Date   : Mon, 27 Apr 2009 19:16:47 +0100
From   : pete@... (Pete Turnbull)
Subject: ADFS Drive Numbers

On 27/04/2009 11:19, Ian Wolstenholme wrote:
> There aren't any jumpers on the host adapter boards I have, and I
> don't want to go messing about cutting anything on them!  It seems like
> the host adapter will only listen to a controller board with ID 0 and the
> controller board will only listen to discs with IDs of 0 or 1.  It looks like
> I can't plug a second Winchester disc into the back of the first one, even
> changing the drive ID of one of them, presumably because both host
> adapters are trying to be mapped into the same area of RAM.

The winchester host adaptor (the little board) is just a bus buffer and 
address selector, essentially it's a 1MHz Bus to SCSI adapter.  It 
doesn't have an ID, AFAIR.

The drive controller board (Adaptec ACB-4000) is a SCSI controller 
which, like most, can be jumpered to be any device from 0 to 7 on the 
(narrow) SCSI bus.  The jumpers are at position J5 on the ACB-4000, and 
A-B (LSB), C-D and E-F (MSB) set the address, in binary.  Installing a 
jumper sets that bit to be a '1', while leaving it off sets a '0'.  J5 
is the set of pins next to the 40-pin IC towards the hard-drive end of 
the board.

The other jumpers K-L and O-P are for testing, and M-N is for drives 
that drop "Seek Complete" during a head change (some removable media 
drives do this).

I thought you could have two Adaptecs on the bus, but I may be wrong. 
ADFS has provision for 4 SCSI devices, but I'm not sure if they have to 
be on the same SCSI address or if it knows to use LUNs 0 and 1 on 
devices 0 and 1.  For those who don't know, narrow SCSI supports 8 
devices (of which at least one is normally the host controller,  in this 
case the Beeb) and each device can theoretically have up to eight 
Logical Unit Numbers attached.  Here, the ACB-4000 is device 0 and the 
two winchesters are LUNs 0 and 1 on device 0.  It only supports those 
two LUNs.

Oh, and just to avoid confusion, the ACB-4000 is built to the original 
SCSI spec, so although it supports signals (like ATN) that SASI 
controllers (eg Xebec S1410) don't, it pre-dates the Common Command Set 
and doesn't support *all* the CCS commands.

-- 
Pete                                           Peter Turnbull
                                               Network Manager
                                               University of York