Re: Weird Floppy stuff

From: fachat (
Date: 2005-05-16 22:36:31

On Mon, May 16, 2005 at 07:22:48PM +0200, Spiro Trikaliotis wrote:
> Changing some parts around, it seems it is the drive MECHANICS which is
> the culprit. Even more interestingly, there are drives where using 
> side 0 (lower R/W head) causes this behaviour, but using side 1 (upper
> R/W head) does not cause this behaviour!

I have not experienced this but could this be because of a delay of the
data signal in the mechanics? Assume the signal gets a delay of the
multiple of half the bit time (i.e. half the time it needs to write a 
GCR bit) both when reading and when writing.

Now write a bit, and change from write to read. Because of the delay,
(half a bit in and half a bit out) the borders of the bits on the medium
are received whithout a phase shift when reading.
If the drive mechanics delays the bits the fourth part of a bit, then
when reading the bit results in a phase shift of half a bit.
So the mechanism to identify the bit values has the problem of 
finding the value because it has to decide which bit to take.

I don't really know how the analog circuitry works, maybe that 
problem does not occur in normal operation, because the SYNC
signal syncs the bit-value-identifier as well?

Do you get what I mean?


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