Date   : Wed, 12 Sep 2007 12:45:11 +0100 (BST)
From   : splodge@... (Richard Gellman)
Subject: 3.5' Drives (Again..)

> 1. Can any 3.5" Floppy Drive be used on the Master/ BBC? Could someone
> indicate a
> Website where information re: required adjustments can be found?

*winds up the gramophone*

Ok, lets run through this again *g*

Modern PC 3.5" drives can be used perfectly well with BBC Micros, and if
you do so it means a better chance of writing disk images to floppies on a
PC for use in a BBC. You only need to be aware of the following:

BBC Micros do not do HD. At all. The FDC hardware just isn't there to do
it. This means you need to use Double Density disks. If you use DD disks,
there will be no problem, as the HD hole will be missing, pushing up a
tiny microswitch in the drive telling it to use DD mode.

HD disks can sort of be used if you're prepared for a bit of fiddling and
pot luck. The surface of a HD disk is slightly different to that DD disk,
which means the DD recording on it will be less reliable, but YMMV. In
order to write DD data to a HD disk, the HD hole (opposite the write
protect hole) needs to be filled. Blu-tack tends to work well for this,
but you would be highly advised to seek DD disks.

The pinout of a BBC micro disk connector does not quite follow the PC
connector standard, and also the drive expects to be on a twisted cable.
This means that on a regular BBC Micro FD cable a PC drive will appear as
drive 1. Theoretically you should be able to change the drive ID to sort
the problem, but due to the cross wiring you'll find that the drive 0 line
isn't connected where it should be. An easier method is to swap the
appropriate control lines (10 and 16 IIRC?) on the cable.

> 2. Do wires have to be twisted for connection? There seems to be varied
> opinions?

Not the full set (see above). Though if you are using two PC 3.5" drives,
there will be a number of wires to "re-route".

As regards software issues, the Master 128 DFS/ADFS will work fine with
3.5" drives. The DFS typically used in BBC B's with the 8271 controller
tends to fail on reading larger files (Repton: Around the world in 40
screens likes to disk error on track 10). A patched DNFS ROM image is
available to deal with this.

I don't fully understand what causes the problem, but I understand its
fixed by retrying the read operation a few more times.

-- Richard