TTL computing

From: Richard Erlacher <>
Date: Sat Apr 13 03:03:12 2002

Yes, I remember the PW memories on the Honeywell 516-types used as the space
shuttle engine controller. I don't recall that it had a read-only command. I
do remember, however, that since the PW held whatever was last stored, it
could retain a failure from one mission to the next. (PW was 200 ns or so
faster than core, so they used that.)

see below, plz.


----- Original Message -----
From: "Ben Franchuk" <>
To: <>
Sent: Friday, April 12, 2002 9:14 PM
Subject: Re: TTL computing

> Richard Erlacher wrote:
> > I hope you're not suggesting that devices that use core memories are in
> > way BETTER than more modern machines that use semiconductor memory.
> Core memory had it's day. However it had the advantage of non-volitile
> that is hard to duplicate in modern memory. The read/write memory cycle
> was well used by computer architecture of the 1960's.
> > A PAL can generate any combinatorial function of its inputs. A prom can
> > that too, but the PAL does it with fewer fuses.
> Did not the early PAL's burn on PROM programers? (512x8 fuse prom)
> Sadly this not true today.
My "early" PALs program on the same programmer that programs my bipolar PROMs,
and my current-generation GALs as well.
> > Before people draw those schematics, they first manipulate the concepts on
> > big dry-mark-board (whiteboard), waving their arms and arguing vehemently
> > their take is the one. Once the blocks have been mapped into the
> > requirements, low-level design meetings are held where they do the same
> > only at more detail. That's where the block that later becomes a PLD is
> > Block 6B divides the clock by 1-1/2 to generate the clock you need and
> > propagates the appropriately divided output to block 5D which demodulates
> > data and passes it to the framing logic in block 2G. Three different guys
> > design those blocks, and they're later implemented in separate PALs, or in
> > single PLD.
> And marketing droids sit on the design 'Go ahead' for months and then
> want it yesterday.
> > They're state machines, but nobody uses them except for repair parts
> > since it's more efficient and cheaper to have 100 GALs costing well under
> > dollar and not having to track stock and worry availability. For simple
> > logic, I always have some 22V10's, 20RA10's, 16V8's and a few 20V8's
> > just for the case where I need some function I don't have in TTL. I don't
> > usually buy the TTL any longer unless it's for a repair. I do scrap old
> > hardware and save the parts, since that saves me driving around. I do
have a
> > tester, after all.
> I use TTL because 1) I don't have programmer ( got any schematic for one
> that does not use PAL's and easy to find TTL) 2) PALs never are the
> right size to replace simple but messy logic -- say a D-F/F followed by
> a 4/1 multiplexer followed a xor gate and another D-F/F.
What's the right size? You can get 'em in whatever SO type you like, so
they'll "fit." Looking pretty isn't part of that deal, though. A 4:1 mux is
easy as SOP and each macrocell has a DFF in the path if you want it. XOR is
just [A*/B + /A*B].
> > I know that wooden ships were a beautiful and quiet solution to the
problem of
> > how to get from England to Central America, but there are lots of them on
> > bottom of the ocean, and I'd rather take my chances with a 747. Does that
> > mean that flying is better than sailing, well, maybe not, but it is the
> > of choice, for most of us, nowadays. If I have two weeks and a lot of
> > I like cruising, but if I have to be at a meeting tomorrow, and don't want
> > put on ten pounds, then I fly.
> Old sailing ships used a lot of man-power. While OIL is cheap wind
> powered modern ships will not be developed.
Some guys are doing it. The Americas Cup bears witness to that doesn't it?
One of my friends is building a sailboat in one of his vacant buildings. He's
been talking about pouring the keel any day now. I want to see that! He says
he wants to sail it around the world. I hope he makes it.
Received on Sat Apr 13 2002 - 03:03:12 BST

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