Re: Daisychaining 5.25 " Drives

["Michael J. Mahon" <mjmahon@aol.com>]

mdj wrote:
> Bill Garber wrote:
>
>
> > The IWM is more than a Disk II. It is
> > actually a Smart Port, just like the
> > one in the IIgs.
>
>
> I think it depends on which "IWM" you look at: The original //c was
> much the same electrically as a standard 5.25" controller card, except
> it had an external interrupt input.
>
> The later iterations used on the IIGS and IIc+ had additional signals
> to activate either the 3.5" or 5.25" drives in the chain.
>
> The limitations of the original IWM in the //c didn't prevent it from
> controlling "intelligent" devices like the UniDisk 3.5" and the CT20c
> hard disk. The specifics of how this worked without interfering with
> two 5.25" disks on the same chain is what I am interested in.

IIRC, the 5.25" drives must be at the end of the daisy-chain, so
the last smartport device must synthesize drive 1 and 2 select lines
for the downstream devices, and must also pass on (or regenerate)
all the standard 5.25" vrive signals.

I expect that there is an signal line that a drive supplies to the
interface that says whether it is a smartport device or not, and
the interface responds accordingly, even through intermediate
smartport devices.

-michael

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