At VCF MW this past weekend, I was playing around with an FPP8/A stuffed
into a PDP-8/M with a fan removed. This hex-wide two-board set will happily
work in a quad-wide backplane, as it needs no signals that an 8/A would
otherwise provide.
I wanted to benchmark the FPP8/A with the software emulation that FORTRAN
IV supposedly does. Mind you, I also don't have an EAE in mine, so software
emulation for integer multiplication/division would also be used.
I tried running a simple program to print some natural logs and square
roots, which ran quite well with the FPP8/A in place.
Without the FPP8/A...all of the results were wrong. Significantly. Negative
numbers in many cases. No clear pattern as to what it's doing.
Would anyone be able to try my program on some other real hardware (or
another emulator) to verify? With and without EAE would also be desirable.
I'm not sure how to disable the EAE in SIMH, else I'd try that too.
Here's what SIMH looks like with my program:
PDP-8 simulator V4.0-0 Current git commit id: d35b8725
sim> at rk0 disk2.fortran.rk05
sim> b rk
.TYPE FLOAT.FT
DO 50 I=1,100
F = FLOAT(I)
G = SQRT(F)
H = ALOG(F)
WRITE(4,100) F,G,H
50 CONTINUE
100 FORMAT(' ',F12.6,F12.6,F12.6)
END
.R F4
*FLOAT/G$
1.000002 1.000002 0.000000
2.000002 1.414215 0.693147
3.000002 1.732053 1.098614
4.000002 2.000002 1.386296
5.000002 2.236070 1.609439
[snip]
98.000001 9.899495 4.584968
99.000000 9.949874 4.595121
100.000023 10.000008 4.605171
.
Much appreciated,
Kyle
> From: Brent Hilpert
> Your conceptualisation around the role of electrons is perhaps a
> little off.
Well, I'm not taking into effect things like the velocity of electrons
passing around the circuit (more current, with the same number of electrons,
effectively), etc, but I value the 'electron-based-view' since it led me to
understand the issue of EI conversion (something I don't recall having seen
called out explicitly - e.g. it's not in that DEC tech manual).
(Speaking of reducing the number of electrons: I recall a physicist - don't
recall who - who jokingly suggested the reason they are all identical is that
there is only _one_ - it travel forward in time an an electron, goes back as
a positron; rinse, repeat! :-)
> You don't need 'more' electrons to generate a higher current, you just
> need to 'expend them' more quickly, using words like 'more' and
> 'expend' loosely
Right, particularly since what's really happening (e.g. during the L
discharge phase) is that electrons are being 'borrowed' from the shells in
the atoms of the conductor, run around the circuit, and then returning from
whence they came.
> Capacitors very much play a role in supplying current to the load.
> Both the L & C play a role as energy reservoirs.
Right, but the C doesn't play a _direct_ role in the EI conversion, the way
the L does? (Or maybe it does - the voltage across the C could I guess play a
role in mobilizing electrons in the circuit?)
>>> The transformer is nonetheless much smaller than it would be in a
>>> straight linear regulator design because the secondary current it has
>>> to supply is several factors lower than for a comparable linear reg.
>> That's because of the higher efficiency of this circuit .. ?
> primarily it's because it's still a higher voltage by several multiples
> ... and thus the current that the transformer secondary has to deal
> with is the same factor lower .. meaning less copper for the secondary
> and less iron for the core.
Ah. Interesting tradeoff!
So it seems like they probably picked the intermediate voltage to be as high
as they could (to reduce the transformer cost), modulo the cost/availablility
of transistors for the switching...
> I haven't seen/read this TofOp.
Here:
http://www.bitsavers.org/pdf/dec/pdp11/1140/1140_SystemManual.pdf
if you're (still) interested; the H744 starts on pg 6-10 (pg 112 of the PDF).
Noel
Maybe you don't want to fix your program.
