Richard Erlacher wrote:
> I hope you're not suggesting that devices that use core memories are in any
> way BETTER than more modern machines that use semiconductor memory.
Core memory had it's day. However it had the advantage of non-volitile
that is hard to duplicate in modern memory. The read/write memory cycle
was well used by computer architecture of the 1960's.
> 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)
Sadly this not true today.
> Before people draw those schematics, they first manipulate the concepts on a
> big dry-mark-board (whiteboard), waving their arms and arguing vehemently that
> their take is the one. Once the blocks have been mapped into the
> requirements, low-level design meetings are held where they do the same thing,
> only at more detail. That's where the block that later becomes a PLD is born.
> Block 6B divides the clock by 1-1/2 to generate the clock you need and then
> propagates the appropriately divided output to block 5D which demodulates the
> data and passes it to the framing logic in block 2G. Three different guys
> design those blocks, and they're later implemented in separate PALs, or in a
> single PLD.
And marketing droids sit on the design 'Go ahead' for months and then
want it yesterday.
> They're state machines, but nobody uses them except for repair parts nowadays,
> since it's more efficient and cheaper to have 100 GALs costing well under a
> dollar and not having to track stock and worry availability. For simple
> logic, I always have some 22V10's, 20RA10's, 16V8's and a few 20V8's around
> just for the case where I need some function I don't have in TTL. I don't
> usually buy the TTL any longer unless it's for a repair. I do scrap old
> hardware and save the parts, since that saves me driving around. I do have a
> tester, after all.
I use TTL because 1) I don't have programer ( got any schematic for one
that does not use PAL's and easy to find TTL) 2) Pals never are the
right size to replace simple but messy logic -- say a D-F/F followed by
a 4/1 multiplexer followed a xor gate and another D-F/F.
>
> I know that wooden ships were a beautiful and quiet solution to the problem of
> how to get from England to Central America, but there are lots of them on the
> bottom of the ocean, and I'd rather take my chances with a 747. Does that
> mean that flying is better than sailing, well, maybe not, but it is the method
> of choice, for most of us, nowadays. If I have two weeks and a lot of budget,
> I like cruising, but if I have to be at a meeting tomorrow, and don't want to
> put on ten pounds, then I fly.
Old sailing ships used a lot of man-power. While OIL is cheap wind
powered modern ships will not be developed.
--
Ben Franchuk - Dawn * 12/24 bit cpu *
www.jetnet.ab.ca/users/bfranchuk/index.html
Received on Fri Apr 12 2002 - 22:14:01 BST