[Coco] Dual UART with FIFO Card for the CoCo

[Gene Heskett]

On Sunday 13 June 2010, Phill Harvey-Smith wrote:
>Gene Heskett wrote:
>> On Sunday 13 June 2010, sales at gimechip.com wrote:
>> 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 guess as long as you always decoded from the complete address bus, you
>could Assert SELNB/DSD for the address ranges $FF04-$FF1F and
>$FF24-$FF3F You would of corse then need to generate an apropreate chip
>select for your device, but this is all easily doable with a small CPLD
>or a few LS type chips.
>
There is an echo in here Phill. ;-)  And as long as we use modern cmos 
chips, the additional drain on the coco's supply should be minimal, 
particularly if we replace some of the old hungry TTL stuff that wouldn't be 
needed as it would just dup what we'll do but we'll do it better.

 We just need to standardize how its done so that we don't have 250 
individually unique versions, one for each of us left.  That would be a 
disaster to the group as a whole.

Hint, leave the stuff at $ff40+ alone, because many of us have worked out 
what works for us already.

-- 
Cheers, Gene
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