Re: Commodore 64 kills APPLE II

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

Michael J. Mahon <mjmahon@aol.com> wrote:

> David Empson replied:
> 
> >The 3.5" drive mechanism is inherently "smarter" than the 5.25" one.  It
> >probably has a microcontroller on the drive itself, which is responsible
> >for details like stepper motor control.  The only head movement
> >supported is complete tracks.  (The drive mechanism uses a command
> >interface for operations like moving the head, with something like a
> >three or four bit command code and one data bit.  It has a similar
> >mechanism for reading status information like the write protect sensor.)
> >
> >Code downloaded to the UniDisk 3.5's on-board 65C02 processor is able to
> >change details like the address marks, but there isn't enough RAM in the
> >drive to do things like entire raw track dumps.
> 
> Very interesting, David.
> 
> Is there a source for documentation on this capability?

The behaviour of the 3.5" drive mechanism is documented to some extent
in one of the early Inside Mac volumes (probably volume 2, which covers
hardware).

The UniDisk 3.5 SmartPort command set is documented in the IIgs Firmware
Reference.

-- 
David Empson
dempson@actrix.gen.nz