ravi@eneevax.UUCP (Ravi Kulkarni) (09/10/85)
I am forwarding this from the info-st developers mailing list.
I have not tried this upgrade but have no reason to think it
would not work.
-ravi
===============================================================
Date: Fri, 30 Aug 85 12:21:57 edt
From: Gyorgy Fekete <gyuri>
Message-Id: <8508301621.AA05765@eneevax.ARPA>
To: info-st
Subject: 5.25 Floppy on the ST.
Status: RO
From: allegra!decwrl!dec-rhea!dec-cgvax2!boiko (Michael Boiko MKO2-2/KO2 264-3626)
Permission to reprint or excerpt is
granted only if the following line
appears at the top of the article:
ANTIC PUBLISHING INC., COPYRIGHT
1985. REPRINTED BY PERMISSION.
HOW I MADE AN IBM-ST
(ST WITH 5 1/4" DISK ACCESS)
By DAVID SMALL
You can read and write IBM PC disks
on your Atari ST -- if you connect a
40-track 5 1/4-inch disk drive to your 3
1/2-inch disk drive.
Or...if you don't need IBM file
compatibility for an ST, you can connect
a 2-sided, 80-track, 5 1/4-inch drive
and store 720K on one disk. This will
save you money because 5 1/4-inch disks
and drives are cheaper than 3 1/2-inch
disks and drives.
But can you use the disk drive from
your 8-bit Atari? Not if the drive is an
810, 1050, or an Atari workalike such as
an Indus, Astra, or Rana. However,
ATR8000 and Percom drives will work.
They are "industry standard" drives that
communicate via standard 34-pin
interlace connector.
THE WARNING
Before actually telling how to hook
up a 5 1/4-inch drive to your ST, we
must caution you this is no job for
electronics beginners. You need to
solder and to understand the circuitry
of whatever 5 1/4-inch you are using.
Debugging your new system can be a
frustrating experience. Not only that,
open up your ST drive and you'll violate
the warranty.
RIBBONS AND PINS
Of the 34 pins in the standard
industry connector, only about 14 are
used. The Atari ST brings these 14 wires
out in a short, thick cable that plugs
from the ST into the first drive's IN
connector. This cable uses a
non-standard 14-pin DIN connector, but
it carries industry standard signals.
Our goal is to get those signals to a
standard 34-pin connctor and thus to a
standard disk drive.
Theoretically we'd put a 34-pin edge
connector on one end of a ribbon cable,
14-pin DIN connector on the other, and
we'd have our disk drive cable. However,
in practice I couldn't find a 14-pin DIN
connector.
INSIDE THE DRIVE
Therefore, the method I chose to use was
to tap into the signals inside the 3
1/2-inch ST drive. Besides voiding your
warranty, this will probably require you
to cut a slot in the drive case for the
new ribbon cable.
If you open up the drive (use a
phillips screwdriver) you'll find the
14-pin DIN connector expands to
(Surprise!) an industry standard 34-pin
ribbon cable.
Of course, it does this inside the
shield to prevent radio noise from
leaking out. A small circuit board has
the two 14-pin connectors (IN and OUT)
mounted on it, and it connects to the
34-pin ribbon cable inside the drive.
I put a "tap" from the 34-pin ribbon
cable in the drive to the 34-pin ribbon
cable running to my remote 5 1/4-inch
disk drive. I then used a DB-40, 40-pin
male and female clamp-on connector to
clamp one side to the ribbon cable and
the other to the remote drive's cable.
Then I plugged the two DB-40s together.
You don't have to use a DB-40. Any
clamp-on connector that covers the first
34 pins will work fine.
KINKY WIRING
But there's a catch. Atari does
something kinky with the drive B select
signal. It's on pin 6 of the DIN
connector when coming from the ST. But
inside drive A it is switched from IN
connector pin 6, to OUT connector pin 5,
where it becomes drive select for drive
B.
This means Atari ST drives always
listen on pin 5 for select, and the
daisy chain scheme gives the proper
drive the correct signal. Thus the two
connectors on the back of the ST drive
are not interchangeable, like other
Atari drives. Plug your ST into the OUT
connector, the drive won't work, period.
Therefore we have to jump from pin 6
of the DIN connect (drive B select) to
pin 12 of the ribbon cable (drive B
select) to get this signal across.
Otherwise it doesn't show up on the
34-pin cable otherwise. This is easy to
do on the bottom of the 3 1/2-inch
drive's DIN connect board.
Now we need to set the remote drive
as drive B. Sometimes it's called drive
1 or drive 2, depending on whether the
manufacturer numbers drives at 0 or 1.
When a drive is idle, a five-volt
signal (HIGH) exists on the BUSY line.
When the computer wants to access the
drive, it pulls down this signal to zero
(LOW).When the computer is finished with
the drive, it releases the signal and
the drive "pulls up" the signal to its
original five volts. If two drives are
hooked up, only one may contain pull up
circuitry because the computer can only
pull down five volts.
Pull-up circuitry usually is
contained in a chip in the drive. And
now you are at a point where you must
know enough about your 5 1/4-inch drive
to figure out where the chip is.
Since the ST drive A contains all the
pull-up termination circuitry we need we
must remove termination packs from the
remote drive. In the case of my Tandon
TM-100-2 drive I also needed to deal
with the select line termination, since
it doesn't go through the resistor pack.
I had to clip resistor R14 from my
Tandon to get rid of the added
termination.
Special Note: The ST monitor throws
out a lots of magnetism. If you don't
keep your drive at least one foot from
the monitor, the disk's heads will pick
up the monitor's signals and confuse he
read data. You'll immediately notice
data error if you get your drive close
to the monitor. This is good reason to
use a fairly long ribbon cable (3 feet
or so) (We haven't noticed this problem
in-house. ANTIC ED)
ALL DONE
All right, assume you have added an
80-track drive. Put the disk in, close
the door and turn on the system. Click
on drive B, select FORMAT, and format
the disk either single-sided or
double-sided.
>From then on, treat the 80-track
drive as an Atari ST drive. Note: 80
track drives have traditionally been
persnickety, which is why 40-track
drives remain popular. Keep a sharp eye
on the drive's alignment. It takes very
little misalignment to make a disk that
only one 80-track drive in the whole
world can read.
If you've added a 40-track drive, you
may use it as an ST drive in only a
limited fashion. You can't use FORMAT
or a track copy, because they'll try to
force the drive past its 40th track.
IBM ST
On the other hand, you can put an IBM
PC disk in that 40-track drive, and
click on the B icon. It'll pull up the
disk's directory into folders and "text
only" files.
You'll notice on the top of the
window an PC-DOS type of "pathname"
consisting of multiple (if needed)
folders and a file name. GEM simply
turns the concept of pathnames into
folder icons and moves you through the
path by your actions of selecting,
opening, or closing a folder.
Of course, you can't run IBM programs
because they are written in IBM assembly
language, which the ST cannot
understand. However, you can freely
copy and use text files and the data
within them. Furthermore, if you write
back out from the ST to the PC disk,
you'll find that an IBM has no trouble
reading what you wrote.
=================================================================
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