Date   : Mon, 04 Mar 2002 18:45:59 +0000 (GMT)
From   : jim <jim@...>
Subject: Re: Xfer

On Mon, 4 Mar 2002, Matt Cocker wrote:
> With regards to the Get disc image, this does not work for me either, I
> asked about this earlier this year and Angus Duggan replied "Is the DFS
> fully 8271-compatible? The disc transfer option uses the 8271 load sector
> commands." I have not looked into which one is in my B+ but it could explain
> the failure.

The B+ uses the WD 1770 disc controller (fitted as standard, as in the
Master), which is not command-compatible with the Intel 8271 found in
normal BBC Bs with disc upgrade. OSWORD &7F commands to read/write sectors
are based around 8271 commands; I imagine that the 1770 DFS converts these
to 1770 commands in software, but if the emulation isn't perfect it could
explain the problem. 

jim
-- 
http://madeira.physiol.ucl.ac.uk/people/jim/
"... I naturally gravitated to London, that great cesspool into which all the
 loungers and idlers of the Empire are irresistibly drained."
                                - Sir Arthur Conan Doyle, "A Study in Scarlet"