From nancy!eecae!super.upenn.edu!rutgers!ukma!uunet!mcvax!unido!incas!mdoerr Fri Oct 23 23:52:03 EDT 1987
Article 4513 of comp.sys.atari.st:
Path: nancy!eecae!super.upenn.edu!rutgers!ukma!uunet!mcvax!unido!incas!mdoerr
>From: mdoerr@incas.UUCP
Newsgroups: comp.sys.atari.st
Subject: Hardware: Read IBM disks with ST - (nf)
Message-ID: <4300001@incas.UUCP>
Date: 8 Oct 87 12:19:00 GMT
Lines: 168
Nf-ID: #N:incas:4300001:000:10128
Nf-From: incas!mdoerr    Oct  8 13:19:00 1987
Posted: Thu Oct  8 13:19:00 1987

This posting is in response to the ever increasing number of people who
want to hook a 80-track 5.25" drive to their ST, but want to read 40-track
IBM-PC diskettes as well. Once upon a time (in 1986) the german magazine
c't published a solution called the step doubler. I recently build that
circuit and am now happily reading and writing 360K MSDOS diskettes
as well as making backups of my hard disk to cheap 5.25" diskettes holding
800K of data each. Below you'll find an UUENCODEed and ARCed Degas Elite
PI3-picture showing that circuit.
*** No warranty implied: If you fry your ST or drive you're on your own. ***
Note 1: Most 5.25" drives do step flawlessly at 3 ms but won't be able to
do 2 steps in 3 ms. That's why one should lengthen the step time of the
switched 5.25" drive to 6 ms. This is done by changing some low memory
variables, which should be mentioned in the Abacus books. I remember that
these addresses even drifted along USENET a long time ago. I actually don't
need to do that, because my Philips X3134 is capable of doing 2 steps in 3 ms!
Note 2: While having a hot soldering iron you should add some open collector
TTL drivers (a 7407 is fine) to the following 3 signal lines:
	Pin 2: Side select
	Pin 5: Drive 0 select
	Pin 6: Drive 1 select
These lines are driven by unbuffered outputs of the Yamaha sound chip that
isn't capable of driving heavy loads and may easily be damaged. All other
outgoing lines on the floppy port are sufficiently buffered.

Have fun, Michael.

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Michael Doerr, Uni. of Kaiserlautern, Germany --- uunet!unido!uklirb!mdoerr
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