Posted By
Csabo
on 2025-03-01
09:23:23
|  Re: graphics area problem
the main program is incompletely loaded.
It's not, it just appears that way. Your first variable assignment is what messes it up.
The core issue is that LOAD/DLOAD from a BASIC program doesn't set the BASIC program end pointer ($2D/$2E, etc).
Here is how you can verify this yourself, perhaps seeing it in action will make it clear. Create a new empty D64 file in YAPE (or insert a blank disk, if you're doing it on a real computer). Write the following program:
0 A=A+1:?"TEST STRING";A:GOTO0
You can run this, works fine. Save it: DSAVE"SECOND". You can RESET, load it from disk (from direct mode), still works fine.
Now let's write another program. NEW (or RESET), then
0 DLOAD"SECOND
Save it: DSAVE"FIRST". So this program just loads the SECOND program.
Try running it! It will load, then the second program will stop, and after LIST, it appears that it been cut off or not loaded completely.
However, that's now what happened. When the FIRST program is loaded, the BASIC program end pointer is set to where THAT program ends. (Obviously!) Then the DLOAD command executes. This loads the SECOND program completely, but the BASIC program end pointer has not changed. All variables are allocated after the end of your program. Therefore, as soon as you use any variables, those will be allocated and written into the memory, overwriting and ruining your code.
What's the solution? The first statement of the program you're loading should be a couple of POKE statements which set up these pointers.
Let's say the program you want to load is from $1001 to $1567. In this case, if you set the end pointer and the start of the variables from $16##, you will be safe. (In other words, you increased the high byte - $15 - by one to $16, therefore you won't have to worry about the low byte at all.) You would have to write $16 to $2E, $30 and $32. This would be POKE 46, 22 : POKE 48, 22 : POKE 50, 22. Problem solved!
Let me know if you have any questions. |
