Re: Apple 5.25 floppy drive

[mwillegal <mike@willegal.net>]

There are actually 69 steps from inside to outside of a disk with
normal DOS disks set up with tracks on the even steps and odd steps
left empty.

The actual number of steps of of the stepper motor is 96*2 when re-
calibrating.   This number is set by the the LDA #$60 instruction at
location $BDD2 of the RWTS DOS driver.

Basically the RWTS is told that we are on track 96 and should seek to
track 0.  Then the actual track we want is stepped to from there.

Depending on where the head is at the beginning of a re-calibrate, we
will bounce off of the stop more or less times.

This re-calibration seems like drastic overkill, though I have never
tried changing the LDA #$60 to something in the low 40s to see what
would happen.

Regards,
Mike Willegal


On Jan 4, 11:26 pm, David Wilson <mcs6...@gmail.com> wrote:
> On Jan 5, 8:48 am, Eric Rucker <bhtoo...@gmail.com> wrote:
>
> > He is. IIRC, when the drive controller is initialized, it basically
> > sends commands to the drive to step down a track 40 times, because it
> > has no idea what track it's on, meaning... if you're on track 35 (the
> > highest track on a normally formatted floppy, although you can
> > sometimes get more than 35 tracks on a floppy,) it will click 4 times.
> > If you're already on track 0, it'll click 40 times.
>
> This used to annoy me so much that I wrote a little program to seek
> the head to track 40 (or perhaps 39) and I would run this before I
> powered the computer off. That way it would seek silently in before
> booting when I powered it up the next time.
>
> Slightly later I obtained a newer 1/2 height direct drive FDD unit
> which was based on a standard drive with a small 20 pin to 34 pin
> adapter circuit board. This circuit used the track zero sensor on the
> drive to disable outward seeks so it booted quietly no matter where
> the head was left.