floppy low level format question

From: Dwight K. Elvey <dwight.elvey_at_amd.com>
Date: Mon Jun 14 20:42:08 2004

>
>> PS: The old Micromation floppy controller (CP/M 1.4 days) used NEITHER
>> chip family, did their own formatin LS TTL, and practically no one can
>> read them.
>
>I have a Micromation Doubler in my CASU Super C (S100 bus CP/M machine).
>>From what I rmemeber the single-density (FM) format is standard, and can
>read/write IBM3740 disks. The double density format, though, is probably
>unique to this card.
>
>> You can probably do all this in a PC sound card these days!
>
>Not many sound cards will handle 500kHz signals, surely?
>
>-tony
>

Hi Tony
 I doubt they'd take it directly. Most have anti-aliasing
filters that roll of before this. I think what the other fellow
was refering to was to use the DSP on a sound card but not
through the audio A/D part. Many sound cards used industry
standard DSP chips the were reprogrammable with flash or
on board RAM. The DSP chip I'm looking at on a modem card
is a AD2116. It runs at about 16 mips and has very efficient
indexed addressing with increment. This is more than fast
enough to bit bang a floppy signal. To sample a digital
signal asynchronously really takes a sample rate of at least
4X ( Shannon's says 2X but that is in theory with analog
and brick wall filters ). Most serial chips use 16X.
 Since you need to detect edges, you need to be running at
a sample rate of near 4 to 8 megherts to stay up with a
signal from a floppy at 500khz data rate.
Dwight
Received on Mon Jun 14 2004 - 20:42:08 BST