

if the resistances of the electrodes must be low. The metal layer

128

can be omitted when the display device is compact. A wiring unit

112

is formed on the upper glass substrate

110

and comprise transparent electrodes

114

and an insulating layer

116

in the same manner as those in the wiring unit

122

on the lower glass substrate

120

.

The direction of the wiring unit

122

is perpendicular to that of the wiring unit

112

. For example, if the long side of the A5-size effective display area

104

is used as a horizontal scanning direction and has a resolution of 400×800 dots, 400 or 800 transparent electrodes are formed in the wiring unit corresponding to the effective display area. In this embodiment, the horizontal scanning direction serves as a common electrode side. 400 transparent electrodes

114

are formed in the upper wiring unit

112

, while 800 transparent electrodes

124

are formed in the lower wiring unit

122

. Transparent electrodes

150

and

151

are formed at an inner portion of the display screen

102

which corresponds to the outer portion of the effective display area

104

. The transparent electrodes

150

and

151

are formed in the same shape as or a shape different from that of the data display transparent electrodes

124

and

114

.

A seal member

130

for an FLC

132

comprises a pair of orientation films

136

for aligning an axis (i.e., Z-axis in

FIG. 44

) of the FLC element, a spacer

134

for defining the distance between the pair of orientation films

136

so as to establish the first or second stable state shown in

FIG. 46. A

seal material

140

such as an epoxy resin is used to seal the FLC

132

. A filling port

142

is used to fill the FLC

132

into the seal member

130

. A filling port seal member

144

seals the filling port

142

after the FLC

132

is filled.

Segment and common drive elements

210

and

310

serve as elements constituting the segment drive unit

200

and the common drive unit

300

, respectively. In this embodiment, 10 and 5 ICs each for driving 80 transparent electrodes are arranged for the segment and common drive units

200

and

300

, respectively. The segment drive elements

210

are formed on a substrate

280

, and the common drive elements

310

are formed on a substrate

380

. Flexible cables

282

and

382

are connected to the substrates

280

and

380

, respectively. A connector

299

connects the flexible cables

282

and

383

to the display drive unit

50

shown in FIG.

1

.

Outlet electrodes

115

and

125

are formed continuously with the transparent electrodes

114

and

124

and are connected to the drive elements

310

and

210

through film-like conductive members

384

and

284

, respectively.

In this embodiment, light is emitted from the light source FL from the outer surface of the lower glass substrate

120

, and the FLC elements are selectively driven in the first or second stable state, thereby displaying information.

(3) General Description of Display Control

When the display unit shown in

FIGS. 2 and 3

is used, the following problems associated with the characteristics of the FLC element are presented. By paying attention to these characteristics, an appropriate arrangement of the display unit

100

using the FLC element and its appropriate drive control are realized.

(3.1) Frame of Display Unit

When the display unit

100

is arranged, as shown in

FIGS. 2 and 3

, the area of the display screen

102

corresponding to the range of the matrix constituted by the common transparent electrodes

114

and the segment transparent electrodes

124

serves as an actual image data display area, i.e., the effective display area

104

. However, an area including at least part of the inner area of the seal member

140

and falling outside the matrix constituted by the common and segment transparent electrodes is preferably used as the display screen

102

so as to perfectly use the effective display area

104

.

However, when the common and segment transparent electrodes are arranged in the matrix form, only common or segment transparent electrodes run through the part of the inner area of the seal member

140

. Therefore, the FLC in this part cannot be sufficiently driven for image data display and therefore is held in a floating state. In this state, the FLC can be set in the first or second stable state. Therefore, a light-transmitting area (white) and a non-light-transmitting area (black) are mixed in such an area corresponding to the above part in the display screen

102

. As a result, a clear display cannot be obtained, and the effective display area

104

cannot be clearly defined, so that the operator may be confused with the unclear display area.

In order to prevent the above phenomenon, the transparent electrodes

151

and

150

(to be referred to as frame transparent electrodes) crossing the common and segment transparent electrodes are arranged outside the effective display area

104

. By properly driving the frame transparent electrodes

151

and

150

, the frame unit

106

is properly defined. For example, 16 electrodes

151

and 16 electrodes

150

are arranged at each side of the common transparent electrodes

114

on the upper glass substrate

110

and each side of the segment transparent electrodes

124

on the lower glass substrate

120

, respectively. For illustrative convenience, only one electrode represents the electrodes in each of the glass substrates

120

and

110

in FIG.

2

.

(3.2) Drive Waveform of Display Element

One of the functions of the FLC display element is a memory function. A problem associated with drive waveforms and caused by applied time dependency of a threshold value (to be described later) and its solution will be described with reference to FIG.

4

.

Referring to

FIG. 47

, of the pixels constituted by intersections between scanning electrodes com

1

. . . , com

5

, . . . and signal electrodes seg

1

. . . , seg

5

, . . . , each hatched pixel corresponds to a “bright” (white) state and a hollow pixel corresponds to a “dark” (black) state. These states correspond to the first and second stable states of the FLC, respectively. A display state on the signal electrode seg

1

in

FIG. 47

is taken into consideration. Pixels A corresponding to the scanning electrode com

1

are set in the “bright” state, while all other pixels B are set in the “dark” state.

FIG. 5A

shows a time sequence of a scanning signal, an information signal applied to the signal electrode seg

1

, and a voltage applied to the pixel A.

When driving is performed, as shown in

FIG. 5A

, and the scanning electrode com

1

is scanned, a voltage 3V exceeding a threshold value Vth

2

is applied to the pixel A in time Δt

2

, and the pixel A is set in one stable state, i.e., the “bright” state regardless of the previous state. Thereafter, during scanning of the electrodes com

2

, . . . , com

5

, . . . , the voltage −V is continuously applied to the pixel A since the voltage does not exceed the threshold voltage −Vth, as shown in FIG.

5

A. In this case, the pixel A maintains the “bright” state.

When one type of signal (corresponding to the “dark” state in this case) is continuously applied to one signal line, a display state is degraded by a large number of scanning lines during high-speed driving.

The above drawback is typically illustrated in FIG.

4

. The drive voltage V is plotted along the abscissa and the pulse width ΔT (applied time) is plotted along the ordinate. As is apparent from

FIG. 4

, the threshold voltage Vth (drive voltage) depends on the applied time. The shorter the applied time becomes, the steeper the drive voltage curve becomes. Assume that the drive waveform shown in

FIG. 5A

is used, a large number of scanning lines are used, and a high-speed element is driven. Since the voltage −V is continuously applied during com

2

and subsequent scanning cycles although the state is changed into the “bright” state during com

1

scanning, the state can be changed by a low threshold value by an integration of the applied time until the scanning electrode com

1

is scanned again. Therefore, the pixel A may be changed to the “dark” state.

In order to prevent this, the waveforms shown in

FIG. 5B

are used. According this method, the scanning and information signals are not continuously supplied. A predetermined time interval Δt′ is provided as an auxiliary signal application interval. During this interval, an auxiliary signal is applied to set the signal electrode at a ground potential. While the auxiliary signal is applied, the scanning electrodes are also grounded. The voltage applied across the scanning and signal electrodes is the reference voltage, thereby substantially eliminating voltage applied time dependency of the threshold voltage for the FLC, as shown in FIG.

4

. Therefore, a change from the “bright” state to the “dark” state of the pixel A can be prevented. This is also applicable to other pixels.

A preferable driving method is practiced such that the waveforms shown in

FIG. 6

are applied to the scanning and signal electrodes.

Referring to

FIG. 6

, a scanning signal is an alternating pulse signal of ±2 V. An information signal is supplied to the signal electrodes in synchronism with the alternating current pulse signal and has two phases, i.e., +V corresponding to “bright” information and −V corresponding to “dark” information. Assume that the time interval Δt′ is provided as the auxiliary signal applied interval while com n (the nth scanning electrode) and com n+1 (the (n+1)th scanning electrode) are selected when the scanning signal is regarded as a time-serial signal. During this interval Δt′, an auxiliary signal having a polarity opposite to that of the signal applied to the signal electrodes during com n scanning. In this case, the time-serial signal pulses applied to the respective signal electrodes are given as, e.g., seg

1

to seg

3

shown in FIG.

6

. That is, auxiliary signals α′ to ε′ have polarities opposite to those of information signals α to ε, respectively. For this reason, when the voltage applied to the pixel A is observed in a time-serial manner with reference to

FIG. 6

, even if the same information signal is continuously applied to one signal electrode, the voltage actually applied to the pixel A is not inverted until desired information (“bright” in this case) formed during com

1

scanning is written because the alternating current voltage having a level lower than the threshold voltage Vth is applied and because voltage applied time dependency of the threshold voltage for the FLC is eliminated.

The above two types of drive waveform are model examples for illustrative convenience. In the subsequent embodiments, different appropriate drive waveforms are used for driving of the effective display area

104

and the frame unit

106

in the display screen

102

and in accordance with actual access modes. The above-mentioned waveforms have positive and negative half cycles which are symmetrical with each other. However, the positive and negative cycles need not be symmetrical.

(3.3) Drive Voltage of Display Element

The FLC display element according to this embodiment is oriented such that its liquid crystal molecules have bipolar moments directed in the direction of the electric field, and this orientation state is kept unchanged even after the electric field is withdrawn, as previously described above.

The change from one stable state to the other stable state varies depending on voltage values applied to the display elements.

FIGS. 7A and 7B

show changes in drive voltage (applied voltage) and FLC transmittance as a function of time.

FIG. 7A

shows a case in which the drive voltage exceeds the threshold voltage −Vth. In this case, the transmittance curve allows a change from one stable state to the other stable state (e.g., from “bright” state to the “dark” state).

FIG. 7B

shows a case in which the drive voltage does not exceed the threshold voltage. In this case, the liquid crystal molecules behave in response to the drive voltage to some extent but their orientation directions are not inverted. In other words, the transmittance of the liquid crystal is changed to the original value.

In addition, the threshold value varies depending on the types and drive temperatures of the FLC, as will be described with reference to FIG.

8

.

As described with reference to

FIGS. 4 and 6

, the required drive voltage values are the positive and negative values of the scanning signal, positive and negative values of the information signal, and the reference potential, i.e., a total of five voltage values. These drive voltages are generated by an apparatus (to be described later) using an appropriate power source.

As is apparent from the above description, appropriate temperature compensation in consideration of the threshold value and the like must be performed to set the drive voltages.

(3.4) Temperature Compensation

Temperature compensation must be particularly taken into consideration for FLC display control of this embodiment due to the following reason. Closely associated drive conditions (e.g., a pulse width (voltage applied time) and a drive voltage value) for the SmC*-phase FLC greatly vary depending on FLC temperatures. The drive condition range at a predetermined temperature is narrowed. Therefore, fine temperature compensation during FLC driving is required.

Temperature compensation is performed by detection of an FLC temperature, detection of an ambient temperature on the display screen

102

in practice, setting of drive voltage values corresponding to the detected temperature, and setting of a pulse width, i.e., one horizontal (1H) scanning period. It is very difficult to perform manual compensation in consideration of an operating speed and the like of the display screen

102

. Therefore, temperature compensation is an essential factor in FLC display element control.

Changes in FLC drive conditions, e.g., changes in pulse width, drive voltage values, and the like as a function of temperature will be described below.

FIG. 4

shows the relationship between the drive voltage value and the pulse width, as described above. The smaller the pulse width ΔT becomes, the higher the drive voltage V becomes.

The pulse width ΔT has an upper limit ΔTmax and a lower limit ΔTmin due to the following reason. During so-called refresh driving, when a frequency f (=1/ΔT) of the applied voltage is about 30 Hz or less, flickering occurs, thus limiting the lower frequency, i.e., ΔTmax. When the frequency f is a video rate or more, i.e., the speed represented by the frequency f exceeds a data transfer speed of the wordprocessor

1

, communication between the display screen

102

and the wordprocessor

1

becomes impossible, thereby providing an upper limit of the frequency f, i.e., ΔTmin.

The drive voltage V also has an upper limit Vmax and a lower limit Vmin. These limits are primarily caused by various functions of the drive units.

FIG. 8

shows the relationship between the drive voltage and the temperature, in which the temperature Temp is plotted along the abscissa and a logarithm of the drive voltage, i.e., logV is plotted along the ordinate. More specifically,

FIG. 8

shows changes in threshold voltage value Vth in accordance with changes in temperatures when the pulse width ΔT is fixed. As is apparent from

FIG. 8

, the higher the temperature becomes, the lower the drive voltage becomes.

As is apparent from

FIGS. 4 and 8

, when the temperature is increased, the drive voltage value is decreased or the pulse width is decreased.

FIG. 9

shows curves for actually driving the display element in accordance with the above various conditions. In other words,

FIG. 9

shows a look-up table (to be described later) in an analog manner. The look-up table stores various drive condition data corresponding to the values detected by the temperature sensor

400

.

The temperature Temp is plotted along the abscissa of

FIG. 9

, and the drive voltage V and the frequency f (=1/ΔT) are plotted along the ordinate. When the frequency f is fixed and the temperature Temp is increased, the drive voltage value V is decreased and becomes lower than Vmin in a temperature range (A). A higher frequency f is given as a fixed value at a temperature (D), and therefore the corresponding drive voltage V is determined. The above operations are repeated in temperature ranges (B) and (C) and at a temperature (E). The shapes of the resultant curves vary depending on liquid crystal properties. The number of stepwise or saw-toothed waves can be properly determined.

