Date   : Mon, 27 Apr 2009 20:00:59 +0100
From   : mu.list@... (Mark Usher)
Subject: ADFS Drive Numbers

> 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.
No, but it does have the capability to select which address it appears at. 

The Advanced User Guide shows that memory locations $FC40 to $FC47 are set
aside for Winchester disk units (these are located in page FRED). The memory
map looks like this:

Controller     Address Read    Write
                       
0      FC40    Data    Data
       FC41    Status  -
       FC42    -       Select
       FC43    -       Interrupt latch
                       
1      FC44    Data    Data
       FC45    Status  -
       FC46    -       Select
       FC47    -       Interrupt latch

Two Winchester drives have been used successfully on one controller, the
first as LUN0, the second as LUN1 and as expected they appear as drive 0 and
1. Unfortunately ADFS 1.30 on the BBC B/B+ doesn't support a second host
adaptor, probably because there was not sufficient space in the ROM for the
extra code

-Mark