From: mdoerr@incas.UUCP
Newsgroups: comp.sys.atari.st
Subject: Hardware: Read IBM disks with ST - (nf)
Date: 8 Oct 87 12:19:00 GMT

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. MS-DOS diskettes  as
as well as making backups of my hard disk to cheap 5.25" diskettes holding
800K. of data each.  Below you'll find a 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 collec-
        tor 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 suffi  -
        ciently buffered.


Have fun!

Michael.

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