Date   : Wed, 08 Mar 2006 19:30:14 +0000
From   : Jules Richardson <julesrichardsonuk@...>
Subject: Re: 6502s and SASI/SCSI.

Fragula wrote:
>> I've occasionally thought that it would be cute to make a little
>> protocol converter board to interface a modern IDE disk to an old-style
>> SCSI/SASI bus, for use with the Acorn winchester controller or something
>> like that.  Kind of like a contemporary equivalent of the Xebec
>> SCSI-ESDI/MFM converters that you used to see back in the day.
> Elegant indeed. Worthy of a good airing!
> 
> Were they not Adaptec ACB-4000's? in the Acron kit? ISTR that's what in
> my ACW. The Xebec is in the Torch box, no?

Torch seem to have used both Xebec and Omti at one point or another, whilst 
Acorn seem to have always been Adaptec fans...

> But *maybe* (time to compare notes with everyone else on the list) the
> two SCSI/SASI<->MFM adaptor (where did ESDI come in?) boards are, at
> least as far as ADFS is concerned, "mostly-compatible"?
> 
> I'm thinking of basic block ops, not formatting and the like, which I'm
> fairly sure are different, both as far as the drive is concerned, and
> the commands used by the format utils, before the Common Command Set was
> widely adopted.

Although the way that the bridge board sets up the drive geometry is different 
between Adaptec / Xebec / Omti, so there's still some varying setup depending 
on the board used. Once that's done then yep, standard SCSI six-byte 
read/write commands can be used to access data.

No idea about the Emulex boards - the only ones (and docs) I have of those are 
tape streamer bridges (SCSI to ummm, QIC02 I think) rather than for disks.

> Now ADFS (and the torch software) can use 7 device IDs

it can? I think original ADFS expects to be talking to a single device on the 
bus, and I'm not sure that it sends a device ID (or possibly it does, but it's 
hard-coded to always be 0?)

 >, and (in theory)
> the Adaptec(which I think this is in the manual) and the Xebec(not
> known) can each handle 2 MFM drives, each with the same SCSI device ID,
> but on LUNs 0 and 1.

Oh, yep - at least for the Xebec boards, if you have two devices connected 
they have to be the same geometry. Don't ask me why, but I seem to remember 
that from the manual.

Not sure if that applies to Adaptec / Omti / Emulex / Anyone else...

cheers

Jules