Re: Screen memory mapping VIC-20

On 07.07.2017 13:39, Marko Mäkelä wrote:
> On Fri, Jul 07, 2017 at 10:11:06AM +0000, Baltissen, GJPAA (Ruud) wrote:
>> I found this in: http://www.zimmers.net/cbmpics/cbm/vic/memorymap.txt
>>> NOTE: When additional memory is added to block 1 (and 2 and 3), the 
>>> KERNAL relocates the following things for BASIC:
>
>> I used my auto disassembler on the ROM and found this:
>
> Hmm, is Pasi Ojala still on this list? He probably implemented some 
> crazy CPU-intensive graphics modes for the Vic-20, programmatically 
> changing the VIC-I registers on every raster line. That would easily 
> use all of the color RAM even with a smaller picture area.
Yes, I'm stll lurking here. :D

The ROM relocates the screen for the sole reason of providing contiguous 
RAM for BASIC.

The memory map changes depending on whether you have 3k or 8k(up to 24k) 
expansions connected.  Note that the VIC-I cannot see any of the 
external RAM.

With just 3k added the start of BASIC changes and the screen stays put. 
With 8k added, the screen moves to the start of the RAM, regardless of 
the presence of the 3k expansion. With 8k+ added the 3k expansion is not 
used for BASIC programs, but you could use it (PEEK/POKE) from your program.

I don't think I have changed the location of the color memory on the fly 
though.

www.iki.fi/a1bert/Dev/ or www.iki.fi/a1bert/Pu-239/

-Pasi


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