(3.5) Drive Method of Display Unit

In this embodiment, in the data access mode of the display screen

102

, line access for every horizontal scanning line (i.e., a line corresponding to the common transparent electrode

114

) and block access in units of blocks each consisting of several lines can be performed. The display screen

102

is scanned in either access mode. A block or line associated with access in the form of real address data from the wordprocessor

1

can be recognized.

FIG. 10

shows m blocks BLK

1

, . . . , BLK, . . . BLKm (1≦l≦m) obtained by dividing the effective display area

104

and including a predetermined number of lines. In this embodiment, 400 common transparent electrodes

114

(i.e., 400 lines) are arranged in the vertical scanning direction. The effective display area

104

is divided into 20 blocks (m=20) each comprising 20 lines. When block access is to be performed, display contents of all lines included in each block are erased, and data are sequentially written in the block from the head line to the last line.

When the display unit

100

is arranged, as shown in

FIGS. 2 and 3

, the FLC element has a memory function and the data which need not be updated is left unchanged, i.e., screen refresh need not be performed. Therefore, only data to be updated is accessed on the display screen.

In this embodiment, refresh driving for continuously refreshing the effective display area

104

from the head line to the last line, i.e., refresh driving equivalent to that for a display unit without a memory function, and partial rewrite driving for rewriting only a block or line subjected to updating can be performed. When the wordprocessor

1

transmits refresh data in the same manner as in refreshing of the display unit without a memory function, a refresh operation is performed. If data updating is required and the image data of the corresponding block or line is transmitted, the partial rewrite operation is performed.

The erase operation of the block and the write operation of the line are performed on the basis of the temperature compensation data described in (3.4). The temperature compensation data is updated in an interval between the end of access of the last line and the start of access of the head line in the refresh drive mode, i.e., in a vertical retrace interval. The partial rewrite operation is performed every predetermined interval by a constant period interrupt.

(3.6) Display Screen Clearing

Since the FLC element according to this embodiment has a memory function, the first or second stable state can be maintained although a voltage is not applied. In other words, the previous screen state is maintained unless a voltage is applied.

The display screen

102

(at least the effective display area

104

) is preferably cleared when the power switch is turned off. Then, for example, the power-off state can be confirmed by the state of the display screen

102

. A display screen clearing state may be changed during the power-off state due to some reason and insignificant data may be displayed on the screen. Therefore, it is preferable to clear the effective display area

104

in order to prevent mixing of the actual display data and the insignificant data when the power switch is turned on.

Based on the above consideration, the effective display area

104

is cleared and the frame unit

106

is formed in this embodiment when the power switch is turned on. The effective display area

104

and the frame unit

106

are cleared when the power switch is turned off. Block erasure described with reference to (3.5) is performed for all blocks when the effective display area

104

is cleared.

The above clear operations are performed without screen erase data (e.g., “all white” data) from the wordprocessor

1

serving as a host device. The load of the wordprocessor

1

is reduced, and data transfer can be omitted, thereby achieving high-speed operation.

(4) Arrangement of Respective Components in Display Control Unit

The respective components in the display control unit

50

for realizing all functions described in “(3) General Description of Display Control” will be described in detail.

(4.1) Main Symbols

Signals and data which are exchanged between the components are summarized as follows:

Signal

Signal Name

Output Side

Input Side

Content

Tout

System clock

Controller

Data Output

Reference clock for the

500 (PORT2)

Unit 600

operation of the data output

unit 600. Time on the control

program is synchronized with

time on the display screen.

The reference clock is input

to controller 500 so as to

guarantee constantly a stable

one horizontal scanning

period.

{overscore (IRQ1)}

Line access

Data output

Controller

One of the interrupt signals

interrupt

unit 600

500 (PORT5)

is input to the controller

{overscore (IRQ2)}

Block access

Data output

Controller

500 in response to the

interrupt

unit 600

500 (PORT5)

interrupt signal IRQ

generated by the data output

unit 600 in accordance with

the real address data

supplied from wordprocessor 1.

MR

Memory ready

MR generation

Controller

Signal for establishing a

unit

500 (PORT5)

timing of access of the

D/A conversion unit 900.

{overscore (INTR)}

A/D conver-

A/D conversion

Controller

Signal for acknowledging the

sion end

unit 950

500 (PORT6)

end of A/D conversion of

acknow-

the detected temperature

ledgement

data.

IBSY

Busy

Controller

Data output

This signal is output

500 (PORT6)

unit 600

to the data output unit 600

so as to signal it to word-

processor 1

Light

Light source

Controller

Word-

This signal requests lighting

control

500 (PORT6)

processor 1

(ON) and nonlighting (OFF)

signal

of the light source FL.

P ON/OFF

Power status

Controller

Word-

This signal requests process-

500 (PORT6)

Processor 1

ing in the ON/OFF operation

of the power source.

DACT

Panel access

Controller

Data output

This signal discriminates

identifi-

500 (PORT6)

unit 600

access/nonaccess of the

cation

and Data

(DACT gener-

effective display area 104.

signal

output unit

ation unit)

600 (GATE)

array 680)

{overscore (RD)}

Read signal

Controller

A/D conver-

This signal is a control

500 (PORT7)

sion unit

signal for reading data from

950 and Data

each input unit.

output unit

600

{overscore (WR)}

Write signal

Controller

A/D conver-

This signal is a control

500 (PORT7)

sion units

signal for causing each

950 and 900

unit to write data.

and Data

output unit

600

DD0-DD7

Data on

Each

Each

system data

component

component

bus

A0-A15

Address

Controller

Data output

This signal is used to cause

signal

500 (PORT1 &

unit 600

data output unit 600 to

PORT4)

select each unit.

{overscore (RES)}

Reset signal

Controller

Controller

This signal resets the CPU

500 (Reset

500 (CPU

in the controller 500.

unit 507)

501)

{overscore (NMI)}

Nonmaskable

Word-

Controller

This signal is set as {overscore (NMI)}

(PDOWN)

interrupt

processor 1

500 (CPU)

in response to PDOWN for

(Power-off

signaling power-off from

interrupt)

the wordprocessor 1 to allow

the controller 500 to perform

proper processing.

E

Clock

Controller

D/A conver-

This clock is output after

500 (CPU)

sion unit

its pulse width is changed

900 and Data

in response to the signal MR

output unit

so as to properly access

600

the D/A conversion unit 900

or the data output unit 600.

D0-D3

Image data

Data output

Segment

These data are generated

unit 600

drive

from image data input as the

unit 200

signal D from the word-

processor 1.

D

Word-

Data output

Signal including data to be

processor 1

unit 600

displayed, real address data,

and the horizontal sync

signal.

CLK

Transfer

Word-

Data output

Transfer clock for the

clock

processor 1

unit 600

signal D.

A/{overscore (D)}

Address/

Data output

Data output

Signal for discriminating

data

unit 600

unit 600

whether the data sent as

discrimi-

the signal D is the image

nation

data or the real address

signal

data.

RA/D

Real address

Data output

Data output

This signal is used to

data

unit 600

unit 600

designate a data display

(Data input

(Register

position and corresponds

unit 601)

630)

to one line. This signal

is superposed on the hori-

zontal sync signal and is

derived from data input from

the wordprocessor 1.

IRQ

Interrupt

Data output

Controller

This signal is output to the

signal

unit 600

500

controller 500 in response to

the signal A/D and is supplied

to the controller 500 as

IRQ1 or IRQ2.

IRQ3

Internal

Controller

Controller

Internal interrupt for

interrupt

500 (Timer)

500 (Timer)

releasing an inoperative

state (sleep state).

{overscore (FEN)}

Frame end

Data output

Data output

This signal is used for

signal

unit 600

unit 600

horizontal frame formation.

({overscore (FEN)} gene-

(Gate array

ration unit)

680)

{overscore (DS0)}

Chip select

Data output

A/D conver-

These signals are generated

signal

unit 600

sion unit

in accordance with the

(Device

950

signals A10 to A15 from the

{overscore (DS1)}

Chip select

selector)

D/A conver-

controller 500 and serve

signal

sion unit

as the chip select signals

900

from the

{overscore (DS2)}

Chip select

Data output

controller 500.

signal

unit 600

(Register

selector)

{overscore (DS3)}

Chip select

Unused

signal

{overscore (LATH)}

Latch signal

Data output

Segment

This signal is used to cause

unit 600

drive unit

the line memory to latch

200 (Segment

the data (image data) stored

drive

in the shift register in

element 210)

the element 210.

CA0-CA6

Line

Data output

Common

Selection signal of the

selection

unit 600

drive unit

horizontal scanning output

signal

300 (Common

line for the element 310.

drive

CA5 and CA6 are used to select

element 310)

the block and CA0 to CA4 are

used to select the line in

the block.

{overscore (CCLR)}

Clear

Data output

Common

signal

unit 600

drive unit

300

CEN

Enable

Data output

Common

signal

unit 600

drive unit

300

CM1, CM2

Waveform

Data output

Common

This signal defines the output

defining

unit 600

drive unit

waveform of the common drive

signal

300

element 310.

{overscore (SCLR)}

Clear

Data output

Segment

signal

unit 600

drive unit

200

SEN

Enable

Data output

Segment

signal

unit 600

drive unit

200

SM1, SM2

Waveform

Data output

Segment

This signal defines the output

defining

unit 600

drive unit

waveform of the segment drive

signal

200

element 210.

{overscore (V1)}-{overscore (V4)}

Frame drive

Data output

Frame drive

This signal defines an output

{overscore (CVc)}, {overscore (SVc)}

unit switch

unit 600

unit 700

of the frame drive unit 700.

signal

V1, V2

Voltage

Power

Common

This signal defines an output

signal

controller 800

drive unit

voltage (+ and −) of the

300

element 310.

V3, V4

Voltage

Power

Segment

This signal defines an output

signal

controller 800

drive unit

voltage (+ and −) of the

200

element 210.

Vc

Voltage

Power

Drive units

This signal defines the

signal

controller 800

200 and 300

reference (“0”) of the output

voltage.

(4.2) Controller

FIG. 11

shows an arrangement of the controller

500

. The controller

500

includes a CPU

501

in the form of, e.g., a microprocessor for controlling the respective components in accordance with a flow chart shown in

FIG. 32

, a ROM

503

for storing a program corresponding to the flow chart of FIG.

32

and various tables data, and a RAM

505

serving as a working memory for storing processed data during a control sequence of the CPU

501

.

The controller

500

also includes I/O port units PORT

1

to PORT

6

. The I/O port units PORT

1

to PORT

6

have ports P

10

to P

17

, ports P

20

to P

27

, ports P

30

to P

37

, ports P

40

to P

47

, ports P

50

to P

57

, and ports P

60

to P

67

. A port unit PORT

7

serves as an output port unit which has ports P

70

to P

74

. I/O setting registers DDR

1

to DDR

6

(data direction registers) in the controller

500

are used to set switching between the input and output directions of the port units PORT

1

to PORT

6

. In this embodiment, the ports P

13

to P

17

(corresponding to signals A

3

to A

7

) in the port unit PORT

1

, the ports P

21

to P

25

in the port unit PORT

2

, the ports P

40

and P

41

(corresponding to signals A

8

and A

9

) in the port unit PORT

4

, the ports P

53

to P

57

in the port unit PORT

5

, the port P

62

in the port unit PORT

6

, the ports P

72

to P

74

in the port unit PORT

7

, and terminals MP

0

, MP

1

, and STBY of the CPU

501

are unused.

The controller

500

includes a reset unit

507

for resetting the CPU

501

and a clock generation unit

509

for supplying a reference operation clock (4 MHz) to the CPU

501

.

Each of timers TMR

1

, TMR

2

, and SCI has a reference clock generator and a register, and the reference clock can be frequency-divided in accordance with a value set in the register. More specifically, the timer TMR

2

frequency-divides the reference clock in accordance with a set value of the register and generates a signal Tout serving as a system clock for the data output unit

600

. The data output unit

600

generates a clock signal which defines one horizontal scanning period (1H) of the display unit

100

on the basis of the signal Tout. The timer TMR

1

is used to synchronize the operating time of the program with the 1H on the display screen

102

. This synchronization operation is performed in accordance with a set value in its register.

The timers TMR

1

and TMR

2

supply an internal interrupt signal IRQ

3

to the CPU

501

at the time of time-up of the period based on the preset value and at the start of time measurement at the time-up timing. The CPU

501

accepts the interrupt signal IRQ

3

as needed.

The timer SCI is unused in this embodiment.

Referring to

FIG. 11

, an address bus AB and a data bus DB are connected between the respective components and the CPU

501

. A handshake controller

511

causes the port units PORT

5

and PORT

6

to handshake with the CPU

501

.

(4.3) Memory Space of ROM

(4.3.1) Arrangement of Memory Space

FIG. 12

shows an arrangement of the memory space in the ROM

503

. Data for designating and accessing the A/D conversion unit

950

and the D/A conversion unit

900

are stored in a memory area at A000H (where H refers to hexadecimal notation) to A3FFH and a memory area at A400H to A7FFH, respectively. Data for designating a display unit drive register (

FIG. 16

) for accessing the data output unit

600

are stored at A800H to ABFFH.

A memory area at C000H to E7FFH is defined as an area to be referred to in response to real address data RA/D output from the wordprocessor

1

. This area comprises a jumping table for discriminating if the address data sent in the block access mode is associated with the block head line, and a line table for designating a common line to be driven in response to the received real address data RA/D.

