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From: Pete Rittwage on 16 Oct 2006 18:18
Wolfgang Moser wrote:
>
> And then the 1571 disk drive: From the factory the index
> hole detector is _only_ connected to the MFM controller
> WD177x. So for giving support for it you will have to
> program the MFM controller and you have to live with the
> latency given due to soem waitstates on the WD177x registers
> noted somewhere on the WD177x datasheet.

It is also worth noting to those that don't know that the sensor will
not pick up the index hole on the second side of a disk. Since it has
to be physically flipped, the hole is in the wrong place.

Now on a 1571, if we were to relocate the IHS to a VIA port, we could
also read the second side of the disk without flipping it, and reverse
the bits. Hmmm...

Can the 1571 IHS be easily relocated? I'd be happy to add this
capability to MNIB to 1571 users.

--
-
Pete Rittwage
http://rittwage.com

C64 Preservation Project
http://c64preservation.com
From: Wolfgang Moser on 17 Oct 2006 01:36
Hi Pete,

Pete Rittwage schrieb:
> Wolfgang Moser wrote:
>>
>> And then the 1571 disk drive: From the factory the index
>> hole detector is _only_ connected to the MFM controller
>> WD177x. So for giving support for it you will have to
>> program the MFM controller and you have to live with the
>> latency given due to soem waitstates on the WD177x registers
>> noted somewhere on the WD177x datasheet.
>
> It is also worth noting to those that don't know that the sensor will
> not pick up the index hole on the second side of a disk. Since it has
> to be physically flipped, the hole is in the wrong place.

This is correct, either you mount a second sensor extra
for flipped disks along with electronic logic to handle
it or you forget about IHS reading of flipped back sides.


> Now on a 1571, if we were to relocate the IHS to a VIA port, we could

This could be as easy as adding an IHS addon in a 1541.


> also read the second side of the disk without flipping it, and reverse
> the bits. Hmmm...

Hmmmm, this would only work, if the top head (back side)
is radially adjusted the same as the bottom head (normal
side). You know, at least with PC disk drives, you are
never able to read track 1 with a backflipped and
reversely read disk.

> Can the 1571 IHS be easily relocated? I'd be happy to add this
> capability to MNIB to 1571 users.

Why not? I don't see a reason, why this should not work.
Take note to fetch the signal before it was routed
through the 74LS241, otherwise it got switched with
the SER/DIR signal. Maybe the latter is of some use
maybe not, I had no investigations yet.


Womo
From: Anssi Saari on 17 Oct 2006 03:15
Pete Rittwage <rcade(a)rittwage.com> writes:

> It is also worth noting to those that don't know that the sensor will
> not pick up the index hole on the second side of a disk. Since it has
> to be physically flipped, the hole is in the wrong place.

I actually had some floppies that had two index holes, back in the
80s. I suppose they were meant to be flipped and in fact a friend of
mine used one of them as two sided in a CP/M machine.
From: Pete Rittwage on 17 Oct 2006 19:00
Wolfgang Moser wrote:
> Hmmmm, this would only work, if the top head (back side)
> is radially adjusted the same as the bottom head (normal
> side). You know, at least with PC disk drives, you are
> never able to read track 1 with a backflipped and
> reversely read disk.

I knew that about PC drives, but I assumed (maybe wrongly) that they are
aligned on the 1571. Anyone know for sure?

--
-
Pete Rittwage
http://rittwage.com

C64 Preservation Project
http://c64preservation.com
From: Nicolas Welte on 20 Oct 2006 13:31
Pete Rittwage wrote:
> Wolfgang Moser wrote:
>> Hmmmm, this would only work, if the top head (back side)
>> is radially adjusted the same as the bottom head (normal
>> side). You know, at least with PC disk drives, you are
>> never able to read track 1 with a backflipped and
>> reversely read disk.
>
> I knew that about PC drives, but I assumed (maybe wrongly) that they are
> aligned on the 1571. Anyone know for sure?

Pretty sure. Jochen Adler made a program to display the flip disk side
directory on a 1571. I seem to remember he also reported the track offset
of the 2nd side head. Look here: www.nlq.de

Nicolas
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