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BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a display apparatus mounted on office
automation machinery such as the word processor, personal computer,
electronic typewriter and the like, and particularly a display apparatus
for use on compact office automation machinery.
(2) Description of the Prior Art
Office automation machinery such as the word processor, personal computer,
electronic typewriter and the like have made rapid progress in recent
years as the central instrument for streamlining office work.
In particular, demands for compact machinery are increasing today and the
CRT display which takes up a large installation space is being replaced by
flat panel type displays requiring less space. Known panel type displays
include a liquid crystal display, an EL display utilizing
electroluminescence, and a plasma display utilizing discharge of plasma
gas. These panel type displays have a smaller number of dots on the screen
and therefore show a smaller number of characters per screen than the CRT
display.
The latest office automation machinery of a relatively sophisticated class
offer a diversified range of mode choice. Some of them are equipped with
functions including a split screen mode wherein the screen is divided into
two or more sections to allow editing work to be carried out on each
screen section independently, and a help menu mode wherein handling
methods are called to the screen when the operator forgets how to operate
the machine. For these display modes it is desirable to have a large
number of characters displayed on the screen.
As means for increasing the number of characters displayed, it is
conceivable to reduce the size of characters and increase the number of
lines thereby to increase the number of characters displayed per screen. A
uniform increase in the number of lines would reduce the size of
characters to an extent that the operator has difficulties in recognizing
the characters, which constitutes a new drawback.
In order to eliminate this problem, it is desirable for the above panel
type display to include means for varying the number of characters per
screen according to purpose.
One of such means is to rewrite character code data stored in the video
RAM. However, this would entail the problem of complication in software
processing and high cost.
SUMMARY OF THE INVENTION
A primary object of the present invention, therefore, is to provide a
display apparatus incorporating a rational improvement for coping with
various display modes.
Another object of the invention is to provide a display apparatus capable
of display in various modes presenting characters in different sizes and
numbers of lines without rewriting character code data stored in the video
RAM.
A further object of the invention is to provide a display apparatus capable
of various mode changes without changing a relative position of a
reference point on the screen.
A still further object of the invention is to provide a display apparatus
capable of coping with various display modes without changing a relative
cursor position.
In order to fulfill the above objects, a display apparatus according to the
present invention comprises a display device having a two-dimensional
screen for displaying the character information; character data generating
means for generating character data corresponding to the character
information to be displayed; display mode judging means for judging a
display mode for displaying the character information on the screen;
operating means for operating a display start address for each display
mode on the basis of a reference position on the screen; control means for
controlling the character data generating means to generate a character
font of a size necessary to each display mode; and display device drive
means for causing the character information to be displayed in a selected
mode on the screen in response to the character data generated by the
character data generating means and the display start address operated by
the operating means.
Specifically, the reference position on the screen is a cursor position.
Further, the character data generating means stores different size
character fonts and generates a character font designated by a font select
command from the control means.
The character data generating means may have an external memory, the
control means being operable to cause a high speed transfer of font bit
data from the external memory to an internal memory, whereby the character
data stored in the internal memory are rewritten for a selected character
size.
In one preferred embodiment of the invention, a display apparatus comprises
a display device having a two-dimensional expanse for displaying the
character information; a video memory for generating character code data;
character data generating means for generating selected character data in
response to the character code data; parallel to serial conversion means
for converting the character data into serial data for input to the
display device; a display sequencer for providing controls to determine a
character to be displayed on the display device and to determine a
position on the display device at which the character is displayed; a CPU
for calculating a display start address for each display mode on the basis
of a cursor position, rewriting a display start address in the display
sequencer, and transmitting a character font size designating signal to
the character data generating means; and a display device drive means for
causing the character information to be displayed in response to a
synchronizing signal received from the display sequencer and a serial
signal received from the parallel to serial conversion means.
