Re: Digital circuits and analog devices

[Guy Dawson]

There's a Sophie Wilson talking head exhibit at the Science Museum in
London where she says the prototype ARM chip worked well but when they went
to measure it power it used they discovered that the power pin was not
connected. The ARM CPU was running on current leaking from the chips it was
connected to!


On 2 December 2016 at 19:22, Mouse  wrote:

> >> I think the original is 'Digital circuits are made from analog
> >> parts'
>
> >> Another of the laws is 'There is no such thing as ground'
>
> This reminds me of an incident of my own which is one of my favourite
> examples of why learning about things at every level possible is
> useful.
>
> I built a PROM reader from discrete logic, to attach to a parallel
> port.  Basically, with 8 output and 3 input pins, you could load an
> address, then read back the ROM's content for that address,
> incremement, repeat.
>
> But every ROM showed 0xFF as the contents for the last byte, even in
> cases where I knew better.
>
> Well, the ROM socket was in one corner of the board.  Some of the
> inputs were tied to specific logic levels; I tied those to the Vcc or
> GND pins of the ROM.  The only inputs from the rest of the circuit were
> the address pins of the ROM.
>
> And, I tied the ROM's Vcc pin to circuit Vcc.  But it turned out I'd
> neglected to tie the ROM's GND point to circuit ground.  As soon as I
> noticed that it all made sense: as long as at least one address line
> was low, it powered the ROM through the input clamping diodes and it
> all worked (apparently one diode drop was not enough to put power
> outside the effective operating range - it may have been slower than
> speed spec, but the circuit was not running anywhere close to that).
> But, as soon as all address lines were high, there was nothing but Vcc
> coming into that corner of the board, so of course there couldn't be
> anything but Vcc coming out.  Grounding that corner's ground point made
> it all work.
>
> But, if I understood the ROM purely at the logic-gate level, this would
> have been mysterious and cryptic.  If I hadn't known that a low-level
> output could sink a fair bit of current with little-to-no voltage rise,
> if I hadn't known input clamping diodes existed, that would have been
> cryptic, incomprehensible magic.
>
> /~\ The ASCII Mouse
> \ / Ribbon Campaign
>  X  Against HTMLmo...@rodents-montreal.org
> / \ Email!   7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B
>



-- 
4.4 > 5.4

Re: Digital circuits and analog devices

[Mouse]

>> I think the original is 'Digital circuits are made from analog
>> parts'

>> Another of the laws is 'There is no such thing as ground'

This reminds me of an incident of my own which is one of my favourite
examples of why learning about things at every level possible is
useful.

I built a PROM reader from discrete logic, to attach to a parallel
port.  Basically, with 8 output and 3 input pins, you could load an
address, then read back the ROM's content for that address,
incremement, repeat.

But every ROM showed 0xFF as the contents for the last byte, even in
cases where I knew better.

Well, the ROM socket was in one corner of the board.  Some of the
inputs were tied to specific logic levels; I tied those to the Vcc or
GND pins of the ROM.  The only inputs from the rest of the circuit were
the address pins of the ROM.

And, I tied the ROM's Vcc pin to circuit Vcc.  But it turned out I'd
neglected to tie the ROM's GND point to circuit ground.  As soon as I
noticed that it all made sense: as long as at least one address line
was low, it powered the ROM through the input clamping diodes and it
all worked (apparently one diode drop was not enough to put power
outside the effective operating range - it may have been slower than
speed spec, but the circuit was not running anywhere close to that).
But, as soon as all address lines were high, there was nothing but Vcc
coming into that corner of the board, so of course there couldn't be
anything but Vcc coming out.  Grounding that corner's ground point made
it all work.

But, if I understood the ROM purely at the logic-gate level, this would
have been mysterious and cryptic.  If I hadn't known that a low-level
output could sink a fair bit of current with little-to-no voltage rise,
if I hadn't known input clamping diodes existed, that would have been
cryptic, incomprehensible magic.

