8-bit IDE

From: Richard Erlacher <edick_at_idcomm.com>
Date: Wed Apr 19 18:41:37 2000

----- Original Message -----
From: John Wilson <wilson_at_dbit.dbit.com>
To: <classiccmp_at_classiccmp.org>
Sent: Wednesday, April 19, 2000 4:18 PM
Subject: Re: 8-bit IDE

> On Wed, Apr 19, 2000 at 08:59:40AM -0600, Richard Erlacher wrote:
> > Gee! I thought I had trimmed the excess from the message I sent.
> And yet, even in *this* message, you included 100% of Allison's message
> to which you were replying. PLEASE just trim it to the paragraphs you're
> actually addressing in your reply, some people are paying per packet to
> receive this list and anyway it's a real pain to have to page through
> many screens of text trying to find the parts that are new.
> > All the
> > while, I've been harping on this notion that there must be SOME drives
> > provided this 8-bit option, else it wouldn't have been in the standard
> > all.
> Well, for that matter, the SCSI-2 standard tells us that wide drives have

<snip a bit of stuff that's true enough>

> the really fancy 2.5" portable ones) wouldn't bother with an 8-bit mode.
> Who would need it?
> > Frankly, I wish the current generation XILINX software would support the
> > 2000 and 3000 series parts, but the former was end-of-lifed some 10
> > ago and the 3000 has been replaced with the 3000-A series and 3100
> > The 3030 would make my job MUCH simpler, but I just can't use one due to
> > software incompatibility.
> All the more reason to use MSI TTL when it's a good fit (and appropriate
> computers from that era).
Well, not if it means more work, particularly drilling holes for IC's. This
is a purely Xilinx problem. They switch software and obsolete parts more
than their competitors. I really prefer devices I can program by
themselves. They do make some nice and cheap CPLD's, though. The choices
in deciding between integrated vs. programmable logic is not so simple. I
do like to keep mod's in the same generation as the original, so it could
have been done at the time.

I find the choice depends on several factors. (1) if I'm building a tool,
all other priorities are off in favor of speed and ease, (2) not everybody
wants to maintain the level of technology of other hardware in the
environment. If, for example, the generational mix is already quite
diverse, I have no reservations whatsoever about using a better part than
was available when the various system components were designed. (3) If
there's a limitation on space or if using new technology, e.g. programmable
logic, will reduce the number of parts involved, particularly if using
denser programmable logic will make the work involved in making an upgrade
or fix happen amount to less, particularly if it's less irreversible effort,
e.g. drilling holes, I prefer the more modern components.

In this case, there's a limitation on space, so I'm inclined to use what's
dense and handy. but only if I can't find a simpler solution. Today's
devices drive as hard, and symmetrically rather than what the old TTL used
to do, as any TTL device. Consequently, it's easy to use one programmable
device in place of a quantity of hardware that wouldn't even fit on several
boards. That's generally not necessary, though I'm tempted simply to remove
all the datapath and glue logic from my various S-100 boards and replace it
with a single CPLD. That way, if something breaks, I just stick in a new
CPLD and it's likely to work. No fiddling around with one component or
another. It's also a cheaper way to do the "shotgun" repair, since there's
only one "logic" component.

BTW, I'm not particularly fond of FPGA's for a number of reasons. One of
these reasons is that the parts that I now find I can't use are the ones I
bought ten years ago for several hundred dollars each.
> John Wilson
> D Bit
Received on Wed Apr 19 2000 - 18:41:37 BST

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