On September 19, 2018, at 5:46 PM, Michael Zahorik via cctalk <cctalk at classiccmp.org> wrote:
Kyle, I have not run my machine since March. Summer is car season. But I thought that maybe I could run this little program quickly. My PDP8E started up, loaded the RIM and SERIAL DISK then OS/8 ran. Everything looked good, BUT...... something is wrong with my FORTRAN 4. Programs seem to compile, but I can't even run a simple test program that prints out whatever I enter from the TTY. Something has gone south. Anyway, I'm not familiar with the command FLOAT(). Do I have to have floating point hardware to use this? Well.... either there is something wrong with my machine or more likely with my FORTRAN software or even more likely operator error (me). So many times after a long summer I have to re learn most of what I learned last winter. Kinda of like when I was in school after summer vacation. ?Mike Zahorik (414) 254-6768
From: Kyle Owen via cctalk <cctalk at classiccmp.org>
To: General Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
Sent: Wednesday, September 19, 2018 5:43 PM
Subject: Floating point math in FORTRAN IV on PDP-8
At VCF MW this past weekend, I was playing around with an FPP8/A stuffed
into a PDP-8/M with a fan removed. This hex-wide two-board set will happily
work in a quad-wide backplane, as it needs no signals that an 8/A would
otherwise provide.
I wanted to benchmark the FPP8/A with the software emulation that FORTRAN
IV supposedly does. Mind you, I also don't have an EAE in mine, so software
emulation for integer multiplication/division would also be used.
I tried running a simple program to print some natural logs and square
roots, which ran quite well with the FPP8/A in place.
Without the FPP8/A...all of the results were wrong. Significantly. Negative
numbers in many cases. No clear pattern as to what it's doing.
Would anyone be able to try my program on some other real hardware (or
another emulator) to verify? With and without EAE would also be desirable.
I'm not sure how to disable the EAE in SIMH, else I'd try that too.
Here's what SIMH looks like with my program:
PDP-8 simulator V4.0-0 Current? ? ? ? git commit id: d35b8725
sim> at rk0 disk2.fortran.rk05
sim> b rk
.TYPE FLOAT.FT
? ? ? DO 50 I=1,100
? ? ? F = FLOAT(I)
? ? ? G = SQRT(F)
? ? ? H = ALOG(F)
? ? ? WRITE(4,100) F,G,H
50? ? CONTINUE
100? FORMAT(' ',F12.6,F12.6,F12.6)
? ? ? END
.R F4
*FLOAT/G$
? ? 1.000002? ? 1.000002? ? 0.000000
? ? 2.000002? ? 1.414215? ? 0.693147
? ? 3.000002? ? 1.732053? ? 1.098614
? ? 4.000002? ? 2.000002? ? 1.386296
? ? 5.000002? ? 2.236070? ? 1.609439
[snip]
? 98.000001? ? 9.899495? ? 4.584968
? 99.000000? ? 9.949874? ? 4.595121
? 100.000023? 10.000008? ? 4.605171
.
Much appreciated,
Kyle
> From: Brent Hilpert
> In typical "down-converters" there are additional current paths in the
> supply, paralleling the input path, that can provide the 'additional'
> electron flow rate. ... the whole rationale of a switching supply is to
> use time (varying switching periods) and temporary energy storage to
> change that EI relationship from input to output without energy loss.
So, two more questions (if you have the time):
I can see that there's a nice synergy between the switching concept and the
buck converter (since the switch does exactly what the buck converter needs,
in terms of turning the input current off and on), _but_ - are there switching
supplies that operate the way I described (up-convert the frequency, then use
a transformer to get directly to more or less the right voltage)? I.e. without
needing to use a buck converter to do the conversion from low current at
higher voltage to higher current at lower voltage? (Although I guess the coil
for the buck might be cheaper than the transformer - even though the use of a
high frequency would reduce the size of the latter - making the buck approach
superior.)
To put it another way, there's no _necessary_ connection between the switching
concept, and the buck converter is there? Does that mean it is in theory
possible to stick a buck converter on the output of a linear supply to do the
V1I1-> V2I2 conversion? (Although I know it's probably a stupid design, because
you'd still need some sort of switcher for the buck converter, so the linear
supply would be basically pointless.)
> If the heatsinks seem huge compared to modern day supplies, that's more
> likely the result of technology improvements - faster devices, and
> moving from bipolar switching transistors to mosfets. Bipolar
> transistors have a near-fixed voltage drop which can't be reduced
Right, I knew bipolars had the fixed drop, but I hadn't made the connection
to that being the cause of the large amount of heat needing to be dumped.
Useful enlightenment!
