Re: Hardware Idea -> IBM drives on Apple //e,GS

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

In article <5NOV199318435913@zeus.tamu.edu>
a0m2504@zeus.tamu.edu (AKITOMO MORITA) writes:
> A question to all you hardware gurus out there.  I've been toying
> with the idea of making a card for the Apple //e or GS to use
> IBM-style high density 5 1/4's and 3 1/5's by using one of the Floppy
> Drive Controller chips used in IBM PC's.

There was a commercially available card for the II which did this.  I
can't remember its name, but I think there was an article about it in
A+ a few years back.  I think the card only supported standard density
5.25" drives.

You would run into problems trying to support high density drives.  I
think the bit cells are one microsecond apart, so you'd have to read
or write a byte every eight microseconds.  This isn't feasible without
using DMA.

By comparison, the Apple II 5.25" drive uses 4 microsecond bit cells,
and the 400k/800k 3.5" drive uses 2 microsecond bit cells.  A 1 MHz
Apple II cannot cope with this speed using a software loop - the IIgs
and IIc+ can do it, because they have faster processors.  Even the
IIgs wouldn't be able to cope with 1 microsecond bit cells unless DMA
was used.

> I don't really have the time or expertise for this, but I wouldn't
> mind seeing a discussion about it here on comp.sys.apple2.  It seems
> like a simple idea to implement, but what am I looking over?

The main thing you would need is software.  The card would need to
implement a ProDOS and SmartPort firmware interface, and preferably
have some special entry point for use by a GS/OS driver, which allowed
multiple sectors to be read or written using a single call.

It may be easiest to implement it in a similar way to the SuperDrive
card: put a microprocessor onto the card, with its own RAM and ROM.
This micro can do all the hard work, and transfer data to and from the
Apple at a slower speed using a software loop on the Apple.
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz                                                
Snail mail: P.O. Box 27-103, Wellington, New Zealand