RE: Cross-talk square-wave?

[W2HX via cctalk]

> The impedance of free space is supposed to be 277 Ohms
377 ohms but you are right about the max impedance. I forgot about that.

> Yes, you can.  The capacitance of typical cables is about 35 pF per foot.  
> Given a couple feet of cable and essentially infinite resistive load, it 
> would be quite likely to give a near square-wave result.  

Except for the fact that in the same cable, the edges of the square wave of the 
clock is creating short pulses on the CS line. Why would the CS line now behave 
totally differently if theoretically coupled to the QBUS line? In theory maybe 
you are correct, but in the practice of troubleshooting this specific issue, I 
would have to say it is unlikely that an adjacent square wave clock line would 
cause spikes and a similarly adjacent square wave QBUS signal would cause a 
square wave. They would both really be expected to have the same effect as long 
as the CS line hasn't changed change in characteristic.

My 2c
Eugene

-Original Message-
From: Jon Elson [mailto:el...@pico-systems.com] 
Sent: Wednesday, March 29, 2017 10:55 PM
To: W2HX; On-Topic and Off-Topic Posts
Subject: Re: Cross-talk square-wave?

On 03/29/2017 08:48 PM, W2HX via cctalk wrote:
> I am still not convinced it is coupling at all. You would expect the affected 
> line to show a signal like dV/dt , no? I just don't think you can get square 
> waves from square waves.
Yes, you can.  The capacitance of typical cables is about 35 pF per foot.  
Given a couple feet of cable and essentially infinite resistive load, it would 
be quite likely to give a near square-wave result.  If you were to load down 
the line with 100 Ohms, then you'd see tiny, short pulses at the edges.
> That's not to say the input of some logic somewhere isn't getting triggered 
> by unintended coupling and then getting "squared up" in some gate to produce 
> the square we see.
>
> Oh, and 270K surely is a transmission line load if the source has a 
> characteristic impedance of 270K. Granted, that seems unusual and I 
> don't know what the circuit looks like,
Well, in fact, it is impossible to make a transmission line with such 
impedance.  The impedance of free space is supposed to be 277 Ohms, IIRC.

Jon

Re: Cross-talk square-wave?

[Jon Elson via cctalk]

On 03/29/2017 08:48 PM, W2HX via cctalk wrote:

I am still not convinced it is coupling at all. You would expect the affected 
line to show a signal like dV/dt , no? I just don't think you can get square 
waves from square waves.
Yes, you can.  The capacitance of typical cables is about 35 
pF per foot.  Given a couple feet of cable and essentially 
infinite resistive load, it would be quite likely to give a 
near square-wave result.  If you were to load down the line 
with 100 Ohms, then you'd see tiny, short pulses at the edges.

That's not to say the input of some logic somewhere isn't getting triggered by unintended 
coupling and then getting "squared up" in some gate to produce the square we 
see.

Oh, and 270K surely is a transmission line load if the source has a 
characteristic impedance of 270K. Granted, that seems unusual and I don't know 
what the circuit looks like,
Well, in fact, it is impossible to make a transmission line 
with such impedance.  The impedance of free space is 
supposed to be 277 Ohms, IIRC.


Jon

Re: Cross-talk square-wave?

[Noel Chiappa via cctalk]

> 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

RE: Cross-talk square-wave?

[W2HX via cctalk]

I am still not convinced it is coupling at all. You would expect the affected 
line to show a signal like dV/dt , no? I just don't think you can get square 
waves from square waves. That's not to say the input of some logic somewhere 
isn't getting triggered by unintended coupling and then getting "squared up" in 
some gate to produce the square we see. 

Oh, and 270K surely is a transmission line load if the source has a 
characteristic impedance of 270K. Granted, that seems unusual and I don't know 
what the circuit looks like, but yes, most probably it is not a matched load. 
Having said that, given such a probable mismatch, then 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 (ie the intentional output of a gate somewhere). 

Looking at this picture
http://pdp10.froghouse.org/qsic/pic_24_1.gif

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. Classic 
dV/dt. scenario.

