From: David Wood (jbevren_at_starbase.globalpc.net)
Date: 2007-12-15 07:12:52
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.
The difference between the '816 and the '02 that comes to mind would be the
posting of the bank address during the off-cycle. This can be captured with
a single 8-bit latch (or in the case of 256k ram, a 2-bit latch). In contrast, mapping 256k of ram to the 6502 would
require a larger latch. Even with 32k banks, you'd need 8 bits of latch to
map the memory about. I'd personally bank 8 or 16k, which requires 32 or 16
bits of latch respectively. This assumes only one window is used (as only
one is really needed if the extra ram is used for buffering).
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.
Got a preview for the board's schematic someplace? :)
-jbev
On Fri, 14 Dec 2007, Jim Brain wrote:
> David Wood wrote:
> > That said, recreating the 1541 board sounds interesting. Is your idea to
> > implement an ide-only version? If so that saves much design, as you won't
> > need the analogue section.
> >
> Truly. I laid out the essentials (6502, 256kB RAM, 64kB EPROM, 6522,
> X-IDE parts, '14, '06, a couple '138s for decoding, 2 IDE connectors and
> a CF connector, IEC, expansion port) on a board 4" by 2.1. No wiring as
> yet, but it looks to all fit, if you put parts on both sides (or, I get
> very creative on layout). It was just a few minutes work; I didn;t
> spend too much time on it. Still, with the right firmware you could
> have a fully functioning computer on a board.
>
> Jim
>
>
>
>
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>
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