/~\ The ASCII Mouse
\ / Ribbon Campaign
 X  Against HTMLmo...@rodents-montreal.org
/ \ Email!   7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B

Re: Digital circuits and analog devices

[Chuck Guzis]

Just about anyone who's ever worked in ECL (non-saturating logic) is
aware of this and doesn't need to be reminded by anyone.  The same for
anyone implementing logic using vacuum tubes.

In fact, the other aspect of digital logic is that it's a study of
transmission lines--and that's often voiced.

Really, any sort of analog-digital divide in thought must surely date
from the use of saturating logic in semiconductors.

So how far back do the citations go? Are they latecomers to the party?

--Chuck

Re: Digital circuits and analog devices

[Tony Duell]

On Fri, Dec 2, 2016 at 1:33 PM, Noel Chiappa  wrote:

> > A related one ... came from Professor M. V. Wilkes
>
> That one I _did_ remember (although I couldn't remember if it was Wilkes or
> Wheeler - I knew it was one of those Cambridge guys :-), but it's not quite
> as pithy as the Vonada one.

I've not seen that one officially written down anywhere (it's not in any of the
books I have by Professor Wilkes). I suspect many recorded versions, especially
on this list, originated from me. And Professor Wilkes told it to me one evening
many years ago, and I may not remember the exact words.

-tomy

Re: Digital circuits and analog devices

[Tony Duell]

On Fri, Dec 2, 2016 at 3:57 PM, Paul Koning  wrote:

>
> On the bit about grounds, I still have tucked away somewhere a very funny 
> (but also serious) memory by Bob Steward (lead designer of a number of VAXen) 
> entitled "Do not cut your grounds".  He described how a poorly chosen PCB 
> layout turned a ground plane into a slot antenna, among other things.

However there are times when cutting away part of a ground plane can
reduce noise in
(say) a sensitive amplifier as it can prevent currents from other
parts of the circuit
going through that part of the ground plane.


>
> These are the sort of issues that supercomputer designers at CDC or Cray all 
> understood thoroughly -- you can't build machines like that without this 
> knowledge.  But a lot of logic designers working at slower speeds weren't 
> taught properly and/or didn't really get it, and they might not get in 
> trouble right away.

I do not believe it is possible to be a digital designer without also
understanding (and understanding well)
RF analogue electronics. There are plenty of people who claim to be
able to do that, suffice it to say
I've seen some of the messes so created.

A lot of the time it's not (just) the clock frequency that matters,
but also the rise time of the signals. So
a modern fast IC has to be decoupled, ground-planed, etc properly even
if you only clock it at 1Hz.

-tony

Re: Digital circuits and analog devices

[Toby Thain]

On 2016-12-02 10:57 AM, Paul Koning wrote:

...
A somewhat related area is the many different ways in which a number

of chip designers messed up the random number generators needed in half
duplex Ethernet. I remember Intel as a particular offender, but probably
not the only one. AMD got it right in the Lance partly because of a lot
of coaching from the DEC Ethernet designers.


...That would be a fun paper to read.

--Toby




paul

Re: Digital circuits and analog devices

[Paul Koning]

> On Dec 2, 2016, at 12:59 AM, Tony Duell  wrote:
> 
> On Fri, Dec 2, 2016 at 2:31 AM, Noel Chiappa  wrote:
>> So I have this memory of a set of law promulgated by an engineer at DEC, one
>> of which was something to the effect that 'all digital circuits are made out
>> of analog devices'. However, my memory doesn't recall where I saw this, and 
>> my
>> Google-fu is not strong enough to turn it up. Can anyone help?
> 
> It's one of Don Vonada's laws. I am pretty sure I first read them in
> 'Computer Engineering', that book produced by DEC. I think the
> original is 'Digital circuits are made from analog parts'
> 
> Another of the laws is 'There is no such thing as ground' which
> 
> (a) means voltmeters have 2 leads, so you can take whatever
> you want as a reference
> 
> and
> 
> (b) all connections have impedance (the inductance is the important
> bit in general) so even if you have 2 points connected to a wire you
> call 'ground' they won't necessarily be at the same voltage all the time.