An area at E800H to EFFFH is used to store various parameters associated with control (to be described later) with reference to

FIGS. 33 and 36A

to

38

. The area at E800H to EFFFH has a block related data area (E800H˜) for storing the number of blocks (20 blocks in this embodiment), a D/A conversion unit related data area (E900H˜) for storing data for controlling the D/A conversion unit

900

so as to variably set the drive voltages for the transparent electrodes, a TMR

2

designation data area (EA00H˜) for storing data TCONR for designating the timer TMR

2

for outputting the clock Tout serving as the reference for setting one horizontal scanning period (1H) on the display unit

100

, and timer TMR

1

designation data areas (respectively EB00H˜, EC00H˜, and ED00H˜) for storing register designation data CNTB, CNTL, and CNTBB for the timer TMR

1

for setting a delay time so as to synchronize the operating time on the display unit

100

and the control operating time.

An area at F000H is a program area for storing programs corresponding to the processing sequences to be described with reference to

FIG. 32

,

FIG. 33

, and

FIGS. 36A

to

38

.

(4.3.2) Jumping Table

In this embodiment, the processing route varies depending on the fact as to whether the real address data RD/D sent from the wordprocessor

1

is related to the block head line due to the following reason. When the address data corresponding to the block head line is supplied, display contents of this block are cleared, and data are sequentially written for the respective lines in the block.

For this reason, it is required to check whether the real address data RA/D sent from the wordprocessor

1

corresponds to the block head line. It is assumed that each input real address data is compared with each address data of each block head line.

However, the above sequential comparison causes an increase in processing time when the number of objects to be compared is increased because the number of comparison steps is increased before and after the program of comparison and discrimination processing step.

In this embodiment, discrimination processing is performed using the jumping table, and the discrimination time is averaged.

For example, as shown in

FIG. 13

, if real address data from the wordprocessor

1

is “03”H (corresponding to line number “3”), this data is shifted by one bit to the left. Both two upper bits are set at logic “1”, and the LSB (least significant bit) is set at logic “0”, thereby obtaining data “C006”H after the offset. This data is used as address data on the memory space, and a code representing whether to indicate the block head line is stored at the address for the memory space. Then, the block head line can be discriminated for all read address data within identical execution intervals.

In addition, if the CPU

501

can use an index register (IX) and can process an instruction (e.g., “JUMP IX”) for jumping the operation to a step represented by the address of the index register, the offset data is stored in the IX, and a jump destination address is written in the jumping table. Therefore, proper processing can be immediately started when the above instruction is executed.

In the above embodiment, a CPU which can use the index register and the above instruction is used as the CPU

501

, and the jumping table (C000H to C31EH) corresponding to the line numbers (

0

to

399

) is arranged, as shown in FIG.

14

. The sequences (head addresses on the program areas of these sequences) are stored at the addresses of the jumping table.

FIG. 14

shows a block erase sequence BLOCK, a line write sequence LINE, and a sequence FLINE accompanied by last line write of the effective display area

104

in the block access mode. These sequences will be described in detail with reference to

FIGS. 36A

to

36

D.

In the line access mode, it is determined whether the line is the last line so as to discriminate whether the temperature compensation data updating sequence is to be performed. Therefore, an object to be compared is one, and the above discrimination using the jumping address need not be performed.

(4.3.3) Line Table

The real address data RA/D must be changed depending on the type of the common drive unit

300

. For example, the drive unit

300

comprises five common drive elements

310

each generating an 80-bit output (80 bits are divided into four blocks). Furthermore,

400

scanning lines are arranged as common lines. In order to select one scanning line:

(1) One of the five common drive elements

310

is selected;

(2) One of the four blocks of the elements

310

is selected; and

(3) One of the 20 lines in the block is selected.

In this embodiment, as shown in

FIG. 15

, a 2-byte line selection address is used. The 12th, to 8th bits of the line selection address are assigned to the element

310

, the sixth and fifth bits of the address are assigned to the block, and the fourth to 0th bits thereof are assigned to the line. Translation or a change from the real address data into the line selection address data can be performed substantially in the same manner as in processing (

FIG. 13

) described with reference to the jumping table. The line selection address data is developed in the line table.

In an arrangement of

FIG. 15

, a decoder

680

performs selection (element chip select) of the element

310

. With this arrangement as well as assignment of 12th to 8th bits for chip selection, the number of elements

310

can be extended to a maximum of 2

5

=32. In this case, 2560 scanning lines can be selectively driven.

(4.3.4) Storage Area for Various Parameters

In this embodiment, the drive conditions, i.e., the drive voltage, one horizontal scanning period, and delay data, of the display unit

100

are changed in accordance with the temperature conditions, thereby performing optimal drive control. Therefore, the drive conditions must be corrected for driving on the basis of the temperature measurement data from the temperature sensor

400

.

An area at E900H to EDFFH is an area for storing this correction data. In this embodiment, the following data are stored to achieve an effective read operation for parameters corresponding to temperatures (to be described later).

If one D/A conversion unit related data can correspond to TCONR and CNTB (CNTL or CNTBB) for one temperature range or one step in a given temperature range, the respective parameters corresponding to the temperatures can be stored in the memory areas having the same two lower bytes. In the same manner as described with reference to

FIG. 13

, temperature data output from the A/D conversion unit

950

or data obtained by properly processing the temperature data is used as two lower bytes of the address data, and the two upper bytes are sequentially updated to obtain parameters corresponding to the temperatures.

For example, if the temperature data is “0080”H, data at address “E980”H obtained by adding “0080”H to “E900”H is accessed to obtain the D/A conversion unit related data (drive voltage) corresponding to the temperature represented by this temperature data. Data at address “EA80”H obtained by adding “E980”H to “0100”H is accessed to obtain timer TMR

2

designation data TCONR (data for generating the fundamental clock which defines one horizontal scanning period on the display screen). Similarly, additions and access cycles are repeated to obtain data CNTB, CNTL, and CNTBB respectively corresponding to the detected temperatures.

(4.4) Data Output Unit

(4.4.1) Arrangement

FIG. 16

shows an arrangement of the data output unit

600

. The data output unit

600

includes a data input unit

601

, coupled to the wordprocessor

1

, for receiving a signal D and a transfer clock CLK. The signal D is obtained by adding an image signal to the horizontal sync signal and is output from the wordprocessor

1

. In this embodiment, the real address data is superposed during the horizontal sync signal period or the horizontal retrace erase interval. The data input unit

601

changes a data output path in accordance with the presence/absence of detection of the horizontal sync signal or the horizontal retrace erase interval and detects a superposed signal component as the real address data. The data input unit

601

outputs the real address data as RA/D. However, when the horizontal sync signal or the horizontal retrace erase interval is not detected, the signal component during detection is detected as image data. In this case, the data input unit

601

outputs the image data as image data bits D

0

to D

3

.

When the data input unit

601

detects the real address data input, it enables an address/data discrimination signal A/{overscore (D)} which is then input to an {overscore (IRQ)} generation unit

603

and a DACT generation unit

605

. The {overscore (IRQ)} generation unit

603

outputs an interrupt signal {overscore (IRQ)} in response to the signal A/{overscore (D)}. The interrupt signal {overscore (IRQ)} is supplied as an interrupt command {overscore (IRQ

1

)} or {overscore (IRQ

2

)} to the controller

500

. Therefore, an operation in the line or block access mode is performed. In response to the signal A/{overscore (D)}, the DACT generation unit

605

outputs the DACT signal for discriminating the presence/absence of access of the display unit

100

. The DACT signal is supplied to the controller

500

, an {overscore (FEN)} generation unit

611

, and a gate array

680

.

In response to a trigger signal output from an {overscore (FEN)} trigger generation unit

613

during an ON duration of the DACT signal, the {overscore (FEN)} generation unit

611

generates a signal {overscore (FEN)} for starting the gate array

680

. The {overscore (FEN)} trigger generation unit generates a trigger signal in response to a write signal {overscore (ADWR)} for causing the controller

500

to instruct the A/D conversion unit

950

to fetch temperature information from the temperature sensor

400

. In this case, the {overscore (FEN)} trigger generation unit

613

is selected in response to a chip select signal {overscore (DSO)} generated by a device selector

621

. More specifically, when the A/D conversion unit

950

is selected to cause the controller

500

to fetch temperature data, the {overscore (FEN)} trigger generation unit

613

is also selected, and frame driving is effected in response to the write signal {overscore (ADWR)}.

In response to a busy signal IBUSY from the controller

500

, a busy gate

619

outputs a signal BUSY signaling a busy state of the display control unit

50

to the wordprocessor

1

.

The device selector

621

receives signals A

10

to A

15

from the controller

500

and outputs chip select signals {overscore (DS

0

)} to {overscore (DS

2

)} for the A/D conversion unit

950

, the D/A conversion unit

900

and the data output unit

600

. A register selector

623

is started in response to the signal {overscore (DS

2

)} and sets a latch pulse gate array

625

on the basis of signals A

0

to A

4

from the controller

500

. The latch pulse gate array

625

selects each register in a register unit

630

and has the number of bits corresponding to the number of registers in the register unit

630

. The register unit

630

comprises 22 1-byte registers. The 22-bit latch pulse gate array

625

has bits respectively corresponding to the 22 registers in the register unit

630

. More specifically, when the register selector

623

performs bit selection of the latch pulse gate array

625

, the corresponding area or register is selected, and data read or write access is performed for the selected register through a system data bus in response to a read singal {overscore (RD)} or a write signal {overscore (WR)} from the controller

500

to the latch pulse gate array

625

.

The lower and upper byte registers RA/DL and RA/DU in the register unit

630

store the lower and upper one-bytes of the real address data RA/D under the control of a real address storage controller

641

.

Horizontal dot count data registers DCL and DCU respectively store lower and upper one-bytes of the data corresponding to the value corresponding to the number of dots (800 dots in this embodiment) in the horizontal scanning direction on the display screen. When a horizontal dot number counter

643

for counting clocks in response to the start of transfer of the image data D

0

to D

3

counts clocks, the number of which is equal to the value stored in the registers DCL and DCU, the counter

643

causes an {overscore (LATH)} generation unit

645

to generate a latch signal.

A drive mode register DM stores mode data corresponding to the line or block access mode.

Common line select address data registers DLL and DLU store lower and upper one-bytes of the 16-bit data shown in FIG.

15

. The data stored in the register DLL is output as block designation address data CA

6

and CA

5

(corresponding to the sixth and fifth bits in

FIG. 15

) and line designation address data CA

4

to CA

0

(corresponding to the fourth to 0th bits in FIG.

15

). The data stored in the register DLU is supplied to the decoder

650

and is output as chip select signals {overscore (CSO)} to {overscore (CS

7

)} for the common drive element

310

.

One-byte areas CL

1

and CL

2

store drive data supplied to the common drive unit

300

in driving (line write) of the common lines in the block access mode, and one-byte areas SL

1

and SL

2

store drive data supplied to the segment drive unit

200

during driving of the segment lines in the block access mode.

One-byte areas CB

1

and CB

2

store the drive data supplied to the common drive unit

300

at the time of driving of the common lines during block erasure in the block access mode. One-byte areas SB

1

and SB

2

store drive data supplied to the segment drive unit

200

in the same manner as in the one-byte areas CB

1

and CB

2

.

One-byte areas CC

1

and CC

2

store data supplied to the common drive unit

300

at the time of driving of the common lines during line write in the line access mode. One-byte areas SC

1

and SC

2

store drive data supplied to the segment drive unit

200

in the same manner as in the one-byte areas CC

1

and CC

2

.

The subsequent three one-byte areas store data for switching the frame drive unit

700

, and a total of 3 bytes are divided in units of 4 bits so as to form registers FV

1

, FCVc, FV

2

, FC

3

, FSVc, and FV

4

.

A multiplier

661

, for example, doubles the pulse signal Tout from the controller

500

. A 3 phase ring counter

663

A is used to divide one horizontal scanning period (1H) into four intervals, a 4 phase ring counter

663

B is used to divide 1H into three intervals, a 6 phase ring counter

663

C is used to divide 1H into two intervals, and a 12 phase ring counter

663

D is used not to divide 1H. The divided duration is called as ΔT. For example, if the 4 phase ring counter is used, 3ΔT is equal to 1H.

A multiplexer

665

selects one of the outputs from the ring counters

663

A to

663

D in accordance with the contents of a drive mode register DM, i.e., in accordance with data representing which division is employed. For example, when a ⅓ division is employed, the output from the 4 phase ring counter

663

is selected by the multiplexer

665

.

A 4 phase ring counter

667

receives the outputs from the ring counters

663

A to

663

D. A multiplexer

669

can be set in the same manner as in the multiplexer

665

.

FIG. 17

shows waveforms of the clock signal Tout, the output from the multiplier

661

, and the outputs from the ring counters

663

A to

663

D. When the multiplexer

665

selects one of the outputs from the ring counters

663

A to

663

D, 4ΔT/1H, 3ΔT/1H, 2ΔT/1H, or ΔT/1H is selected, and its output waveform is supplied as shift clocks to a shift register unit

673

(to be described later). The shift register

673

outputs on/off data for every ΔT. An output from the 4 phase ring counter

667

is selected by the multiplexer

669

, and its output waveform is supplied as a shift/load signal to the shift register unit

673

. An operation is set in accordance with a selected division value.

