Generic 3.5 Inch Double Sided Disk Drive for the Atari 520/1040 Series
Generic 3.5 Inch Double Sided Disk Drive for the Atari 520/1040 Series
by James Lacassagne
Purpose:
This document is a description of the hook-ups and modifications 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 system, 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 compatible!!(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 insulation when the cover is forced in place. Since most of the wires in the cable go to the top row of the connector (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 operation. 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 connector 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 Connector.(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 connector 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 Compuserve No. 72257,1613.
Atari, Radio Shack, and Toshiba are Registered Trademarks.