> If you supply a link & location to a schematic I'll take a look
Here:
http://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/H744.tifhttp://ana-3.lcs.mit.edu/~jnc/tech/pdp11/jpg/H744.jpg
Thanks to everyone for taking the time and energy to reply!
Noel
Hi folks,
I am trying to find an out-of-print tech book for a research project I'm
doing. The book is called Porting Macintosh Applications to Windows 95 and
NT by Greg Stone, dated December 1996, ISBN 0471118516, published by Wiley.
It's listed on Amazon but not available; I've searched on
<http://usedbooksearch.net/> usedbooksearch.net and even WorldCat, with no
luck. Wondering if anyone has any ideas how I could find a copy?
Figure someone on this list could point me in the right direction. Would
love any help.
Thanks,
* Bill.
Bill Rosenblatt
GiantSteps Media Technology Strategies
157 Columbus Ave., Suite 409
New York, NY 10023
(212) 956-1045
Skype: billrosenblatt
Twitter: @copyrightandtec
Blog: https://copyrightandtechnology.com/
LinkedIn: https://www.linkedin.com/in/billrosenblatt/
Forbes: https://www.forbes.com/sites/billrosenblatt/
Visitors to the RICM like to play SPACEWAR! in the PDP-12. Unfortunately
using the console switches is uncomfortable, not intuitive, and is tough on
the switches. We would like to recreate the switch boxes used on the PDP-1
to make playing a better experience.
We modified the source
<http://www.ricomputermuseum.org/Home/equipment/dec-pdp-12/dec-pdp-12-source…>
>from D.E. WREGE
<http://www.pdp8.net/pdp8cgi/os8_html/SPCWR3.PA?act=file;fn=images/jby/jbyos…>
to use the LINC SXL instruction to read the PDP-12 GPIO signals, and
prototyped two switch boxes using recycled toggle switches. This works
great, so now we need to make better switch boxes.
This CHM article shows what we want to recreate.
<http://www.computerhistory.org/pdp-1/a87ddd9510aeebf6485c47a35f8a26aa/>
This article shows a sketch of the switch boxes.
<http://thedoteaters.com/?attachment_id=6416>
A generous donor made these boxes for us.
<https://scontent.fbos1-1.fna.fbcdn.net/v/t1.0-9/37971884_2342940525721951_2…>
The lever switches are turning our to be difficult to find at a reasonable
price. We found some NOS SwitchCraft lever switches that looked like the
sketch and the PDP-1 pictures and were a reasonable price, but our order
was rejected because they only had one in stock. eBay has Mossman and
SwitchCraft, but they are either very expensive (more than $50 each), or
they only have one available.
The switches that we are looking for need to be SPDT, three-position,
non-locking, center off. (If the switches have more than one pole we can
remove the extra poles to keep the operational force low.) Before we cave
in and buy some modern C&K toggle switches, does anyone have a source for
Mossman or SwitchCraft switches at a reasonable price?
--
Michael Thompson
> From: Brent Hilpert
> With the given 20-30VAC input (do I have that right?)
Yup.
> A glance at the schematic ... you might think it's just a linear
> regulator
And the writeup in the maint manual gives that impression too, which didn't
help! (Hence my assumtion that it was acting in the way a plain linear
regulator might, in terms energy efficiency.)
> Diode D5 provides the current path for L1 to supply energy to the load
> when the source is switched off.
Right. What is the role of the pair of big caps, C8/C9. Is that just to
filter ripple, or do they play a role in the provision of current when the
supply is switched off (by Q2)?
(My guess would be only the former, since unlike the energy stored in L1,
which can be used provide electrons when Q2 is off, capacitors only store
electrons, so they can't play much of a role in the conversion of V1I1 to
V2I2, which requires 'creation' of more electrons when I2>I1. Oh, reading the
maint manual, when Q2 is on, they store some of the current coming through
L1. So I guess they have a peripheral role in the overall operation.)
> The subtle thing about designs like this is where does the switching
> oscillation come from?, as there is no obvious oscillator present.
The maint manual does cover that. It more or less says that as the output
voltage rises through 5.05V, the voltage regulator turns off Q2, and as
it falls through 4.95, it turns it back on. (Presumably when the whole
works is first turned on, the output voltage is less than 4.95V, so Q2
stays on until it gets to the turn-off voltage.)
Q7 is part of the over-current sensing, it says.
