Specifications

CONSTRUCTION
just as in ‘d’,
with 64 being
the code. The
table low-ad-
dress is also
10 64 and the
high address
equals 10 64
+ 80, and so
on. Further,
we need not even write these codes in
any order, because we are at liberty to
write any address in the look-up table!
(That works really when we ask several
persons to prepare the font codes and mix
them together!)
How exactly does one prepare the
table of dots? Take a graph sheet and
make 12 x 12 rectangles. Paint the char-
acter in this slot, as it would appear when
printed. The dots must be darkened to
show up the character. Positioning is im-
portant; one has to make sure that hooks,
if appended to this character, will fall
within the space of 12 x 12 without cut-
ting or merging. For example, ‘kra’ and
‘ku’ and ‘koo’ writing must be possible by
adding these respective hooks to the char-
acter, if required. Then, looking at Fig. 3,
for ‘ka’ (d), we read the dots (in nibbles)
in complimentary form and write them
down as under:
Line 1 … 000 Line 5 … 010 Line 9 … 1D6
Line 2 … 000 Line 6 … 1D6 Line 10 … 010
Line 3 … 000 Line 7 … 139 Line 11 … 000
Line 4 … FFF Line 8 … 139 Line 12 … 000
The values are complemented and
written as two nibbles at a location.
Complementing is necessary to make FF
appear as blank on the screen. The table
thus obtained for ‘ka’ (d), occupying 18
bytes (36 nibbles), is shown below:
Address Code
14 B4 FF FF FF FF F0 00 FE FE
14 BC 29 EC 6E EE F0 1E FE FF
14 C5 FF FF
The table for each language will not
need more than 8 pages in an EPROM or
2k bytes in a file. Thus in one 2764, it is
possible to house the character generator
codes for four languages, say English and
three other Indian languages.
PC based design
In the PC based design, the software writ-
ten in BASIC loads a table of codes from
a file. This file is having the same data
as the EPROM in the dedicated micro-
processor based design.
The software for the computer based
display is made simple enough to be used
with any PC, without the need for large
memory or disk space. It could work even
with one floppy system, with just a 386
based PC even. The C++ or other lan-
guages are more library oriented and re-
quire a hard disk to work with. The C++
library already has different fonts and
sizes for English and we use this library
to write varied size of text on screen in
English. But, until the library for Indian
languages becomes similarly available, the
C++ is of no use here. Software makers
would have made fonts for several Indian
languages, but they have not put them in
a library form as the promoters of the ‘C’
language did it for English language. No
libraries for video display for Indian lan-
guages are currently available exploiting
the compactness of the C++. Until then,
we need to write code as and when we
want, and hence BASIC is better suited.
Hence this program has been devel-
oped in BASIC rather than C++ or other
Windows based software, for the simple
reason that it could be used for education
by institutes possessing even simple PC-
AT computers.
The program for a computer based
Hindi, English, and Tamil display is given
in BASIC language on page 49. This works
on an IBM PC with no restrictions of
memory, and can work directly from a
single floppy. This minimises the cost of
the computer system for the display. The
program given is based on Turbo BASIC
version 1.0, but the same is compatible
with Quick BASIC or other similar BA-
SIC interpreter-compilers working on the
PC.
The program first loads the file for
characters for four languages. Then the
user is asked to enter F1 to F4 keys to
select the language and S or L (capital)
for selecting small or large-size font. Any
time during typing text on screen, the
function keys may be pressed to change
the language, if desired.
F1 … Tamil
F2 … English
F3 … Tamil
F4 … Fourth language
The character generator here is a file.
It contains the same set of codes that are
used for the hardware based design
that follows. This is stored as file
‘chtamil2’, which is read and saved in the
array ‘ad (lan%,I%)’ that stores the dots.
This array is used in the program
throughout.
That makes it convenient to type sev-
eral sentences, up to 30 in a VGA moni-
tor screen on the computer, and then on
the next screen. For example, on one
screen, a Hindi poem could be typed to-
gether with its English and Tamil trans-
lations.
Printing a page is simply done using
the ‘Graphics.com’ program, which comes
with DOS. This must be run prior to run-
ning BASIC as:
A> Graphics
Then
A> BASIC
After entering text on one page, it can
be printed using shift + print screen keys.
This program is a simple version, and
other versions with file storage and print-
ing facility can be prepared with extra
statements.
For the use of the typist, it is neces-
sary to write the character strokes of the
respective language(s) on key tops of the
IBM PC keyboard, at least during the ini-
tial typing stage.
Note: The program in BASIC, to-
gether with its compiled .EXE file, will
be presented in Sept. 2000 EFY-CD. The
8 kilo-byte ‘chtamil2’ file containing the
Fig. 2: Keyboard for English, Hindi, and Tamil languages
Fig. 3: Character code
generation in 12x12 format
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