Date   : Fri, 18 Nov 2005 14:47:58 +0000
From   : Richard Gellman <splodge@...>
Subject: Re: SASI/SCSI

Mark Usher wrote:

>Yes, the ATN line I think is the difference from memory.
>Now as far as I remember, ADFS 1.30 is the last Beeb ADFS and ADFS 1.50 was
>the revision for the Master. Maybe this is one of the differences, support
>for SCSI opposed to SASI.
>
>Simplest way to find out would be to plug the adapter in to the Beeb and see
>if it works! Also, if Richards SCSI bits were implemented in BeebEm, we
>could also try it with ADFS 1.30 and a BBC emulation. Might also be easier
>to debug if things are slightly different.
>  
>
I'm 90% sure the BBC Micro doesn't use the ATN line - by which I mean 
the ADFS ROM has no support for it. Its basically used in devices that 
supported "disconnected operation" - this is where the device knows that 
the requested operation is going to take a while, and notifies the host 
that it will "disconnect" while it does it, leaving the bus free for 
other operations, and will attract the host's ATteNtion when its ready. 
I believe the BBC just specified "no disconnect" in its command block, 
so the ATN line is not used.

Certianly the BeebEm/SCSI emulation never requested disconnected transfers.

-- Richard