Re: usb disk controller to read c64 disks.

From: Uffe Jakobsen <uffe_at_uffe.org>
Date: Fri, 23 Sep 2011 10:46:11 +0200
Message-ID: <4E7C4753.5080006@uffe.org>
On 2011-09-22 22:02, Wolfgang Moser wrote:
> Hi Olaf,
>
> Rhialto schrieb:
>> On Wed 21 Sep 2011 at 23:31:28 +0200, Wolfgang Moser wrote:
>>> so then get a Panasonic JU-475-4 or -5 drive and file away the
>>> mechanical stop a little bit. The rails and other mechanical parts are
>>> long enough to allow the head to step back to track -4 (ca. 2.15mm).
>>
>> Won't that mean that if you format a new disk on it, it will have the
>> tracks on the top offset by (about) 4?
>
> I did not test this yet, but there is still the optical track-00 sensor.
> Because I didn't touch it it should be still correctly aligned so that
> disks get formatted correctly. The Kryoflux people reserved one of the
> lines of their controller to temporarily disable the track-00 signal so
> let the drive controller IC "think" that the sensor is not hit yet. If
> this line is not active, then the sensor is in fact hit, recognised by
> the drive controller and therefore the head is repositioned to track 00.
>
> Does this make sense for you?
>

I'm afraid that I'm short of some background knowledge here.

I guess that there is only one track zero sensor that works for both 
heads as they are mounted on the same rails ?

Using a standard 5.25" floppy drive - at what level is track zero 
signalling enforced ?
Is the track zero signal "information only" to the controller/software 
that track zero is reached ?
Or will the drive electronics *actively* prevent any further head 
movement in that direction once track zero is signalled.

When the track zero sensor triggers (on a standard 5.25" floppy drive) 
the top side head is at physical track zero while the back/flip-side is 
at physical track 4 - is that correctly understood ?

/Uffe




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