Re: PDP-8 building instructions in your kitchen...

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>
>
> > 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
hack
> > around and build a pdp-8.
>
> 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
> the unexpected occurs. Have plenty of distilled water and various
> neutralising
> solutions handy, and a phone to call the local medics. ALWAYS work in
pairs.
> I'm not joking. If one guy can't see to dial the phone, the other must
wash
> out his eyes and call for him. If you have any children nearby DON'T
EVEN
> THINK ABOUT IT. Really. This means you.
>
> If you're in the states, I'd recommend a mutual waver-signing too. So
no-one
> involved will sue the others.