Referring back to

FIG. 16

, in the register unit

630

, on/off data for every ΔT of clear and enable signals {overscore (CCLR)} and CEN output to the common side drive unit

300

are stored in the areas CL

1

, CB

1

, and CC

1

; and on/off data for every ΔT of drive waveform defining signals CM

1

and CM

2

are stored in the areas CL

2

, CB

2

, and CC

2

. On/off data for every ΔT of a clear signal {overscore (SCLR)} and an enable signal SEN output to the segment drive unit

200

are stored in the areas SL

1

, SB

1

, and SC

1

; and on/off data for every ΔT of waveform defining signals SM

1

and SM

2

are stored in the areas SL

2

, SB

2

, and SC

2

.

In this embodiment, each signal data storage area is a 4-bit area, and one bit corresponds to the on/off data of 1ΔT. That is, a maximum division number of 1H in this embodiment is 4.

A multiplexer unit

671

is coupled to the areas CL

1

to SC

2

and selects signal data in the line write operation in the block access mode, the block erase operation in the block access mode, and the line write operation in the line access mode in accordance with the content of the drive mode register DM. The multiplexer unit

671

comprises a multiplexer MPX

1

for selecting 4-bit data for the signal {overscore (CCLR)} from the area CL

1

, CB

1

, or CC

1

, a multiplexer MPX

2

for selecting 4-bit data for the signal CEN, a multiplexer MPX

3

for selecting one of the 4-bit data for the signal CM

1

from the area CL

2

, CB

2

, or CC

2

, and a multiplexer MPX

4

for selecting 4-bit data for the signal CM

2

. A multiplexer MPX

5

selects one of the 4-bit data for the signal {overscore (SCLR)} from the area SL

1

, SB

1

, or SC

1

. A multiplexer MPX

6

selects 4-bit data for the signal SEN. A multiplexer MPX

7

selects one of the 4-bit data for the signal SM

1

from the area SL

2

, SB

2

, or SC

2

. A multiplexer MPX

8

selects 4-bit data for the signal SM

2

.

A shift register unit

673

comprises parallel/serial (P/S) conversion shift registers P/S

1

to PS/

8

respectively connected to the multiplexers MPX

1

to MPX

8

in the multiplexer unit

671

. An output from a multiplexer

665

is output as a shift clock signal to define an output interval ΔT of the 1-bit on/off data. An output from a multiplexer

669

is output as a preset signal for performing an operation in accordance with a preset division number.

A multiplexer unit

675

comprises multiplexers MPX

11

to MPX

18

respectively coupled to the shift registers P/S

1

to P/S

8

and outputs P/S-converted on/off data on the basis of the bit selection data (stored in the register DM) of 4-bit on/off data stored in the registers CL

1

to SC

2

.

An output unit

677

performs the same operation as those of the shift register unit

673

and the multiplexer

675

for the registers FV

1

, FCVc, FV

2

, FV

3

, FSVc, and FV

4

. A gate array

680

is enabled in response to the signals DACT and {overscore (FEN)} to gate switch signals {overscore (V

1

)} to {overscore (V

4

)}, {overscore (CVc)} and {overscore (SVc)} to the frame drive unit

700

.

An MR generation unit

690

outputs a signal MR to the controller

500

upon activation of the chip select signal DS

1

for the D/A conversion unit

900

, i.e., during access of the D/A conversion unit

900

, and changes the pulse width of a clock E generated by the CPU

501

.

(4.5) A/D Conversion Unit

FIG. 18

shows an arrangement of the A/D conversion unit

950

. The conversion unit

950

comprises an A/D converter

951

and an amplifier

953

for amplifying a detection signal from the temperature sensor

400

to a level matching with sensitivity of the A/D converter

951

.

At the time of temperature detection, the controller

500

sends the chip select signal {overscore (DS

0

)} through the device selector

621

in the data output unit

600

. At the same time, the controller

500

generates the write signal {overscore (WR)} (illustrated as {overscore (ADWR)} in this case). In response to these signals, the A/D converter

951

converts an analog temperature detection signal obtained from the temperature sensor

400

through the amplifier

953

into a digital signal. At the end of A/D conversion, the A/D converter

951

activates the interrupt signal {overscore (INTR)}, thus signaling the end of A/D conversion to the controller

500

.

In response to the signal {overscore (INTR)}, the controller

500

supplies a read signal {overscore (RD)} (illustrated as {overscore (ADRD)} in this case) to the A/D converter

951

. The A/D converter

951

supplies the digital temperature data as signals DD

0

to DD

7

to the controller

500

through the system bus.

When refresh driving is performed to continuously refresh the display contents from the head line to the last line in the effective display area

104

, the temperature detection timing falls within the vertical retrace interval from the end of driving of the last line to the start of driving of the start line. When partial rewrite driving is performed to rewrite only the block or line subjected to display data updating, for example, this operation can be cyclically performed in response to a timer interrupt.

(4.6) D/A Conversion Unit and Power Controller

FIG. 19

shows an arrangement of the D/A conversion unit

900

and the power controller

800

.

The D/A conversion unit

900

comprises a D/A converter

901

and an amplifier

903

for amplifying an output from the D/A converter so as to match with a level in the next stage.

The power controller

800

comprises variable gain amplifiers

810

,

820

,

825

,

830

, and

840

for generating voltage signals VI, V

2

, VC, V

3

, and V

4

, respectively. The voltage V

1

is generated by supplying an output from the amplifier

903

to the amplifier

810

. The voltages V

2

, VC, V

3

, and V

4

are generated by supplying the output from the amplifier

810

to the amplifiers

820

,

825

,

830

, and

840

. The power controller

800

also includes an inverter

821

arranged between the amplifiers

810

and

820

, and an inverter

841

inserted between the amplifiers

810

and

840

.

The voltages V

1

and V

2

are respectively positive and negative drive voltages supplied to the common drive unit

300

. The voltages V

3

and V

4

are respectively positive and negative voltages supplied to the segment drive unit

200

. The voltage VC is the reference voltage applied to the drive units

200

and

300

. These voltage signals are also supplied to the frame drive unit

700

.

The gains of the amplifiers

810

,

820

,

825

,

830

, and

840

are set such that the ratio of differences in the voltages V

1

, V

2

, VC, V

3

, and V

4

to the VC is set to be 2:−2:0:1:−1 while the reference voltage VC is fixed.

When the drive voltages are changed in accordance with changes in temperature, the controller

500

generates the chip select signal {overscore (DS

1

)} through the device selector

621

in the data output unit

600

to select the D/A converter

901

. In this case, when the fundamental clock for operating the D/A converter

901

is different from that for operating the controller

500

, the signal {overscore (DS

1

)} is also supplied to the MR generation unit

690

in the data output unit

600

, thereby generating the signal MR. The controller

500

supplies the proper clock signal E to the D/A converter

901

. The controller

500

activates the write signal {overscore (WR)} (illustrated as {overscore (DAWR)} in this case) and the digital data DD

0

to DD

7

are supplied to the D/A converter

901

through the system bus. The D/A converter

901

converts the input data into an analog signal. The analog signal is then output through the amplifier

903

.

When the voltage V

1

is generated by the amplifier

810

, the voltages V

2

, VC, V

3

, and V

4

having the above ratio with respect to the voltage V

1

are generated.

In the arrangement shown in

FIG. 19

, the voltage V

2

and the like are generated with respect to the voltage V

1

. However, the output from the amplifier

903

may be supplied to the variable gain amplifiers

810

,

820

,

825

,

830

, and

840

. Alternatively, variable gain amplifiers capable of programming gain control may be used. The arrangement of the power controller

800

is not limited to the above arrangement, but various arrangements may be employed if a multi-value voltage can be generated in accordance with the operation modes of the drive units

200

and

300

.

(4.7) Frame Drive Unit

FIG. 20

shows an arrangement of the frame drive unit

700

. The frame drive unit

700

includes switches

710

,

715

,

720

,

730

,

735

, and

740

for connecting/disconnecting the supply paths of the voltage signals V

1

, VC, V

2

, V

3

, VC, and V

4

. The switches

710

,

715

,

720

,

730

,

735

, and

740

are controlled in response to switch signals {overscore (V

1

)}, {overscore (CVc)}, {overscore (V

2

)}, {overscore (V

3

)}, {overscore (SVc)}, and {overscore (V

4

)} supplied from the gate array

680

in the data output unit

600

through inverters

711

,

716

,

721

,

731

,

736

, and

741

.

When frame driving is performed, the switches

710

,

715

, and

720

are switched in accordance with the contents of the registers FV

1

, FCVc, and FV

2

arranged in the register unit

630

in the data output unit

600

, i.e., the states of the signals {overscore (V

1

)}, {overscore (CVc)}, and {overscore (V

2

)}. A signal having a waveform with three values for {overscore (V

1

)}, {overscore (VC)}, and {overscore (V

2

)} can be applied to the frame transparent electrodes

151

parallel to the common lines. The switches

730

,

735

, and

740

are switched in accordance with the contents of the registers FV

3

, FSVc, and FV

4

, i.e., the states of the signals {overscore (V

3

)}, {overscore (SVc)}, and {overscore (V

4

)}. A signal having a waveform with three values of V

3

, VC, and V

4

is applied to the frame transparent electrodes

150

parallel to the segment lines.

(4.8) Display Drive Unit

(4.8.1) Segment Drive Unit

FIG. 21

shows a schematic arrangement of the segment drive element

210

constituting the segment drive unit

200

. The segment drive element

210

includes a 4×20-bit shift register

220

for sequentially inputting image data D

0

to D

3

to produce 80-bit parallel data. The shift register

220

is operated in response to the shift clock SCLK. The segment drive element

210

also includes an 80-bit latch unit for latching 80-bit latch data when the image data D

0

to D

3

are sequentially supplied to the shift register

220

in the segment drive element

210

and 80-bit parallel data is set in all shift registers

220

in the 10 elements

210

, i.e., when the latch signal {overscore (LATH)} is supplied from the {overscore (LATH)} generation unit

645

in the data output unit

600

.

An input logic circuit

240

receives the signals {overscore (SCLR)}, {overscore (SEN)}, SM

1

, and SM

2

from the data output unit

600

, and performs predetermined logic processing. A control logic unit

250

generates segment drive waveform defining data corresponding to the bit data from the latch unit

230

in accordance with the operation data of the input logic circuit

240

. A switch signal output unit

260

has a level shifter and a buffer, both of which perform level shifting of the data output from the control logic unit

250

. A driver

270

receives the voltage signals V

3

, VC, and V

4

, is switched in response to an output from the switch signal output unit

260

, and supplies the voltage V

3

, VC, or V

4

to the segment lines S

80

to S

1

.

FIG. 22

shows a detailed arrangement of the segment drive element

210

shown in FIG.

21

. The shift register

220

includes a D flip-flop

221

corresponding to one bit, i.e., a one-segment line. The latch unit

230

includes a latch circuit

231

. The switch signal output unit

260

includes a level shifter

261

. The driver

270

includes switches

275

,

273

, and

274

for connecting/disconnecting the supply paths of the voltages VC, V

3

, and V

4

in response to the switch signals from the switch signal output unit

260

.

(4.8.2.) Common Drive Unit

FIGS. 23 and 24

show a schematic arrangement and a detailed arrangement, respectively, of the common drive element

310

constituting the common drive unit

300

. The common drive element

310

comprises an input logic circuit

340

. The input logic circuit

340

selects the block in response to the signals CA

5

, CA

6

, and CEN when the chip select signal {overscore (CS)} is supplied from the decoder

650

in the data output unit

600

. The input logic circuit

340

receives the line select signals CA

0

to CA

4

, and the signals {overscore (CCLR)}, CM

1

, and CM

2

and performs predetermined logic processing.

A decoder unit

345

selects a common line to be driven on the basis of the line data related to the signals CA

0

to CA

4

supplied from the input logic circuit

340

. Each element

310

can select a maximum of 80 lines. In this embodiment, 20 lines constitute one block, and four blocks are assigned to one element

310

. As shown in

FIG. 24

, a section which decodes 20-line data in the decoder unit

345

is surrounded by the dotted line.

A control logic unit

350

receives the drive data related to the signals CM

1

, CM

2

, and {overscore (CCLR)} supplied from the input logic circuit

340

and generates drive waveform defining data for the block selected by the input logic circuit

340

or the line selected by the decoder unit

345

.

A switch signal output unit

360

includes a level converter and a buffer and performs level conversion of the data generated by the control logic unit

250

. A driver

370

receives the voltage signals V

1

, VC, and V

2

, is switched in response to the output from the switch signal output unit

360

, and selectively supplies the voltage signal V

1

, VC, or V

4

to the common lines C

1

to C

80

.

This embodiment comprises five common elements

310

. In other words, the effective display area

104

corresponds to 400 common lines.

The common drive element

310

shown in

FIG. 24

also includes a level converter

361

, and switches

375

,

371

, and

372

for connecting/disconnecting the supply paths of the voltages VC, V

1

, and V

2

in response to the switch signals from the switch signal output unit

360

.

(4.9) Drive Waveform

(4.9.1) General Description of Display Unit

FIG. 25

shows a schematic arrangement of the display unit

100

. The common lines com correspond to the common transparent electrodes

114

formed on the upper substate

110

, and the segment lines seg correspond to the segment transparent electrodes

124

formed on the lower substrate

120

. An FLC is filled between the common and segment lines com and seg. Frame common lines Fcom are formed parallel to both sides of the common lines com, and frame segment lines Fseg are formed parallel to both sides of the segment lines seg. A set of intersections (

FIG. 25

) between the common and segment lines com and seg constitute the effective display area

104

on the display screen

102

. A set of intersections between the frame common and segment lines Fcom and Fseg and the segment lines seg and a set of intersections between the frame segment lines Fseg and the common lines com constitute the frame unit

106

outside the effective display area

104

.

