Re: Daisy-Chaining Unidisks (was Re: $20 unidisk repair)

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

In article <mnementhCrLrKH.6rL@netcom.com>,
David R. Villegas <mnementh@netcom.com> wrote:
> tf3@pro-lightning.oau.org (Austin C. Phelps) wrote:
> >On a IIe I ran 3 UniDisk. The extra were mapped to Slot 2 (my card was in
> >slot 5). On a IIc, it might work. Never tried running 3 UniDisk on a IIc.
> 
> How many Unidisks will the Unidisk card handle?

There are four potential limits:

1. The number of addresses available (127).
2. The number of drives supported by the firmware on the card (at
least three, from reports I've seen so far, but I don't know what this
limit is).
3. Amount of power that can be provided by the IIe power supply.
4. Signal strength of the SmartPort bus driver chips on the card (the
more drives there are, the more loading there will be on the card).

The usual limit I've seen quoted for number 4 is four drives.  The
usual limit for number of disk drives is 4 (or perhaps 6) in the whole
system.  I don't know what limits the card's firmware has, but it
probably supports at least four drives.


I have the newer card (Apple II 3.5 Disk Controll Card, alias
"SuperDrive Card") in my IIgs.  Its manual explicitly states that you
can only connect two drives to the card.  It might be erring on the
side of caution though.  You certainly cannot connect more than two
Apple 3.5 Drives or SuperDrives, because they use a single select line
which only has two possible states.  You may be able to connect more
than two drives to the card, but at least one of them would have to be
a UniDisk 3.5.  The firwmare may be limited to supporting two drives.

> Also, can anything besides a Unidisk work daisychained to a Unidisk?
> I'm hesitant to see what would happen if I attached an Apple 3.5 or a
> Duodisk. 

It depends on the controller card or disk port you have the drive
connected to.  When daisy chaining drives, always put drives in the
following order:

1. Apple 3.5 Drive or SuperDrive (up to two in total, any order)
2. UniDisk 3.5 or other "intelligent" SmartPort devices.
3. 5.25" drives (Disk ][, UniDisk 5.25 or DuoDisk).

The various interfaces support drives as follows:

Disk ][, UniDisk 5.25 or DuoDisk card: only supports 5.25" drives.

UniDisk 3.5 Card: only supports UniDisk 3.5 and other intelligent
SmartPort devices.

Apple II 3.5 Disk Controller Card: Apple 3.5 Drive, SuperDrive,
UniDisk 3.5 (and probably other intelligent SmartPort devices).

IIc disk port: UniDisk 3.5 (if you have ROM version 0 or later), 5.25" drive.

IIc+ disk port: Apple 3.5 Drive, UniDisk 3.5, 5.25" drives.

IIgs disk port: Apple 3.5 Drive, UniDisk 3.5, 5.25" drives.

Universal Disk Controller: Apple 3.5 Drive, 5.25" drives, some types
of Macintosh 3.5" drive.  Some versions may also support the UniDisk 3.5.


The SuperDrive can be used in place of an Apple 3.5 Drive, but it will
only be able to access 400k and 800k disks.  If you want to use it to
access 720k or 1.44MB (MFM) disks, you have to connect it to the
"SuperDrive card" (Apple II 3.5 Disk Controller Card).


(If the above isn't in the FAQ, it probably should be.)
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand