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1995-04-22
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This program will help you learn how
to re-define the Atari character set.
It will draw an 8x8 graph in the top
left corner of the screen. This is
what you use to draw your new
character in. I highly recommend
having a sketch already made on graph
paper. It's MUCH easier that way!
Anyway, you start at the top line,
and in each bit you want to turn on,
enter the letter X. To move around
each line, use the arrow keys,
WITHOUT the CONTROL key. If you make
a mistake and enter an X in the wrong
spot, use the BACK ARROW to go to
that box, then hit the BACKSPACE key
to delete it from the grid and
memory. When finished with a
particular line, hit RETURN and that
line is saved. After hitting return,
there is no way to get back to that
line, so be careful!
When you hit RETURN after the last
line, you will be asked for the
specific character you wish to
replace. Enter the exact character,
NOT its ASCII code or anything else.
The program will do that. It will
then change the character, which
takes about 30 seconds. Afterwards,
it will display a DATA line that you
would use if you wrote the program
to re-define the charcters (see
below).
Things to note:
Use the left and right ARROW
keys to move around each line.
Enter an X in each spot (bit)
you wish to turn on.
To delete an X, use the ARROW
key to get to that spot, then
hit the BACKSPACE key.
Hit RETURN only after you know
the line is error-free.
Now, an attempt at a little character
re-definition information...
A character is roughly equal to one
byte of memory, made up of 8 bits.
Depending on which bits are set to
"on", you can create different shapes
for whichever characters you want.
When you enter an X in this program,
you are setting that BIT to on.
There is an easy way to re-define the
character set, and it was printed
in the February, 1984 issue of Antic.
This is what I used to help create
this program. At the end of the
program that was in Antic, you need
DATA statements that hold the
information needed to re-shape the
character. The first number is the
character number (different from its
ASCII code) and the other 8 numbers
tell which bits to turn on. When you
run my program, it will supply you
with the DATA statements for each
character you create. You then take
down these DATA statements and put
them in the program out of Antic.
So, my program will re-define one
character at a time, but you can do
as many as you want with the Antic
program, using the DATA statements
from my program! Got all that?!
The following program was in Antic,
written by Chris Chabris, and will
re-define the Atari character set:
(you may use your own line numbers,
of course)
10 CH=PEEK(106)-8:CH=CH*256
20 FOR LOOP=0 TO 1023:BYTE=PEEK(57344+LOOP):POKE CH+LOOP,BYTE:NEXT LOOP
30 RESTORE 100
40 READ NUM:IF NUM=-1 THEN (END, RETURN, GOTO, whatever)
50 NUM=NUM*8:FOR LOOP=0 TO 7:READ BYTE:POKE CH+NUM+LOOP,BYTE:NEXT LOOP
60 GOTO 40
100 DATA (from my program)
110 DATA
120 DATA
130 DATA
...and so on...
200 DATA -1
If you have any questions, refer to
Antic, February, 1984, or leave me
a message and I'll try to help.
Enjoy!
Tom Bellucco
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