Looking at this one
http://pdp10.froghouse.org/qsic/pic_24_2.gif

again, I don't know the circuit, but I have personally witnessed this behavior 
on my PDP-8/e where a 7474 flip flop chip was bad. The input looked great and 
the output was "half baked" 
Here is a screenshot of what I was seeing (look for "Line OUT E29 pin5" on the 
scope screenshot...)
http://w2hx.com/x/VintageComp/PDP-8e/M8650/LecroyScreen14.png
(post on that subject is here:  
http://www.vcfed.org/forum/showthread.php?55171-PDP-8-e-Project/page6 ) 

Anyhow, I dunno. My jury is still out on this one.

Eugene


-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of dwight via 
cctalk
Sent: Wednesday, March 29, 2017 8:33 PM
To: Al Kossow; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Cross-talk square-wave?

270K is not a transmission line load.

As I recall ribbon cable is around 100-150 ohms

impedance some place.

The signal does look nice and square.

I doubt is is inductive coupling, with that high a

load, I'd say it was capacitive.

inductive coupling requires current flowing.

Dwight



From: cctalk  on behalf of Al Kossow via cctalk 

Sent: Wednesday, March 29, 2017 2:35:54 PM
To: cctalk@classiccmp.org
Subject: Re: Cross-talk square-wave?



On 3/29/17 2:14 PM, David Bridgham via cctalk wrote:
> And I think this picture is the smoking gun.
>
> http://pdp10.froghouse.org/qsic/pic_24_2.gif
>
> Again, the bottom trace is the CS signal in question and the upper 
> trace is now one of the QBUS DAL lines (after the bus transceiver and 
> level
> converter) that's running across the ribbon cable near the CS signal.
> It does appear that induction can make a fairly clean square wave.
>
>

simple thing to try is split the ribbon cable between the two signals

Re: Cross-talk square-wave?

[dwight via cctalk]

270K is not a transmission line load.

As I recall ribbon cable is around 100-150 ohms

impedance some place.

The signal does look nice and square.

I doubt is is inductive coupling, with that high a

load, I'd say it was capacitive.

inductive coupling requires current flowing.

Dwight



From: cctalk  on behalf of Al Kossow via cctalk 

Sent: Wednesday, March 29, 2017 2:35:54 PM
To: cctalk@classiccmp.org
Subject: Re: Cross-talk square-wave?



On 3/29/17 2:14 PM, David Bridgham via cctalk wrote:
> And I think this picture is the smoking gun.
>
> http://pdp10.froghouse.org/qsic/pic_24_2.gif
>
> Again, the bottom trace is the CS signal in question and the upper trace
> is now one of the QBUS DAL lines (after the bus transceiver and level
> converter) that's running across the ribbon cable near the CS signal.
> It does appear that induction can make a fairly clean square wave.
>
>

simple thing to try is split the ribbon cable between the two signals

RE: Model 28 Teletypes in Edmonton, Alberta

[Richard Loken via cctalk]

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!"
  ** rllo...@telus.net ** :- Arthur Black

RE: Model 28 Teletypes in Edmonton, Alberta

[W2HX via cctalk]

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


-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Richard Loken 
via cctalk
Sent: Wednesday, March 29, 2017 6:42 PM
To: cctalk@classiccmp.org
Subject: Model 28 Teletypes in Edmonton, Alberta

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!"
   ** rllo...@telus.net ** :- Arthur Black

Model 28 Teletypes in Edmonton, Alberta

[Richard Loken via cctalk]

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!"
  ** rllo...@telus.net ** :- Arthur Black

Re: Cross-talk square-wave?

[Al Kossow via cctalk]

On 3/29/17 2:14 PM, David Bridgham via cctalk wrote:
> And I think this picture is the smoking gun.
> 
> http://pdp10.froghouse.org/qsic/pic_24_2.gif
> 
> Again, the bottom trace is the CS signal in question and the upper trace
> is now one of the QBUS DAL lines (after the bus transceiver and level
> converter) that's running across the ribbon cable near the CS signal. 
> It does appear that induction can make a fairly clean square wave.
> 
> 

simple thing to try is split the ribbon cable between the two signals

Re: Cross-talk square-wave?