According to the above construction, when the operator selects a certain
display mode by pressing keys, the CPU recognizes the selection, instructs
the character data generating means to select a suitable character font
size. In parallel with this, the CPU calculates a display start address on
the basis of a cursor position, and input the address to the display
sequencer. Consequently, character data designated by the display start
address appear on the display screen in the selected character size. In
this case, the data are presented over a range available on the display
screen, using the cursor position for the basis in order to involve no
change in the cursor position. Since tis display is effected without
rewriting contents of the video memory, the apparatus according to the
present invention reduces the load on software and provides an advantage
of low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects or features of the present invention will become
apparent from the following description of preferred embodiments thereof
taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a block diagram of a display apparatus according to one
embodiment of the present invention,
FIG. 2 is a view illustrating an example of mode change between a standard
mode and a reduction mode,
FIG. 3 is a view illustrating a relationship between a display screen and
video RAM addresses at a mode changing time,
FIG. 4 is a flowchart of an operation for changing from the reduction mode
to the standard mode,
FIG. 5 is an explanatory view illustrating a change on the screen between
the standard mode and a split screen mode,
FIG. 6 is an explanatory view illustrating a change on the screen between
the standard mode and a help menu mode,
FIG. 7 is a view showing display mode changes, and
FIG. 8 is a partial block diagram of another embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail hereinafter with
reference to the drawings.
FIG. 1 is a block diagram of a display apparatus according to one
embodiment of the invention. This display apparatus comprises a CPU 1, a
display sequencer 2, a video RAM 3, a latch 4, a character generator
memory 5, a shift register 6, and a display 7.
The CPU 1 is connected through a data bus A to the display sequencer 2,
video RAM 3, latch 4 and character generator memory 5. The CPU 1 transmits
a rewrite command regarding the number of lines to be displayed to the
display sequencer 2, a character font select command to the character
generator memory 5, and a character code data rewrite command to the video
RAM 3. This character code data rewriting does not include rewriting of
characters having different sizes. According to the present invention,
when there is a request for different size characters to be displayed, the
CPU 1 transmits the character font select command to the character
generator memory 5 and the number of lines rewrite command to the display
sequencer 2.
The display sequencer 2 transmits a character address signal to the video
RAM 3 through a bus line B, a raster address signal to the character
generator memory 5 through a bus line E, and a synchronizing signal to the
display 7 through a signal line G. The character address signal
corresponds to a character position on the screen of display 7. Upon
receipt of this signal, the video RAM 3 outputs a character code data
corresponding to a character address in the video RAM 3. The display
sequencer 2 comprises an HD68451 manufactured by Hitachi, for example.
As described above, the video RAM 3 is accessible to the CPU 1 and the
display sequencer 2. One display cycle period is divided into two parts,
one of which is allocated for the access by the CPU 1 and the other for
the access by the display sequencer 2.
The character code data output from the video RAM 3 are retained at the
latch 4 during one display cycle, and are successively input to an address
input terminal of the character generator memory 5 through a bus line C.
The character generator memory 5 receives, along with the character code
data, the raster address signal from the display sequencer 2, and outputs
character bit data corresponding to the two signals. The character
generator memory 5 stores a multiplicity of character fonts including
those of different size characters in particular. However, the character
code data and raster address signals do not serve to the extent of
selecting a character font size. The font size selection is effected by a
font size select command output from the CPU 1.
The bit data output from the character generator memory 5 are applied to
the shift register 6 through a data line D, where the bit data are
subjected to parallel to serial conversion for input to the display 7 as a
video signal. The display 7 shows characters determined by the video
signal on the screen and in response to the video signal and to the
synchronizing signal output from the display sequencer 2.
According to the above construction, the display mode is fixable to a
selected mode and a change of characters for display is effected by a
character code data rewrite command given from the CPU 1 to the video RAM
3. When the mode is changed to an input mode, edit mode, split screen mode
or help menu mode, characters are displayed on the screen with a character
size and the number of lines corresponding to the selected mode without
rewriting the character code data and without changing the relative
position of the cursor. This operation will be described next. The split
screen mode is intended for carrying out editing work on each divided
section of the screen independently. The help menu mode is for providing
the operator with an operational guidance. In either mode, the greater the
number of displayed line is, the more convenience is given to the
operator. In the case of input mode and edit mode, on the other hand, the
larger the character size is, the easier it is for the operator to work,
advantageously with a small number of lines displayed on the screen.
