From: Jim Brain (
Date: 2007-12-17 22:49:24

David Wood wrote:
> Sounds interesting no doubt.  If youre using more than 64k RAM, would you
> consider using a 65816 for linear access to the memory?  I'm not trying to
> turn the project into a super-computer with 16M ram.  Rather, I'm attempting
> to simplify buffering/ram access programming.
Wow, *WAY* ahead of me.  I just pulled the parts onto a board, and made 
sure they would all physically fit on there.  No design as yet :-) Sorry 
to burst the bubble.
> Re-reading your reply, it would seem that the 6522 could easily be used to
> control bank addressing with a 16k window if all of its lines are dedicated
> to the bank address.  This eliminates lines for the IEC bus though.  Quite
> the challenge.
Yeah, I pulled the '22 into the design simply for compatibility with SW 
expecting to see a '22 there.  There are far better parts for banking.
> Got a preview for the board's schematic someplace? :)
As noted, sorry, you're way ahead of me.  If you'd like to fire up EAGLE 
and start, I'm happy to work with you on it.

Thinking out loud:

    * Check out the 134 with on-board IO and such.  It's not much more
      expensive that an 02.
    * I like your idea of a 816 design, but I don't know if such a
      design would hurt compatibility.  I assume it would not any more
      than using IDE, but it's a deviation.
    * I was going to suggest the C265S as the be all solution, but not
      at that price.  I don't pay that much for an MPU, no matter how
      good it is.
    * Someone needs to consider the amount of RAM in a design like this 
      At some point, you need more more DOS buffers (16 or so is plenty,
      I think), and some scratchpad area for IDE writes.  That's a bout
      5kB.  What else would be needed?
    * ROM needed.  Should a drive contain a static large ROM/FLASH for
      the DOS, or should it contain a small minimal one and load a bunch
      of RAM with the real DOS and then protect the RAM?  I tend to like
      the latter, but dunno.


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