[David Bridgham via cctalk]

And I think this picture is the smoking gun.

http://pdp10.froghouse.org/qsic/pic_24_2.gif

Again, the bottom trace is the CS signal in question and the upper trace
is now one of the QBUS DAL lines (after the bus transceiver and level
converter) that's running across the ribbon cable near the CS signal. 
It does appear that induction can make a fairly clean square wave.

Well, the purpose of a prototype is to learn and this has been one
learning experience after another.

Re: Cross-talk square-wave?

[David Bridgham via cctalk]

> There are few things that come to mind here. The op seemed to indicate the 
> lines are terminated. If they are not terminated in the characteristic 
> impedance of the source and the transmission line, it is very unlikely he 
> would be seeing nice square waves at either end. The reflections would 
> distort the square wave. Given the reported squareness and that the op 
> indicates terminated line, I do not think impedance mismatch is the issue 
> here. 

There's certainly some ringing there but it's not the spike followed by
an exponential decay that I'd expect from an induced signal.  However,
maybe I just don't know what an induced signal can look like so that's
the question.

> I also agree that an induced current in an adjacent line would not be square. 
> So I agree with the op's thoughts that this signal is getting on this line in 
> some other fashion, I don't believe this is an issue of cross talk. However, 
> some pictures of some waveforms would be interesting to see

Ask and receive.  See: http://pdp10.froghouse.org/qsic/pic_24_1.gif

The bottom signal is the one in question and the top signal is the clock
I'm sending to the SD card (which isn't plugged in at this time).  I
wanted to see if it was the clock single I was seeing coupled here and
it's obviously not, though you can clearly see the clock inducing some
noise in the CS signal. 

The other thing I'm seeing from this trace that I hadn't really noticed
before is that 0 is not 0.  The 0 for the bottom trace is where the 2 is
on the left side.  This line is suppose to be going from the 270k
resistor to ground on one side across the ribbon cable to an FPGA pin
which is set to high-impedance on the other.  Clearly something else is
going on here.

Re: Apple 1, Commodore 65, Enigma Machine, Inventor of C++

[Ian Finder via cctalk]

On Wed, Mar 29, 2017 at 1:29 AM, Christian Corti via cctalk <
cctalk@classiccmp.org> wrote:

> On Tue, 28 Mar 2017, Evan Koblentz wrote:
>
>> "What do an Apple 1, Commodore 65, Enigma Machine, and the inventor of
>> C++ all have in common?"
>>
>
> They're just overestimated pieces of junk ;-)  (and C++, not its inventor)
> [duck...]
>
>
*applause* (except the enigma is neat)


-- 
   Ian Finder
   (206) 395-MIPS
   ian.fin...@gmail.com

Re: Cross-talk square-wave?

[Paul Koning via cctalk]

> On Mar 29, 2017, at 1:25 PM, Paul Koning via cctalk  
> wrote:
> 
> ...
> SD cards are not SPI, they are a variation of MMC. 

Sorry about that, it turns out I was working from obsolete memories.  That used 
to be true, isn't any longer. 

In any case, you're dealing with pretty fast signals, treating them as 
transmission lines is going to be important.

paul

RE: Cross-talk square-wave?

[W2HX via cctalk]

There are few things that come to mind here. The op seemed to indicate the 
lines are terminated. If they are not terminated in the characteristic 
impedance of the source and the transmission line, it is very unlikely he would 
be seeing nice square waves at either end. The reflections would distort the 
square wave. Given the reported squareness and that the op indicates terminated 
line, I do not think impedance mismatch is the issue here. 

I also agree that an induced current in an adjacent line would not be square. 
So I agree with the op's thoughts that this signal is getting on this line in 
some other fashion, I don't believe this is an issue of cross talk. However, 
some pictures of some waveforms would be interesting to see

Eugene W2HX


-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Parent Allison 
via cctalk
Sent: Wednesday, March 29, 2017 11:54 AM
To: Noel Chiappa; General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Cross-talk square-wave?


On Mar 29, 2017, at 9:40 AM, Noel Chiappa via cctalk  
wrote:

> 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!)

Oops!  

