Stephen Shaw <xstephenx@apple2.org.za> wrote:

> On Thu, 14 Mar 2002 12:39:52 +1300, David Empson wrote:
> 
> > The biggest hurdle is that the Mac and Apple II use pin 10 of the disk
> > connector for different purposes.
> 
> David, I'd just like to clarify something. The 'early' (first ?) Mac uses
> an IWM chip. Is this the same as the IIc IWM chip? Or if you use the Mac IWM
> chip in the IIc can you just bend pin 10 up when you socket it?

I was talking about the physical disk interface (the D19 connector), not
the IWM chip.

The Mac 128 through Mac Plus have a 28 pin DIL package IWM chip which is
identical to the one installed in the IIc.  It is soldered onto the
motherboard.  The SE and Mac II probably use the square pack version in
a socket, which can be upgraded to the SWIM chip.  Later models have a
SWIM chip as standard.

The IWM chip is not responsible for all the signals on the disk
connector.  A few of the incidental control lines (e.g. head select for
3.5" drives) are implemented through I/O peripherals controlled directly
by the CPU (e.g. the VIA chip in the case of the Mac).

-- 
David Empson
dempson@actrix.gen.nz