Date   : Sat, 25 Jun 2005 13:04:49 +0100
From   : Tom Seddon <tom@...>
Subject: Re: Watford Electronics DFS

The address assignments assumed by 1.54T are same as those assumed by 
the Acorn 1770 DFS, and with the same latch bits:

       Bit       Meaning
       -----------------
       7,6      Not used.
       5        0
       4        0
       3        density select (0=double 1=single)
       2        side select (0=0 1=1)
       1        select drive 2
       0        select drive 1

However, it inverts the "track 0" bit in the status register, a handy 
tip I found in the BeebEm source :)

I just gave 1.40, 1.50 and 1.53 a quick spin on model-b with the 
"watford" settings, and I got track faults (1.40, 1.50) and a hang 
(1.53); presumably they are designed for a slightly different revision 
of the Watford board. They don't work at all with the Acorn board. This 
could of course be emulation bugs!

I've put a zip with 1.40, 1.50 and 1.53 on the model-b web site:

http://modelb.bbcmicro.com/watford.zip

--Tom

Greg Cook wrote:
> On 24 Jun 2005 10:22:22 +0100, Jonathan Graham Harston wrote:
> 
> 
>>If I come across the information I'll let you know. Otherwise, if
>>anybody had Watford DFS 1.5x earlier than 1.54 I could disassemble
>>it and work it out.
> 
> 
> Probably it reuses the 8271 address space, which is the simplest
> solution.  A list of known address assignments can be seen at:
> 
> http://www.nvg.org/bbc/doc/wd1770.txt
> 
> The Opus option is the most likely candidate.  The control latch
> structure is probably different from Acorn's as well, see the above
> link.
> 
> Greg
> 
> 
> 
>           
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