Re: Daisychaining 5.25 " Drives

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

Knut Roll-Lund <kr-lund@nogarbage.online.no> wrote:
> 
> Someone wrote earlier that a duodrive could be daisychained... I guess
> the 5.25" controller allows for this. Making it more than two drives but
> of course only one daisychain.

I haven't seen a DuoDisk in the last decade and never owned one, so I
don't recall whether it has a daisy-chain connector.

If it does, it isn't much use, because the Apple II 5.25" disk
controller only has two drive select output signals, and they would both
be used by a DuoDisk, leaving no select signals to pass on to a
daisy-chained drive.

The disk controller circuitry on the card also has a single bit selector
to choose the active drive, so even a hardware hack to somehow wire up
another drive select pin wouldn't work without replacing the controller
card with something that has non-standard registers (which then wouldn't
work without a special device driver and wouldn't be compatible with
standard DOS 3.3 or self-booting OS-less software like games, but it
could work with ProDOS).

The Apple /// has more wires in its drive connector, so it is possible
that an Apple /// might be able to support more than two 5.25" drives,
and a DuoDisk on an Apple /// might allow daisy chaining further drives.

It is also worth pointing out that this thread is only discussing 5.25"
drives. There are two other sets of rules for 3.5" drives (one for the
Apple 3.5 Drive or SuperDrive, and the other for the UniDisk 3.5).
-- 
David Empson
dempson@actrix.gen.nz