[Coco] coco2 MC6883/6847 memory map

[Arthur Flexser]

Sorry, the correct link for the Key264K manual is

ftp://ftp.maltedmedia.com/coco/NEWLY-RECEIVED/Key-264K.pdf

Art

On Mon, Nov 10, 2014 at 6:53 PM, Arthur Flexser <flexser at fiu.edu> wrote:

> P.S.  The docs, which are here:
>
>
> http://www.colorcomputerarchive.com/coco/Documents/Manuals/Applications/Key264K%20(Key%20Color%20Software).pdf
>
> have a copyright date of 1983, quite a bit before the recent estimates
> here of when CoCo multitasking began.
>
> The program is here:
> http://www.mmnt.net/db/0/0/ftp.maltedmedia.com/coco/SOFTWARE/DISK/Applications/Key-264K
>
> Art
>
> On Mon, Nov 10, 2014 at 4:47 PM, Arthur Flexser <flexser at fiu.edu> wrote:
>
>> There was a program for the CoCo that sounds similar to the Dragon
>> program described.  I believe it was called KEY264K, and was advertised in
>> Rainbow.  You could have two Basic programs simultaneously, one in each of
>> the 32K RAM banks, and either switch between them or have both running at
>> once, with one running in the background.  I suppose that could be
>> considered multitasking, possibly before OS-9 came on the scene.  (Somebody
>> was asking when CoCo multitasking first appeared.)
>>
>> Art
>>
>> On Mon, Nov 10, 2014 at 9:50 AM, Tormod Volden <lists.tormod at gmail.com>
>> wrote:
>>
>>> On Mon, Nov 10, 2014 at 2:39 PM, Brett Gordon wrote:
>>> > 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
>>> >
>>>
>>> The SAM (6883/74LS783) has a memory map type /and/ a RAM page switch.
>>> Brett is talking about the memory map type which basically switches
>>> between RAM+ROM (map 0) or all-RAM (map 1).
>>>
>>> The page switch decides which of the 32K RAM banks is accessed in map 0.
>>>
>>> This was used by Sarah from the Dragon forums for her "Double Dragon"
>>> - multitasking two (32K mode) BASIC programs/environments on a Dragon
>>> 64:
>>> http://archive.worldofdragon.org/phpBB3/viewtopic.php?f=5&t=488&p=2620#p2620
>>>
>>> > On Mon, Nov 10, 2014 at 7:53 AM, didier derny wrote:
>>> >> I'm trying to understand how the coco 2 works J
>>> >>
>>> >>
>>> >>
>>> >> It's relatively clear except for one thing
>>> >>
>>> >> [I probably missed something in the datasheets]
>>> >>
>>> >>
>>> >>
>>> >> When a coco2 is running with the basic I suppose it is in map type 0
>>> >>
>>> >> With 32k rom/io  and 2 pages 32k ram  (if 64k installed).
>>> >>
>>> >>
>>> >>
>>> >> If the processor is in page 0  where is the video ? page 0 or page 1 ?
>>>
>>> The processor is happily unaware about the page switching. It is the
>>> SAM that is in page 0 or 1. The video ram access goes through the SAM,
>>> to the active page.
>>>
>>> Tormod
>>>
>>> >>
>>> >>
>>> >>
>>> >> And what happens if I switch from page 0 to page 1
>>> >>
>>> >> The video also switch  ?
>>>
>>> --
>>> Coco mailing list
>>> Coco at maltedmedia.com
>>> https://pairlist5.pair.net/mailman/listinfo/coco
>>>
>>
>>
>