> 
> 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?
> 
Transmission line theory applies.  Adjacent lines see the electric and magnetic 
fields nominally seen along transmission lines.  Some would say it this way, 
you get induction from one line to another based on how those wires are routed 
and terminated.

Its only 375khz... No, its pulses with rise and fall times in the Nanosecond 
region with bandwidth of hundreds of Mhz.


> (My guess is there's a leakage path in the circuitry on one end or the 
> other, not cross-talk in the cable, but...)

No.  You have to treat those wires as transmission lines ( like coaxial 
cable or parallel pair) for signals.  Its not DC leakage.  You send a pulse (or 
a train of them) down a transmission line and if the line is not terminated the 
pulse energy will be reflected rather than absorbed.  Is there is a signal line 
next to it it will see the resulting fields from the currents flowing.

Add to that your ground for the SD card is remote so there will be a current 
flowing on that lead as well from circuit ground and the actual ground pin.

This is why people do not remote SD cards (unless someone is forcing it).  Its 
input looks like a capacitor at the end of a transmission line and incorrectly 
handled you get reflections and ringing.  Just like backplanes and all sorts of 
other media.


Allison

> Thanks!
> 
>   Noel

Re: Cross-talk square-wave?

[David Bridgham via cctalk]

> 270k seems like a rather strange value, it certainly can't be a termination 
> and it isn't a plausible pulldown either.  The SD spec should explain what is 
> expected; I knew it at one time but forgot by now.

I'll agree that 270k is a strange value.  The idea is that the SD card
contains an internal 50k pull-up on that line (dat[3]) so if you put a
270k pull-down on the board then you can use it for card detection. 
It's a little funky and I wish I'd just gone with an SD socket that had
a card-detect switch but this is supposed to work too.

The 1V square pulse, whereever it's coming from, is just enough that I'm
detecting the card presence when there's no card plugged in yet.   I can
work around this in various ways but I want to understand it well enough
that I'm sure I'm not ignoring a problem that's going to bite when we go
to a production board.  In other words, if it's simply a result of the
silly ribbon cable, then I'm happy for now with a work-around.

Re: Cross-talk square-wave?

[David Bridgham via cctalk]

> 1v across 270K represents 3.7 microamps, which isn't much, particularly
> at 25MHz. (I assume that you're using SPI to access the card, but the
> observation still holds).

Yup, I'm planning to use the SD card in SPI mode (at least for now). 
And this line is the CS/CD line, so it's not even running at 25MHz.  And
as Noel pointed out, this is happening without the SD card even being
plugged in.  I'm not surprised at cross-talk, I'm surprised that the
cross-talk appears so clean.  It's not spikes but fairly clean, 1V
square pulses.

> And if you're using SPI, have you installed
> pullups on unused pins?

Yup, I put in all the pull-ups.

> I'd go to interleaved ground cable or UTP for the device. Also, make
> sure that your 3.3V supply is adequately decoupled--an SD card can draw
> somewhere n the neighborhood of 100ma when operating, if the datasheets
> are to be believed.   I use a separate 3.3V LDO regulator at the SD card
> socket.

Good point.  I really should have put a good decoupling cap nearby and
the production card should have its own regulator.

Re: Cross-talk square-wave?

[Parent Allison via cctalk]

On Mar 29, 2017, at 9:40 AM, Noel Chiappa via cctalk  
wrote:

> 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!)

Oops!  

> 
> 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?
> 
Transmission line theory applies.  Adjacent lines see the electric and magnetic 
fields 
nominally seen along transmission lines.  Some would say it this way, you get 
induction
from one line to another based on how those wires are routed and terminated.

Its only 375khz… No, its pulses with rise and fall times in the Nanosecond 
region
with bandwidth of hundreds of Mhz.


> (My guess is there's a leakage path in the circuitry on one end or the other,
> not cross-talk in the cable, but…)

No.  You have to treat those wires as transmission lines ( like coaxial 
cable or parallel pair)
for signals.  Its not DC leakage.  You send a pulse (or a train of them) down a 
transmission line 
and if the line is not terminated the pulse energy will be reflected rather 
than absorbed.  Is there is 
a signal line next to it it will see the resulting fields from the currents 
flowing.

