Re: 5.25 drive and IIgs

[dempson@actrix.gen.nz (David Empson)]

In article <32dj3r$rjk@bmerhc5e.bnr.ca>,
Jeffrey Robertson <jeffr@bmerha2a.bnr.ca> wrote:
> In article <CuDGF3.Mu7@actrix.gen.nz>,
> David Empson <dempson@actrix.gen.nz> wrote:
> >
> >If you are using a "UniDisk" style drive, it can be daisy-chained
> >_after_ any 3.5" drives you have connected to the IIgs disk port.  You
> >must have slot 6 set to "Disk Port" in the Control Panel to be able to
> >access the drive.
> >
> >A Disk ][ can be connected in the same manner, if you have an adaptor
> >cable to convert the 20-pin IDC connector to a DB-19 plug.
> 
> Where can one get this kind of connector?

Alltech Electronics sells something called a "19-pin drive converter"
for US$14.  I expect this is the correct adaptor.  (It might be
an adaptor to connect a UniDisk 5.25 drive to a Disk ][ controller
card, but I doubt it, because this a rather rare requirement.)

Alltech Electronics
2618 Temple Heights
Oceanside, CA 92056

Orders Only: 800-995-7773
Inquiries & Tech Support: 619-724-2404
Fax: 619-724-8808

> Can you connect two Disk ][s after a 3.5"?

Yes, but you would need a double adaptor, wired to set up one of the
drives as drive 1 and the other as drive 2.  I haven't seen or heard of
such an adaptor being readily available, but it isn't much harder to
make.

Note that you cannot connect two Disk ][s after a UniDisk 5.25 - you
can only have two 5.25" drives in total on each disk drive controller,
including the disk port of the IIc and IIgs.  Note that the IIc's
internal drive counts as one, so you can only connect one external
5.25" drive on a IIc.

There is also a limit of two Apple 3.5" drives per disk controller
(you must have a controller which supports the drive, of course).
There is a theoretical limit of 126 UniDisk 3.5 drives per controller,
but the hardware and firmware limit you to about 4.

You shouldn't connect more than four drives to the IIgs disk port.

> Is this the sole use for this adaptor cable, or might one find it in
> non-Apple computer stores?

Some electronics supply houses may have this cable as a standard item.
Otherwise, it is only useful on an Apple II, so it is unlikely to be
available elsewhere.

I have made up one of these adaptors - it requires a ribbon cable, a
DB-19 connector (which I hear are difficult to obtain the USA, but I
can easily get them in New Zealand), a male IDC-20 connector, and a
little soldering and cutting to rearrange a few of the wires.

Of course, if you make up one of these cables and get anything wrong,
you could fry your disk drive and/or computer.  Probably better to buy
a pre-made one, for peace of mind.

> Do you have to modify the Disk ][ in any way?

No.  You can remove the adaptor and use it as normal on a Disk ][
controller card.


There is one potential problem with using this type of adaptor: unless
it is specially made, it is unlikely to be shielded and the connection
may cause RF interference.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand