Re: Apple floppy adaptor. I'm stuck!

["Michael J. Mahon" <mjmahon@aol.com>]

Tristan Mumford wrote:
> G'day.
>
> As you may or may not know I've been working on a little device to allow PC
> 3-1/2" floppy drives to be used on a disk ][.
>
> It can now do the following:
>
> * de/Select and spin up/down the drive.
> * Detect the write-protect state of an inserted floppy.
> * Move the head around.
>
> What it can't seem to do is read and write. The basic question I want to ask
> is whether the apple2 has an active high or low for read and write pulses.
> I believe it's active high, but I'm starting to doubt myself a little.

Actually, it's *neither*!  The Disk ][ Controller *toggles* the state
of the write line each time that it writes a "1".  No toggle = "0".

> By the way. The slow stepping gives the PC floppy that satisfying "GRONK"
> sound of the apple drives.

The Apple stepping algorithm is much more sophisticated than the PC's.
It accelerates and decelerates the stepping rather than just stepping
at a constant rate, reducing the total time to seek.  (Of course, the
time constants were chosen for a Shugart Associates SA390, so the
software seek could be speeded up quite a bit for newer drives.)

> Another possibility I guess is that I have some kind of weird error in the
> head movement causing it to move to the wrong tracks.
>
> Is there some kind of low level format that I can do on an apple floppy. I
> tried the ProDOS format, but it looks like it only does track 0, somewhere
> in the middle, and track35? I just got that from watching the head
> movements.

Then there is something wrong with the head movements, because both DOS
and ProDOS format all 35 tracks, starting with track 0.

> I'm hoping I can get this issue sorted, because it's nearly done! I hope I
> can get it working right, because I actually decided to use a calculator to
> figure out final storage capacity *Gasp!*. A 2HD disk should hold 640kb. In
> it's current form a normal 2HD disk appears as one big single-sided 160
> track disk.

Several places in the Disk ][ driver/RWTS think that a disk has at most
40 or so tracks--like recalibration.

-michael

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