[Coco] Dual UART with FIFO Card for the CoCo

[Gene Heskett]

On Sunday 13 June 2010, sales at gimechip.com wrote:
>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

John, I'll have to plead guilty to not ever chasing through the CC3 logic to 
see that.  Thank you.

Stuff in the MPI generally has its own decoders, and this would open up 2 
sets of $10 wide addresses.  Whats not to like?

-- 
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)
People in general do not willingly read if they have anything else to
amuse them.
		-- S. Johnson