Referring to

FIG. 25

, only four common lines com and four segment lines seg and only one frame common line Fcom and one frame segment line Fseg are illustrated for the sake of simplicity. However, in practice,

400

common lines com and

800

segment lines seg are arranged, and each line can be independently driven. 16 frame common lines Fcom and 16 frame segment lines Fseg are arranged at corresponding sides and are simultaneously driven, as described above.

(4.9.2) Drive Mode of Display Unit

In this embodiment, the display unit

100

is driven as follows.

As described in (3.5), in the effective display area

104

, in the block access mode, a block is erased and the write operation is performed in units of lines. In the line access mode, the write operation is performed in units of lines. In this embodiment, the area

104

is driven with different waveforms in the block erase mode in the block access mode, the line write operation in the block access mode, and the line write operation in the line access mode.

A frame portion (to be referred to as a horizontal frame hereinafter) of the frame unit

106

along the frame common lines Fcom and a frame portion (to be referred to as a vertical frame hereinafter) along the frame segment lines Fseg are driven at different timings with different waveforms. More specifically, the horizontal frame is formed by the lines Fcom and lines Fseg and seg at the non-access time (e.g., the vertical retrace interval during refresh driving and the timer interrupt duration in the partial rewrite mode) of the effective display area. The vertical frame is formed by cooperation of the frame segment lines Fseg and the common lines com in accordance with the waveform matching with the drive waveform of the common lines com during the line write operation in any mode.

(4.9.3) Drive Waveform of Effective Display Area

In this embodiment, one horizontal scanning period (1H) is divided into three intervals ΔT. In each interval, the voltage V

1

, VC, or V

2

is applied to the common lines com, while the voltage V

3

, VC, or V

4

is applied to the segment lines seg.

Table 1 shows data set in the register areas CL

1

to SC

2

in the register unit

630

in the data output unit

600

. Mark “x” in Table 1 represents an unused bit. In this embodiment, the predetermined data in Table 1 are stored in the 6th to 4th bits of the register areas CL

1

to SB

2

and the 2nd to 0th bits thereof in the initialization of the program to be described with reference to FIG.

33

. During the process of the program execution, the register area DM in the drive mode stores: the data for causing the multiplexer

671

to discriminate the block erase operation in the block access mode, the line write operation in the block access mode, and the line write operation in the line access mode and select the registers CB

1

to SB

2

, the registers CL

1

to SL

2

, or the registers CC

1

to SC

2

; and the data for designating switching of the multiplexers

665

and

669

, selection of 3-bits, i.e., bit

6

to bit

4

or bit

2

to bit

0

, and sequential output of one-bit data within the ΔT intervals.

TABLE 1

Register

bit

7

6

5

4

3

2

1

0

Line Write Data in

C L 1

{overscore (CCLR)}

x

1

1

1

CEN

x

1

1

1

Block Access Mode

C L 2

CM2

x

0

1

0

CM1

x

1

0

0

S L 1

SM2

x

1

1

0

SEM

x

1

1

1

S L 2

SM1

x

1

0

0

{overscore (SCLR)}

x

1

1

1

Block Erase Data in

C B 1

{overscore (CCLR)}

x

1

0

1

CEN

x

1

1

0

Block Access Mode

C B 2

CM2

x

0

0

0

CM1

x

0

0

0

S B 1

SM2

x

0

1

0

SEN

x

1

1

1

S B 2

SM1

x

0

0

0

{overscore (SCLR)}

x

1

0

1

Line Write Data in

C C 1

{overscore (CCLR)}

x

1

1

1

CEN

x

1

1

1

Line Access Mode

C C 2

CM2

x

1

1

1

CM1

x

1

1

0

S C 1

SM2

x

0

1

1

SEN

x

1

1

1

S C 2

SM1

x

0

1

0

{overscore (SCLR)}

x

1

1

1

TABLE 2

Truth Table of Common Drive Element 310

CEN

{overscore (CCLR)}

CM1

CM2

{overscore (CS)}

V

0

X

X

X

X

VC

1

0

X

X

0

V1

1

1

0

0

0

VC

1

1

0

1

0

V2

1

1

1

0

0

V1

1

1

1

1

0

V1

TABLE 3

Truth Table of Segment Drive Element 210

SEN

{overscore (SCLR)}

SM1

SM2

Q

V

0

X

X

X

X

VC

1

1

X

0

X

VC

1

0

X

1

X

V4

1

1

1

1

0

V3

1

1

0

1

0

V4

1

1

1

1

1

V4

1

1

0

1

1

V3

Tables 2 and 3 are truth tables of the common and segment drive elements

310

and

210

. Mark “x” in Tables 2 and 3 represents a case wherein the drive voltage V to be selected is not influenced regardless of the logic value, i.e., logic “0” or logic “1”. Q in Table 3 is 1-bit data, i.e., image data output from the latch

231

(

FIG. 22

) in the latch unit

230

. If Q=0, then white data-is output. If Q=1, then black data is output.

FIG. 26A

shows waveforms of the signals CEN, {overscore (CCLR)}, CM

1

, and CM

2

based on the contents (Table 1) of the registers CB

1

and CB

2

and the waveform of the voltage signal V applied to the common lines com by the logic (Table 2) of the common drive element

310

.

FIG. 26B

shows waveforms of the signals SEN, {overscore (SCLR)}, SM

1

, and SM

2

based on the contents (Table 1) of the registers SB

1

and SB

2

and the waveform of the voltage signal V applied to the segment lines seg of the logic (Table 3) of the segment drive element

210

.

During the block erase operation in the block access mode, the element

310

selected in response to the chip select signal {overscore (CS)} drives the block selected by the signals CA

5

and CA

6

so as to apply the difference between the voltages applied to the common and segment lines, i.e., a combined voltage waveform (

FIG. 27

) to intersections of the common and segment lines com and seg. The block information is cleared to white data by a value 3V

0

of the voltage applied within the interval ΔT.

In this case, the interval ΔT, the 1H, and the voltages V

1

to V

4

and VC are corrected in accordance with the temperature, as previously described.

FIG. 28A

shows the waveforms of the signal CEN and the like based on the contents of the registers CL

1

and CL

2

and the waveforms of the voltage signals V based on the logic of the common drive element

310

.

FIG. 28B

shows the waveforms of the signal SEN and the like based on the contents of the registers SL

1

and SL

2

and the waveforms applied to the segment lines seg on the basis of the logic of the segment drive element

210

and the contents (Q) of the image data.

During the line write operation in the block access mode, in the block of the element

310

selected by the chip select signals {overscore (CS)} and the signals CA

5

and CA

6

, composite voltage waveforms shown in

FIGS. 29A and 29B

are applied to the intersections of the common and segment lines com and seg selected by the signals CA

1

to CA

4

. Display data updating does not occur at a point applied with the waveform shown in FIG.

29

A. That is, this point maintains the white data state obtained by the previous block erase operation. However, the point applied with the waveform shown in

FIG. 29B

is changed to the white data state by the voltage value. 3V

0

applied during the first interval ΔT and then to the black data state by the voltage value −3V

0

applied during the next interval ΔT.

FIG. 30A

shows the waveforms of the signal CEN and the like based on the contents of the registers CC

1

and CC

2

and the waveforms of the voltage signals V applied to the common lines com on the basis of the logic of the common drive element

310

.

FIG. 30B

shows the waveforms of the signal SEN and the like based on the contents of the registers SC

1

and SC

2

and the waveforms applied to the segment lines seg on the basis of the logic of the segment drive element

210

and the contents (Q) of the image data.

During line write operation in the line access mode, the intersections between the selected common and segment lines con and seg receive a composite voltage waveform shown in

FIG. 31A

or

31

B. At the point applied with the voltage signal having the waveform shown in

FIG. 31A

, the voltages 2V

0

and V

0

are applied within the first and next intervals ΔT, so that the voltage level of this point exceeds the threshold value for obtaining the white data. However, the voltage level of this point does not exceed the threshold value because the voltage V

4

is applied thereto within the last ΔT interval, thereby displaying white data. At the point applied with the waveform shown in

FIG. 31B

, white data is displayed within the first two intervals 2ΔT, and the voltage −3V

0

applied thereto within the last interval ΔT inverts the display state. Therefore, black data is displayed.

(4.9.4) Mode of Frame Driving

In this embodiment as described above, the horizontal frame is formed during the vertical retrace interval or periodically and simultaneously at the start of driving of the A/D conversion unit

950

. The vertical frame is formed during the line write operation in the effective display area

104

. The frame has the same color as a background color of the effective display area

104

. If information is displayed in black, the frame is displayed in white.

Table 4 shows data set in the registers FV

1

, FCVc, FV

2

, FV

3

, FSVc, and FV

4

to perform switching of the frame drive unit

700

so as to form a frame. The frame common lines Fcom are substantially independent of driving of the effective display area

104

. Therefore, the contents of the data {overscore (V

1

)}, {overscore (CVc)}, and {overscore (V

2

)} are not changed. In this embodiment, the drive data for the frame common lines Fcom is set such that its waveform is the same as the drive waveform for the common lines com shown in

FIG. 26A

at the time of horizontal frame formation.

When different drive waveforms for the frame common lines Fcom and the common lines com are applied for horizontal frame formation, for vertical frame formation during the line write operation in the block access mode, and for the line write operation in the line access mode, the registers FV

3

, FV

4

, and FSVc are changed and set for the frame segment line Fseg so as to display white data.

More specifically, when the horizontal fame is formed, the same waveform as the drive waveform for the segment lines seg, as shown in

FIG. 26B

, is applied as the drive data for the frame segment lines Fseg. When the vertical frame is formed during the line write operation in the block access mode, the same waveform as the drive waveform (Q=0) for the segment lines seg, as shown in

FIG. 28B

, is applied as the drive data for the frame segment lines Fseg. When the vertical frame is formed during the line write operation in the line access mode, the same waveform as the drive waveform (Q=0) for the segment lines seg, as shown in

FIG. 30B

, is applied as the drive data for the frame segment lines Fseg.

As a result, the waveform shown in

FIG. 27

is used to form the horizontal frame. In the block or line access mode, the waveform shown in

FIG. 29A

or

31

A is used to form the vertical frame.

TABLE 4

Register

bit

7

6

5

4

3

2

1

0

Frame Common Line Data

FV1 * FCVC

{overscore (C Vc)}

x

1

0

1

{overscore (V)} 1

x

0

1

0

Frame Segment Line Data

during Line Write Operation

FV2 * FV3

{overscore (V)} 2

x

0

0

0

{overscore (V)} 3

x

1

0

0

in Block Access Mode

FSVc * FV4

S Vc

x

0

0

1

{overscore (V)} 1

x

0

1

0

Frame Segment Line Data for

Horizontal Frame Formation

FV2 * FV3

{overscore (V)} 2

x

0

0

0

{overscore (V)} 3

x

0

0

0

FSVc * FV4

{overscore (S Vc)}

x

1

0

1

{overscore (V)} 4

x

0

1

0

Frame Segment Line Data

during Line Write Operation

FV2 * FV3

{overscore (V)} 2

x

0

0

0

{overscore (V)} 3

x

0

1

0

in Line Access Mode

FSVc * FV4

{overscore (S Vc)}

x

1

0

0

{overscore (V)} 1

x

0

0

1

(5) Display Control

(5.1) General Description of Control Sequence

Display control according to this embodiment has two major features. First, when the signal Busy is supplied from the display control unit

50

to the wordprocessor

1

, data exchange can be synchronized with the operation of the display screen

102

. This is based on the assumption that one horizontal scanning period is changed by the temperature so as to obtain effectiveness of an operation in the display element using the FLC.

Second, although the conventional processor sequentially, periodically, and continuously (so-called refresh mode) transfers only the image data, the wordprocessor

1

according to this embodiment transfers address data capable of designating a pixel to be driven by image data prior to transfer of this image data. This image data is not transferred in the refresh mode but only a specific image data portion accessed by the address data is transferred and driven. This operation is based on the assumption that the display element using the FLC has a memory function and only the pixels required for information updating need be accessed.

In order to achieve the above display control, the wordprocessor

1

according to this embodiment includes a function for interrupting transfer of the address data upon reception of the signal Busy and a function for transferring the address data with, e.g., the horizontal sync signal, in addition to the functions of the conventional wordprocessor.

By effectively utilizing the second feature in display control, the following two display control modes can be obtained.

Two display control modes are block and line access modes. Operations in the block access mode are performed as follows. For example, 20 scanning electrode lines constitute one block, and a one-block information in the effective display area

104

is erased at once. This block is set in the “all white” state. Information of the block is sequentially accessed in units of scanning lines, and characters and the like are written on the screen. To the contrary, in the line access mode, access is performed in units of scanning lines to write information. All the pixels in the block need not be set to be in the “all white” state.

These display control modes are shown in a program flow chart of FIG.

32

. The general operation of display control in this embodiment will be described with reference to FIG.

32

.

