From: Armin Vogl (Armin.Vogl_at_gmx.net)
Date: 2007-12-05 21:18:33
Hi !
> I do not know much about the low-level electronics- I've only studied what
> the drive sees with varying patterns of missing '1' bits. On old 1541
> hardware, patterns emerge based on the density setting and rotation speed
> that look like this:
>
> 11 11 11 12 22 22 22 24 44 44 44 44 48 88 88 88 88 11 11 11
I think the "ideal" pattern derived from the drive schematic is like this:
DISC: 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0
DRIVE: 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0
1 0 0 0 1 0 0 0 1
When a "1" bit is found, you get back the correct bit. After that you get
three times "0" and then 1 time "1". After that the pattern repeats: 3
times "0" and 1 time "1" ......
Depending on how the drive is synced, this would result in either 11,22,44
or 88.
What I don't understand is, why the drive should switch from 11 to 22 to 44
to 88 etc. without changing the "density" setting. It should only change the
pattern in case the density is changed and the pattern should only change
once not more than once. Maybe I have to look at the schematics more closely
:)
Rotation speed should also be not relevant if the track contains no "1" bits
after the sync.
I think I understand this protection much better now, thanks !
Armin
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