[Coco] Dual UART with FIFO Card for the CoCo

[sales at gimechip.com]

Gene,
In response to your following question:
======================================
"I would like to ask how much trouble it would be if we could figure out a 
way to isolate the first $40 of page $FF by more fully decoding the two 
PIA's it uses, so they would not see a /cs except at $FF00-03, and $FF20-23.
That would clear out and make usable a considerable amount of i/o address 
space, allowing this to be addressed at $FF10-1F for instance.  That would
still leave room for 6 more 4 bit wide devices.
So basically, we first need a kit that will fix all of our coco's, freeing 
up this very sorely need i/o space."
======================================
RESPONSE:
--------------
The CoCo 1 and 2 wastes most of the $FF0x/$FF2x space and this waste is 
"mirrored" with the $FF1x/$FF3x area. It wouldn't be too difficult to modify 
the CoCo 1 and 2 so that the PIA's were not mirrored in the $FF1x/$FF3x 
space thus freeing the $FF1x and $FF3x areas for use.

On the CoCo 3 however, the PIA's only occupy the $FF0x and $FF2x areas. The 
$FF1x and $FF3x areas are already available for use on the CoCo 3. In fact, 
the Y3 select output of the 74LS138 provides a select signal that is active 
on $FF1x/$FF3x - this select could be easily decoded further for user 
projects.

-John


----- Original Message ----- 
From: "Gene Heskett" <gene.heskett at gmail.com>
To: <coco at maltedmedia.com>
Sent: Sunday, June 13, 2010 5:37 PM
Subject: Re: [Coco] Dual UART with FIFO Card for the CoCo


> On Sunday 13 June 2010, sales at gimechip.com wrote:
>>On CoCo3.com, I asked for project ideas and requests. One request was for
>> a Dual UART card w/FIFO. I thought this would be a good one, so I spent
>> yesterday studying the datasheets and then, this morning I created a
>> preliminary design using E.A.G.L.E. The complete project is now posted
>> here:
>> http://www.coco3.com/community/2010/06/a-dual-uart-with-fifo-card-for-the
>>-coco Let me know if you spot any potential problems with the design.
>>Thanks - John
>
> The only problem I see is the additional i/o addresses it needs.  8 per 
> chip
> sure beats the original 16450's 16 per chip, but with the coco's very
> limited I/o mapping, at least in os9, finding that space is going to be 
> fun.
>
> In my own situation, I do have a dual port ACIA, addressed adjacent to 
> each
> other from FF64 to FF6B (iirc), which meant I had to hack Rogers BT pack 
> to
> use FF60-63.
>
> I would like to ask how much trouble it would be if we could figure out a
> way to isolate the first $40 of page $FF by more fully decoding the two
> PIA's it uses, so they would not see a /cs except at $FF00-03, and 
> $FF20-23.
>
> That would clear out and make usable a considerable amount of i/o address
> space, allowing this to be addressed at $FF10-1F for instance.  That would
> still leave room for 6 more 4 bit wide devices.
>
> So basically, we first need a kit that will fix all of our coco's, freeing
> up this very sorely need i/o space.
>
> I looked at that myself but about 2 decades ago, so any ideas I may have 
> had
> then are moot now.  And I of course am not the least bit allergic to
> plugging in my iron and fixing it as long as I can adequately see what I'm
> doing.  Diabetes is trying to fix that for me now.  But, I'm still a 
> C.E.T.,
> so I'd be willing to be a test site, I have more than 1 coco3 here.
>
> -- 
> Cheers, Gene
> "There are four boxes to be used in defense of liberty:
> soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> The secret of happiness is total disregard of everybody.
>
> --
> Coco mailing list
> Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco


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