Re: Apple floppy adaptor. I'm stuck!

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

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.)

> > In addition to the WRITE DATA signal, there is a /WRITE REQUEST line
> > (pin 10) that is active low.
> >
> > I'm sure you've already sorted this, but the write protect switch is
> > connected in a very interesting way in a Disk ][ drive.  ;-)  If phase 1
> > is high, then a drive *always* appears to be write protected.  (I don't
> > think that any Apple software depends on this.)
>
>
> Yeah all done. Hopefully correctly. Seems to be according to a combination
> of UTA2, various diskII pinouts, pc floppy pinouts, and a datasheet for a
> PC floppy drive I managed to dredge up.
>
> I do have some doubts on the hex inverter I'm using to keep up with the
> datarate though. It's about 20 years old. So I might pinch one from a 386
> motherboard I've been stripping for parts.

Any LS part shouldn't have any difficulty with the 250kHz data rate,
consisting of 1usec pulses.  50ns is a long time for these parts.

> Thanks for your input!

You're welcome, and I hope it all works for you!

-michael

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