From to_stdnet@stag.UUCP Thu Dec  8 12:19:00 1988
Path: caen.engin.umich.edu!mailrus!tut.cis.ohio-state.edu!cwjcc!hal!nic.MR.NET!umn-cs!pwcs!stag!daemon
From: to_stdnet@stag.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: 5 1/4 drives for the ST
Message-ID: <673@stag.UUCP>
Date: 8 Dec 88 17:19 GMT
Sender: daemon@stag.UUCP
Lines: 47

From: dynasoft!john@stag.UUCP (John Stanley)

[patrickm@htsa (Patrick Mans E47) writes...]

> I have been working on a 5 1/4 drive for my 1040 for quite a while
> now, but without succes, unfortunately.
> I was told that the connections from the 1040 are suitable for a 
> standard Shugart(IBM) drive.

  They are... almost...

> I only would have to buffer all the lines and get the drive selection
> right, and then it would work. However it doesn't.

  Getting the drive selection right is more involved than you may think.

> I've tried all possible settings, but the only thing that happens is that
> the motor starts running,... no head movements, and no data output.
> Could someone fill us both out on this, I'm getting quite desperate. I
> seem to have lost all faith in my technical abbillity.

  Don't give up yet...  Atari took one shortcut in designing the drive
contoller circuits that makes this 100 times more difficult to figure out
than it should ever have to be.

>                                   greetings
>                                   pat.

  I ran into -exactly- the same problems when I tried to get a 5.25" drive
to work on my machine.  It's not necessary to buffer -all- the lines.  As
a matter of fact, the cable I use doesn't have any buffers at all.  Just a
direct connection between my ST and the drive.  (I did, however, have to
make a small alteration to my drive....)

  The drive select circuit on the ST doesn't source enough current to take
care of many 5.25" (and a few 3.5") drives.  The fix involves first making
sure you've removed the termination resistor pack from the 5.25" drive
(the internal drive has one already).  Next, trace the drive select lines
on the disk drive itself to find the drive select pullup (yes, UP)
resistor.  You'll probably find a 300-400k resistor.  If you replace it
with a 600 to 1000k resistor, your drive select problems should go away.

  Good luck...

---
John Stanley (dynasoft!john@stag.UUCP)
Software Consultant / Dynasoft Systems