> the switching is taking place after the transformer rather than
> straight off the mains, this allows the switcher design to be simpler
> and get away with using much lower voltage semiconductors.
Ah, I was wondering about why they did it that way.
> The transformer is nonetheless much smaller than it would be in a
> straight linear regulator design because the secondary current it has
> to supply is several factors lower than for a comparable linear reg.
That's because of the higher efficiency of this circuit, as opposed to a
straight linear regulator, which would need more mains power in to produce an
equivalent power out?
> Q5 is functioning as a common-base stage in the driver chain ...
> It is not part of the +15V supply to the 723, that is provided by
> R2, zener D2, C2.
I was confused by the maint manual, which says "D2 is used with Q5 and R2
to provide +15V to E1".
> There are a thousand configurations for power supplies possible
> depending on what needs to be accomplished ... It's useful to keep in
> mind that regulation and EI conversion are different objectives but
> they can be achieved either separately or in concert.
Got it.
> bipolars have a fixed MINIMUM drop, which can be used in a switching
> supply to as much advantage as possible with bipolars, but have a
> varying drop in a linear regulator
Right.
OK, I think I've got a decent grip on all this now - although I still
wouldn't want to try and _repair_ one... :-)
Noel
> Date: Sun, 23 Sep 2018 10:46:48 -0400
> From: Michael Thompson <michael.99.thompson at gmail.com>
> To: cctech <cctech at classiccmp.org>
> Subject: SPACEWAR! Switch Boxes for a PDP-12
> Message-ID:
> <CAH1BU=_4OVdEjGgMMcbyLZS9-aDCXp0sZxh1SiEJrtsuWu96Pw at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Visitors to the RICM like to play SPACEWAR! in the PDP-12. Unfortunately
> using the console switches is uncomfortable, not intuitive, and is tough
> on
> the switches. We would like to recreate the switch boxes used on the PDP-1
> to make playing a better experience.
>
> We modified the source
> <http://www.ricomputermuseum.org/Home/equipment/dec-pdp-12/dec-pdp-12-source…>
> from D.E. WREGE
> <http://www.pdp8.net/pdp8cgi/os8_html/SPCWR3.PA?act=file;fn=images/jby/jbyos…>
> to use the LINC SXL instruction to read the PDP-12 GPIO signals, and
> prototyped two switch boxes using recycled toggle switches. This works
> great, so now we need to make better switch boxes.
>
> This CHM article shows what we want to recreate.
> <http://www.computerhistory.org/pdp-1/a87ddd9510aeebf6485c47a35f8a26aa/>
> This article shows a sketch of the switch boxes.
> <http://thedoteaters.com/?attachment_id=6416>
> A generous donor made these boxes for us.
> <https://scontent.fbos1-1.fna.fbcdn.net/v/t1.0-9/37971884_2342940525721951_2…>
>
> The lever switches are turning our to be difficult to find at a reasonable
> price. We found some NOS SwitchCraft lever switches that looked like the
> sketch and the PDP-1 pictures and were a reasonable price, but our order
> was rejected because they only had one in stock. eBay has Mossman and
> SwitchCraft, but they are either very expensive (more than $50 each), or
> they only have one available.
>
> The switches that we are looking for need to be SPDT, three-position,
> non-locking, center off. (If the switches have more than one pole we can
> remove the extra poles to keep the operational force low.) Before we cave
> in and buy some modern C&K toggle switches, does anyone have a source for
> Mossman or SwitchCraft switches at a reasonable price?
>
> --
> Michael Thompson
Michel,
I did just what you did for being able to play Spacewar! on my PDP-8a (I
have KK8E with EAE, VC8E and the DK8E real time clock). But since the
frontpanel doesn't have proper switches for the switch register I had to
build game hand controls.
I built them just like those that can be spotted in the video from CHM:
https://www.youtube.com/watch?v=1EWQYAfuMYw but smaller.
I just used ordinary arcade style buttons and connected them to the
digital inputs on the DKC8A board and modified the source code for that.
Those hand controls have two switches for rotate left/right, one for fire
and one for acceleration. The last one is for hyper speed but that is
triggered by pressing left/right switches at the same time. I intended to
fix this so it should be triggered by the last button but never came to
it.
Unfortunately I haven't written on my page https://www.pdp-9.net/pdp-8a on
this yet...
/Anders
