Re: I demand an answer!

[dempson@actrix.gen.nz (David Empson)]

Leon Howell <puritan_2076@yahoo.com> wrote:

> > > *W*H*Y* won't the Hard Disk 20 work with the Apple II?
> > 
> > Because the electrical interface
> 
> The interface is the same as the Apple ][ as far as the floppies are
> concerned

No it isn't.  They are very closely compatibile, including having the
same connector and MOST of the pins are the same, but there are some
differences.

For example, the early Mac floppy port has an output which is controlled
by one of the multifunction outputs of its VIA chip, able to generate
square waves and other signals without much software intervention.  This
signal is used to control the rotation speed of the 400K Mac drive (and
possibly the early 800K drive) according to which track is being
accessed.  (This is done automatically by the Apple 3.5 Drive.)

This timing signal is not available from an Apple II's disk port (except
for the Universal Disk Controller) so you can't normally connect a
Macintosh 400K drive to an Apple II.

I'd have to go hunting to find out which pin is used for this signal,
but my recollection is that is the pin used to sense the write protect
status of a 5.25" drive on the Apple II.


The HD20 might be dependent on using this pin for a special function. If
so, it cannot be used on a standard Apple II disk port, because there is
no way to output a signal on that particular pin.

-- 
David Empson
dempson@actrix.gen.nz