IBM 1.44 FDD for an Amiga 500
Franc Zabkar
Instructions for installing an IBM 1.44 floppy drive in an Amiga 500
--------------------------------------------------------------------
The major differences between IBM and Amiga FDDs lie in two pins:
Pin 34 is IBM's DISKCHANGE output while pin 2 is a LO/HI DENSITY
input.
Pin 34 is the Amiga's READY output while pin 2 is the DISKCHANGE
output.
IBM's outputs are open collector. Its inputs are pulled up high on
the drive.
IBM's drives are setup as drive number 1 rather than drive number 0.
With this in mind, do the following:
1/ Make up a 34-way ribbon cable as follows:
At the drive end of the cable, cut out conductors 10 thru 12 and
twist them IBM fashion. This serves to accommodate the FDD as
drive number 1. Install a 34-way female IDC header.
At the A500 PCB end, snap on a similar header some 5cm from the
end, leaving some extra cable for attaching additional
electronics.
Cut and peel back conductor number 2 at the drive end, and bare
the end.
Cut and peel back conductor number 34 at the PCB end, from the
drive side of the header, and bare the end.
Solder the two ends together and place a sleeve of heatshrink
tubing over the join. (Let's keep it neat!)
2/ Add some electronics on a small piece of Veroboard or similar to
the 5cm of trailing cable at the Amiga end. Only pins 34, 2, 10,
8, 26, 28, 30 are needed, the remainder can be cut off.
This electronics is needed to simulate the READY signal that
Amiga requires but which IBM does not provide. Several pull-up
resistors (say 2K2) are also needed. See below.
3/ Add a power cable consisting of two wires (+5V, GND) terminating
in a 3-pin header (+5V, GND, key) somewhere on the Amiga PCB.
Choose your own spot. You may also choose to hardwire the supply
from the PCB.
4/ Re-use as much of the Amiga mounting hardware as is appropriate.
You may need to pack the standoffs with washers to bring the FDD
to the correct height.
5/ You may need to cut a hole in the side of the Amiga cover for
access to the disc eject lever. You may also need to extend the
length of this lever by some suitable means.
6/ Note that some FDDs keep spinning a second or so after the
Amiga's disc activity LED has extinguished. Don't change
diskettes until you hear the disc motor come to a stop.
Alternatively reroute the FDD's own disc activity LED to a
visible position.
External IBM drives can also be accommodated in similar fashion.
Circuit diagram for "READY electronics"
---------------------------------------
+5V
_
|
|
/
\ 2K2
/
\
|
Pin 34 <-------|------------------------------------
|
|
|
+5V |
_ |
| |
| |
/ |
\ 2K2 |
/ |
\ |
| |
Pin 2 <-------|-------------- |
| |
| |
| |
| -------\ |
|--------| \ |
+5V | | |
| 7438 |O----
- | |
| |-------| /
2K2 | | -------/
/ |
-------\ \ |
|--| \ / |
| | | \ |
Pin 10 <---| | 7438 |O----|----|
| | |
|--| /
-------/
Amiga PCB pin # IBM FDD pin #
--------------- -------------
to circuit ----- 2 ------------------------ 34 disc change
4 ------------------------ 4
6 ------------------------ 6
pullup res ---- 8 ------------------------ 8
to circuit ---- 10 ------------------\ /--- 10
\ cable twist
12 ------------------/ \--- 12 (drive select)
14 ------------------------ 14
16 ------------------------ 16
18 ------------------------ 18
20 ------------------------ 20
22 ------------------------ 22
24 ------------------------ 24
pullup res ---- 26 ------------------------ 26
pullup res ---- 28 ------------------------ 28
pullup res ---- 30 ------------------------ 30
32 ------------------------ 32
to circuit ---- 34
N/C -- 2 lo/hi density
(not used)
1,3,5,7...33 ------------------------ 1,3,5,7...33
signal grounds
- Franc Zabkar
Franc Zabkar
I received the following e-mail message from "header checksum failure"
<nos...@ricochet.net>:
>Franc Zabkar <SZA...@Bigpond.com> wrote:
> Instructions for installing an IBM 1.44 floppy drive in an Amiga 500
> --------------------------------------------------------------------
>many thanks for the info. please make sure this goes into warren blocks
>hardware guide information library for others to find easily..
Not being a Commodore user, I don't know who Warren Block is.
If anyone feels my info is worthy of inclusion in his database, please
feel free to do so.
- Franc Zabkar