16 Jun
2015
16 Jun
'15
3:35 p.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of tony
duell
Sent: 16 June 2015 17:29
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: using new technology on old machines
I assume you mean M452 here, I can't find a reference to M484.
I did don't know where 484 came from
It's
also that this is the 'classic computers' list. To me, classic
computing means rather more than just the hardware. It also covers
the design and construction methods, technology and so on. And there
seems to be precious little of that in a modern microcontroller
acting as a clock oscillator.
There isn't., but some-times we have to compromise, and sometimes we
choose to compromise. I looked at the circuit of the M484 and I might
not have the parts in the parts box...
I suspect many of the parts are not that critical.
I don't think so either, but I see from:-
http://dustyoldcomputers.com/pdp-common/reference/drawings/modules/m/m452.pd
f
that the original appears to use a 2k 10-turn pot, and a 7440 output buffer,
neither of which are in my rather extensive junk box.
In fact the 7440 are rather rare, and I see the cheapest I can get them for
is around $4.00 each.
I do however have a tube of pic 16f84 chips and a few 4Mhz crystals and so
could build a suitable generator with 1 x IC and 1 xtal.
The great thing about PIC, Arduino and FPGA is they allow the creation of
something which is as functionally identical to the original as you can get
without duplicating it.
.. its also a
nasty hybrid design with DC biased NPN and PNP
transistors. I find it ugly and can see it being a pig to debug,
though it simulates fine in LTspice...
I didn't find it that hard to basically understand in my head. After all,
are only 4 transistors, and 2 of those are just an
output buffer. Quite
why
having both NPN and PNP transistors makes it harder to
understand I do not
know.
I am really used to RF circuits so am puzzled there is no inductor. It kind
of looks like a Darlington Pair but it isn't.
What I don't understand is why the emitter of Q1 is spliced in what I assume
is a voltage divider in the collector of q2.
I was expecting a multivibrator circuit...
I will leave the flames about Spice and simulation packages in general for
another day.
You are touchy. Would it help if I used the original Spice2 written in
Fortran IV. It still works. Sadly I don't have a real mainframe but have to
use Hercules to run it....
-tony
Dave