Referring to

FIG. 32

, when a power switch in the wordprocessor

1

is turned on, the INIT routine is automatically executed (step S101). The signal Busy is set to be “ON”. In the power-on state, the frame unit

106

is driven, the effective display area

104

is erased, and temperature compensation therefore is performed. Finally, the signal Busy is set to be “OFF”, and the system waits for an interrupt request {overscore (IRQ

1

)} or {overscore (IRQ

2

)}. The interrupt request {overscore (IRQ

1

)} or {overscore (IRQ

2

)} is generated when address data is transferred from the wordprocessor

1

. When the address data is not sent, the program is not executed, and the contents of the display screen

102

are not changed.

When the address data is transferred and the interrupt is generated, the flow branches in accordance with the type of internal interrupt request. In the decision step S102, if the internal interrupt request is the interrupt request {overscore (IRQ

1

)}, the flow advances to a LASTART routine. However, if the internal interrupt request is the request {overscore (IRQ

2

)}, the flow advances to a BSTART routine. The above decision step determines the block or line access mode. More specifically, if the flow advances to the START routine, the line access mode is set. Otherwise, the block access mode is set.

In this embodiment, the interrupt request {overscore (IRQ

1

)} or {overscore (IRQ

2

)} is manually set by a switching means

520

arranged at a proper position of the display control unit

50

.

If the line access mode is set by such a switching means

520

and the interrupt request {overscore (IRQ

1

)} is generated, the LSTART routine is started and such a program is executed. In this case, the address data transferred from the data output unit

600

is read to determine whether this address data represents the last line of the effective display area

104

(steps S103 and S104). If the line is determined not to be the last line, the program branches into the LLINE routine. In this routine, the signal Busy is set to be “ON”, and one-scanning line write is performed on the basis of the image data transferred next to the address data. The signal Busy is then set to be “OFF”, and the system waits for the interrupt request {overscore (IRQ

1

)} (step S105). When the interrupt request {overscore (IRQ

1

)} is supplied, the LSTART routine is started again.

If the address data is determined in step S104 to represent the last line, the program branches into the FLLINE routine. In this routine, the line write operation of the last line is performed on the basis of the transferred image data. Frame driving and updating of the temperature compensation data are performed. The signal Busy is set to be “OFF”, and the system waits for the interrupt request {overscore (IRQ

1

)} (step S106). When the interrupt request {overscore (IRQ

1

)} is generated, the LSTART routine is started again. As described above, display control in the line access mode is performed.

When the block access mode is set by the above switching means

520

and the interrupt request {overscore (IRQ

2

)} is generated, the BSTART routine is started. In this case, the signal BUSY is set to be “ON”, and the transferred address data is read to discriminate whether the data represents the head line of the block, the last line of the effective display area

104

, or a line excluding the above lines (steps S107 and S108). If the address data is discriminated not to represent the head or last line, the flow branches into the LINE routine. In this routine, one-line write operation is performed on the basis of the transferred image data. The signal Busy is set to be “OFF”, and the system waits for the next interrupt (step S109). If the interrupt is discriminated to be the internal interrupt request {overscore (IRQ

2

)}, the BSTART routine is started again.

If the address data is discriminated in step S108 to be the last line of the effective display area

104

, the flow or program branches into the FLINE routine. In this routine, one-line write operation is performed, the frame is driven, and the temperature compensation data is updated. The signal Busy is set to be “OFF”, and the system waits for the interrupt request (step S110). When the interrupt request {overscore (IRQ

2

)} is generated, the BSTART routine is started again.

If the address data is discriminated in step S108 to represent the head line of the block, the flow is branched into the BLOCK routine. In this routine, all blocks related to the lines designated by the address data are erased, and the areas of these blocks are set to be “white” (step S111). The flow advances to the LINE routine (step S109), and the same operations as described above are performed. Display control in the block access mode is performed in accordance with the steps described above, and information write operations are performed.

When the wordprocessor

1

sends a power down signal {overscore (PDOWN)} to the controller

500

, this signal enables a nonmaskable interrupt request NM

1

, and the signal PWOFF is enabled. In this case, the signal Busy is set to be “ON”, and the effective display area

104

is erased to set the entire area to be “white”. The power status signal and the signal Busy are set to be “OFF”, thereby deenergizing the wordprocessor

1

(step S112).

As is apparent from the above description, even if either the block or line access mode is set, refresh driving is performed in accordance with the address data which are sequentially, cyclically, and continuously transferred throughout the entire effective display area. However, if address data of predetermined portions are intermittently transferred, partial rewrite driving is performed.

In the control sequence described in detail below, assume that address data and image data are transferred from the wordprocessor i in a refresh mode.

(5.2) Details of Control Sequence

(5.2.1) Power On (Initialization)

When the power switch of the wordprocessor

1

is turned on, automatically started operations will be described with reference to

FIGS. 33 and 34

.

FIG. 33

is a flow chart of the started processing i.e., the INIT routine described with reference to FIG.

32

.

FIG. 34

is a timing chart of the INIT routine and a PWOFF routine (to be described later). The operations performed by the controllers

500

will be described step by step.

S201

The power status (P ON/OFF) signal is set to be “ON”, and the signal Light is set to be “OFF”. At the same time, the signal Busy is set to be “ON” through the data output unit

600

and is output to the wordprocessor

1

. While the signal Busy is output, no address data is transferred from the wordprocessor

1

because one horizontal scanning period is changed by a change in temperature so as to effectively drive the FLC display element. Since the FLC display element drive time in the effective display are a

104

cannot be perfectly synchronized with the data transfer time of the wordprocessor

1

, in other words, VRAM operating time in the wordprosessor

1

, the signal Busy is output from the display control unit

50

to synchronize the FLC display element drive time with th e data transfer time (time {circle around (1)} in

FIG. 34

; only a numeral will be described below).

S203

Drive waveform generation control data for initial frame driving and effective display area driving are set in the register unit

630

in the data output unit

600

. More specifically, the waveform generation control data stored in the ROM

503

in the controller

500

are set in the register unit

630

in the data output unit

600

, as shown in Tables 1 and 4.

S205

Initial frame drive data of drive voltage values and system clocks serving as the reference clocks of one horizontal scanning period are set in the D/A conversion unit

900

and the register TCONR in the timer TMR

2

in the controller

500

. The reference time data in block access, the line access, and block access in the power-on/-off operation are set.

S207

The controller

500

transfers the frame drive control data from the data output unit

600

to the frame drive unit

700

, and the frame drive unit

700

performs frame driving on the basis of these input data. Such frame driving improves the image quality of the frame unit

106

, and the display screen

102

is always kept in the top condition due to the following reason. A change in transmittance is prevented upon an application of a voltage to the frame unit

106

while the effective display area

104

is being driven. Therefore, misting of part of the frame unit

106

and hence degradation of image quality of the frame unit

106

are prevented.

In this embodiment, the frame unit

106

is set in the “white (orientation state for transmitting light from the light source FL) state”, the effective display area

104

is set in the “white (a state for transmitting light) state”, and character information and the like are displayed in “black”. The “black” and “white” states in the display mode are not limited to the one described above. The “black” and “white” states may be inverted, or the frame unit

106

may be distinguished from the effective display area

104

according to the display device of the present invention.

Frame driving in step S207 is performed throughout one horizontal scanning period. During this period, voltage signals are supplied to the frame transparent and segment electrodes

150

and

124

formed on the lower glass substrate

120

and the frame transparent electrodes

151

parallel to the common electrodes

114

and formed on the upper glass substate

110

. Therefore, the entire frame is not always driven, but the remaining frame unit (i.e., the vertical frame) is driven by also using the common electrodes when the effective display area

104

is erased in step S213 (to be described later).

In this step, the above-mentioned frame driving is performed together with A/D conversion. A/D conversion is performed such that ambient temperature information of the display screen

102

which is detected by the temperature sensor

400

, that is, FLC temperature information, is read by the A/D conversion unit

950

, and the read information is converted into digital data (times {circle around (2)} and {circle around (3)}).

S209

Temperature compensation is performed. The A/D-converted data is read, and the look-up table (

FIG. 12

) stored in the ROM

503

in the controller

500

is referred to, thereby obtaining temperature-compensated drive voltages V, system clocks, and delay data.

The above operations will be described in detail with reference to FIG.

35

.

FIG. 35

shows an algorithm and a look-up table when the A/D-converted data is converted into the drive voltage V, the system clock as a reference for one horizontal scanning period, and each delay time. Assume that temperature data 80H shown in

FIG. 35

is obtained. A hexadecimal code “80”H represents lower bits of the address data in the table. In the above A/D conversion operation, the analog temperature data is converted to digital temperature data corresponding to the lower bits of the address data.

An arithmetic and logic unit ALU in the controller

500

sets in 0080H data E900H corresponding to the upper bits of the address data of the drive voltage data table area (D/A conversion unit related data area). The content of the index register IX can be set to be E980H, and the data corresponding to this address is obtained. The temperature-compensated drive voltage value is output to the power controller

800

through the D/A conversion unit

900

. The arithmetic and logic unit ALU then does not update the lower bit data of the index register IX and increments the upper bit data by one, so that the content of the register IX becomes EA80H. This content corresponds to the address in the system clock table, thereby obtaining the temperature-compensated data. The system clock data serving as a reference for one horizontal scanning period is set in the time constant register TCONR in the timer TMR

2

.

The respective time data in block access, line access, and block access in the power-on/-off operation are set in the registers CNTB, CNTL, and CNTBB for the timer TMR

1

.

S211

The start time of driving of the effective display area

104

is synchronized. More specifically, in order to establish perfect synchronization between the start of program access and the start of actual driving of the effective display area, an internal interrupt request IRQ

3

is generated in the CPU in the controller

500

at, e.g., a leading edge of the clock output pulse Tout having the timer TMR

2

in the controller

500

, thereby starting actual driving of the effective display area (time {circle around (4)}).

S213

The effective display area

104

is erased. In other words, the entire area is set to be “white”. This operation together with previous frame driving allows a good state of the display screen

102

in the power-on operation.

The erase operation of the effective display area

104

is performed by driving the area

104

in units of blocks each consisting of, e.g., 20 scanning lines. Therefore, one block is erased in one horizontal scanning period.

This driving is not performed by receiving image data “white” for the entire effective display area

104

, but by automatically setting a predetermined block erase waveform on the program. Therefore, the effective display area can be erased upon the power-on/-off operation.

S215

One horizontal scanning period is controlled. More specifically, delay data in the register CNTBB is set in the counter, and the timer TMR

1

counts its own clock pulses on the basis of this data. The operation of the effective display area

104

during one horizontal scanning period can be synchronized with the actual program execution time. When a predetermined time interval has elapsed, the CPU generates the internal interrupt request IRQ

3

.

The timer TMR

1

sets the predetermined time interval on the basis of the reference time data set in step S205 and the delay time data obtained by temperature compensation in step S209. When the predetermined. time interval is measured from a proper moment, the internal interrupt request is generated.

S216

The operations in steps S211, S213, and S215 are performed in units of blocks, i.e., every horizontal scanning. In step S216, the controller

500

discriminates whether an end of all blocks in the effective display area

104

is detected. If NO in step S216, the flow returns to step S211. The above operations are repeated until the end of all the blocks is detected (time {circle around (5)}).

S217

When the end of all the blocks (effective display area) is detected in step S216, the signal Busy is set to be “OFF”, and the signal D from the wordprocessor

1

can be transferred. At the same time, the signal Light is set to be “ON”. In this case, the operator at the wordprocessor

1

turns on the power switch. When the display screen

102

is displayed, the operator knows that the wordprocessor

1

has been powered. In the operations in steps S201 to S215, driving of the frame unit

106

of the display screen

102

and of the effective display area

104

has been performed as initial display control (time {circle around (6)}).

S219

The controller

500

waits for the interrupt request {overscore (IRQ

1

)} or {overscore (IRQ

2

)}. The interrupt request {overscore (IRQ

1

)} or {overscore (IRQ

2

)} is generated when the address data is transferred from the wordprocessor

1

. Various programs to be described later are executed in response to the interrupt request. The standby program is executed to maintain the common and segment lines at the same potential or the ground potential until the address data is transferred. In this case, the contents of the display screen

102

are not updated. Instead, the display unit

100

may be powered off. For example, the voltage signal may be disabled by interrupting the power supply, e.g., the power controller

800

.

As described above, generation of either the request {overscore (IRQ

1

)} or {overscore (IRQ

2

)} is preset. This presetting can be arbitrarily determined by the operator in accordance with an application of the wordprocessor, data processed by the wordprocessor, and the like.

(5.2.2) Block Access

Block access display control started in response to the interrupt request {overscore (IRQ

2

)} after the predetermined initial control (INIT routine) will be described with reference to

FIGS. 36A

to

36

D and

FIGS. 39A and 39B

.

FIGS. 36A

to

36

D are flow charts of programs related to display control and stored in the ROM

503

in the controller

500

in the form shown in FIG.

12

. These programs are initialized in steps of block access display control.

FIGS. 39A and 39B

are timing charts of such display control.

When address data is transferred to the control unit

500

which is set in the standby state upon “OFF” operation (time {circle around (1)} in

FIGS. 39A and 39B

; only the numeral will be described below) of the signal Busy, i.e., when time {circle around (2)} reaches, the interrupt request {overscore (IRQ

2

)} is input (time {circle around (3)}), and the BSTART routine shown in

FIG. 36A

is started (time {circle around (4)}). Display control in the BSTART routine will be described with reference to FIG.

36

A.

S301

Address data is read. Address data RA/D transferred to the data output unit

600

is read in the controller

500

.

S303

Address translation described in (4.3.2) is performed on the basis of the read address data. The jumping table shown in

FIG. 12

is referred to, and address data (destination address) for a program to be executed is set.

