1 Dec
2016
1 Dec
'16
6:31 p.m.
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
1 Dec
1 Dec
6:34 p.m.
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-bounces at classiccmp.org] On Behalf Of Noel Chiappa
Sent: Thursday, December 01, 2016 9:31 PM
To: cctalk at classiccmp.org
Cc: jnc at 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
8:17 p.m.
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 <w2hx at 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-bounces at classiccmp.org] On Behalf Of Noel
Chiappa
Sent: Thursday, December 01, 2016 9:31 PM
To: cctalk at classiccmp.org
Cc: jnc at 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
8:46 p.m.
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
9:59 p.m.
On Fri, Dec 2, 2016 at 2:31 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> 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
10:18 p.m.
On Thu, Dec 1, 2016 at 10:59 PM, Tony Duell <ard.p850ug1 at gmail.com> 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.
2 Dec
2 Dec
7:57 a.m.
On Dec 2, 2016, at 12:59 AM, Tony Duell
<ard.p850ug1 at gmail.com> wrote:
On Fri, Dec 2, 2016 at 2:31 AM, Noel Chiappa <jnc at mercury.lcs.mit.edu> wrote:
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
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.
9:13 a.m.
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
9:29 a.m.
On Fri, Dec 2, 2016 at 3:57 PM, Paul Koning <paulkoning at comcast.net> 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
11:22 a.m.
> 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.
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2:50 p.m.
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 <mouse at rodents-montreal.org> wrote:
--
4.4 > 5.4
> 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.
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X Against HTML mouse at rodents-montreal.org
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
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ard.p850ug1＠gmail.com -
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toby＠telegraphics.com.au -
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