[Coco] Copying zip file from the sdc card

[RETRO Innovations]

On 4/24/2020 6:01 PM, Gene Heskett wrote:
> On Friday 24 April 2020 18:20:22 L. Curtis Boyle wrote:
>
>>> On Apr 24, 2020, at 4:17 PM, Gene Heskett <gheskett at shentel.net>
>>> wrote:
>>>
>>> But since the sc6551 is AFAIAC a broken chip, we really ought to be
>>> designing a better rs232 pack.  Bruce Istead had the right idea with
>>> his DACIA, but its a rare bird I've never seen. Could Bruce be
>>> talked into another run of those?
>>     Unfortunately, I think the 6552 chip itself is rare, and not cheap.
>> Once we have fully working 16550 drivers, I think that will be the way
>> to go.
> Unforch the 16550 needs a block of 16 addresses for all its control
> registers. We simply don't have that many free addresses in the coco's
> i/o space.

Um, so much to unpack here:

  * $ff40-5f is uniquely decoded for each MPI slot.  A card in that area
    will not conflict with anything else in an MPI.
  * 16x50 UARTs don't need 16 bytes, just 8.

> We might be able to multiplex it down to 6 but thats still
> too wide for the conventional 4 byte wide block the coco is designed to
> use. Only if someone rips out the existing decoders and designs a hack
> to make everything from $FF00 to $FF7F into a proper 4 byte wide cs
> scheme, will that ever get fixed.

So much more to unpack here:

  * I know of no 4 byte slot system.  The PIAs use 4, indeed, but that's
    not a rule, just how much they needed.  Lots of carts take 2 (OR90),
    while otehrs take 8 (FDC) and some take 9 (SuperIDE/Glenside IDE). 
    4 is nor more a standard than 8 or 2.
  * You keep pushing for the fully decoded address space, and it's
    indeed possible to do in a cart, but I hope you realize that SW
    through teh years has begun to rely on the mirrors, so it will be
    very difficult to chop of the PIA space ($ff00-3f) and have all SW
    continue to work.  Your comments have not fallen on deaf ears,
    they've fallen on ears that worked out the equations and deemed it
    incompatible with the CoCo.  Move on.

> We could then fit 7 more cards into
> the space between the pia's, and another 7 into the space between pia2
> and the floppy at $FF40. But I've been preaching to an empty cornfield
> on that subject for 30+ years now.  Sigh.  And it wasn't the 6552 I was
> thinking of, ISTR there is a candidate in the 68xx area we could use.

  * The 6850 is worse than the 6551.  You might be thinking about the
    68681, which is a 68K-based Dual UART.  It indeed does take 16 bytes
    of address space, and it's far less useful than the 16550 and relations.

>
> Cheers, Gene Heskett


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