Add to that your ground for the SD card is remote so there will be a current 
flowing on that lead as well 
from circuit ground and the actual ground pin.

This is why people do not remote SD cards (unless someone is forcing it).  Its 
input looks like a capacitor 
at the end of a transmission line and incorrectly handled you get reflections 
and ringing.  Just like backplanes 
and all sorts of other media.


Allison

> Thanks!
> 
>   Noel

Re: Scrounging - was Floating point routines for the 6809

[jim stephens via cctalk]

On 3/28/2017 9:58 AM, Mike Stein via cctalk wrote:

- Original Message -
From: "Liam Proven via cctalk" 
To: "General Discussion: On-Topic and Off-Topic Posts" 
Sent: Tuesday, March 28, 2017 11:23 AM
Subject: Re: Floating point routines for the 6809


On 28 March 2017 at 08:54, jim stephens via cctalk
 wrote:

I need to scrounge around


I always wonder why someone understands what I mean and has to go to 
such a length to try to say I mean something else.  Especially that I am 
stealing it.


Sort of insulting, but to each their own.  I have a lot of 6809 code 
that I'd like to scrounge for and share, and it is all by my hand.


thanks
jim

Re: Scrounging - was Floating point routines for the 6809

[Paul Koning via cctalk]

> On Mar 29, 2017, at 2:18 PM, Fred Cisin via cctalk  
> wrote:
> 
>>> It's amazing how isolated pockets of our cultures can be from each
>>> other! "Multiple peoples divided by a common language"
> 
> On Wed, 29 Mar 2017, Chuck Guzis via cctalk wrote:
> ...
>> Or the time an English co-worker related the story surrounding her
>> initial job interval in the US.  She described the stunned look on the
>> face of the desk clerk at the local Holiday Inn when she asked to be
>> knocked up at 7:30 the next morning.
> 
> British V American/"Colonial"? idioms are not surprising.
> What's more surprising are the mutually exclusive variations within a country.

Not at all.  Linguists have a term for this: dialects.  Actually, that applies 
anywhere, country borders are not relevant; it simply means two variations of a 
language that are "mutually intellegible".  That may be a bit of a judgment 
call.  As a not-native speaker of English I tend to have trouble with, say, the 
Welsh dialect of English.

If dialects diverge to the point that they aren't mutually intellegible, a 
linguist calls that two languages.  So China has lots of languages, not just 
many dialects.  Conversely, some argue that Norway and Sweden use two dialects 
of a single language.

paul

RE: Cross-talk square-wave?

[Noel Chiappa via cctalk]

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

Re: Scrounging - was Floating point routines for the 6809

[Fred Cisin via cctalk]

It's amazing how isolated pockets of our cultures can be from each
other! "Multiple peoples divided by a common language"


On Wed, 29 Mar 2017, Chuck Guzis via cctalk wrote:

This is something that continually delights me, from the time that I was
ridiculed by the downstate Hoosier farmers' sons for calling a green
runner bean a "string bean".  "Those ain't string beans, they're green
beans.  String beans are yellow."  One wonders what would have been the
reaction if I'd referred to them as haricot beans.


SOME people insist that "haricot beans" are navy beans or Boston beans!


Or the time an English co-worker related the story surrounding her
initial job interval in the US.  She described the stunned look on the
face of the desk clerk at the local Holiday Inn when she asked to be
knocked up at 7:30 the next morning.


British V American/"Colonial"? idioms are not surprising.
What's more surprising are the mutually exclusive variations within a 
country.




It's a wonder that we can communicate so well between continents on this
list in spite of regional differences.  It used to be that there were
very substantial differences in the vocabulary used by different
manufacturers (cf. "Label" vs. "VTOC") but that seems to have
standardized greatly now.


Some manufacturers seemed to go out of their way to AVOID using the same 
terms as their competitors.  Even on stuff as simple as a disk space 
allocation unit.


--
Grumpy Ol' Fred ci...@xenosoft.com

Re: Cross-talk square-wave?

