Re: 3.5" drives on the IIc (was Re: n)

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

In article <Dt2spv.DM5@gonix.com>, Carl Knoblock <cknoblo@gonix> wrote:
> buggie@enzu.unm.edu (stephen e buggie) writes:
> : I have an 8 MHz ZIP CHIP in my Flagship IIC.  Will this extra speed allow 
> : the IIC to operate a platinum 3.5" drive, or are there other 
> : complications prevent it?
> 
> The disk drive interface in the //c is designed for the UniDisk 3.5 only.
> An accelarator is not enough to fix that. The //c+ has the newer 
> controller chip.

Not exactly.  The IIc and IIc+ have the same disk controller chip, the
IWM (Integrated Woz Machine), which is also used on the UniDisk 3.5
card for the IIe, and on the IIgs motherboard.  (The same chip is also
used in all Macs up to the Mac II, and there is another one inside the
UniDisk 3.5, for talking to the computer and controlling the drive.)

The SuperDrive card, and the Mac IIx and later use the SWIM chip
(Super Woz/Wendell Integrated Machine, I think) which adds support for
MFM and high density disks (transfer rate twice as fast as the Apple
3.5 Drive).


The IIc+ has some extra hardware to allow it to support an Apple 3.5
Drive.  It is a little hard to follow the circuit diagram, but it
appears that there is a special controller chip with some attached
timing and support hardware, and a 2K RAM chip.  This is responsible
for processing the data sent to/from an Apple 3.5 Drive.  It is
probably not used (or is transparent) for 5.25" and UniDisk 3.5
accesses.

These chips also provide the extra signals needed to control and detect
the Apple 3.5 Drive.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand