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

From: Richard Erlacher <richard_at_idcomm.com>
Date: Tue Jul 4 20:17:36 2000

The hardware isn't the principal challenge in this case, friends, it's the
software to interpret what's read or to-be-written. Moreover, trimming the
file size down is just a part of the process, since it has to be reduced and
then re-inflated in order to position the transitions correctly to effect
write-precompensation. That requires diligent study of the various formats,
modulation schemes, and error-detection/correction codes. Reducing the
sampled data to binary files is not trivial, but once one has the hang of
finding the data field after a probably somewhat disorderly write-splice on
the diskette it's probably not that bad. Since the time used in the
write-splice is limited, it can be found easily enough, simply counting

This is a VERY achievable task, and particularly with the inexpensive XIlinx

Please see embedded comments below.


----- Original Message -----
From: <CLASSICCMP_at_trailing-edge.com>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, July 04, 2000 2:53 PM
Subject: Re: Tim's own version of the Catweasel/Compaticard/whatever

> >The only problem I'd point out is the the 9500 series CPLD's drive only 8
> >per output and, unless you were planning to pair them up, i.e. use
> >pins tied together to drive the FD cable, you might have problems.
> The biggest problem is with the outputs that'll drive the floppy disk bus.
> Typically it's an open-collector output terminated to +5V with 150 ohms,
> you have to be able to sink 30 mA or so. So yes, this may be a concern.
> (Or you can cheat and tie the lines high with "only" 220 or 300 or 470
ohms -
> shouldn't be a big problem as long as there's only one drive on the bus.)
What can be done in this case is to take a page out of IBM's book and
terminate with 1K and keep the cable short. Now, they terminated with 1K on
BOTH drives, but since it works on one, it works on both. If the cable is
quite short, you can get away with a 1k pullup. The limit on package
dissipation, can be dealt with by considering that only a very few lines
will ever be driven at one time: DSn*, STP*, DIR-IN*, WG*, and DATA*. If
you're worried about the dissipation, you can use multiple pins to drive
these lines, and spread them around the device so you don't get "hot-spots"
on the die.
> Do any CPLD's have "real" open-collector outputs, or can you fake it by
> sending the output into tristate mode? (I'm asking this as a guy who's
> never designed with CPLD's but does know 74XX00 series logic pretty
> well.) I don't think it's an issue either way with exactly one controller
> and one floppy drive on the bus.
Some have open-drain outputs, but the tristate ones are as good. Instead of
driving a negative going signal into the cable, you drive a buffered ground
to the cable, enabled with the data. It's as fast as OC and just as easy.
> --
> Tim Shoppa Email: shoppa_at_trailing-edge.com
> Trailing Edge Technology WWW: http://www.trailing-edge.com/
> 7328 Bradley Blvd Voice: 301-767-5917
> Bethesda, MD, USA 20817 Fax: 301-767-5927
Received on Tue Jul 04 2000 - 20:17:36 BST

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