How Define set characters in BASIC with POKE ??

[Andrea]

Hello User's ATARI,

 

How to Define set characters in BASIC with POKE ??

 

 

[+gnusto]

Here's an article with basic examples that shows how to define, animate, and rotate character sets: https://www.atariarchives.org/agagd/chapter3.php

 

[zzip]

45 minutes ago, Andrea said:

Hello User's ATARI,

 

How to Define set characters in BASIC with POKE ??

 

 

each character is 8-bytes, one byte for each row.    They are stored in ATASCII order, first 128 characters only.  The trick is there is a pointer that you need to change to point to your new character set, and I forget where that pointer is offhand.

[TGB1718]

I believe each character set is 1K in size, the register that points to the character sets is 756 (Hex $2F4) it's called CHBASE

Default is 224 for upper case characters and 226 for lower case.

 

So if you create your own character set, it must reside on a page boundary, then poke the high byte of the address into location 756

 

First reserve the memory you want

 

Lower RAMTOP by 1K to place your new character set.

10 TOP=(PEEK(106)-4)*256

20   POKE 106,PEEK(106)-4  

 

in your program, have the new character set as DATA statements

then something like 

 

30 I=0

40 RESTORE 10000

50 READ A: IF A = -1 THEN 100

60 POKE TOP+I

70 I=I+1: GOTO 50

 

100 YOUR PROGRAM HERE

110 POKE 756,PEEK(106) : REM POINT AT YOUR NEW SET

.

.

9999 END

10000 DATA 1,23,3,4,65,77,88,99 

10010 DATA .... the rest of your CHAR set

11000 DATA , 33,44,55,66,77,88, -1  :REM end with a -1

 

Edited August 13, 2020 by TGB1718

[StickJock]

2 hours ago, TGB1718 said:

30 I=0

40 RESTORE 10000

50 READ A: IF A = -1 THEN 100

60 POKE TOP+I

70 I=I+1: GOTO 50

 

Your POKE is missing the value.  Should be POKE TOP+I,A

BTW:  Since the character set is a known size, you could change this to use a FOR/NEXT loop, which would take less code, likely be faster and also save the extra -1 in the data statements.

[TGB1718]

 thanks, just knocked that up to give an idea