TTL computing

From: Richard Erlacher <>
Date: Sun Apr 14 02:41:53 2002

see below, plz.


----- Original Message -----
From: "Tony Duell" <>
To: <>
Sent: Saturday, April 13, 2002 4:35 PM
Subject: Re: TTL computing

> >
> > > A PAL can generate any combinatorial function of its inputs. A prom
can do
> > > that too, but the PAL does it with fewer fuses.
> >
> > Did not the early PAL's burn on PROM programers? (512x8 fuse prom)
> Not that I've seen. The early MMI PALs (which were about the first ones
> to be made) used a strange programming algorithm (IIRC you had to program
> the chip in 2 halves, and the functions of pins swapped deneding on which
> half you were programming). But at least the algorithm was published so
> you could make your own programmer. Most manufacturers these days do not
> publish the programming algorithms :-(
The stuff was published, but that didn't mean just anyone would even want to
tackle the problem. Today, publishing the programming algorithms would
produce a service headache for them, so they don't do it.
> The older PLAs (like the 82S100), had a really nasty programming
> algorithm using about 4 different voltages. I don't recomend trying it...
> > I use TTL because 1) I don't have programmer ( got any schematic for one
> I use TTL because (although I have a programmer) it's faster to solder in
> a TTL chip than fire up the programmer, type in the equations, compile
> them, and blow the chip. I'm also not clever enough to design everything
> at once -- I like to design a bit, build and test it, and so on. And so
> the smaller/simpler the chips the better.
Programmers for EPROMS, EEPROMS, bipolar PROMS, and Small Programmable Logic
Devices (SPLD) are pretty cheap, and, quite common nowadays. The software is
free, and today's small devices are reprogrammable so they can be
incrementally developed and programmed. Larger devices are programmalbe
in-situ, and the software to do that, as well as to develop the logic is also
free, at least with some manufacturers, (Altera, Xilinx, Lattice, Atmel, among
others) The only real problem I've encountered myself is dealing with the
packages. The cheaper packages are all surface mounted, and adapters from
those packages to more conventional and easily handled packages are quite
expensive (on the order of $1k) Prototyping boards are available, but
they're ridiculously costly as well.
> I've also learnt the hard way that if you're designing something that you
> want other hobbyists to build, then avoid programmed chips. Almost nobody
> has a device programmer, so you end up having to supply programmed chips.
> That's bad enough, but you're also expected to replace them free when
> they don't work (even if the idiot has tried to run them straight off a
> car battery).
If you don't sell 'em anything, you can't be held responsible for what they do
with it. If they buy a few parts from somewhere and abuse them, it's not on
you. If you specifically tell them they're not allowed to build your
circuit, as you retain the rights to it, but choose to share the information
contained in it anyway, you certainly can't be held responsible if they build
it. Just wait until someone sues you because you used parts in your design
that cost more than some other combination of parts, thereby causing their
costs to go up. That'll get you to stop that sort of stuff.
Received on Sun Apr 14 2002 - 02:41:53 BST

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