Apparatus for generating a special font character by using normal font character data

A character font generating apparatus comprising character ROM for storing font data of a character in a form of a plurality of horizontal lines each of which consists of a predetermined number of dots, a shift register with a data storing portion including the same number of flip-flops as the predetermined number, which stores data in parallel in response to a storing timing signal and outputs the stored data in serial in synchronization with a transfer clock signal, italic generation timing circuit for generating storing timing signals to be supplied to the shift register such that each of the storing timing signals is generated for each horizontal line of the font data stored in the character ROM on a different timing from timing of the other storing timing signals with respect to a time when a scan of a line is started, and display control circuit for controlling a data transfer from the character ROM to the shift register such that dot data of each horizontal line of a font data stored in the character ROM is transferred to the data storing portion of the shift register for storing the dot data into the storing portion in parallel based on a storing timing signal generated by the italics generation timing circuit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a image displaying apparatus which generates 
italic font character by using normal font character dot data which are 
stored in a character ROM. 
2. Description of the Related Art 
Recently, On Screen Display (OSD) function is built in many television 
receivers for displaying current channel, current level of volume on a 
screen. A user may change these parameters while viewing the parameters 
displayed on the screen. The OSD function is realized by a single-chip 
microcomputer used in a television receiver and is controlled by an image 
display unit. Further, at present, by utilizing the OSD function, not only 
channels and volume levels, but also operation procedures of the receiver 
or subtitles are displayed on a screen. Under these circumstances, the 
requirements for such an image display unit are becoming higher and more 
diverse. As one of the requirements is to display characters in italics. 
FIG. 7 is a block diagram showing a conventional image displaying apparatus 
which generates italics font, described in Japanese Laid-Open Patent 
Application HEI 5-181447. In FIG. 7, reference numeral 16 denotes a data 
shift control circuit, 17 denotes a decoder, 1 denotes a readout address 
control circuit, 10 denotes a RAM for storing display data, 13 denotes a 
superimposing circuit, 14 denotes a shift register, 15 denotes a display 
control circuit. 
FIG. 8(a) is a figure showing the character "A" in a normal font and FIG. 
8(b) is a figure showing the character "A" in italics which is generated 
by the conventional apparatus of FIG.7. 
A font selection bit signal S1 is outputted from the display data RAM 10 
and inputted to the decoder 17. The font selection signal S1 is a signal 
which is outputted from the display data RAM 10 together with display mode 
data for each character such as character code data and color information 
data. This signal S1 indicates information whether a character is 
displayed in a normal font or in italics. The count value signal V1 is 
outputted from the readout address control circuit 1, indicating which 
horizontal line of a character is being read out. The signal V1 is 
inputted to the decoder 17 as well as the display control circuit 15. 
FIGS. 9(a), 9(b), 9(c) show a configuration of shift register 14 and a way 
in which character data is stored into the shift register 14. The shift 
register 14 consists of serially connected 16 flip-flops 18a-18p. Further, 
the shift register 14 is constituted such that data may be transferred and 
stored in parallel to any consecutive flip-flops out of the 16 flip-flops 
18a-18p. An italic font character is generated by varying a set of 10 
flip-flops for storing horizontal line data depending on the order of the 
current horizontal line. The storing of the 10 dot horizontal line data is 
controlled by the data shift control circuit 16 based on the signal S2 
from the decoder 17. When a character in a normal font is displayed, the 
output signal S2 becomes constant. As shown in FIG. 9(c), the storing 
position in the shift register 14 is the same regardless of the order of 
the current horizontal line of a character. 
On the other hand, when a character in a italic font is displayed, the font 
selection bit signal S1 activates the decoder 17. For example, when a 
character should be shifted one dot for each two horizontal lines as shown 
in FIG. 8, the character dot data of 1st and 2nd horizontal lines are 
stored in the flip-flops 18g-18p of the shift register 14. The pieces of 
character dot data of 3rd and 4th horizontal lines are stored in the 
flip-flops 18f-18o of the shift register 14. As in the same way, the 
pieces of character dot data of the horizontal lines 5 and 6, 7 and 8, . . 
