Hi, a question about generic analog stuff.
In the process of getting SD cards to work, Dave is seeing square-wave noise
on a line. (1V of square wave, with pulses about 400ns long, running at
375kHz.) The line runs through a flat cable of modest length, along with
other signal-carrying lines. (No, we were not smart, and didn't put ground
lines between each pair of signal lines!)
Could cross-talk cause this kind of noise? We would have thought that you'd
only get spikes, associated with the rising and trailing edges of a signal in
a parallel wire, not a whole square-wave. During the constant-current period
in the middle of the pulse, there shouldn't be any cross-talk? Is there some
mechanism I/we don't understand that could do that?
(My guess is there's a leakage path in the circuitry on one end or the other,
not cross-talk in the cable, but...)
Thanks!
Noel
Wyse, Link, etc.
Does anyone still use these on actual terminals?
I have some guys coming to scrounge on Saturday, and they want them for is
to desolder the switches.
If you need some for actual use, please let me know the exact model you want
so it does not get parted out.
Cindy Croxton
Electronics Plus
Some time ago I came across the MC6839 ROM which contains floating point
routines for the 6809. The documentation that came with it stated:
Written for Motorola by Joel Boney, 1980
Released into the public domain by Motorola in 1988
Docs and apps for Tandy Color Computer by Rich Kottke, 1989
What I haven't been able to find is the actual *source code* to the
module. Is it available anywhere? I've been playing around the the MC6839
on an emulator but having the source would clear up some issues I've been
having with the code.
-spc
Hi PDP-11 game players ?
I found that the famous QIX game was ported to the PDP-11 !!
See http://imgur.com/a/gtPfh
Back in the days, I spend quite a few Guilders on this addictive game.
Does anybody have a lead to the software? That would be awesome!
Thanks,
Henk
> From: Eugene (W2HX)
> I am still not convinced it is coupling at all. ... I just don't think
> you can get square waves from square waves. ...
> it is even harder to believe one could successfully couple a square
> wave onto such a transmission line unless the signal is actually being
> asserted on the line at a low impedance ...
> Looking at this picture ... this shows exactly what I would expect to
> see with cross talk the little glitches on the CS line that correspond
> to edges on the clock signal.
Exactly. That sort of cross-talk we understand (and have seen before). But
a square wave? How can that be? That was the motivation for my original post.
It's not super-critical to understand, because like I said, this is on a
pre-prototype, and the actual unit will be arranged nothing like this (no
cable, etc, etc), so we're just going to fix this with whatever kludge makes
it go away, so we can focus on the things we really do need to work on.
But we'd still like to understand what is happening here, and how. Could
cross-talk (of whatever form, inductive or capacitive) do this, or does this
more or less have to be signal leakage (on the board at one end, or the
other) somehow?
Noel
On Wed, 29 Mar 2017, W2HX wrote:
> I might have missed it, but did you offer this on the greenkeys list (or
> would you like me to forward it?) they are tty enthusiasts. Eugene
No, I have never been a member of the green keys list and there is no point
in joining now. Punt the message to the green keys list if you can.
I still have (because they are small and portable) a set of model 28
service manuals, a keyboard assembly, a print mechanism (a carriage
assembly?), a box of unperforated five level tape rolls, and a few
unused but quite elderly ribbons if anybody has a use for them.
--
Richard Loken VE6BSV : "...underneath those tuques we wear,
Athabasca, Alberta Canada : our heads are naked!"
** rlloken at telus.net ** : - Arthur Black
So, my ex-wife sent my Model 28 RO and Model 28 ASR (along with a Conn
vacuum tube electronic organ) to the landfill yesterday. I am told by
my son that they went to the Eco Station Reuse Area at either the Ambleside
or kennedale Eco Station.
So, in the unlikely event that somebody wanting a 28 tty and within
travelling distance of Edmonton, Alberta reads this, those items are
reported to be there for taking. Oh, and bring a truck and a very strong
friend.
--
Richard Loken VE6BSV : "...underneath those tuques we wear,
Athabasca, Alberta Canada : our heads are naked!"
** rlloken at telus.net ** : - Arthur Black
"What do an Apple 1, Commodore 65, Enigma Machine, and the inventor of
C++ all have in common?"
"They all be at VCF East this weekend."
You should go, too.
________________________________
Evan Koblentz, director
Vintage Computer Federation
a 501(c)3 educational non-profit
evan at vcfed.org
(646) 546-9999
www.vcfed.orgfacebook.com/vcfederationtwitter.com/vcfederation
> From: Dwight Kelvey
> Is there any load resistance at the end of the line?
Yes, 270K to ground (i.e. pretty large). How does that have an effect on
whether cross-talk can create a square wave? Sorry, I'm not understanding.
Noel
I should mention that this is a pre-prototype; the final thing won't have a
cable at all; so this isn't a fundamental issue with the design (if it is
cross-talk). And the SD card isn't even plugged in when we see this - if it is
cross-talk, it has to be some other signal carried in the cable.
We're just trying to figure out how cross-talk can possibly produce an induced
square-wave.
Noel
