[Coco] CocoFlash Updates

RETRO Innovations go4retro at go4retro.com
Sun Sep 18 22:12:58 EDT 2016

On 9/18/2016 6:03 AM, Gene Heskett wrote:
 > Because most address decoding in the carts we have, are in 4 byte wide
 > bits, no one has put anything at $FF7C-D-E because $FF7F is the
 > multipack slot register. I have not verified the MPI's response to the
 > C-D-E address myself, but if you only need one byte wide, I expect a
 > little wrapping wire patch to your decoding could test it.
I can test it no problem, but the Registered Port Address List shwos 
those addresses as being used:

$ff7c: PBJ Buss slot select
$ff7d:e: Speech/Sound pak

I like the idea though.  $ff7e would be ideal.

 > I have lamented for at least 25 years because someone hasn't made a one
 > chip addin board for the coco itself, restricting the address space used
 > by the PIA's to the 4 byte wide access they need, which would free up 7,
 > 4 byte wide addresses from $FF04-FF1F, and 7 more 4 byte wide blocks
 > from $FF24-FF3F. Thats 14 more 4 byte wide devices we could address in
 > those two spaces. A single 74ALS138 could manage that easily with one
 > trace cut, two connections to the power rails, a bit of wirewrapping
 > wire to put the 74ALS138 output into the CS logic of the 74LS138 in
 > there now. Feed this '138 with A2 and A3 so that if either is true, the
 > internal ls138 is disabled. This I repeat, would give us 14 more usable
 > address blocks for a total of 21, as opposed to the 7 spaces we have
 > now.
Well, I think it is easier to do.  What would you like to put there?  I 
think I can disable them from the expansion port.

Give me an idea of what to put there, and I can whip up a prototype for 
you to test.


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