. , 13 and 14 are stored in the shift register 14, while shifting a 
position of the flip-flops thereby producing a character in italics as 
shown in FIG. 8(b). 
SUMMARY OF THE INVENTION 
The conventional character font generating apparatus is constituted as 
explained above and it is necessary for the apparatus to have a shift 
register having larger number of bits than a number of dots of a 
horizontal line of a character. This is one of the reasons for the 
difficulty in making the size of the apparatus smaller. Further, in the 
conventional apparatus, the movement of dot data of one horizontal line is 
performed with a precision corresponding to a cycle of a transfer clock 
signal for a shift register. 
Therefore, an object of the invention is to provide a character font 
generating apparatus which generates a special character font from the 
normal character font data without storing special character font data in 
the apparatus with a smaller size and with a high precision. 
In order to accomplish the above object, the character font generating 
apparatus comprising means for storing font data of a character in a form 
of a plurality of horizontal lines each of which consists of a 
predetermined number of dots; a shift register including a data storing 
portion with an area of the same number of bits as the predetermined 
number, which stores data in parallel in response to a storing timing 
signal and which outputs the stored data in serial in synchronization with 
a transfer clock signal; means for generating storing timing signals to be 
supplied to the shift register such that each of the storing timing 
signals is generated for each horizontal line of the font data stored in 
the font data storing means on a different timing from the other storing 
timing signals with respect to a time when a scan of a line is started; 
and means for controlling a data transfer from the font data storing means 
to the shift register such that dot data of each horizontal line of a font 
data stored in the font data storing means is transferred to the data 
storing portion of the shift register for storing the dot data into the 
storing portion in parallel based on a storing timing signal generated by 
the storing timing signals generating means. 
Therefore, a special character font may be produced by using a shift 
register having the area of storing only the dot data of one line of a 
character. This contributes to making a lighter and smaller apparatus. 
Further, in the character font generating apparatus of this invention, the 
font data stored in the font data storing means is a normal font character 
data, the storing timing signals generating means generates storing timing 
signals to be outputted to the shift register such that a storing timing 
signal for a later horizontal line is generated earlier with respect to a 
time when a scan of a horizontal line is started, and the shift register 
outputs an italic character data corresponding to the normal font 
character data. 
Therefore, an italic font may be produced by using a shift register having 
the area of storing only the dot data of one line of a character. This 
contributes to making a lighter and smaller apparatus. 
Further, in the character font generating apparatus of this invention, the 
storing timing signals generating means generates storing timing signals 
to be supplied to the shift register for all the horizontal lines on a 
constant timing with respect to a time at which a scan of a horizontal 
line is started when a font selection signal indicative of normal font is 
inputted to the storing timing signals generating means and the storing 
timing signals generating means generates storing timing signals to be 
supplied to the shift register such that a storing timing signal for a 
later horizontal line is generated earlier with respect to a time at which 
a scan of a horizontal line is started when a font selection signal 
indicative of italic font is inputted to the storing timing signals 
generating means. 
Therefore, a font may be selected between an italic font and normal font by 
storing only the data of normal font character. 
Further, in the character font generating apparatus of this invention, the 
storing timing signals generating means generates storing timing signals 
with a precision corresponding to half a cycle of the transfer clock 
signal by using timing of leading edges and trailing edges of the transfer 
clock signal. 
Therefore, a more smooth character font may be obtained and displayed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
The first embodiment of the invention will be explained in detail with 
reference to the figures. 
FIG. 1 is a block diagram showing the constitution of the image display 
apparatus of this invention by using a single-chip microcomputer. In this 
figure, reference numeral 20 denotes a CRT control register, 30 denotes a 
vertical position register, 40 denotes a character size register, 50 
denotes a horizontal position register, 60 denotes a display data RAM, 70 
denotes a CRT port control register, 80 denotes an oscillating circuit, 90 
denotes a display position control circuit, 100 denotes a display control 
circuit, 110 denotes a character ROM, 120 denotes an italics generation 
timing circuit, 130 denotes a shift register, 140 denotes a flip flop, 150 
denotes an output circuit. 