There are probably lots of people who have spoken or written along these lines. 
 I heard the "everything is analog" from my manager Tony Lauck, the head of the 
DECnet architecture and A-D group and a polymath (as were  a number of others 
in that group).  He specifically emphasized the point in connection with 
metastability issues.  But since the statement is both true and all too often 
forgotten, I assume it has been said many times before.

On the bit about grounds, I still have tucked away somewhere a very funny (but 
also serious) memory by Bob Steward (lead designer of a number of VAXen) 
entitled "Do not cut your grounds".  He described how a poorly chosen PCB 
layout turned a ground plane into a slot antenna, among other things.

These are the sort of issues that supercomputer designers at CDC or Cray all 
understood thoroughly -- you can't build machines like that without this 
knowledge.  But a lot of logic designers working at slower speeds weren't 
taught properly and/or didn't really get it, and they might not get in trouble 
right away.

A somewhat related area is the many different ways in which a number of chip 
designers messed up the random number generators needed in half duplex 
Ethernet.  I remember Intel as a particular offender, but probably not the only 
one.  AMD got it right in the Lance partly because of a lot of coaching from 
the DEC Ethernet designers.

paul

Re: Digital circuits and analog devices

[Liam Proven]

On 2 December 2016 at 15:11, Noel Chiappa  wrote:
> Since you'd done all the hard work (typing them in), I uploaded them (less
> typos :-), to:
>
>   http://gunkies.org/wiki/Vonada's_Engineering_Maxims
>
> Interestingly, there's a typo in the originall: "worse-case".  :-)


Splendid -- tweeted, with credit!

Well, I've buffered the first dozen, anyway...

-- 
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: Digital circuits and analog devices

[Noel Chiappa]

> From: Eric Smith

> The full set from the book (any typos are mine)

Since you'd done all the hard work (typing them in), I uploaded them (less
typos :-), to:

  http://gunkies.org/wiki/Vonada's_Engineering_Maxims

Interestingly, there's a typo in the originall: "worse-case".  :-)

Noel

Re: Digital circuits and analog devices

[Noel Chiappa]

> From: Tony Duell

> It's one of Don Vonada's laws.

Ah, thank you, thank you, that's the one I was looking for!
I knew _you_'d know it! :-)

> A related one ... came from Professor M. V. Wilkes

That one I _did_ remember (although I couldn't remember if it was Wilkes or
Wheeler - I knew it was one of those Cambridge guys :-), but it's not quite
as pithy as the Vonada one.

Noel

Re: Digital circuits and analog devices

[Eric Smith]

On Thu, Dec 1, 2016 at 10:59 PM, Tony Duell  wrote:

> It's one of Don Vonada's laws. I am pretty sure I first read them in
> 'Computer Engineering', that book produced by DEC. I think the
> original is 'Digital circuits are made from analog parts'
>
> Another of the laws is 'There is no such thing as ground' which
>

That's where I saw them also.  The full set from the book (any typos are
mine):

Vonada's Engineering Maxims

1. There is no such thing as ground.
2. Digital circuits are made from analog parts.
3. Prototype designs always work.
4. Asserted timing conditions are designed first; unasserted timing
conditions are found later.
5. When all but one wire in a group of wires switch, that one will switch
also.
6. When all but one gate in a module switches, that one will switch also.
7. Every little pico farad has a nano henry all its own.
8. Capacitors convert voltage glitches to current glitches (conservation of
energy).
9. Interconnecting wires are probably transmission lines.
10. Synchronizing circuits may take forever to make a decision.
11. Worse-case tolerances never add -- but when they do, tehy are found in
the best customer's machine.
12. Diagnostics are highly efficient in finding solved problems.
13. Processing systems are only partially tested since it is impractical to
simulate all possible machine states.
14. Murphy's Laws apply 95 percent of the time. The other 5 percent of the
time is a coffee break.

