Re: Mac Plus floppy interface

[Patrick Schaefer <patrick.schaefer@topmail.de>]

Simon Biber schrieb:

> It seems quite promising; is writing a driver to support this drive
> feasible?

As mentioned before, the whole Disk II controller circuit is contained
within the IWM chip. That means every drive that runs from a Disk II
controller will run from an IWM.

However, there will be a couple of problems: 
1) The Mac runs its IWM at nealy 8 MHz, the Apple II supplies 7,15 MHz. 
Someone mentioned that it is possible to configure the IWM for both
clock rates, if not you will have to add a hardware modification
(multiplexer) that supplies both clock rates.
2) Your Mac doesn't start from the hard disk. It seems that the Mac ROM
only checks for smartport devices during startup and doesn't expect any
Ph0..3 step motor drives. Therefore a ROM modification will be
necessary.

And of course you will need a lot of knowledge about Mac OS (System
6.0.8 or 7.1) programming :-)


Nevertheless, this will be an interesting project for a 68k assembler
freak. BTW: I've learned a lot about the IWM chip from the Apple Lisa
schematics and bootrom listings available on the net (look for "Lisa
Emulator Project"). Some more information could be found in the "Apple
IIGS Technical Reference", but unfortunately I don't own this book.

The Mac floppy interface is decribed in the "Macintosh Family Hardware
Reference". From these schematics you will see that there is no hardware
difference between the IIc/IIGS and Mac implementation (except for the
400k PWM signal that you can ignore and the different clock rate
mentioned above).


Patrick