At 11:29 pm 24/08/2001 +0100, you wrote:
>> That's fair enough. Personally, I doubt any of the older computers are
>> *truly* elegant internally - there was too much learning going on. I'm not
>> even sure if it's true of modern computers either.
>>
>> Of course, you'll prove me wrong now... ;)
>
>If 'internally' covers electronic desgin, then you've clearly never
>worked on PDP11/45s, PERQs, HP9100 calculators, or a dozen other older
>machines I could name!
Nope, afraid not. You could say I missed the "golden age" of computing
(although I'd say I didn't); having got into it in the early '80s (about
'81 I think). Bear in mind I was at primary school at the time, so I have a
good excuse.... :)
My first "real" computer was a QL, and at various times I owned/used an
MZ-80K and an 8032-SK. I used an HP briefly (I've no idea which one it was
now) before getting dragged - inevitably - into the Wintel world, from
which I have never emerged. I write this on a dual P3 1GHz box running[1]
Win2K... So I missed the world of PDP8, 11, etc., and although I've used
various Vaxen (the 8800 being the only one I can remember the designation
of), an IBM m/f (again, I forget it's number), and an elderly Tandon,
Wintel has been my mainstay.
However useful the Wintel box, it's (to use a technical term) dull as f**k.
My interest in the late '70s and '80s machine stems entirely from the fact
I'm - basically - catching up with my mis-spent yoof...
>I often think that many good design tricks were discovered at least
>twice. They were commonly used in minicomputers, then forgotten about
>(for all almost all of them were documented) and then re-discovered for
>microprocessors...
That sounds about right. I also wonder how many tricks have been lost &
rediscovered several times....not necessarily in the field of computing.
[Too wide for the rack]
>
>So whether it was Commodore's original intention that PETs be used to
>control lab instruments, it is clear that they were used for this. So
>making a case just to wide to sit inside a rack (this case was first sold
>long after the PET) seems to be somewhat silly.
Possibly - but I suspect Commodore were aiming at the style-concious
businessman, much like (say) Dell and their sleek black PCs are these days.
After all, a computer on the desk in the early '80s would be a fashion
statement, a "look at me, I'm sophisticated and 'up there with the new
technology'".
>> controlling 'scopes and the like through the 488 bus, but I don't recall
>> them having external drives, printers, etc. controlled via it. ICBW...
>
>I think this is lack of experience again. Most classic HP machines have GPIB
Probably - again, I joined in in the early '80s, so anything that predates
that I'm unlikely to have used, or even seen...
>
>> Well, true.... Are GPIB connectors still reasonably available? I ask
>
>I've never seen the combinded plug-and-socket ones for sale other than on
>cables (these cables are certainly still available, at a price).
>Individual plugs and sockets are not hard to get in solder-tail, PCB
>mounting or IDC versions (Try RS or Farnell -- Maplin no longer do them
>in useful sizes :-().
Predictable. When I was first doing electronics (again, mid '80s), Maplin
was the be all and end all of suppliers. Then their catalogues dropped the
fancy artwork and became "professional", and somehow the range of products
became less useful...
>The things that are not easy to find are the
>screw-down posts with M3.5 therads used on the chassis mount connector
>for the jackscrews on the cable connector to screw into. The quickest way
>for me to get those is to make them from scratch. More normal people, I
>guess, ask a friendly local model engineer...
Should I add a lathe to my list of requirements? :)
>> No, there's just a bunch of signal wires which drop down onto the main
>> board, and two AC lines which mosey up on into the monitor cabinet (which,
>> awkwardly, are soldered directly to the PSU).
>
>Thats' the sort of time that I do a non-original mod and add a 2-pin
>in-line connectort to the monitor power wires (Molex 0.062" or 0.093"
>series, AMP mate-n-lock or similar).
That makes sense. TBH, any kind of in-line connector would do - except
maybe a DIN type (for the soldering reasons given elsewhere)...
>> With the old 8032, I find a suitably calibrated pile of books behind the
>> machine can be used to rest the back of the monitor, so you can open the
>> case to the extent of the hinge. I used a similar trick with the 8032SK...
>
>FWIW< the HP9100 calculator has a hingged top case (containing the PSU
>and CRT + driver boards). It would latch in a reasonably open position,
>but could be opened right back if necessary. HP actually sold a chain
>with suitable end fittings to fix to the 2 parts of the case so that the
>unit could be held further open than the internal latch would manage.
The Sharp MZ-80K had a device somewhat like that I've seen on drop-down
shelving, a kind of encapsulated "bonnet stay". Nice, but a PITA if you
need to do work at the back of the machine. If I needed total access to the
inside of a PET, I'd probably unscrew the hinge.
>> :) I have used 'scopes in the past, I guess it's just a case of remembering
>> how. And maybe (shock, horror) reading the instructions.
>
>Get the real Tektronix manuals (user and service if they are different)
>if you end up getting a 465. There's a lot of good information in such
>manuals, and they are worth reading.
I've asked the old man to see if he can dig me up a 'scope; meanwhile I've
got two other offers - so one way or the other I should end up OK. Not sure
if it'll be a Tek though.
>> >> Is there any way to test for a drying cap?
>> >
>> >YEs, you need an ESR meter (or a good impedance bridge). The former is
>>
>> ESR?
>
>Effective Series Resistance.
>
>Remember in an electrolytic capacitor, the electrolyte is not the
>dielectric (that's an oxide film on the surface of the +ve plate). The
>electrolyte is actaully the -ve plate of the capacitor.Which means that
>when the capactitor dries up, it behaves as though it has in internal
>series resistance. That is why dried-up capacitors don't work too well.
>
>An ESR meter displays the effective balue of this ineternal resistance
>(the lower, the better, of course).
I shall have to read that again in the morning - it went all blurry just
now ;)
>> However, whilst I like the idea of learning embedded systems, I'll probably
>> start simple and use a Z80 or similar - I can't (yet) think of anything
>> where I'd use some super-fast chip. Incidentally, what's with these PIC
>> chips? They seem to be very popular at the moment.
>
>A PIC Is a type of microcontroller (chip containing microprocessor and
>memory, and possibly some I/O).
Ah - I'd half-guessed that from reading the EPE website; I don't know why,
but somehow it sounds like cheating to me...
>The disadvantage, at least with many of them, is that you can't add
>external program memory (EPROM, etc) -- what you have on chip is all you
>have. And you can't write self-modifying code for much the same reason
>(you can't keep on reprogramming an internal 'ROM' location, and you
>can't store programs in RAM).
Eek - self modifying code? Dangerous....
>Still, they are very useful chips for many small control systems. They
>are cheap enough that they are worth using even for trivial problems.
Maybe once I've got the hang of using a bus, I'll be more inclined to use
them. For now, I've a hankering after learning how it's done properly, so
to speak.
[1] I say "running W2K", using the broadest sense of the word.... It works,
mostly, but I have to re-boot it about 7-10 times a week. Grrr...
Cheers!
Ade.
--
B-Racing: B where it's at :-)
http://www.b-racing.co.uk
Received on Fri Aug 24 2001 - 19:31:14 BST