Re: How many 5.25 inch floppies with the IIc support

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

David Betz <dbetz@xlisper.mv.com> wrote:

> "Mike" <mike@bogus.address.net> wrote in message
> ubaf5dql0l15ea@corp.supernews.com">news:ubaf5dql0l15ea@corp.supernews.com...
> > David Betz wrote:
> >
> > > Can I connect more than one external 5.25 inch floppy to a IIc? Can the
> > > IIc support external 3.5 inch floppies? If so, how many?
> >
> > For the 5.25, just one external drive.
> 
> Thanks! I thought maybe it would support more than one because it looks like
> the drives can be chained together. I guess that only works on the IIgs?

This feature isn't unique to the IIgs - you can also do it on the IIc+
(which has an internal 3.5" drive) and on the II+/IIe with a UniDisk
5.25 controller.

The disk controller only supports two 5.25" drives, so you cannot have
more than two such drives connected to each controller.  The IIc has a
single drive controller, and the internal 5.25" drive is connected as
drive 1.  This only leaves one drive select signal on the disk port for
an external drive.

In a machine with slots, you can install multiple disk controller cards
and have two 5.25" drives attached to each card (possibly limited by the
capacity of the power supply).

The UniDisk 3.5 uses a different mechanism for selecting the drives, so
you can connect at least two to the IIc, in addition to an external
5.25" drive.  The theoretical limit is 127 UniDisk 3.5 drives, but the
power supply and signal loading limits it to something in the order of
four drives.  The firmware may also impose an artificial limit.

> I've got two Apple IIc's. One is a Model A2S4000 and it has FF stored at
> FBBF. I guess I'm out of luck with that one.

You can update the firmware to the version which supports the UniDisk
3.5.  Your other IIc has the right firmware (FBBF = 00), so you can copy
the ROM from this machine.

You need a 27C256 EPROM (32Kx8).  Installing it in the older IIc
requires two minor modifications to the motherboard: a track cut and a
solder blob.  Both are near the ROM, and are clearly marked.

-- 
David Empson
dempson@actrix.gen.nz