Re: DISK ][

["Michael J. Mahon" <mjmahon@aol.com>]

Roger Schmidt wrote:
> Has anyone ever made like a DISK ][ to another interface. I have read 
> some of the documentation on the net and cant see why it isnt 
> possible?!? Or am I just kidding myself?

Not everything is possible.  It is possible to design an interface
(typically based on a microcontroller) to read normally formatted
Apple II disks.  It is not practically possible to design an
interface (without a cycle-accurate Apple II driving it) to read
arbitrary copy-protected Apple II disks.

Splitting the difference, it is possible (and practical) to build
an interface that allows the reading (and writing) of *many* copy-
protected disks, as well as normal ones.

Most such designs put a lot of the work into the host machine's
software (just like the Apple II).  The Catweasel card is an early
"universal" disk controller, though its Apple II support is meager.

Various Apple II "emulator" cards for the IBM PC (ISA interface)
could read and write Apple II disks, which they did by essentially
implementing an Apple II and its disk controller on the card.

Reviewing Sather's description of the Apple II disk subsystem will
give you some insight as to why a general adaptation to another
machine is extremely difficult.

> Where can i get a schematic of the DISK][ interface card?

The DOS Manual contains schematics of both the disk drive (a much
simplified Shugart SA 390) and the Disk ][ Controller, a Woz design
of real finesse.

> Does anyone have a bin or decompile of the PROM on the interfacecard?

There are two PROMs, one is the boot PROM and the other is the
state machine PROM that does synchronization and data separation.

Check out the chapter on the Disk ][ and its controller in Sather's
Understanding the Apple II or Understanding the Apple //e.

PDF versions are available on the web.

-michael

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