To facilitate understanding, the following explanation will be limited to
two display modes, the standard mode S and reduction mode R. The standard
mode S here means a screen mode presenting a minimum number of lines on
the screen of display 7 whereas the reduction mode R means a screen mode
presenting a maximum number of lines.
The difference in arrangement between the standard mode S and reduction
mode R lies in the number of dots (the number of rasters for one
character) in the vertical direction of the character font and the number
of lines shown on the screen of display 7.
As described hereinbefore, a plurality of character fonts of different
character sizes are stored in the character generator memory 5, and a
desired character size is selected upon input of a font select signal from
the CPU 1. In parallel with the font selection, the CPU 1 transmits the
number of lines rewrite command to the display sequencer 2.
The rewriting of the number of lines is effected by rewriting a one
character raster register, a number of lines register and a display start
address register in the display sequencer 2. In other words, the number of
scan lines necessary for forming one character is determined by rewriting
the one character raster register, the number of lines arranged vertically
is determined by rewriting the number of lines register, and a display
start position is determined by rewriting the display start address
register. FIG. 2 illustrates an example of mode change where the reduction
mode R has a character size half the character size of the standard mode
S. When the standard mode S is changed to the reduction mode R, the number
of rasters for one character is halved and the number of lines doubled,
thereby to form a blank space BL for displaying new characters input
through an external input device. In the standard mode S, for example, the
area for one character may be set to 8 by 12 dots, the entire screen area
to 48 letters by 24 lines, and the character display area excluding the
blank area to 32 letters by 16 lines. Then, the one character raster
register is set to 12 and the number of lines register is set to 16. When
the mode is changed from the standard mode S to the reduction mode R and
an 8 by 6 dot character font is selected by the font select signal, for
example, the one character raster register is set to 6 and the number of
lines register to 32, whereby the character display area on the screen
becomes 32 characters by 32 lines. The display start address is calculated
on the basis of the cursor postion. The method of this calculation will be
described with reference to FIG. 3 which illustrates a relationship
between the display screen and the addresses in the video RAM at a time of
mode change from the standard mode S to the reduction mode R. As shown in
FIG. 1, the video RAM retains certain character code data corresponding to
the reduction mode R. However, a display in the standard mode S is
effected without changing the cursor position on the screen and contents
of the video RAM, by moving the display start address register from A1 to
A2. Assuming that A1 represents the display start address for the
reduction mode R provided there is no blank lines on the display screen,
A3 represents the cursor address, N represents the number of lines, and L
represents a line buffer size of the video RAM (an area on the memory in
the video RAM corresponding to one line on the display screen), then a
leading address A4 of the line on which the cursor is present is obtained
by subtracting the remainder of (A3-A1)/L from A3. Consequently, if the
standard mode S has the number of lines M, the display start address A2
for the standard mode S is derived from the following equation:
A2=A4-L.times.K,
where
K=(A4-A1).times.(M/N).times.(1/L) (1)
If there are blank lines on the display screen, the leading address A4
corresponds to a line point for the line to which the cursor belongs.
Therefore, by obtaining the address of this line pointer, the display
start address A2 for the standard mode S may be obtained in the above
manner.
When the mode is changed from the standard mode S to the reduction mode R,
the display start address may be obtained by substituting (N/M) for (M/N)
in the above equation (1).
The display start address thus obtained is set to the display start address
register in the display sequencer.
