Re: Daisychaining 5.25 " Drives

["mdj" <mdj.mdj@gmail.com>]

Michael J. Mahon wrote:

> There are several "redundant" power wires on the Disk ][ interface,
> and if the Smartport interface treats one of these as an input and
> a smartport device ties it low, then the interface will have a simple
> level to indicate smartport vs. Disk ][.
>
> This is all speculation--if I get desperate I'll have to go look
> at a schematic.  ;-)
>
> Of course, once the controller knows it's talking to a smartport
> device, there's lots of protocol to exchange information.

This would work, but the documentation I have (original IIc reference
manual) indicates the port is electrically identical to the old 5.25"
controller for the IIe, with the exception that one extra input line is
added for external IRQ, and 5V is only supplied on one pin instead of
two. There was a lot more redundancy on the original 20 pin connector
than there is on the DB19's

> > I seem to recall there was a modification made to analog controller
> > board in the Platinum 5.25" drives that allowed them to respond to a ID
> > request while still essentially being 'dumb' devices - the Apple 3.5"
> > and Superdrive have the same feature, I think.
>
> I doubt that--except for selectively wiring the redundant power
> lines as noted above.

I'm positive that change was made with the introduction of the Platinum
drive (AppleDisk 5.25") which accompanied the IIgs, platinum IIe and
then the IIc+

Two of the redundant power lines (one of the 5V lines and one ground)
are re-used on the second generation SmartPort to signal 3.5/5.25",
which I assume caused the 3.5" drives first in chain to handball
signalling to 5.25"'s down the chain, and head select, used for obvious
purposes on Apple 3.5" drives.

> > Surely the electrical characteristics of SmartPort are documented
> > somewhere? Perhaps in one of the IIGS reference manuals I don't have.
>
> I'm thinking I'd start in the IIc Technical Reference Manual...

The one I have unfortunately doesn't even cover the 32k ROMS, so
there's no mention of it except as a Disk Port to control the Disk IIc

Matt