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Forums > C64 Coding > VIC Bank @ $c000-$ffff

2013-04-03 01:00

robo

Registered: Nov 2012
Posts: 9

VIC Bank @ $c000-$ffff

I'm trying to code a game and got into trouble with free memory space.
So I want to use RAM behind I/O and kernal ROM for graphics data storage.

I know how to manage that $01 and $dd00 things, but how can I upload data to that area >$cfff?
I'm using kernal routines for loading and don't know how to do it another way, so I will have to switch RAM off.
Is it possible since writes to ROM locations are sent to RAM?
I guess at least this will not work for $d000-$dfff.

If I'm totally wrong, how would you do it?

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2013-04-03 17:25

tlr

Registered: Sep 2003
Posts: 1790

Quoting JackAsser

How do one guarantee that writing to $dd00 doesn't screw up loading? How did you do it TLR?

I assumed CLK and DATA (and ATN) would be the same state after fetching a byte. A quick check of ACPTR ($EE13) indicates that is true.
So basically I just replicate that setup in every mirror. Timers are set to $FFFF and IRQs and timers disabled.

Quoting Oswald

one other question arises, whats up with mirrored VIC/SID/CIA registers? and I guess mirroring changes from machine to machine, so that demo might not be compatible with all machines.

On all stock C64s it should be the same. On the C128 it is different IIRC (is that true for C64 mode?) but as long as there are no (too evil) side effects on those additional mirrors it could work.

Quoting Count Zero

Also IO1 and 2 need to be taken care of whenever cartridges are active :)

I write those all 00 as I assumed it would be the "safest". Verified working with AR in vice.
In hindsight I should have made the load address $00ae though to force cartridges to use kernal load. Now you need to do OFF.

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