Floppy interface

From: Dwight K. Elvey <dwightk.elvey_at_amd.com>
Date: Wed Aug 20 16:20:01 2003

>From: Federico <nuvola66_at_katamail.com>
>Fabio Finotti wrote:
>I would like project a circuit to emulate a old 8 inch floppy disk
>(tandon tm848 e).
>So i would like to know wath kind of signal the controller send to
>floppy drive and the reponse
>of floppy to controller.
>Thank you.

 You should look at a data sheet for something like
a WD1793 or nec765. This will help in understanding
normal formats. Of course, you do not have to use these.
 There are a number of control and status signals
to deal with head load, motor control, stepping, index
detection and door closed. There are usually to data
lines, one for read and one for write ( with the exception
early 8" that had built-in clock/data separators.
 Typically, the clock and data are encoded with one
of several methods. FM, MFM and M2FM are a few. These
are methods of keeping the clocking with the data.
On floppies, it is necessary to have regular transitions
of the write signal ( no long strings of constant levels ).
This is because most early read heads used coils and
required edges to be detected ( coil heads are differentiators ).
New hard disk heads may use techniques that see the actual
strength of field.
 Most soft sectored formats use illegal clock/data sequences
to make the beginnings of sectors( by illegal I mean that
they can't exist in the data portion ). These are usually called
address marks.
 Like I said, look at the data sheets. They explain these things.
Received on Wed Aug 20 2003 - 16:20:01 BST

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