[Coco] CocoFlash Updates
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
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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