Philip Pemberton wrote:
  Yes, I've seen the SA400 manual, and a few of the
Tandon 5.25" drive
 manuals. What I haven't seen are any manuals that cover 3.5" drives,
 though I suppose 99% of the interfacing stuff is the same. 
Yep, it should be the same - although the BBC doesn't use that nasty cable
twist in the drive cable like a PC, so the drive will be jumpered differently
to a PC drive in terms of drive select.
It's probably worth checking what levels pins 2, 4, 6 are at when the drive's
hooked up to the beeb - ISTR these are a bit open to interpretation.
  I did want to get a primitive MFM data-separator
working tonight, but
 I've spent all afternoon scratching my head over this and come up with
 nothing. 
I was going to do all that in software - seemed like a lot easier way of doing
it than having two different data streams from the hardware to deal with (MFM
versus "something else").
cheers
Jules