The display sequencer transmits a display start address signal and a signal
of the number of lines register to the video RAM 3 through the bus line B,
which are then input to the character generator memory 5 through the latch
4, to generate a selected bit pattern with the one character raster
address. This bit pattern is subjected to the parallel to serial
conversion at the shift register 6 and thereafter is presented on the
display 7. The size of the character displayed corresponds to a selected
mode, the number of lines equals a number set to the number of lines
register, and the display start point is at a position designated by the
display start address. The display apparatus having the described
construction permits the standard mode S to be selected when a large
character size is desirable such as for the input mode and the edit mode,
and the reduction mode R to be selected to display a large number of lines
for the split screen mode and the help menu mode. Moreover, this apparatus
requires only a small load for software and is economical since the
switching between the reduction mode and the standard mode is effected by
operating the character generator memory 5 and without rewriting the
character codes stored in the video RAM 3.
FIG. 4 shows a flowchart illustrating the operation of the above display
apparatus for changing the mode from the reduction mode to the standard
mode.
In particular, FIG. 4 is a flowchart showing the operation executed by the
CPU 1 for converting the display from the reduction mode into the standard
mode.
At Step 1, when a mode conversion command is input by a mode change key,
the address f the video RAM 3 which stores the code data of the character
indicated by the cursor on the display 7, i.e., the cursor address A3, is
read from the display sequencer 2.
At Step 2, using the above cursor address A3, the display start address in
the standard mode is obtained with equation (1) above.
At Step 3, the font select signal is sent to the character generator memory
5 in order to select the character font for the standard mode.
At Step 4, the display sequencer 2 registers are equipped with the display
start address, the maximum raster address, and the number of vertical
lines. Then the standard mode display is carried out.
FIG. 5 shows a change on the screen occurring with a mode change between
the standard mode and the split screen mode. In this case also, the screen
pattern is rearranged between the two modes without changing the relative
position of the cursor. More particularly, a cursor position on the screen
for the standard mode corresponds to a cursor position in a window (i.e.
each divided section formed on the screen) produced in the split screen
mode, whereby the operator is free from an extra operation for moving the
cursor.
FIG. 6 shows a change on the screen occurring with a mode change from the
standard mode to the help menu mode. The help menu mode produces a menu
window on a section of the screen (the shaded portion in FIG. 6), and
therefore the cursor may be fixed to a position on the screen during the
mode change.
FIG. 7 is a mode change diagram illustrating the display modes and various
input steps for establishing these display modes. Though keys such as a
mode change key, a split key and so on are not shown in the drawings so
far referred to, these keys are provided on a keyboard belonging to the
display apparatus.
In particular, FIG. 7 shows the relationship between the display modes and
the input keys. This embodiment has four display modes: standard,
reduction, split screen, and help menu. A mode conversion, shown by the
arrows in FIG. 7, is executed by operating a particular mode conversion
key (i.e., split key, split close key, menu key, or menu close key) while
in another mode.
FIG. 8 shows another embodiment of the present invention. In this example,
the character generator memory 5 comprises a RAM to which an external
memory 8 such as an external ROM or an external disk storing character
fonts is connected. Upon receipt of a command from the CPU 1, the external
memory 8 transfers bit data of a selected character font to the character
generator memory 5 by high speed transfer such as direct memory access.
Thereafter the character data in the character generator memory 5 are
rewritten for a selected character size, and the CPU 1 transmits a command
to the display sequencer 2 for rewriting the number of lines. The
rewriting of the number of lines is carried out in the same sequence as in
the embodiment of FIG. 1 and its description will not be repeated.
According to this embodiment, when selecting a desired character font,
such as a character font for the reduction mode R, this character font may
just be transferred from the external memory 8 to the character generator
memory 5. This permits the character generator memory 5 to have a small
capacity. This embodiment is particularly effective for operating the
apparatus with many character font sizes.
Although the present invention has been fully described by way of examples
with reference to the accompanying drawings, it is to be noted that
various changes and modifications will be apparent to those skilled in the
art. Therefore, unless otherwise such changes and modifications depart
from the scope of the present invention, they should be construed as being
included therein.
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