21 Sep
2008
21 Sep
'08
6:44 p.m.
Subject: Re: Z80 home brew with FDC
From: Eric Smith <eric at brouhaha.com>
Date: Sun, 21 Sep 2008 18:02:25 -0700
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at
classiccmp.org>
Alexis wrote:
Actually it's pretty decent. However as you point out if you really
need the ultimate in relaibility and are throwing crap media with loose
drives in the system then a PLL may help somewhat.
The FDC-1 uses a FD179x controller and it appears
it uses the same
data clock and raw data inputs as the 765.
Not quite. I don't recall the details of the difference, but I think it
may have just been the polarity of one of the signals. The 9229 and
9239 had a configuration input to select between 179x and 765 modes.
The 9216 would directly connect to one, and needed a small amount of
logic (maybe just an inverter) for the other.
The decoder is made up of a 74LS197 (clock
divider), a dual 74LS74 flip-flop,
both used, a 74LS163 counter and an inverter. There are also some open
collector NAND gates to select the clock rate for either 8" or 5.25" drives.
It'll use more individual IC packages, but they're *much* easier to find.
Sure, but it doesn't sound like it's a very good data separator. The
good ones have a PLL (either analog or digital), because it is necessary
to track speed variations, not just of the drive that you're using to
read a disk, but also of the drive that wrote it. Non-PLL data
separators work OK when the disk is both written and read under optimal
conditions, but are unreliable otherwise.
The 9216, 9229 or 9239 are *highly* recommended, as
they have a good
digital data separator. The 9229 and 9239 also contain write precomp
logic. The 9239 uses higher resolution timing for its PLL, so it may
perform better.
yep, now just fine one.
Me I gave up on floppies as even at 1.44Mb they are slow and small.
IDE of CF offer more space and less interface headches.
Allison
22 Sep
22 Sep
1:19 p.m.
Allison wrote:
Actually it's pretty decent. However as you point
out if you really
need the ultimate in relaibility and are throwing crap media with loose
drives in the system then a PLL may help somewhat.
I worked with many different 179x-based floppy controllers at a job from
1980-1982, and my experience was that the only ones that worked
consistently and reliably were the ones that used a PLL. Many of the
non-PLL ones weren't even completely reliable reading disks written by
the same drive and controller. That's why ALL of the later followons to
the 179x and 765 that had internal data separators used PLLs (either
analog or digital).
I'd be extremely reluctant to use a controller with a non-PLL data
separator even if I NEVER needed to read floppy disks that were written
on other people's disk drives.
yep, now just fine one.
I haven't had any trouble locating the 9216 and 9229 as recently as last
year. Naturally you won't find them from distributors since they were
discontinued more than ten years ago, but there are still plenty
available from resellers and (spit!) brokers.
Me I gave up on floppies as even at 1.44Mb they are
slow and small.
IDE of CF offer more space and less interface headches.
So when you find a piece of old software on an floppy disk, how exactly
are you going to shove that into your CF reader?
Eric
2:19 p.m.
Eric Smith wrote:
The ttl implmetation I last used was synthetic PLL. Takes three TTL one
being
a bipolar prom (or any 25ns prom).
I still have (at least 40) systems that can read and write floppies. I
will not start a new system with floppy and llikely new programs will be
either on line (saerial down load) or on media thaats compatable with an
existing system. If incompatable
then its either a coding issue for a differrnt format but still within
exisiting
softector capability (1771, 1783, 765) or its oddball enough to be
likely some hardsector format I don't have. The trouble maker know is
Intel DD 8" (m2FM)
as there are no chips for that and it is softsector.
Allison
Me I gave up on floppies as even at 1.44Mb they
are slow and small.
IDE of CF offer more space and less interface headches.
So when you find a piece of old software on an floppy disk, how
exactly are you going to shove that into your CF reader?
Eric
5935
days inactive
5935
days old
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