Posted By
Fuzzweed
on 2024-10-09
08:22:26
|  Zero page usage
Just enquiring about 'safe' spaces in the zero page for user variables.
I think I read $Dx (only) is given while the ROM routines are available. Is this correct?
And with roms banked out is it all available or are some locations still used for internal processes?
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Posted By
Harry Potter
on 2024-10-09
08:36:52
| Re: Zero page usage
There's a Plus4/C16 memory map at https://www.zimmers.net/anonftp/pub/cbm/maps/index.html. 
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Posted By
Fuzzweed
on 2024-10-09
09:16:47
| Re: Zero page usage
Thanks. Yeah that's shows the $D8 to $E8 user space, so that's ticked that one off.
The rest of it....
My hunch is if I'm not making any rom calls it's all mine, just not 100%sure, I'm quite new to 6502
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Posted By
Harry Potter
on 2024-10-09
09:18:42
| Re: Zero page usage
I'm glad to be of assistance.
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Posted By
Fuzzweed
on 2024-10-09
09:32:55
| Re: Zero page usage
:)
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Posted By
Harry Potter
on 2024-10-09
09:37:37
| Re: Zero page usage
I believe that $00 and $01 are used by the hardware, just like in the C64, but if you're not using the ROMs at all, everything else should be free.
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Posted By
SukkoPera
on 2024-10-09
10:34:17
| Re: Zero page usage
You should check SVS's Ultimate Map, it will tell you exactly which ZP bytes are used and which one are not.
For the ones that are used, if they are needed by BASIC and you never call its functions, you can use them freely. Same goes for those that are used by the KERNAL (ROM) functions (but be careful).
$00 and $01 are always reserved, as they aren't even actually mapped to RAM.
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