S305

The signal Busy is set to be “ON” (time {circle around (5)}), and the next address data transfer is inhibited.

S307

The flow branches into the program at the designated address set in step S303 (time {circle around (6)}). If the address data RA/D is discriminated to represent the head line of the address, the BLOCK routine is executed. However, if the data RA/D is discriminated to represent the last line of the effective display area, the flow is branched into the FLINE routine. Otherwise, the flow is branched into the LINE routine.

When the BLOCK routine shown in

FIG. 36B

is started, the following operations are performed.

S309

The address is changed and set up. More specifically, the address is changed to select a line to be driven (described in (4.3.3)) on the basis of the the address data RA/D transmitted to the registers RA/DL and DA/DU in the register unit

630

in the data output section

600

. The changed address is used to retrieve data in the line table shown in

FIG. 12

, and the corresponding address data is obtained. The address data is then set in the registers DLL and DLU in the register unit

630

in the data output unit

600

.

S311

The drive mode is set to be the block access mode. In other words, data representing the block erase operation in the block access mode is set in the register DM in the register unit

630

in the data output unit

600

.

S313

The operation start time is synchronized. More specifically, in order to perfectly synchronize the operation on the effective display area

104

and the execution of the program, as described above, the internal interrupt request IRQ

3

is generated at, e.g., a leading edge of the clock output pulse Tout of the timer TMR

2

in the control unit

500

. The output pulse Pout is synchronized with the execution timing of the program. Therefore, since the output pulse Tout serves as a reference pulse for one horizontal scanning period and the operation timing in the effective display area

104

, the execution of the program is synchronized with the operation of the effective display area

104

.

S315

Time is adjusted until the completion of image data transmission. More specifically, as shown in the timing chart in

FIG. 39A

, image data transmission is performed immediately after address data transfer. When this transfer is completed (time {circle around (7)}), the controller

500

starts to access the effective display area

104

.

The image data transmission time is defined as a time interval as a sum of a transfer time of 40 μsec required for transferring 800-bit one-scanning image data in units of 4-bit parallel data at a speed of 5 MHz, and a time required for storing the image data in the segment drive unit

200

.

The routine BLOCK aims at erasing the block. The image data is transmitted although the block erase operation does not require image data because data transfer or transmission of the next line access is performed. Alternatively, instead of performing image data transmission, the program may be interrupted for a period of time equal to the image data transmission time.

S317

The controller

500

starts to erase a block (time {circle around (7)}). One block, e.g., 20 scanning lines, is accessed within one horizontal scanning period (1H) so as to set all pixels in the block to be “white”. This operation is not performed upon reception of all “white” image data but performed by setting a predetermined block erase waveform.

As is apparent from

FIG. 39A

, at the start time of the block erase operation (time {circle around (7)}), the write operation of the last line of th previous block is completed, or the vertical retrace interval is ended in the effective display area

104

.

S319

One horizontal scanning period (1H) is adjusted on the program. As previously described, the access time in the effective display area

104

is changed in accordance with a change in temperature of the FLC display element. The program execution time is adjusted in accordance with the length of one horizontal scanning period in the effective display area

104

.

More specifically, the timer TMR

1

in the control unit

500

starts its operation from the time (i.e., time {circle around (4)}), e.g., when the address data is transferred and the program is started in response its own clock pulse. When a predetermined period of time has elapsed, the internal interrupt request IRQ

3

is generated in the CPU

501

in the controller

500

, and the flow is branched into the next program routine.

The predetermined period of time is determined as follows. As described in step S209 in (5.2.1), a time interval as a sum of the program execution time and the delay time is stored as a count data in the table area CNTB in

FIG. 12

as a result of temperature compensation. The timer TMR

1

compares the count of its own clock pulses with the content of the CNTB. When a predetermined count is reached, the internal interrupt request IRQ

3

is generated.

When the predetermined period of time has elapsed and the interrupt request IRQ

3

is generated, the program branches into the LINE routine (time {circle around (8)}).

FIG. 36C

is a flow chart of the LINE routine. This routine is started as a continuation of the BLOCK routine or directly as a continuation of the BSTART routine. In the following description, the LINE routine is regarded as a continuation of the BLOCK routine. The same step operations as described above will be omitted.

S321

When the LINE routine is started in response to the internal interrupt request IRQ

3

(time {circle around (8)}), the address is changed and set up.

S323

The controller

500

sets the drive mode to the line write of the block access mode. In other words, data presenting the line write of the block access mode is set in the register DM in the register unit

630

in the data output unit

600

.

S325

The controller

500

synchronizes the operation start time.

S327

The controller

500

adjusts the time until completion of image data transmission. If the image data transmission is not performed in the previous BLOCK routine, data transmission need not be performed. Time equal to the data transmission is idled on the program.

S329

The controller

500

starts a line write operation (time {circle around (9)}). In this moment, the block erase operation is ended. Information of one scanning line for the head line of the block is written or displayed in accordance with the transmitted image data of one scanning line.

S331

The controller

500

adjusts one horizontal scanning period (1H) (time {circle around (10)}).

S333 and S335

The signal Busy is set to be “OFF” (time {circle around (11)}), and the controller

500

waits for the interrupt request {overscore (IRQ

2

)}. Meanwhile, execution of the program is not started.

When the address data is transferred (time {circle around (12)}), the interrupt request {overscore (IRQ

2

)} is generated (time {circle around (13)}), and the BSTART routine is started (time {circle around (14)}). The LINE routine follows the BSTART routine, and the second scanning line of the block is written. As described above, the BSTART and LINE routines are executed, and the write operation of all scanning lines in the block is completed. The next block erase operation and the next line write operation are performed.

When all the operations described above are completed and the address data representing the last line of the effective display area

104

is transferred, processing is started as shown in the flow chart of FIG.

36

D and the timing chart of FIG.

39

B.

When the address data which represents the last line of the effective display area

104

is transferred (time {circle around (2)} in

FIG. 39B

; only the numeral will be described later), the interrupt request {overscore (IRQ

2

)} is generated (time {circle around (3)}), and the above-described BSTART routine is started (time {circle around (4)}). In this case, since the address data represents the last line of the effective display area

104

, the FLINE routine (

FIG. 36D

) follows (time {circle around (6)}) after the above routine.

The operations in steps in the FLINE routine will be described with reference to

FIG. 39B

together mainly with FIG.

36

D. The same operations as described above are omitted.

S336, S337, S339, S341, and S343

The signal Busy is set to be “ON”, and the designated address is changed and set up. The controller

500

sets the drive mode to line write of the block access mode, and synchronizes the operation start time. In addition, the controller

500

adjusts the time until completion of the image data transmission.

S345

The controller

500

starts the writing of the last line (time {circle around (7)}). At this moment, the write operation of the second last line of the effective display area

104

is completed.

S347

The controller

500

discriminates whether the end of the last line write in the effective display area

104

is detected. If YES in step 347, the flow advances to step S349. This discrimination is performed when the last line of the effective display area

104

is accessed. Otherwise, the controller

500

simply monitors the access start time.

S349

In this step, the waveform control data for frame driving in the next step is set in the register unit

630

in the data output unit

600

to update the data. If a separate frame drive system is arranged, only frame driving can be performed without updating the data.

In the INIT routine shown in

FIG. 33

, as described above, the waveform data and the frame drive voltage values are set. However, as in this step, frame driving performed during the vertical retrace interval uses as the reference value of the drive voltage values obtained by temperature compensation in the INIT routine.

S351 and S353

The controller

500

starts the driving of the frame unit

106

and A/D conversion (time {circle around (8)}). The vertical retrace interval is started from time {circle around (8)}. At the end of A/D conversion, the drive voltage values, the system clock and the delay time data are obtained. In other words, the temperature-compensated data is updated.

In frame driving in step S351, the frame unit

106

is partially (i.e., only the horizontal frame) driven to obtain all “white” pixels, but the remaining part (i.e., the vertical frame) is then driven simultaneously with driving of the effective display area

104

, as described with reference to in the INIT routine. However, if the driving system of the frame unit

106

is arranged independently of the driving system of the effective display area

104

, all parts of the frame unit

106

can be simultaneously driven.

The frame unit

106

is electrically driven to obtain high image quality of a portion outside the effective display area

104

. However, the frame unit

106

may be mechanically driven or a coating is formed on the frame unit

106

without considering the image quality outside the effective display area

104

.

S355 and S357

The signal Busy is set to be “OFF”, and the controller

500

waits for the interrupt request {overscore (IRQ

2

)} (time {circle around (9)}).

As described above, frame driving and temperature compensation are performed during writing of the last scanning line of the effective display area

104

and during the vertical retrace interval immediately after writing of the last scanning line.

Thereafter, when the address data, i.e., address data on the uppermost scanning line of the effective display area

104

is transferred (time {circle around (10)}), the interrupt request {overscore (IRQ

2

)} is generated (time {circle around (11)}), and the BSTART routine is executed (time {circle around (12)}). The block erase and line write operations in units of blocks are performed.

(5.2.3) Line Access

Line access display control started in response to the interrupt request {overscore (IRQ

1

)} after predetermined initial control (INIT routine) will be described with reference to

FIGS. 37A

to

37

C, and

FIGS. 40A and 40B

.

FIGS. 37A

to

37

C are flow charts of display control programs stored in the ROM

503

in the controller

500

in the form shown in FIG.

12

. These programs are started in the respective steps of line access display control.

FIGS. 40A and 40B

are timing charts of such a display control.

Line access in this embodiment is different from the previous block access in that the block erase operation is omitted. Information is updated and displayed in units of scanning lines without erasing the scanning lines beforehand. The same operations as in the previous block access display control are omitted.

The signal Busy is set to be “OFF” (time {circle around (1)} in

FIG. 40A

; only the numeral will be described below). The controller

500

in the standby mode receives the interrupt request {overscore (IRQ

1

)} (time {circle around (3)}) generated upon address data transmission (time {circle around (2)}) and causes the LSTART routine (

FIG. 37A

) to start (time {circle around (4)}). Display control in the LSTART routine will be described with reference to FIG.

37

A.

S401

The address data is read.

S403

The controller

500

determines whether the read address data represents the last scanning line of the effective display area

104

. If YES in step 403, the flow is branched into the FLLINE routine. Otherwise, the flow branches into the LLINE routine.

Display control in the LLINE routine will be described with reference to

FIGS. 37B and 40A

.

S405, S407, and S409

The signal Busy is set to be “ON” (time {circle around (5)}), and the designated address is changed and set up. The controller

500

changes the drive mode into the line access mode.

S411 and S413

The controller

500

synchronizes the operation start time and adjusts time until image data transmission.

S415

The controller

500

starts line access (time {circle around (6)}). Information of one scanning line is written. At this moment, the write operation during the vertical retrace interval or the immediately preceding scanning line is completed.

S417, S419, and S421

The predetermined period of time is awaited to adjust one horizontal scanning period, and the program is restarted upon generation of the internal interrupt request IRQ

3

(time {circle around (7)}). The signal Busy is set to be “OFF” (time {circle around (8)}), and the controller

500

waits for the interrupt request {overscore (IRQ

1

)}.

Information of one scanning line is written, and the LSTART and LLINE routines are repeated on the basis of the address data sequentially and continuously transferred, thereby continuing scanning line write operations.

When the transferred address data is discriminated to be the last scanning line of the effective display area

104

in step S403 of the LSTART routine, the flow branches into the FLLINE routine.

Display control of the FLLINE routine will be described with reference to

FIGS. 37C and 40B

.

S422, S423, and S425

The signal Busy is set to be “ON” (time {circle around (5)} in

FIG. 40B

; only the numeral will be described below), and the designated address is changed and set up. The controller

500

sets the drive mode in the line access mode.

S427 and S429

The controller

500

synchronizes the operation start time and adjusts the time until completion of image data transmission.

S431

The controller

500

starts line access (time {circle around (6)}). At this moment, the write operation of the immediately preceding line is completed.

S433

The controller

500

discriminates whether the end of last line write is detected. If YES in step S433, the flow advances to step S435.

S435

In this step, waveform control data for frame driving to be performed in the next step is set.

S437 and S439

The controller

500

starts driving the frame unit

106

and AID conversion (time {circle around (7)}). At this time, the write operation of the second last scanning line of the effective display area

104

is completed. Temperature-compensated data is updated simultaneously with the end of A/D conversion.

S441 and S443

The signal Busy is set to be “OFF”, and the controller

500

waits for the interrupt request {overscore (IRQ

1

)} (time {circle around (8)}).

As described above, the write operation of the last scanning line of the effective display area

104

, and frame driving and temperature compensation are performed during the above write operation and during the vertical retrace interval immediately after the write operation.

When the address data, i.e., the address data of the uppermost scanning line of the effective display area

104

is transferred (time {circle around (9)}), the interrupt request {overscore (IRQ

1

)} is generated (time {circle around (10)}), and the LSTART routine is started (time {circle around (11)}). Subsequently, the line write operation is performed in units of scanning lines.

(5.2.4) Power-Off

When the operator at the wordprocessor

1

turns off the power switch with a key or the like, a PWOFF routine related to the power-off display control is started.

Such display control will be described with reference to the timing chart of FIG.

34

and the flow chart of FIG.

38

.

When the operator manipulates a key or the like to cause system power-off, the wordprocessor

1

supplies the {overscore (PDOWN)} signal to the controller

500

. A nonmaskable interrupt NMI is supplied to the CPU

501

in the controller

500

, thereby starting the PWOFF routine. The interrupt request NMI is an unconditional interrupt, and the PWOFF routine is immediately started regardless of the operating state of the controller

500

. The PWOFF routine will be described below.

