Tim's own version of the Catweasel/Compaticard/whatever

From: Tim Mann <mann_at_pa.dec.com>
Date: Tue Jul 4 19:51:23 2000

Let me interject a few notes about the Catweasel here. Quoting from Tim
Shoppa's original message:

> 1. The Catweasel uses some custom LSI parts, as far as I can figure out.

It uses a PLD. The 1996 version, which I have, uses a MACH 211. I'm not
sure what the new 2000 version uses; probably something similar. The PLD
equations aren't released, though, so knowing this doesn't tell you much.

> My circuit is much more "hackable", anyone with a TTL databook can figure
> out what it does and improve on it. Or you can build one yourself from
> scratch. (Other than the 128K*8 SRAM, all the other parts were literally
> purchased from the local electronics shop. Heck, most of the chips can
> be bought at Radio Shack!) Total cost for the chips in my buffer is
> about $30.00, about half of that in the SRAM chip.

I sympathize with that, but for those of us who are much better at software
than hardware, something off-the-shelf is a big plus. You can get a Catweasel
for $85 to $95 completely assembled.

> 2. The Catweasel uses a proprietary, largely undocumented programming
> interface. My circuitry is entirely open, and I think it's pretty easy
> to program. (My first hack at acquiring data with the new buffer was
> dashed off in about half an hour under QBASIC.)

You can now get the documentation for the programming interface just by
asking the designer (Jens Schoenfeld). He told me that it isn't secret
anymore. The document is in German, but I could provide a translation
if anyone needs it. (My German isn't that great, but the document is
so simple you can almost read it without knowing any German.) There is
also an open-source Linux driver, and the program I wrote for reading
FM and MFM disks to one of the TRS-80 emulator formats (cw2dmk) is also
open source.

> 3. The Catweasel requires a bus slot inside a PC-clone. My new buffer uses
> a much more general purpose parallel interface. So you can hook it up
> to a laptop, or even to something that isn't a PC-clone at all.

That's a real plus; on the other hand, if you do have a PC clone with an
ISA slot, it's more convenient having the board inside the computer than
hanging off the parallel port (especially if you're already using the parallel
port for something else).

> Those are what I see as advantages over the Catweasel. There are also
> some disadvantages:
> 4. You can't just go out and buy my buffer, but you can buy Catweasels
> off the shelf.
> 5. My buffer is strictly "read-only" as I use it. I think the Catweasel
> (and Compaticard) both allow writing.

Yes, the Catweasel allows writing. I haven't tried this yet, though.

Another point to note is that the Catweasel samples at 7 or 14 MHz (software
selectable). In reading some old 8" MFM disks, I found that there had
been a lot of bit-shifting over the years (or maybe there was not enough
write precomp applied to begin with), and I had to use an extra heuristic
to make them readable at all. I'm not sure that 4 MHz would have been
a high enough sample rate for these.

Tim Mann tim.mann_at_compaq.com http://www.tim-mann.org
Compaq Computer Corporation, Systems Research Center, Palo Alto, CA
Received on Tue Jul 04 2000 - 19:51:23 BST

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