The horizontal synchronization signal HSYNC and the vertical 
synchronization signal VSYNC are supplied to the display position control 
circuit 90. An external crystal oscillator 81 is connected to the 
oscillating circuit 80 which oscillates at a certain frequency while the 
circuit is being reset by each vertical synchronization signal VSYNC. The 
crystal oscillator 81 may be replaced by a ceramic oscillator. The output 
signal from the oscillating circuit 80 is used as a reference clock for a 
display which is supplied to the display position control circuit 90 and 
the output circuit 150. 
The data for displaying a desired character or a pattern is inputted to the 
display data RAM 60 and the registers 20, 30, 40, 50, 70 via the data bus 
160 in accordance with instructions from a CPU whose description is 
omitted from the FIG. 1. The data stored in the CRT control register 20 is 
supplied to the display control circuit 100 and the output circuit 150 for 
controlling ON/OFF of character display. The pieces of data corresponding 
to vertical position and horizontal position at the time of starting a 
character display are inputted to the vertical position register 30 and 
the horizontal position register 50, respectively. The data corresponding 
to a size of a character to be displayed is inputted to the character size 
register 40. The pieces of data stored in these registers 30, 40, and 50 
are supplied to the display position control circuit 90. RGB (Red, Green, 
Blue) signals are outputted from the output circuit 150 based on the 
values of data stored in the CRT port control register 70. The display 
data RAM 60 includes character code data, color code data, attribute data 
indicating characteristics of characters. 
A value of data stored in the horizontal position register 30 is compared 
with a counted number of the horizontal synchronization signals HSYNC in 
the display position control circuit 90. Then, a value of data stored in 
the horizontal position register 50 is compared with a counted number of a 
display clock outputted from the oscillating circuit 80. As a result of 
the comparisons, when the values in the registers 30 and 50 coincides with 
the counted values, respectively, the display position control circuit 90 
sends a display permission signal to the display control circuit 100. 
Responsively to the display permission signal, the display control circuit 
100 is activated, thereby the count number of horizontal synchronization 
signal HSYNC is supplied to the display data RAM 60 and then the character 
code data from the display data RAM 60 is inputted to the character ROM 
110 in the order in which the corresponding characters are displayed. The 
color code data and the attribute data are supplied to the output circuit 
150. On the other hand, the character codes are decoded by referencing the 
character ROM 110 and each line data of a normal font character data 
corresponding to the character code data is sent to the shift register 130 
where each line data is stored in parallel. The data from the display 
control circuit 100 for generating a character in italics is supplied to 
the italics generation timing circuit 120 regularly. 
FIG. 2 is a block diagram showing a constitution of the shift register 130. 
As shown in this figure, the shift register 130 includes ten flip-flops 
D0-D9, which are serially connected with each other. One line data from 
the character ROM 110 is stored into these flip-flops D0-D9 in parallel. 
The data stored in the shift register 130 is supplied to the flip-flop 140 
by a bit-by-bit basis in synchronization with a shift register transfer 
clock provided by the italics generation timing circuit 120. 
FIGS. 3(a)-3(d) are timing charts which show an operation of the shift 
register 130. FIG. 3(a) shows a shift register transfer clock signal. SC. 
FIG. 3(b) shows a shift register storing timing signal ST which shows 
timing of storing one line data from the character ROM 110 into the shift 
register 130 in parallel. FIG. 3(c) shows data outputted at the point a in 
FIG. 2. FIG. 3(d) shows data outputted at the point b in FIG. 2. As shown 
in FIGS. 3(a)-3(d), the shift register 130 performs a shift operation at 
the leading edge T31 of the shift register transfer clock SC and the 
flip-flop 140 performs a latch operation at the trailing edge T32. 
