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Generic
3.5 Inch Double Sided Disk Drive
for
The 520/1040 Series
by
James Lacassagne
Purpose: This document is a description of the hook-ups and mod-
ifications that I found necessary in adding a 3.5 inch
double sided drive to my Atari(tm) 520. It is intended
solely as a guide to anyone who is interested in saving
a few dollars by using an "industry standard" drive in
place of the Atari SF314.
Warning: This installation seems to function properly for my sys-
tem, but I cannot guarantee anything. Also, the only way
that a saving will result is if a suitable power supply
is already available, or can be obtained at a very low
price.
Requirements: 1 3.5" Double Sided Drive w/ Installation kit @ $130
(The Unit I used was a Toshiba(tm) ND-352
which came with a multi-purpose mounting
kit. BE SURE that the unit is XT compat-
ible!!(720 K etc))
1 5v/12vdc Regulated Power Supply @ $ 25
(The supply must be capable of supplying
5V.+/-5% @200 mA and 12V.+/-5% @300 mA.
I saved some money here by using the same
supply that I used for adding a 5 1/4 in.
drive as described in numerous articles
in magazines and on Bulletin Boards.)
1 34 pin Card Edge Connector @ $ 3
(Yes, This is the "industry standard"
used on all XT's and Clones. I got mine
at Radio Shack (P/N____________).)
1 Standard Atari(tm) 3.5 in Disk Drive Cable @ $ 8
(Preferably, one of the After Market types
6' or so in length.)
1 Disk Drive Case @ $ ?
(This is optional--I still haven't found
a good cheap one, but the drive seems to
work fine.)
Procedure: There are two ways to proceed with this project depending
on whether you want the new drive to be A or B. The Drive
B method is the simpler, so I will start with it.
Cut the Standard Drive Cable in half (Save the other
half for another project--maybe!)
Strip back about 2" of the outer insulation from the
cable. Do Not cut off the shield wire (a layer of wire
woven around the multiple conductors in the cable).
Carefully unweave the shield, and twist it to form a
wire of its own.
Since the 34 pin connector that I used was designed for
ribbon cable, some ingenuity is required here. Each pin
on the connector ends in a V shaped stud designed to
separate the ribbon cable wire and cut only its insul-
ation when the cover is forced in place. Since most of
the wires in the cable go to the top row of the con-
nector (the even numbered pins) and the shield goes
to the bottom row, along with the wires from pins 3 and
7 of the Atari connector, I divided them accordingly and
routed them above and below the connector cover. Very
carefully, I pushed each wire far enough into the cor-
responding Vstud to hold it in place. I then forced
the cover down, forcing the wires the rest of the way
into the V. By trial and error I found that the two
ground wires (pins 3 and 7) in the cable did not provide
a sufficient ground path, causing unreliable drive oper-
ation. I overcame this by (gasp!) tying the shield to
ALL of the odd numbered pins on the connector. (That's
what the twisted shield wire is used for.) Carefully
lay it over the bottom row of Vstuds before putting
the connector cover on. The Connections Follow:
(NOTE: the colors mentioned are for an Atari Cable
You should check if you are using an After Market
Cable.)
34 pin conn. Atari conn. Signal Color
2 * media chng
4 N/A in use
6 N/A d4 sel
8 4 index yellow
10 5 d0 sel green
12 6 d1 sel violet
14 N/A d2 sel
16 8 motor on brown
18 9 direction orange
20 10 step grey
22 11 wrt data pink
24 12 wrt gate lt. blue
26 13 track 0 lt. brown
28 14 wrt prot lt. green
30 1 read data red
32 2 side 0 white
34 * rdy/med ch
(any 3 logic gnd blue
odd) 7 logic gnd black
Assemble the Disk Drive and Adapter kit. It should have
come with a power cable adapter with a std XT con-
nector on the end. You can either buy a mating
connector or cut it off and splice directly to the wires.
(Generally, pin 1 (red) is 5V, pin 4 (yel) is 12V, and
pins 2&3 (blk) are Ground.) The Installation Kit may
refer to a jumper on pin 34, but this can be ignored.
Now, the only modification to the drive can be made.
On the Installation Kit PC Board, a Jumper must be
soldered between pin 2 and pin 28 of the Drive Con-
nector.(This is the one that actually connects to
the Disk Drive. It is identical in pin layout to the
Std connector, with pin 2 on the top left as you look
at it.) This connects the Media Change signal on pin
2 to the Write Protect signal.(Thanks to Analog2 for
pointing me in the right direction on this one.)
These are both open collector, active low signals, and
can be safely wired together.(wired or configuration)
This should be all that has to be done to make the
drive work. Simply plug the cable into the OUT con-
nector of the first drive or the 1040, and away you
go.
If you have a 520 and want this to be drive A, the
procedure is the same, except DO NOT CUT THE CABLE
IN HALF. Instead, strip a 3-4 in. section in the
center of the cable, Cut and unweave 1/2 of the
shield. Lead the wires over the Vstuds as before,
but cut the wires from the Atari connector pins 5&
6.(computer end) Pin 5 wire is connected to the Std
connector pin 10 and pin 6 wire is connected to the
remaining end of pin 5.(The part that will go to the
second drive.) This brings the ds1 signal to the
ds0 pin on the second drive, just like Atari does it.
You can cut off the remaining pin 6 wire if you like,
since it doesn't get used. Don't forget to attach the
shield to the odd number connector pins.
If you have understood and followed my directions, the
drive should function properly. If not, there is not
much that can cause damage. My version will read and
format and write to double and single sided disks
without any problems. If you encounter any difficulty,
I can be contacted through Delphi as JIMSL or Com-
puserve No. 72257,1613.
Atari, Radio Shack, and Toshiba are Registered Trademarks.