Date   : Sun, 12 Mar 2006 17:06:25 +0000
From   : Phil Blundell <philb@...>
Subject: Re: SASI/SCSI <>IDE, distracting thoughts.

Hi M.,

On Sun, 2006-03-12 at 15:01 +0000, Fragula wrote:
> It probably would't be to (for a BBC-only variant) hard to scrap the
> "SCSI" side altogether, and just interface (address decoding and a
> buffer or latch) the AVR direct to the 1MHz bus, no? Much narrower
> application tho. Still looks like the same thing as far as ADFS is
> concerned, just removes the requirement for a 1MHz adaptor board, which
> probably a lot of people don't have.

Yeah, that would certainly be possible.  There isn't a whole lot of
logic on the 1MHz board; it's mostly just buffers and latches.  On the
other hand, like you say, you'd then lose the ability to use it with
anything other than a Beeb, whereas things like Filestores and MDFSs
might benefit from being able to use newer disks as well.  And, given
that the 1MHz board doesn't have any very high technology on, it
wouldn't be that hard to build a standalone copy of it.

> OTOH SMDing the rest on a tight PCB could make it a "back of drive"
> adaptor, giving it a wide appeal to the older computer user. (i mean
> user of older computers, of course..:-)

Right.  I had a quick go at a component placement, and it seems to fit
on a 75x100mm board, which ought to be easily small enough to go under a
3.5" disk.  If you're interested, I put the output at:

http://freedesktop.org/~pb/scsi-ata.output_assembly.pdf

As you'd expect, aside from the connectors the parts that take up the
most space are the 7438 buffers (which, AFAIK, you can't get in anything
other than a DIP package) and the 22V10 GAL (which does, admittedly,
exist in a PLCC package).

p.