Alan (I think was the one who posted this originally)....
Dude, please email/point me to the directions for this. I'd love to
hack
around and build a pdp-8. Jeesh the way we prototype asics/uP's is
cobble together one (or lots for happy uP's) of FPGA's, burn your "supposedly
stable" version and go to town with hardware sim....... But
talk about expensive fpga's! Gessh... $100 bucks, my kitchen and a
PDP-8
chip... that would be really cool... I'm already thinking of really
stupid things you could do with a host of pdp-8's....
Thanks, Chuck
From: "Charles N. Choukalos" <chuckc@btv.ibm.com>
> Alan (I think was the one who posted this originally)....
Yup.
> Dude, please email/point me to the directions for this. I'd love to
OK, I'll help however I can. It was in 1983 that I last did this, BTW, helping
a complete nutter who I worked with, just before the Falklands War. I haven't
done this for 20 years, so availability etc of chemicals is unknown.
This is what I would advise:
First, get a good book on Digital Machinery. You're going to need this
in order to design the circuitry for a PDP-8. Fortunately, the PDP-8's
12-bit architecture is so mind-numbingly simple that it's no big deal.
FWIW my 3rd year DM course final exam was simple: "Here is the instruction set
of a CPU. Using the components you have built over
the course, design and build one. (2 hours)". Of course it was a PDP-8,
but I didn't know it at the time.
Anyway, I'd talk to your local education people about this, they may be able
to lend a hand here. Even supply some equipment. This is a suitable
Undergraduate or even senior High School project (with supervision, see note
below)
Second, breadboard your CPU using discrete components. In other words, debug
your design before even thinking about manufacture.
If you can pick up a Heathkit H-8, even better, as this has the design
work done for you, it's just a matter of soldering things together.
Thirdly, get a photoengravers kit. I'd recommend doing an Adult Education
course (I didn't do this bit, my nutter friend did). Be warned, the chemicals
involved are toxic, you'll need good ventilation ( a kitchen fan is ideal).
Fourth, once you've got some amorphous silicon (dunno where you'd get it if
you're in the states, but shouldn't be too hard), use your Boys Own
Photoengraving Kit to make some simple components on a large scale. We're
talking about single transistors and diodes here. Get a good multimeter and
test, test, test.
Fifth, design and build some simple flip-flops using the same
techniques. At this point, try to shrink the component size while maintaining
quality. There'll be some trial and error here, it won't be a quick process.
Sixth, make a number of flip-flops on the same plate. Connect them to
become an ALU. Do the same so you have a working design for 12 bits of memory
(ie a single word).
Seventh, shrink them down as much as you can. You should be able to make at
least 1k of memory on one plate, with yield >30% before going any further.
This will be a painful process. It will take a long time. There will be
batches with yields of 0%. Don't give up, back up one step and see what went
wrong.
Now try to implement your design on a large plate, just the CPU. Don't get
discouraged, our yield on first attempt was less than 10% IIRC.
Shrink further, until either you have it as small as you want it, or your
yield becomes unacceptably low. We got a basic CPU in about a 1" square with
good yields, less than that we got one or two out of a hundred. But then
again, we were amateurs.
The good thing is that once you've got it right, mass-production is as
easy as producing 1.
------IMPORTANT!!!!!------
Again, a stern warning: the chemicals are DANGEROUS. Don't just have adequate
ventilation and protective gear, have a plan on what to do if
Gads...Sounds easier to wait for someone else to do it first, then buy your
chips...
BTW A group of students have replicated the entire ENIAC computer on a CMOS
chip. The entire thing is only about 6mm square, and contains about 174,569
transisters. Here is the URL:
http://www.ee.upenn.edu/~jan/eniacproj.html)
Donald Hosford
> Alan and Carmel Brain wrote:
> From: "Charles N. Choukalos" <chuckc@btv.ibm.com>
Don't get
> discouraged, our yield on first attempt was less than 10% IIRC.
From: "Donald Hosford" <Hosford.Donald@ACD.net>
> Gads...Sounds easier to wait for someone else to do it first, then buy
Easier, yes, unless you've got a low-tech infrastructure. Which is the
reason for this thread in the first place.
> BTW A group of students have replicated the entire ENIAC computer on
Sounds like the PDP-8 was a "pocket calculator"...or would be these
days...8D
From: "Donald Hosford" <Hosford.Donald@ACD.net>
> Sounds like the PDP-8 was a "pocket calculator"...or would be these
No - or rather, yes. Considering a pocket calculator these days is the
equivalent of