TTL computing

From: Richard Erlacher <>
Date: Sun Apr 14 02:28:37 2002

see below, plz.


----- Original Message -----
From: "Tony Duell" <>
To: <>
Sent: Saturday, April 13, 2002 5:01 PM
Subject: Re: TTL computing

> > > 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
> > and my current-generation GALs as well.
> Everyone knows you can get 'universal' device programmers that program
> PROMs, PALs, GALs, EPROMs, microcontrollers, and so on. The original
> question was clearly asking whether early PALs used a similar programming
> algorithm to the bipolar PROMs of the same time period. I don't think
> they ever did.
Yes, they did, "burn" in programming circuits similar to what was used to
program bipolar PROMs. These were simple circuits pretty completely specified
in the datasheets.

The process of specifying which fuse was to be programmed how was less well
specified, but with enough attention, you could figure it out.

Once MMI was no longer a player, and Signetics was sold to Philips, the
programming circuits and logic quickly disappeared from the scene. Both
Signetics and MMI had published circuits that could be used to program bipolar
proms. The same strategies and similar circuits were used to program the
small bipolar PALs. The details on how to address the various fuses was less
clearly specified as time wore on, ultimately disappearing completely.

The circuits that did the work were based on multiple voltage regulators and a
few switches to set addresses. When the address switches were set, the bits
to be programmed to '1' (I think, but maybe to 0) were, one at a time,
connected to ground through momentary switches. This served to program them.
Bipolar parts were always a mite fragile in the "verify" process, since some
people thought it had to be done with the supply voltage elevated. With PALs,
you couldn't use a current source to a negative supply as you might with some
PROMs, because of the feedback circuitry.
> > > 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
> Yes, and by analogy some people are still designing with TTL.
Not for serious work, though. TTL's too slow, uses WAY too much power, and
requires too much board space. While some advances in ship design have come
from the countless millions spent by the yacht-racing community, I doubt
anything worthwhile to the electronics industry will come from taking old
technology like the techniques once popular with TTL and then using them and
the old TTL devices to build on a dozen boards, what one could build in a
single FPGA. It could happen, I guess, but nothing new is likely to spring
from it as it has in the yach-racing context.
> > One of my friends is building a sailboat in one of his vacant buildings.
> > been talking about pouring the keel any day now. I want to see that! He
> > he wants to sail it around the world. I hope he makes it.
It is a mental masturbation project, though. There's no hope that it will
produce anything other than amusement. He's got enough money, so he doesn't
need any more of that, and he's being more or less retired more of the time.
Just the same, he's not sure he's going to finish the job, since he found on
his last voyage, that he really doesn't like shipboard life that well.
> I think most people agree that sailing ships don't make sense today for
> commercial transport. And equally most people agree that TTL rarely makes
> sense for commercial production (well, the odd chip maybe, but not great
> boards of ths stuff).
Without belaboring that issue too much, I'd say that lots of people think
bicycles are no longer practical. I think they're wrong, and I'm not alone.
I don't think anybody expects anything but amusement from wiring up TTL,
> But just as some enthusiasts like making and operating sailing ships, so
> some enthusiasts like wiring up TTL.
True, but those guys don't have much influence on the nomenclature, and they
certainly don't do that under the guise of doing useful work.
Received on Sun Apr 14 2002 - 02:28:37 BST

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