[sebhc] diskette drive

Lee Hart leeahart at earthlink.net
Sun Jun 6 17:01:14 CDT 2004

Patrick wrote:
> The spirit and function of [the 765] chip persists in many modern
> "Super-I/O" implementations like the SMC FDC37669 and the National
> PC87322. These are readily available and implement essentially the
> same interface, with the added benefit of a couple of serial ports,
> a parallel port, and an IDE interface.

Yes, but they left out all the features of the 765 that weren't used in
the PC. For instance, they left out single-density mode, which is the
standard format for all Heath distribution disks.

> Howard Harte has done such a board for S-100 systems, and it's a
> real beauty.

Yes, it really is a beautiful board. But it is also very expensive, and
beyond what the average hobbyist could build. If this is what you want,
and you have the determination to stick to it to the end, by all means,
go right ahead!

> On the issue of DMA and/or use of polled I/O and processor speed,
> I assert that a clever designer would simply have an on-board RAM
> buffer that the I/O chip can read/write directly during DMA, and
> that can be separately read/written by the 8080 or Z80 through
> either memory mapping or I/O ports.

Quite true. ANYTHING can be done if you're clever enough. But to me, I
like Dr. Dobbs old motto "running light without overbyte". I really
enjoy the old Heath computers because they are simple, straightforward,
and work well. Their apparent simplicity hides the fact that the
designers were extremely clever, and made excellent choices on how to do
things. For instance, they got disk controllers to work *without* DMA,
on a very slow CPU.

I know, this makes me an old fogey. The modern design philosophy is "who
cares how much hardware it takes -- chips are cheap. Just throw enough
of them at the problem. Who cares how much software it takes -- memory
is cheap. Throw in a few more megabytes. If it's too slow, raise the
clock speed -- who cares how much power it takes."

There is satisfaction in finding a simple, elegant way to solve a
problem. Rarely are such solutions found by using whatever is expedient
(already in my junk box), or whatever is cheapest, or copying whatever
everyone else uses. I enjoy the challenge of finding elegant solutions;
in fact, the journey in finding them is probably more enjoyable than
actually using the product they produce.
"Never doubt that the work of a small group of thoughtful, committed
citizens can change the world. Indeed, it's the only thing that ever
has!" -- Margaret Mead
Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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