14 Apr
2002
14 Apr
'02
2:41 a.m.
see below, plz.
Dick
----- Original Message -----
From: "Tony Duell" <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Saturday, April 13, 2002 4:35 PM
Subject: Re: TTL computing
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 Most manufacturers these days do not
publish the programming algorithms :-(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.
>
> > 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)
The older PLAs (like the 82S100), had a really nasty programming
algorithm using about 4 different voltages. I don't recomend trying it...
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 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.
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.