Date   : Fri, 29 Aug 2008 13:10:56 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Question about 1770 DFS interface testing it on a B

Andy Ford wrote:
> I just wondered if anyone can confirm on a B, if the usual Acorn 1770
> DFS message should show up (on startup) or with *H. regardless of
> weather the actual module is fitted to IC78 or not assuming the ROM is
> present.
 
If there is no floppy disk controller present, DFS disables itself
on Service Call 1 by setting b7 of its workspace byte at
&DF0+romnum. The service call handler checks this bit and ignores
everything if it is set. Consequently, if there is no FDC, there
will be no startup banner, no response to *HELP, no DFS *commands,
etc.
 
8271 DFS and NFS do the same. If the hardware the firmware requires
isn't present, the firmware disables itself.
 
> further. The module had four pins missing but I managed to
> carefully attach some small lengths of wire and a bit of a broken
 
Are you sure those pins aren't supposed to not be there?
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
05:10:36, 18-Nov-2008 - RISC OS time rolls over to &5000000000