Re: EDD + CARD

[mjmahon@aol.com (Michael J. Mahon)]

antoine wrote:

>I'm on the way to finish a Nixie clock using a PIC microcontroller and was
>thinking about doing an interface to grab the disk signal.
>
>The idea is to use a PIC running at 20 MHz (or more) to decode the data from
>the floppy and store the raw bytes into Ram.
>
>We work done in the state machine with the Prom and the shift register will
>be done by software.
>
>This way you can store the full 40 tracks in memory 256 KB.
>
>Then with a serial link you can move the data from and to the Ram from any
>PC.
>
>Change of track is not a challenge using the 4 phase lines.
>
>My idea is to be able to grab a whole disk and also replay it. The tricky
>part would be to find correct bit length of the track to wrap around each
>'revolution'.
>
>
>
>The hardware is quite simple: a Pic, a 16 bits counter for the ram addresses
>bus, static ram and a level converter for the serial link.
>
>
>
>Any volunteer to help me? Any suggestion is greatly welcome :))
>
>
>
>By the way, do you have any idea if this would be of any interest the
>Apple ][ freaks ?

Yes, I think it would be.  ;-)

The scheme you describe should work perfectly.

Finding the exact length of a track is done by finding a unique string of
"nibbles"--any string that doesn't repeat on this track--and searching for
its second appearance, which is the track wrap point.  The unique string
may vary from track to track, but a good starting point is a long string of
10-bit "self sync" nibbles (1111 1111 00).


-michael

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