[Paul Koning via cctalk]

> On Mar 29, 2017, at 1:17 PM, Chuck Guzis via cctalk  
> wrote:
> 
> On 03/29/2017 07:08 AM, Noel Chiappa via cctalk wrote:
>>> 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.
> 
> 1v across 270K represents 3.7 microamps, which isn't much, particularly
> at 25MHz. (I assume that you're using SPI to access the card, but the
> observation still holds).  And if you're using SPI, have you installed
> pullups on unused pins?
> 
> SD cards can be very noisy devices--remember that they have "smarts"
> inside, so they're not passive devices.
> 
> I'd go to interleaved ground cable or UTP for the device. Also, make
> sure that your 3.3V supply is adequately decoupled--an SD card can draw
> somewhere n the neighborhood of 100ma when operating, if the datasheets
> are to be believed.   I use a separate 3.3V LDO regulator at the SD card
> socket.

SD cards are not SPI, they are a variation of MMC.  As with other 
interconnects, it's good to consider the connections as transmission lines, and 
look at what termination is expected.  270k seems like a rather strange value, 
it certainly can't be a termination and it isn't a plausible pulldown either.  
The SD spec should explain what is expected; I knew it at one time but forgot 
by now.

paul

Re: Cross-talk square-wave?

[Chuck Guzis via cctalk]

On 03/29/2017 07:08 AM, Noel Chiappa via cctalk wrote:
>> 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.

1v across 270K represents 3.7 microamps, which isn't much, particularly
at 25MHz. (I assume that you're using SPI to access the card, but the
observation still holds).  And if you're using SPI, have you installed
pullups on unused pins?

SD cards can be very noisy devices--remember that they have "smarts"
inside, so they're not passive devices.

I'd go to interleaved ground cable or UTP for the device. Also, make
sure that your 3.3V supply is adequately decoupled--an SD card can draw
somewhere n the neighborhood of 100ma when operating, if the datasheets
are to be believed.   I use a separate 3.3V LDO regulator at the SD card
socket.

--Chuck

Re: Scrounging - was Floating point routines for the 6809

[Tony Duell via cctalk]

On Wed, Mar 29, 2017 at 6:01 PM, Chuck Guzis via cctalk
 wrote:

> Or the time an English co-worker related the story surrounding her
> initial job interval in the US.  She described the stunned look on the
> face of the desk clerk at the local Holiday Inn when she asked to be
> knocked up at 7:30 the next morning.

Another one

An English lady had a lot of explaining to do when she asked
'Where can I buy a joint for the weekend'. In England, 'joint'
often means a piece of meat for roasting, not a cigarette
containing drugs.

-tony

Re: Scrounging - was Floating point routines for the 6809

[Chuck Guzis via cctalk]

On 03/29/2017 09:05 AM, Fred Cisin via cctalk wrote:

> It's amazing how isolated pockets of our cultures can be from each
> other! "Multiple peoples divided by a common language"

This is something that continually delights me, from the time that I was
ridiculed by the downstate Hoosier farmers' sons for calling a green
runner bean a "string bean".  "Those ain't string beans, they're green
beans.  String beans are yellow."  One wonders what would have been the
reaction if I'd referred to them as haricot beans.

Or the time an English co-worker related the story surrounding her
initial job interval in the US.  She described the stunned look on the
face of the desk clerk at the local Holiday Inn when she asked to be
knocked up at 7:30 the next morning.

Even in the last few days, discussion on another list concerned the
words "proctor" and "invigilate".  USA English uses the word "proctor"
both as a verb and a noun to denote the task of supervising a written
examination.  British English uses "invigilate" and "invigilator" for
that.  "Proctor" occurs only as a noun--and when not a church official,
denotes someone whose job description involves discipline. "Invigilate"
is pretty much unknown in US English, though Canadian English uses it.

It's a wonder that we can communicate so well between continents on this
list in spite of regional differences.  It used to be that there were
very substantial differences in the vocabulary used by different
manufacturers (cf. "Label" vs. "VTOC") but that seems to have
standardized greatly now.

For whatever it's worth,
Chuck

Re: PSU protection with resettable polyfuse

[Eric Smith via cctalk]

On Wed, Mar 29, 2017 at 9:24 AM, Systems Glitch via cctalk <
cctalk@classiccmp.org> wrote:

> > Any downsides to resettable polyfuses?
>
> If you hit them hard enough, they'll sometimes permanently open, which is
> desirable anyway but does require rework. I don't remember how they stack
> up speed-wise, I'm sure it's in the datasheets.
>

They're not very fast. They're comparable to a slow-blow fuse.

