Universal drive

From: Eric Smith <eric_at_brouhaha.com>
Date: Thu Oct 1 20:46:16 1998

Tony Duell wrote:
> Hmmm... I don't know of one built commercially, but how about a board
> based round an FPGA (for the non-hardware types, basically a configurable
> chip that you can make just about any logic circuit out of) linked to an
> floppy drive. Oh, and some kind of programmable clock (I don't think
> dividing down a master clock with the FPGA would really do it)/PLL thingy
> to act as a read clock.

Overly complicated, no (hardware) PLL necessary. Just sample the data from
the drive at a sufficient multiple of the channel code data rate (8x should be
plenty), and do the data separation in software. That way it really is
completely independent of the data format. That's the way I designed my
closed-caption decoder (5x), and it works quite well.

Note that this doesn't deal with all of the weird Apple ][ copy protection
schemes (like spiral tracks), but it will deal with some of them.

I have a twiggy disks for the Lisa 1 with a bad sector. I've always wondered
whether hacking the drive electronics to allow software control over the
read amplifier gain and/or data slice threshold would let me recover that
sector.

Cheers,
Eric
Received on Thu Oct 01 1998 - 20:46:16 BST