see below, plz,
Dick
----- Original Message -----
From: "Tony Duell" <ard_at_p850ug1.demon.co.uk>
To: <classiccmp_at_classiccmp.org>
Sent: Tuesday, April 16, 2002 7:01 PM
Subject: Re: TTL computing
> >
> > Yes, supply of costly parts is a problem. However, once you're in the
process
> > of designing a device, it's not helpful to be constrained by what you have
or
>
> Are you saying that I should design round parts I can't get? Becuase I
> fail to see how that could ever be useful to me...
>
No, absolutely not! I'm saying you should design only with parts you're
certain you can get when the ones you've designed in decide to break. It's
easier to stock programmable parts, since you don't have to stock a wide range
of them.
>
> > what you can easily get. In the '80's, there wasn't anything, TTL-wise,
that
> > was particularly hard to get, so you designed with the stuff as though you
had
> > it all at your disposal. Occasionally there would be shortages, with long
> > lead-times, that fouled up delivery schedules and manufacturing. In '80
and
> > '81, ISTR that 74LS38 and LS245 were in such demand that it didn't matter
what
>
> I remember that. '245s were like gold dust in the UK. We used the 4 bit
> versions ('243?) as that was all we could get in 1-off quantities...
>
> > Last month, I had to build a programmer for a microcontroller. It
required
> > only three components other than the MCU. There was an oscillator, a
MAX232A,
> > and a 74HCT125. I had no trouble getting a suitable oscillator, and I
> > generally have a few MAX232's around. It took weeks to find the HCT125,
> > though, given that I didn't want to pay $10 for shipping of a $.25 part.
In
>
> Well, I can generally find plenty of other components I could use from
> such companies. So it would be $10 shipping for perhaps a $100 order...
>
There's that $100 that would buy you an almost-current-generation PC with an
installed OS.
>
> > the meantime, I'd built the thing with a GAL16V8. Overkill, well, true,
but I
> > didn't have to deal with the widespread search.
>
> As I said, over here I could get the HCT125 much more easily than the 16V8.
>
Over here too, but I already had the programmable part (I pulled it out of a
Pentium motherboard where it was socketed). I have plenty of them around, but
I was looking for an HC/HCT 125.
>
> >
> > Aside from the pinout, there's little you can't build in a 16V8 that would
> > otherwise fit in a 20-pin packaged TTL part, and you don't have to search.
>
> That's probably true. Hang on, I'd love to see you fit a '245 into a 16V8 !
>
Your're right, the bidirectional parts, e.g. '245, '543, '646, etc would be a
problem in 20-pin parts.
> > The 16V8 cost around $0.60 last time I bought 'em, and is one of those
parts
>
> Well, admittedly I've not bought them for a bit, but last time I bought a
> 16V8 (new, not surplus), it cost about 10 times that.
>
It must have been a while ago. I bought them from an international
distributor for $0.60 in a single rail (18 pieces) plus shipping. The
shipping was a bear, though, since the vendor, who'd charged me on my credit
card sent the order FedEx, COD, with Saturday delivery, even though I told him
that any delivery sooner than 90 days was adequate. I haven't ordered from
that distributor since.
>
> > As for prototyping quantities of Xilinx FPGA's, I doubt you'll find a TTL
> > vendor as willing to give you samples as the Xilinx people are. This
wasn't
>
> We never got free samples of Xlinix chips in the UK when I was using them.
>
Their policies here in the U.S. have gotten quite a bit more liberal. I think
it's the competition. When I was using the 2000 and 3000 series parts, (early
1990) at which time I was designing the logic and someone else, more adept
with the tools, was handling the implementation details (on an Apollo system),
even the small parts cost $200 or so. Then, XILINX had the market pretty much
to themselves. Altera was making mid-sized CPLD's, (Max-5000 series) at their
top end and, since Cypress was their fab, Cypress made the same parts as thir
'340 series. Today, there are much cheaper parts all around and many more
manufacturers. There aren't many convenient packages, though.
>
Received on Wed Apr 17 2002 - 01:23:12 BST