Re: Scrounging - was Floating point routines for the 6809

[Fred Cisin via cctalk]

On 29 March 2017 at 17:05, Toby Thain via cctalk  wrote:

But you must have overlooked the intransitive definition below: "to search
about and turn up something needed from whatever source is available".
I'm pretty sure that's the sense Jim was using (and it's certainly not
restricted to North America; I learned it in British English).


On Wed, 29 Mar 2017, Liam Proven via cctalk wrote:

No, it's a fair cop, I did notice that. I specifically looked for an
American source today, but yesterday I didn't.
It seems very odd to me to talk about scrounging something that you
already own, though, that's the point.


It's amazing how isolated pockets of our cultures can be from each other!
"Multiple peoples divided by a common language"

I definitely grew up with "scrounging" meaning to forage/scavenge 
something from one's own junk heap.

"I needed to add a cleat, so I scrounged up a cutoff scrap of 2x4"
(I wonder if "up" in that is important?)
"need a doorstop, go scrounge up a Timex/Sinclair"


Similarly, it often surprises me to encounter people who have 
significant differences in nursery rhymes or idiomatic phrases from one 
another.  "But, EVERYBODY says it that way!"


For all of our international communications, we still end up with isolated 
pockets of minor, but very definite, differences.   Usually, but not 
always geographically based.


My family was "bi-coastal", alternating between Berkeley and Washington, 
DC.  My PhD thesis advisor was British.   So, I can mispell things in 
several variants.


--
Grumpy Ol' Fred ci...@xenosoft.com

Re: PSU protection with resettable polyfuse

[Adrian Graham via cctalk]

On 29 March 2017 at 16:24, Systems Glitch  wrote:

> If you hit them hard enough, they'll sometimes permanently open, which is
> desirable anyway but does require rework. I don't remember how they stack
> up speed-wise, I'm sure it's in the datasheets.


I don't mind that, better rework that distribution than whatever's been
belted. I didn't know resettable fuses existed until I accidentally zapped
a Raspberry Pi by dragging it under my metal iMac. That's got a 2A polyfuse
and it was back in service 30 mins later.

-- 
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk

Re: PSU protection with resettable polyfuse

[Systems Glitch via cctalk]

> Any downsides to resettable polyfuses?

If you hit them hard enough, they'll sometimes permanently open, which is 
desirable anyway but does require rework. I don't remember how they stack up 
speed-wise, I'm sure it's in the datasheets.

Thanks,
Jonathan

Re: Scrounging - was Floating point routines for the 6809

[Liam Proven via cctalk]

On 29 March 2017 at 17:05, Toby Thain via cctalk  wrote:
> But you must have overlooked the intransitive definition below: "to search
> about and turn up something needed from whatever source is available".
>
> I'm pretty sure that's the sense Jim was using (and it's certainly not
> restricted to North America; I learned it in British English).

No, it's a fair cop, I did notice that. I specifically looked for an
American source today, but yesterday I didn't.

It seems very odd to me to talk about scrounging something that you
already own, though, that's the point.


-- 
Liam Proven • Profile: https://about.me/liamproven
Email: lpro...@cix.co.uk • Google Mail/Talk/Plus: lpro...@gmail.com
Twitter/Facebook/Flickr: lproven • Skype/LinkedIn/AIM/Yahoo: liamproven
UK: +44 7939-087884 • ČR/WhatsApp/Telegram/Signal: +420 702 829 053

PSU protection with resettable polyfuse

[Adrian Graham via cctalk]

Hi folks,

The PSU for my Executel 8085 system is an Astec AC8151-01 40W 5A unit that
puts out +5/+12/-12V. A while back somone suggested using an ATX PSU in its
place which TBH I'd forgotten about untl I saw a breakout board that you
plug a 20 or 24 pin ATX supply into and it terminates each rail in whatever
you choose to solder in. ukp8, rude not to :)

My only worry is an ATX PSU is capable of putting out a lot more than 5A if
it goes wrong so I'd like to protect each rail with an appropriate fuse.
Any downsides to resettable polyfuses?

