Re: On attempting to make the 3.5" floppy adaptor to work...

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

Tristan Mumford wrote:
> Michael J. Mahon wrote:
>
>
> > Tristan Mumford wrote:
> >
> > > Michael J. Mahon wrote:
> > >
> > >
> > >
> > > > Michael J. Mahon wrote:
> > > >
> > > >
> > > > > 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".
> > >
> > >
> > > So are you saying instead of the PC floppy dataline pulsing the data low
> > > for a phase change, the disk ii analog card just changes state and stays
> > > that way until the next phase change?
>
>
> > The WRITE DATA line stays whichever way it is until the next "1" (which
> > is the next flux reversal).
> >
> > (I find using "phase" in this context confusing, since the head stepper
> > is positioned using "phase" signals.)
>
>
> Because I had to "upgrade" to the bigger uC, it also ended up with a 12MHz
> crystal driving it. Because it only involved very minor work I decided to
> send the write signal via the uC to change it from flux reversals to
> pulses.
> It's probably too slow to do it though. It didn't work. Or maybe it's
> reading it back via the hex inverter that didn't work.
> Unless I misunderstood UTA2's section on the disk ii, the controller card
> gets data from the drive in a series of 1uS, active high pulses, which
> apart from the inverted state seems to be compatible with PC floppy drive
> standards.

That sounds right.

> I also managed to turn an 18f452 into a nice heating element. When I did the
> reshuffling I managed to short the -12v to one of its IO lines, which would
> have resulted in a nice 17v potential difference inside the chip. Or is it
> 16v. Doesn't matter anyway. Now I have something to throw at the neighbours
> cats.

Aaaack.  ;-(

Just the other day, I found an Apple ][+ ROM (the E8 ROM) that is
a near short from +5v to ground--it also makes a nice heating element!

This is the first time I've found a ROM with this failure mode.

> I just want this silly thing to work. Using a touch of modern embedded
> processing the task should be trivial.
> That and I plain don't like when things don't work.
>
> On one final note, I think I _may_ have some of those PC floppy controller
> tape drives and unopened tapes in the shed. I can't remember if I sold
> them. I think it would be kind of fun to get them working with a custom
> driver. A //e with a 250mb (capacity probably vastly reduced for apple)
> tape drive. What an odd idea. 
>
> So, am I heading in the wrong direction?

It all sounds like good fun to me.  ;-)

-michael

NadaNet networking for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."