S501

The signal Busy is set to be “ON”, and at the same time the signal Light is set to be “OFF” (time {circle around (8)} in

FIG. 34

; only the numeral will be described below).

S503

The controller

500

synchronizes the operation start time in the same manner as described above.

S505

The controller

500

starts driving the effective display area

104

(time {circle around (9)}). This driving aims at erasing one block in the effective display area

104

within one horizontal scanning interval in the same manner as in the INIT routine. That is, all blocks in the area

104

are set in the “white” state, and the image quality of the area

104

is improved to prepare for the next display cycle.

S507

The controller

500

adjusts one horizontal scanning period (1H). This processing is the same as described above.

S509

Steps S503, S505, and S507 are performed for every block erase cycle. In step S509, the controller

500

discriminates whether all blocks, i.e., the entire effective display area

104

, are erased.

S511

If YES in step S509 (time {circle around (10)}), the power status (P ON/OFF) signal is set to be “OFF”, and at the same time the signal Busy is set to be “OFF” (time {circle around (11)}). When the P ON/OFF signal is disabled, the entire display device including the wordprocessor

1

is powered off (time {circle around (12)}).

(6) Effect of Embodiment

The embodiment has the following effects.

(6.1) Effect of Frame Formation

When the display device is arranged using the FLC element, the frame unit

106

is formed outside the effective display area

104

on the display screen

102

in this embodiment. Poor display of the display screen

102

which is caused by an unstable state of the FLC element corresponding to the area outside the effective display area

104

can be prevented. In addition, an unclear boundary of the effective display area

104

and confusion of the operator can also be prevented.

In the above embodiment, particularly, when frame electrodes are arranged in correspondence with the frame unit

106

and the frame is electrically formed, mechanical layout adjustments are not required unlike in a mechanical arrangement in which a mechanical member comprising a plastic material is used to form a frame or a film is coated to form the frame to define the effective display area

104

. In addition, the dead space caused by disposing a mechanical member depending on a location of the display device can be eliminated. Furthermore, the frame may be colored with the same color as that of the background of the display data or a color different therefrom, thereby improving flexibility in frame formation.

(6.2) Effect of Temperature Compensation

Since drive energy (voltages and pulse widths) of the FLC elements corresponding to the effective display area

104

and the frame unit

106

is compensated for depending on temperature changes immediately prior to write timings, stable driving free from temperature changes can be achieved. Therefore, reliability of the display device using FLC elements can be improved.

In this embodiment, the compensated data is updated during the vertical retrace interval, and therefore effective display processing can be achieved. At the same time, the horizontal frame can be driven in response to a temperature data detection command, i.e., the drive command for the A/D conversion unit

950

, thereby further improving display processing efficiency.

(6.3) Effect of Control in Response to Image Data Input

The means for waiting for an image data input from the host device is arranged, and the operation is started in response to the input. The display device can perform not only refresh driving for continuously changing the display state regardless of its contents as in the display having a display element without a memory function, but also intermittent driving for updating display data only when updating of its contents is required. Since the display device can perform refresh driving, changes in technical specifications of the existing host device need not be performed. In addition, intermittent driving allows a decrease in power consumption. Data is transmitted from the host device when screen updating is needed. Therefore, software or hardware load on the host device can be reduced.

The busy signal is output to the host device in response to a unit image data input (e.g., one line), and various modes can be then set. In this case, the host device additionally includes a function for receiving the busy signal and waiting for image data transmission.

In the above embodiment, the start/stop of the operation is controlled in accordance with the presence/absence of a real address data input supplied together with the image data from the wordprocessor

1

serving as the host device. The block or line to be accessed is detected on the basis of the real address data, thereby allowing the partial rewrite operation. Furthermore, the temperature-compensated data during refresh driving can be updated during the vertical retrace interval.

(6.4) Effect of Display Drive Unit Arrangement

There are provided a plurality of voltage supply lines and the switches for connecting the plurality of voltage supply lines to the electrodes (common electrodes com, segment lines seg, frame common lines Fcom, and frame segment lines Fseg) formed on the display unit

100

constituted by FLC elements and/or disconnecting the voltage supply lines from the electrodes. There is also provided the means (common drive unit

300

, segment drive unit

200

, and frame drive unit

700

) for switching the switches in accordance with the waveform data. Therefore, the electrodes can be optimally driven with various proper drive waveforms in accordance with the contents of the waveform data.

In the above embodiment, the waveform data are properly changed and generated during control, and therefore, driving in block erasure, image formation, frame formation, and screen clearing can be performed with appropriate waveforms, and image quality can be improved.

(6.5) Effect of Screen Forcible Clearing

The display screen

102

of the display unit

100

constituted by the FLC elements is cleared at the time of power-on and -off operations. The operator can check the state of the display device while the display screen

102

is cleared. The operator can easily check the power-off state.

In particular, the display screen can clear its display contents without receiving clear data (e.g., all white data) from the host device at the time of power-on/-off operation. Therefore, the load of the host device can be reduced, and clearing can be performed at high speed.

Self-clearing of the screen has the following advantage. The display device need not receive all white data from the host device but can receive only a clear command therefrom so as to perform self-clearing.

(6.6) Effect of Power Controller Arrangement

Since the values of the voltages applied to the electrodes (lines con, seg, Fcom, and Fseg) arranged on the display unit

100

constituted by the FLC elements are changed, the voltages having optimal values can be supplied to the electrodes in accordance with the temperature and drive conditions.

In this embodiment, particularly, the positive, negative, and reference voltages are applied to the common lines com and Fcom, and another negative voltage, another positive voltage, and the reference voltage are applied to the segment lines seg and Fseg (i.e., a total of five voltage values can be generated). In this case, one value (VC) is fixed, and other values are set to be variable at a predetermined ratio with respect to the fixed value. In addition, some output voltages are used to set other output voltages, thereby generating five types of voltages. Therefore, the voltage values can be appropriately adjusted in accordance with temperature conditions and the like.

ICs used in the common drive element must have a high breakdown voltage, while ICs used in the segment drive elements must have a high operating speed. When one voltage is fixed and other voltages are determined in a predetermined ratio with respect to the fixed voltage, different types of ICs described above can fall within the predetermined range of technical specifications, and the manufacturing process can also be simplified.

(7) Modification

(7.1) Arrangement of Frame Unit

106

In this embodiment, the frame unit

106

is electrically formed. However, the present invention is not limited to this. A portion corresponding to the frame unit

106

on the display screen

102

may be replaced with a mechanical means such as a plastic member or a coating. In this case, the image quality in the area outside the effective display area

104

need not be taken into consideration. When the frame unit is electrically driven, a separate frame drive system allows simultaneous driving of all the parts of the frame unit. Furthermore, when frame formation is electrically performed, the color of the frame unit can be the same as that of the background or that of the data.

In the above embodiment, the frame transparent electrodes

150

and

151

are driven by the frame drive unit

700

independent of the drive units

200

and

300

. However, the elements

210

and

310

or equivalent drive elements may be arranged in one or both of the units

200

(

300

) and

700

and may be driven when the drive units

200

and

300

are driven.

(7.2) Temperature Compensation Timing and Partial Rewrite

In the above embodiment, temperature compensation is performed within the vertical retrace interval. This can be achieved under the assumption that the address data and the image data are cyclically and continuously (i.e., in the refresh mode) transferred. However, the temperature compensation timings may be arbitrarily determined. For example, when address data of specific portions are intermittently transferred, the vertical retrace interval is not present. Therefore, temperature compensation is not performed in the above display control which is thus regarded to be improper.

When driving is performed in the partial rewrite mode, it is preferable to perform temperature compensation at predetermined intervals. For this purpose, time is measured by a timer in the controller

500

, and an internal interrupt request is generated at predetermined intervals. After the signal Busy is set to be “ON”, temperature compensation can be performed.

In order to allow driving in the partial rewrite mode, the wordprocessor includes the functions of the wordprocessor in the above embodiment and functions for transferring the address data of specific portions and the corresponding image data. When the address data is transferred in the refresh mode as in the above embodiment, an arrangement may be utilized to discriminate whether to start display control in accordance with the presence/absence of the image data following the address data.

Temperature compensation need not be performed in accordance with the table system described above, but can be performed by proper arithmetic operations.

(7.3) One-Horizontal Scanning Period and Drive Voltage Value

The relationship between the temperature range and corresponding frequency (i.e., one horizontal scanning period) and drive voltage values shown in

FIG. 9

is not limited to the one described above. For example, if the temperature range is narrowed and the frequency and drive voltage values are properly set in correspondence with the temperature range, fine temperature compensation can be performed.

(7.4) Waveform Setting

In the above embodiment, once the waveform data for image formation is set in the register unit

630

, except for the frame drive waveforms, the set waveform data is not updated. With the arrangement in this embodiment, however, it is apparent that the waveforms and 1H-dividing control data can be updated at proper timings in display control. Therefore, drive waveforms corresponding to various drive conditions can be generated.

In addition to selection of waveform data corresponding to the drive conditions, the waveform data can be changed in accordance with temperatures, thereby obtaining appropriate waveforms. In this case, waveform defining data corresponding to the temperatures may be stored in the unused area at EE00H˜ as shown in

FIG. 12

in the same manner as other data, and the waveform data may be changed in the same manner as in the read operation using the above jumping table. In addition, the display device of this embodiment can be used to arbitrarily change the waveform data to determine optimal waveforms.

(7.5) Selection of Block Access or Line Access

Block or line access, i.e., the interrupt request {overscore (IRQ

2

)} or {overscore (IRQ

1

)} is selected by the operator in accordance with the form of write data and the application of the display device in the above embodiment due to the following reason. For example, if the size of one block on the display screen

102

corresponds to the size of a character train displayed thereon and write data consist of only characters and numeric values, block access simplifies processing of the character trains.

If the image to be displayed comprises various different symbols and graphic patterns, display and rewriting of a size exceeding each block must be performed. In this case, line access is more convenient than block access.

(7.6) Number of Scanning Lines

In the above embodiment, one block comprises 20 scanning lines, and the effective display area comprises 400 lines. However, in the display device using FLC display elements, the change in selection time/line does occur even if the number of scanning lines is increased. Therefore, the number of scanning lines can be increased to obtain a large, high-resolution display screen.

(7.7) Erasure of Effective Display Area

104

In order to obtain an initial state of the display screen, the effective display area

104

is automatically performed at the time of power-on/-off operation without receiving the all “white” data from the wordprocessor

1

in the above embodiment. In this case, the screen may be cleared at the time of either power-on or power-off operation. The effective display area may be erased regardless of the data to be transmitted, if the effective display area is required to be entirely erased during display control of block or line access.

For this purpose, a control signal such as an unconditional interrupt signal is output upon operation of, e.g., a key or the like in the wordprocessor

1

, and the effective display area

104

in the control unit

500

can be erased.

(7.8) Position of Temperature Sensor

400

The temperature sensor

400

is arranged at a proper position so as to represent a temperature in a temperature profile on the basis of the FLC temperature profile obtained by an experiment or the like beforehand. In order to perform more accurate temperature detection, a plurality of temperature sensors may be used.

(7.9) Display Unit

100

, Display Control Unit

50

, and Wordprocessor

1

The form of signals exchanged between the wordprocessor

1

and the control unit

50

, i.e., the signals D (including the signal A/D, the image data, and the real address data), may be limited to the one described in the above embodiment. A proper form may be used.

In the above embodiment, the display unit and the display control system are described with reference to the wordprocessor. However, the arrangements are not limited to the above embodiment. The present invention may be applied to a display of a computer display or a television set.

A display unit having a larger screen than that of the existing television set may be arranged as an application obtained by effectively utilizing the memory function of the FLC display element.

The present invention is also effectively applicable to image display of a still image or an image having a low frequency of screen updating. When the present invention is applied to a display unit such as a 7-segment display element in a receiver for, e.g., a teletext and information service equipment, a face in timepiece equipment, or display display units in various equipment, driving is performed only if screen updating is required, thereby contributing to a decrease in power consumption.

In these cases, the screen can be entirely or partially updated if partial updating is required in the same manner as in partial rewrite operation. In these cases, temperature compensation is performed at predetermined intervals of interrupt operations. The screen to be updated next is a driven/corrected screen. When the interval of screen updating is long or partial rewrite operation is required, the display data can be output again from, e.g., a VRAM during temperature compensation. Therefore, a constant display state can be obtained with uniformity.

Number	Name	Date
3903516	Mauro, Jr.	Sep 1975
4099247	Mikada et al.	Jul 1978
4100540	Fujita et al.	Jul 1978
4379293	Boisvert et al.	Apr 1983
4380008	Kawakami et al.	Apr 1983
4536856	Hiroishi	Aug 1985
4630122	Morokawa	Dec 1986
4655561	Kanbe et al.	Apr 1987
4691200	Stephany	Sep 1987
4693563	Narada et al.	Sep 1987
4923285	Ogino et al.	May 1990
5448383	Kane et al.	Sep 1995

Number	Date	Country
0149899	Jul 1985	EP
2544884	Oct 1984	FR
2581209	Oct 1986	FR
2175725	Dec 1986	GB
2134300	Aug 1994	GB

	Number	Date	Country
Parent	08/051821	Apr 1993	US
Child	08/422609		US

Display device

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CPC

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