Discussion:
Why does the colour map move on the VIC-20?
(too old to reply)
Lawrence Woodman
2020-12-10 19:34:05 UTC
Permalink
Hello,

Does anyone know why the colour map moves between $9400 and $9600 on the
Vic? Is there a reason it couldn't stay at a single location such as
$9400?

I've wondered about this for a while and there is probably an obvious
reason that I'm missing but I would love to know. My interest in this was
renewed recently when I was creating a video (links below) which shows
the colour map being used as a location to store data and now it seems
I really should find out. I've posted about this on vcfed.org but
there's been no answer yet so am hoping someone here will know.

Run Code and Store Data in Display Memory on the VIC-20
Video:

Article: https://techtinkering.com/articles/code-and-data-in-display-memory-on-the-vic-20/


Best wishes


Lorry

---
Retro, VIC-20, CP/M, etc
https://techtinkering.com
https://youtube.com/techtinkering
Tom Lake
2020-12-10 20:30:39 UTC
Permalink
Post by Lawrence Woodman
Hello,
Does anyone know why the colour map moves between $9400 and $9600 on the
Vic? Is there a reason it couldn't stay at a single location such as
$9400?
I've wondered about this for a while and there is probably an obvious
reason that I'm missing but I would love to know. My interest in this was
renewed recently when I was creating a video (links below) which shows
the colour map being used as a location to store data and now it seems
I really should find out. I've posted about this on vcfed.org but
there's been no answer yet so am hoping someone here will know.
Run Code and Store Data in Display Memory on the VIC-20
Video: http://youtu.be/EkfBijC8MSU
Article: https://techtinkering.com/articles/code-and-data-in-display-memory-on-the-vic-20/
Best wishes
Lorry
Maybe they didn't really plan on memory expansion cartridges?
Lawrence Woodman
2020-12-11 07:51:35 UTC
Permalink
Post by Tom Lake
Post by Lawrence Woodman
Does anyone know why the colour map moves between $9400 and $9600 on
the Vic? Is there a reason it couldn't stay at a single location such
as $9400?
Maybe they didn't really plan on memory expansion cartridges?
Memory expansion cartridges shouldn't really make any difference, as far
as I can make out, as the full 1Kb 4-bit RAM is addressable whether
memory cartridges are being used or not.


Lorry

---
Run Code and Store Data in Display Memory on the Commodore VIC-20
https://techtinkering.com/articles/code-and-data-in-display-memory-on-the-vic-20/
Dennis Katsonis
2020-12-12 00:23:00 UTC
Permalink
-=> Lawrence Woodman wrote to All <=-

LW> Hello,

LW> Does anyone know why the colour map moves between $9400 and $9600 on
LW> the Vic? Is there a reason it couldn't stay at a single location such
LW> as $9400?

LW> I've wondered about this for a while and there is probably an obvious
LW> reason that I'm missing but I would love to know. My interest in this
LW> was renewed recently when I was creating a video (links below) which
LW> shows the colour map being used as a location to store data and now it
LW> seems I really should find out. I've posted about this on vcfed.org
LW> but there's been no answer yet so am hoping someone here will know.

LW> Run Code and Store Data in Display Memory on the VIC-20
LW> Video: http://youtu.be/EkfBijC8MSU
LW> Article:
LW> https://techtinkering.com/articles/code-and-data-in-display-memory-on-th
LW> e-vic-20/


LW> Best wishes

I think it had to do with how the VIC chip addressed memory internally. It was
only able to "see" a portion of the Vic 20 memory map, and if you moved the
screen memory, then the color RAM would also have to move so it would map
correctly.

http://tinyvga.com/6561

... Dennis Katsonis
=== MultiMail/Linux v0.52
Lawrence Woodman
2020-12-18 12:41:52 UTC
Permalink
Post by Dennis Katsonis
-=> Lawrence Woodman wrote to All <=-
LW> Does anyone know why the colour map moves between $9400 and $9600 on
LW> the Vic? Is there a reason it couldn't stay at a single location such
LW> as $9400?
I think it had to do with how the VIC chip addressed memory internally. It was
only able to "see" a portion of the Vic 20 memory map, and if you moved the
screen memory, then the color RAM would also have to move so it would map
correctly.
http://tinyvga.com/6561
Unfortunately, I don't think it really solves the mystery as while I
understand that the 14-bit address used by the VIC restricts where the
screen map can be, I don't think this alone explains why the colour map
changes between $9400 and $9600 as it uses the same number of bit
positions either way.

Having said that, the link you gave has some excellent information and I
love how it is presented. Thanks for posting it.

Lorry

---
Run Code and Store Data in Display Memory on the Commodore VIC-20
https://techtinkering.com/articles/code-and-data-in-display-memory-on-the-vic-20/
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