Amiga floppy drives are a bit special. They follow the 34pin Shugart interface but usually floppy drives for PC computers do not work straight out of the box.
1) PC floppies are usually hardwired to Drive Select 1.
2) They generate a Disk Change signal on PIN 34
3) They do not generate a ready signal
Amiga floppy drives require:
1) DS0 set for the internal drive
2) Disk Change signal on PIN 2
3) Ready Signal on PIN 34
Now in the old days (until the middle of 90s) PC floppy drives used to come with all the jumpers that could be changed for satisfy the above requirements.
Recent floppy drives however (cost cutting?) do not sport any jumpers.
I was lucky enough to find a TEAC FD235HF – A700 somewhere in my old hardware closet.
This floppy DOES have the necessary jumpers.
For the back it looks like that:
How do you set the jumpers to make it compatible with the Amiga?
In the picture you can see 7 rows of PINs. They are labelled as A, B, C, …, G.
Each row has 3 columns of pins, apart from the last 2 rows, F and G where you can see an extra column (at the left) of 2 pins. This column just makes a short between the frame of the floppy and DC 0V so we can ignore it.
For the rest of the pins lets have a look at the following picture:
The red box shows 6 pins. Those controls the DS settins of the drive.
In the picture DS0 is selected, as shown in the yellow box (I didn’t have a spare white jumper so I used a small black one from an old hard drive that unfortunately can not be seen in the picture)
The jumper shown with the blue arrow controls the Ready signal: in this settings it goes on pin34 as required by the Amiga.
The yellow arrow shows the jumper that controls the DISK CHANGE signal. In the setting shown here is goes to pin 2 of the shugart interface which is, again, what Amiga is expecting.
That leaves us with the jumper controlling the HD behaviour. As shown in the image it is set to AUTO. This has the side effect, that HD 1.44 floppies WILL NEED a tab covering the 1.44 hole to work as 880 floppies.
There is another alternative of placing this jumper vertically, on the last set of pins on the right columns (between rows F-G). This will force the floppy to guess the density from the HD IN signal on PIN 2 of the shugart interface. I guess Amiga will not send such a signal on PIN 2 so the drive will default to double density.
HOWEVER, since the Disk Change Jumper that we described earlier occupies one of the pins, I could not find an easy way of having all those 3 pins jumpered. Does anybody know if jumpers that can occupy 3 pins in a row exist?