Cheers,

-- 
adrian/witchy
Owner of Binary Dinosaurs, the UK's biggest home computer collection?
www.binarydinosaurs.co.uk

Re: Scrounging - was Floating point routines for the 6809

[Toby Thain via cctalk]

On 2017-03-29 10:50 AM, Liam Proven via cctalk wrote:

On 28 March 2017 at 18:58, Mike Stein via cctalk  wrote:

Maybe it has a slightly different connotation on this side of the pond; I don't think it 
would mean "borderline theft" for most people.


I did Google it first! :-)

Note definition 1 here:

https://www.merriam-webster.com/dictionary/scrounge

"Steal, swipe"






But you must have overlooked the intransitive definition below: "to 
search about and turn up something needed from whatever source is 
available".


I'm pretty sure that's the sense Jim was using (and it's certainly not 
restricted to North America; I learned it in British English).


--T

Re: Scrounging - was Floating point routines for the 6809

[Liam Proven via cctalk]

On 28 March 2017 at 18:58, Mike Stein via cctalk  wrote:
> Maybe it has a slightly different connotation on this side of the pond; I 
> don't think it would mean "borderline theft" for most people.

I did Google it first! :-)

Note definition 1 here:

https://www.merriam-webster.com/dictionary/scrounge

"Steal, swipe"




-- 
Liam Proven • Profile: https://about.me/liamproven
Email: lpro...@cix.co.uk • Google Mail/Talk/Plus: lpro...@gmail.com
Twitter/Facebook/Flickr: lproven • Skype/LinkedIn/AIM/Yahoo: liamproven
UK: +44 7939-087884 • ČR/WhatsApp/Telegram/Signal: +420 702 829 053

Re: Cross-talk square-wave?

[Noel Chiappa via cctalk]

> 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

Re: Cross-talk square-wave?

[dwight via cctalk]

Is there any load resistance at the end of the line?

Dwight



From: cctalk  on behalf of Noel Chiappa via 
cctalk 
Sent: Wednesday, March 29, 2017 6:40:22 AM
To: cctalk@classiccmp.org
Cc: j...@mercury.lcs.mit.edu
Subject: Cross-talk square-wave?

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

Cross-talk square-wave?

[Noel Chiappa via cctalk]

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

Re: Ann Arbor Ambassador XL / Re: pile of gear for sale (DEC, Sun, PC, ephemera, v.35 cables, etc etc)

[Ian Primus via cctalk]

I'm definitely interested in the Ann Arbor terminal - I have sent you
a couple of messages but haven't heard back - I'm not sure if I have
the right address? Let me know. Thanks!

-Ian

On Wed, Mar 29, 2017 at 1:35 AM, Andrew K. Bressen via cctalk
 wrote:
>
>> On Tue, Mar 28, 2017 at 02:22:34PM -0700, Brent Hilpert via cctalk wrote:
>>>(Not sure what the XL designates, I knew them as just Ann Arbor Ambassador).
>>
>
> John Wilson via cctalk  writes:
>> It's a newer version.  I think maybe 60 lines vs. 48 for the classic AAA?
>> Could be wrong.
>>
>> John Wilson
>> D Bit
>
> Yeah, it has a pretty tall aspect ratio, 60 lines seems very believable.
>
>

Re: QIX game on PDP-11

[Christian Corti via cctalk]

On Tue, 28 Mar 2017, Systems Glitch wrote:
Looks similar to a Mentec KDJ11-B workalike, I don't remember their 
designation. Onboard RAM and DLV11-J from what I remember...


The board says SBC J11-8, so that should give a hint.

Christian

Re: Apple 1, Commodore 65, Enigma Machine, Inventor of C++

[Christian Corti via cctalk]

On Tue, 28 Mar 2017, Evan Koblentz wrote:
"What do an Apple 1, Commodore 65, Enigma Machine, and the inventor of C++ 
all have in common?"


They're just overestimated pieces of junk ;-)  (and C++, not its inventor)
[duck...]

Christian