In this embodiment, the shift register storing timing signal ST is 
generated at a leading edge of the shift register transfer clock signal 
SC. The pulse ST32 of the shift register storing timing signal ST is 
subsequently generated at the tenth trailing edge of the shift register 
transfer clock signal SC for storing subsequent line data into shift 
register 130 from the pulse ST31 of the shift register storing timing 
signal ST generated at the italics generation timing circuit 120 because a 
number of dots in horizontal direction of a character is 10. 
Next, the operation of generating a normal font character will be 
explained. When the font selection signal indicative of normal font from 
the display data RAM 60 is sent to the italics generation timing circuit 
120, each one line data is stored into the shift register 130 at the 
constant timing from the start of scanning each line regardless of the 
order of the horizontal line. After the storing of one line data (10 dots 
data) is finished, the one line data is sent in serial to the flip-flop 
140 in synchronization with leading edges of the shift register transfer 
clock signal SC outputted from the italics generation timing circuit 120. 
The data outputted to the flip-flop 140 is latched at the timing of a 
trailing edge of the shift register transfer clock signal SC and is 
outputted to the output circuit 150 in sequence. In accordance with color 
code data and attribute data sent from the display data RAM 60, the output 
circuit 150 performs coloring and attribute processing to a normal font 
character and resultant RGB signals are outputted accordingly. 
Next, the operation of generating a character in italics will be explained. 
FIG. 4 shows shift register transfer clock SC, shift register storing 
timing signal ST for each horizontal line, character "1" in italics 
obtained by changing the timing of storing one line data into the shift 
register in sequence. 
When a font selection signal indicative of italics from the display data 
RAM 60 is inputted to the italics generation timing circuit 120, the 
italics generation timing circuit 120 produces shift register storing 
timing signals whose timings are different from each other based on shift 
register storing timing data sent from the display control circuit 100. 
These produced shift register storing timing signals are supplied to the 
shift register 130. Namely, as shown in FIG. 4. the shift register storing 
timing pulse ST41 for the first line is produced after the time period TD1 
elapses from the first transfer clock pulse in synchronization with a 
leading edge of the shift register transfer clock. Next, the shift 
register storing timing pulse ST42 for the second line is produced after 
the time period TD2 elapses from the first transfer clock pulse in 
synchronization with a leading edge of the shift register transfer clock. 
Similarly to the above, shift register storing timing pulses for the lines 
after the second lines are produced such that a shift register storing 
timing pulse is produced gradually earlier for a later horizontal line. 
The data of 10 dots of each line is stored into the shift register 130 in 
parallel in synchronization with a leading edge of the produced shift 
register storing timing signal ST. The stored data is shifted in 
synchronization with a leading edge of the shift register transfer clock 
SC. The flip-flop 140 latches inputted data in synchronization with a 
trailing edge of the shift register transfer clock signal SC. As stated 
above, data for a character in italics is sent to the output circuit 150 
by making the timing of storing data into the shift register earlier for a 
later horizontal line. In accordance with color code data and attribute 
data sent from the display data RAM 60, the output circuit 150 performs 
coloring and attribute processing to the italic font character and 
resultant RGB signals are outputted accordingly. 
In this embodiment, a character in italics is generated by advancing the 
timing of storing data into the shift register by one line, however, 
italic character may be produced by advancing the timing of storing data 
into the shift register by a plurality of lines. Further, a character in a 
font other than italics may be generated by advancing and delaying the 
timing of storing data into the shift register, and by changing the amount 
of the period to be advanced or to be delayed by one line or plurality of 
lines. 
Embodiment 2 
The second embodiment of the invention will be explained with reference to 
the figures. In the above embodiment, the data is stored into the shift 
register in synchronization with a leading edge of the shift register 
transfer clock signal SC. That is, the precision of the horizontal 
movement for one line is defined by one cycle of the shift register 
transfer clock signal SC. However, in this embodiment, the precision of 
the horizontal movement for one line may be doubled. the constitution of 
the image display apparatus of this embodiment is the same as that shown 
in FIG. 1 except for the italics generation timing circuit 120a and 
duplicate explanation is omitted. 