Re: Digital circuits and analog devices

[Tony Duell]

On Fri, Dec 2, 2016 at 2:31 AM, Noel Chiappa  wrote:
> So I have this memory of a set of law promulgated by an engineer at DEC, one
> of which was something to the effect that 'all digital circuits are made out
> of analog devices'. However, my memory doesn't recall where I saw this, and my
> Google-fu is not strong enough to turn it up. Can anyone help?

It's one of Don Vonada's laws. I am pretty sure I first read them in
'Computer Engineering', that book produced by DEC. I think the
original is 'Digital circuits are made from analog parts'

Another of the laws is 'There is no such thing as ground' which

(a) means voltmeters have 2 leads, so you can take whatever
you want as a reference

and

(b) all connections have impedance (the inductance is the important
bit in general) so even if you have 2 points connected to a wire you
call 'ground' they won't necessarily be at the same voltage all the time.

A related one, which I don't know if it was ever written down in an
official book (he told it to me in person) came from Professor M. V. Wilkes

'A digital circuit is like a tame animal. An analogue circuit is like a
wild animal. Every so often the tame animal goes back to the wild'

-tony

-tony

>
> Noel

Re: Digital circuits and analog devices

[Chuck Guzis]

On 12/01/2016 06:31 PM, Noel Chiappa wrote:
> So I have this memory of a set of law promulgated by an engineer at
> DEC, one of which was something to the effect that 'all digital
> circuits are made out of analog devices'. However, my memory doesn't
> recall where I saw this, and my Google-fu is not strong enough to
> turn it up. Can anyone help?

I don't know if he was the first--probably not--but the late Bob Pease
often echoed the sentiment.  Of course, his specialty was analog design...

--Chuck

Re: Digital circuits and analog devices

[drlegendre .]

You don't really find many examples of discrete states, anywhere in the
natural world. Just not a whole lot of quantization out there, unless you
reduce to the subatomic level - and while you'll find discrete states
(quanta) there, they are by nature indeterminate.

Have to admit, we did get an interesting universe.



On Thu, Dec 1, 2016 at 8:34 PM, W2HX <w...@w2hx.com> wrote:

> Not only are they made of analog devices, but at the speeds things have
> been running at for the last 20 (maybe 30) years, they often behave like
> analog devices. Things like transmission line theory, crosstalk,
> oscillation, etc are all important design considerations.
> Eugene
>
>
> -Original Message-
> From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Noel
> Chiappa
> Sent: Thursday, December 01, 2016 9:31 PM
> To: cctalk@classiccmp.org
> Cc: j...@mercury.lcs.mit.edu
> Subject: Digital circuits and analog devices
>
> So I have this memory of a set of law promulgated by an engineer at DEC,
> one of which was something to the effect that 'all digital circuits are
> made out of analog devices'. However, my memory doesn't recall where I saw
> this, and my Google-fu is not strong enough to turn it up. Can anyone help?
>
> Noel
>

RE: Digital circuits and analog devices

[W2HX]

Not only are they made of analog devices, but at the speeds things have been 
running at for the last 20 (maybe 30) years, they often behave like analog 
devices. Things like transmission line theory, crosstalk, oscillation, etc are 
all important design considerations.
Eugene


-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Noel Chiappa
Sent: Thursday, December 01, 2016 9:31 PM
To: cctalk@classiccmp.org
Cc: j...@mercury.lcs.mit.edu
Subject: Digital circuits and analog devices

So I have this memory of a set of law promulgated by an engineer at DEC, one of 
which was something to the effect that 'all digital circuits are made out of 
analog devices'. However, my memory doesn't recall where I saw this, and my 
Google-fu is not strong enough to turn it up. Can anyone help?

Noel

Digital circuits and analog devices

[Noel Chiappa]

So I have this memory of a set of law promulgated by an engineer at DEC, one
of which was something to the effect that 'all digital circuits are made out
of analog devices'. However, my memory doesn't recall where I saw this, and my
Google-fu is not strong enough to turn it up. Can anyone help?

Noel