[Coco] coco2 MC6883/6847 memory map

[Brett Gordon]

Hey Didier,

The coco2's video processor is logically separate from the memory
mapping.  When basic starts up it is in Page 0 mode... where the
bottom (lowest address) 32k is routed to ram, and the top 32k is
routed to the ROM (BASIC).  If you switch to page 1 the lower half of
RAM remains the same, but the upper 32k of address space is routed to
additional RAM (if it exists).  Video takes it's memory from anywhere
in the logical map, but BASIC setups this up at address 0x400, in
lower address space.  I found the use of the word "PAGE" for the
memory in the docs to be a misnomer.   And switch from Page 0 to Page
1 doesn't do anything to Video... it still takes its memory from the
LOGICAL address space.  Just the Top 32k of the logical map is
switched out.

-B

On Mon, Nov 10, 2014 at 7:53 AM, didier derny <didier at aida.org> wrote:
> I'm trying to understand how the coco 2 works J
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> It's relatively clear except for one thing
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> [I probably missed something in the datasheets]
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> When a coco2 is running with the basic I suppose it is in map type 0
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> With 32k rom/io  and 2 pages 32k ram  (if 64k installed).
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> If the processor is in page 0  where is the video ? page 0 or page 1 ?
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> And what happens if I switch from page 0 to page 1
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> The video also switch  ?
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> --
>
> Didier
>
>
> --
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-- 
Brett M. Gordon,
beretta42 at gmail.com