FIG. 5 is a circuit diagram of an italics generation timing circuit 120a of 
this embodiment. As shown in this figure, the italics generation timing 
circuit 120a includes the dividing circuit 121 which produces the shift 
register transfer clock SC with 50 percent duty ratio and with half a 
frequency of the reference clock, the shift register storing timing 
generation circuit 123 which generates the shift register storing timing 
signal ST, and the timing control circuit 122 which controls the shift 
register storing timing generation circuit 123. The shift register storing 
timing generation circuit 123 includes the transmission gate 125 and the 
clocked inverter 124 connected in parallel to the transmission gate 125. 
The font selection signal FS from the display data RAM 60 is inputted to 
the timing control circuit 122. The line signal LN indicating which line 
is being displayed and the data ID for generating an italic character are 
transferred from the display control circuit 100 to the timing control 
circuit 122. 
Next, the operation of displaying a normal font character will be 
explained. In this case, the timing control circuit 122 keeps the clocked 
inverter 124 off continuously. Then, the timing control circuit 122 
produces a shift register storing timing signal by making the transmission 
gate 125 on during one clock cycle period at the constant timing from the 
start of scanning lines for each of the lines. The produced shift register 
storing timing signal is supplied to the shift register 130. 
Next, the operation of displaying an italic character will be explained. 
FIGS. 6(a)-6(c) show the timing charts of the signals shift register 
transfer clock SC, signal INV outputted from the clocked inverter 124 and 
shift register storing timing signal ST, respectively. 
As shown in FIG. 6, for the first line of a character, the timing control 
circuit 122 keeps the clocked inverter 124 off continuously and keeps the 
transmission gate 125 on during a predetermined period after a certain 
time period elapses from the start of scanning the line, thereby the pulse 
ST61 of the shift register storing timing signal ST is generated. For the 
second line, the timing control circuit 122 keeps the transmission gate 
125 off continuously and keeps the transmission gate 125 on during a 
predetermined period after a certain time period elapses from the start of 
scanning the line, thereby the pulse ST62 of the shift register storing 
timing signal ST is generated. In this case, the timing control circuit 
122 controls the shift register storing timing generation circuit 123 such 
that the pulse ST62 is generated earlier than the pulse ST61. For the 
third line, the timing control circuit 122 keeps the clocked inverter 124 
off continuously and keeps the transmission gate 125 on during a 
predetermined period after a certain time period elapses from the start of 
scanning the line, thereby the pulse ST63 of the shift register storing 
timing signal ST is generated. In this case, the timing control circuit 
122 controls the shift register storing timing generation circuit 123 such 
that the pulse ST63 is generated earlier than the pulse ST62. Similarly to 
the above, for the other lines, the timing control circuit 122 controls 
the shift register storing timing generation circuit 123 such that pulses 
of the shift register storing timing signal ST are generated gradually 
earlier with respect to the start of the scanning a line. The operations 
after the shift register storing timing signal ST is supplied to the shift 
register 130 are the same as those of the first embodiment and the 
duplicate explanation is omitted. 
As explained above, in this embodiment, a shift register storing timing 
signal ST may be prepared on the timing of half a cycle of the shift 
register transfer clock signal SC. Namely, the precision of the horizontal 
movement in one line may be twice as high as that of the first embodiment, 
thereby more smooth italic character may be produced. 
Similarly to the first embodiment, an italic character may be produced by 
advancing the timing of storing data into the shift register by a 
plurality of lines. Further, a character in a font other than italics may 
be generated by advancing and delaying the timing of storing data into the 
shift register, and by changing the amount of the period to be advanced or 
to be delayed by one line or plurality of lines. Especially in the second 
embodiment, movement of dots in one line may be set more precisely. 
Therefore, the apparatus of this embodiment is suitable for preparing a 
character in a special font other than italics as well.