guy@ns.network.com (Guy D'Andrea) (06/10/91)
Here is the hardware hack to create an Amiga floppy drive external connector
for your AT Bridgeboard. Now you can take an external Amiga floppy drive and
connect it to the AT Bridgeboard, just like XT Bridgeboard's built in connector!
********************************************************************************
From: mmm@reaper.chi.il.us (Michael Marvin Morrison)
Subject: Re: AT Bridgeboard and an "Amiga" external floppy drive?
Ok, here's your solution:
Purchase a 'standard' drive cable from a dealer (to work with, just in case it
get's messed up, you don't wanna loose your only drive cable.. about $3..). By
'standard' I mean 34 pin Female push-pin type connector on the BB end, and 2
34 pin Card-edge connectors on the other (with the little twist) A crimp-on
type DB-23/25F connector, preferably with a metal casing, but the plastic ones
will work. If you can only find a 25 pinner, you will have to cut the end 2
pins off (push the plastic out through the metal connector, chop them off, and
push it back through the metal casing) This may be kind of tough.. you could
file it, or I cut it off with a REAL sharp exacto knife. Preferably cut the
13/25 pin end, so that the top row at least will still be the correct numbers..
remember not to go by the connector numbers after cutting a 25 pinner.. :-)
Pin 1->o o o o o o o o o o o o /o <- Whack this end.
o o o o o o o o o o o /o
New Pinout:
Pin 1-> o o o o o o o o o o o o <- Pin 12
Pin 13-> o o o o o o o o o o o <- Pin 23
To make this guy look professional (or not.. up to you) is to get one of those
metal slot connectors (the part chrome part that shows on the back of the
Amiga), and have it cut with the pattern of a DB23/25, so that this can be
mounted.
Or if you notice, there are 2 metal slots that can be removed to the immediate
right of the card space that could also be punched with the design.
__ ________________
| |
| Standard Card |
| __________ |
|_____|
^
This part.
You could also use one that is pre-cut (you may have one from an old IBM
serial/parallel card lying around that had the extended connector on it)
Close to where you are gonna mount the DB23/5 mark a diagonal line across the
cable so that you can keep the pins strait for the next step. (Felt tip)
Now, the hard part.. Here's where it will take a little time. Take an exacto
knife, and CAREFULLY cut between each of the wires on the 34 pin cable (close
to where you are gonna mount the connector, make sure there is enough cable to
still reach the other drive) and pull them away from each other, but not for
more than a couple inches of the cable:
________________________________
BB | -------
End | -------
| -------
^^^^ Separated from each other.
Every odd pin is ground on the 34 cable, so my suggestion is to take 23 little
pieces of tape, and write numbers on them, and affix them to the wires so that
you don't get lost!! It may be best to do this when you cut the cable, and if
you get lost, just line up the diagonal mark you made, and then your sure that
you are correct.. (that's what it was for) and remember that pin 1 is the
Colored one..
Now, here is your mission, you must line the wires up in this order, starting
with pin 1, and pin 1 on your connector so that you don't have to start over
again.
**** As per usual with these type of projects, I can't be responsible for any
damage you may cause to your system in installing this little goodie.
Ok. Here are the pins we will be using:
34Pin-Out 23Pin-Out
--------- ---------
8 - INDEX 2 - READ DATA
10 - DRVSEL 1 8 - MOTOR ON
12 - DRVSEL 2 9 - DRVSEL 2
16 - MOTOR ON 13 - SIDE SEL
18 - DIR SEL 14 - WRITE PROT
20 - STEP 15 - TRACK 00
22 - WRITE DATA 16 - WRITE GATE
24 - WRITE GATE 17 - WRITE DATA
26 - TRACK 00 18 - STEP
28 - WRITE PROT 19 - DIR SEL
30 - READ DATA 21 - DRVSEL 1
32 - SIDE SEL 22 - INDEX
12 - +5
23 - +12
3-7 - GND
Here are the signal lines to connect:
34Pin Ribbon 23Pin Crimp on
8 22
10 21
12 9
16 8
18 19
20 18
22 17
24 16
26 15
28 14
30 2
32 13
* NOTE: The pin count for the 34 pin connector is counted as the ribbon cable
comes directly from the AT Bridgeboard - without the twist!
Since the IBM drive connector uses the "uncrossed" connector for drive B, which
is what you want your 3.5 to be, a pin-for-pin to the proper signal will work
just fine in this case. Take 5 lines at random from the odd pins on the 34 pin
connector and connect them to 3-7 on the 23 pin Crimp on (ground).
Now for the power:
Since the IBM connector didn't have pins for power, you will have to whip out
your soldering iron and run some cables from one of the power connections on
the supply that was meant to go to another drive. The easiest thing to do
would
be to get one of the male connectors that fits the power plug, or you can do
one
of these numbers:
Power line======--====
^^ Cut small amount of insulation off of the cable, and solder
your wire there. Seal with electrical tape!!
One of the power connections should be able to handle 2 3.5's running at the
same time, but it's better to use one that isn't currently being used.
Definitely do not hook it to the 5.25 drive (or your hard drive), as these draw
much power when running.
___________
\ O O O O /
\_______/
+5 GND +12
The middle 2 pins are ground, but I'M NOT SURE WHICH IS +5/+12. Please take a
meter and check!!!! I believe this is correct, though. If this is wrong, you
will more than likely have a fried drive on your hands.
Now take the +5 line, and run it to pin 12, and the +12 line and run it to pin
23.
Now crimp the connector on over the pins, and you should have a slick drive
interface off of your AT BB.
If you have any further questions please write. And note that I obviously
can't be responsible for anything that happens bad.. (I'll take resp. for the
good stuff though..:-) To the best of my knowledge this data is correct, but I
haven't built one of these myself (since I have an XT BB).
Michael M Morrison /| |\
mmm@reaper.chi.il.us <or> | | Cash, for Cache.. | |
reaper!mmm@miroc.chi.il.us \| Hmm.. sounds fair. |/
-------------------------------------------------------------------------------
Well folks, I DID make this cable up and I now can move my external Amiga
floppy drive to the AT Bridgeboard when I need to run 3.5" 720k IBM stuff!!!
It works just like when I had my XT Bridgeboard which DID come with an external
connector. The only problem I had was the first time I tried the cable, both
drive lights came on at the same time. I then switch pin 10 with 12 on the
34 pin connector and then everything was fine. So if you have the same
problem, swap those two pins and it should run for you.
Any questions, leave me mail and I will see if I can help...
Many thanks should go out to Michael Morrison for filling this need for AT
Bridgeboard users!!!
--
guy@nsco.network.com //
Guy Dandrea \\ //
Network Systems Corp., Mpls. MN \X/
1-800-328-9108 Fax:(612)424-1736 "Me and my Amiga...anything is possible?"