Date   : Sun, 19 Nov 2006 21:21:13 +0000 (GMT)
From   : debounce@... (Greg Cook)
Subject: Unusual piece of equipment available.

On Sat, 18 Nov 2006 04:58:57 -0600, Jules Richardson
<julesrichardsonuk@...> wrote:

> Jonathan Graham Harston wrote:
> >> Message-ID: <45492360.7020500@...>
> >  
> > Richard Gellman <splodge@...> wrote:
> >> What we have on offer here is a floppy disc drive cable (of the
> BBC
> >> Micro variety) with one edge connector on the end, but fitted with
> a
> >> switch to convert an 80-track drive into a 40/80 switchable.
> >  
> > How? There are no connections on the disk drive connector to
> > control the number of tracks or the stepping rate. Some disk
> > drives have links or pads on them that a switch can be wired to,
> > but that is on the PCB, not on the drive connector.
> 
> I seem to recall that there are a couple of pins where the function
> varies 
> between drives, though, and for some machine / drive setups they
> aren't needed 
> at all. It may be that the beeb doesn't use all of the lines - so
> that there's 
> one free which could be used to control the number of tracks.
> 
> Of course you need knowledge of the floppy drive being used and have
> to hack 
> it, but I suppose it could be done *for a specific drive*
> 
> (having the track count selectable via software on the beeb would be
> kinda 
> cool, but I'm not sure how much flexibility is available in the
> beeb's FDC 
> circuitry)
> 
> cheers
> 
> Jules

Couldn't the Current Track register be massaged instead to get the
desired stepping? See "Copy40" on the Acorn User cover discs for the
principle.  Acorn 1770 DFS on the B+ and Opus DDOS had double stepping
built in; in DFS it would need a short routine to intercept OSWORD &7F
and add the appropriate commands.

If you really wanted to go the hardware route, there is an unused Fault
Reset output on the 8271 that could be brought out on the cable with
suitable buffering.  But again this would need an intercept routine to
set the output according to the drive.

Greg Cook
debounce@...
http://homepages.tesco.net/~rainstorm/


Send instant messages to your online friends http://uk.messenger.yahoo.com