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 [ 10 posts ] 
 Series Prefix Subtractor or Manchester Magnitude Comparator 
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Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
Works even better in 74CBT transmission gates...

But I've got a three rails of ten MY4N 12VDC QPDT relays to attempt a logic demo.
Sadly, the internal LEDs only light one direction and not terribly bright at that...


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Sat Sep 03, 2022 3:37 am

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
How a similar but not exactly identical ALU might appear as 6nS ICs...
Wired for Manchester Carry this time, omitted zero, and combined some controls.


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Last edited by Ken KD5ZXG on Sat Sep 03, 2022 9:43 am, edited 2 times in total.



Sat Sep 03, 2022 3:49 am

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
If drawings failed to make the point, No Ripple.

A simple maze of switches can be setup by A vs B without waiting to know carry, borrow, or equal.
That maze quickly solves itself by path of least resistance.

250pS propagation delay per switch (74CBT3253). Perhaps a little more considering fanout to final XOR.
But 6ns to prefix those 5ohm switches occurs in one step of parallel time. Without a parallel prefix tree.

Where it breaks from Manchester: Generate isn't hardwired to VDD. Annihilate isn't hardwired to GND.
Instead, control lines LT GT allow new magnitude comparator functions.

Where it breaks from Konrad Zuse: Open circuit is not a valid logic level. Logic lows are driven.

Where it breaks from i8086, you would have to read Ken Sherriff's blog for that (different Ken).
http://www.righto.com/2020/08/reverse-e ... 8086s.html


Sat Sep 03, 2022 9:40 am

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
You might be thinking "The above doesn't look much like i8086".
Not yet, but let's observe where this is going...

Mucking with this puzzle in attempt to include rotation I also let
XOR vs NXOR determine the propagation of CARRY vs BORROW.
This allowed to omit the ADD vs SUB control line.

Was about then I notice the other Ken had blogged a teardown
and partial reverse engineer of the i8086. Scroll down about 1/3
of the article to find his drawing "One bit of the ALU."

At least my way of rotating still looks different. RP is short for
"Replacement", the new flag to shove when propagation of a
prior carry/borrow/equal flag does not occur. Also a convenient
signal to intercept for rotations and reversal by RP loopback.


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Sat Sep 03, 2022 6:59 pm

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
This would be my pile of junk to build the relay version.

Coils solve XOR in either direction. MOVs clamp flyback
+/- 18VDC in either direction. But they don't allow the
one-way LED built into the relay to work either direction.

Thus you see a bag of diode bridges to replace MOVs.

Simulation given with OP of this thread chose lamps
that don't care a direction. No bridges are needed to
solve XOR. Bridges also solve XOR, but redundant to
coil or lamp logic and not really the purpose.


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Sat Sep 03, 2022 8:03 pm

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
Lamps... Maybe I don't need diodes or MOVs. As drawn in the sim, a low resistive lamp is bidirectional and should also damp coil flyback. Just learned Christmas surplus may be strung with 12V lamps and sockets, or lamp leads might screw down without sockets. Far cheaper than pinball bulbs. Wouldn't take much to outshine that dim one-way LED inside each relay.


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Last edited by Ken KD5ZXG on Thu Sep 22, 2022 7:03 am, edited 2 times in total.



Wed Sep 21, 2022 9:01 pm

Joined: Mon Oct 07, 2019 2:41 am
Posts: 365
Ken KD5ZXG wrote:
Lamps... Maybe I don't need diodes or MOVs. As drawn in the sim, a low resistive lamp is bidirectional and should also damp coil flyback. Just learned Christmass surplus may be strung with 12V lamps. Replacements available and cheap (far cheaper than pinball bulbs) . Wouldn't take much to outshine that dim one-way LED inside the relay.

How do you do a lamp test, to check for dead bulbs?


Wed Sep 21, 2022 11:00 pm
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Joined: Sun Dec 19, 2021 1:36 pm
Posts: 8
Location: Michigan USA
Ken, Is this your first attempt to build a hardware relay-based logic unit, or possibly you have other photos or designs that you put into hardware? Looks like really interesting stuff. Michael


Wed Sep 21, 2022 11:21 pm WWW

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
oldben wrote:
How do you do a lamp test, to check for dead bulbs?

Probably isn't any input condition that would light all bulbs at once.
Input conditions to test the Zero lamp have already been shown.
Two other settings should cover the rest...


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Last edited by Ken KD5ZXG on Thu Sep 22, 2022 6:57 am, edited 1 time in total.



Thu Sep 22, 2022 5:45 am

Joined: Sat Sep 03, 2022 3:04 am
Posts: 19
mmruzek wrote:
Ken, Is this your first attempt to build a hardware relay-based logic unit, or possibly you have other photos or designs that you put into hardware? Looks like really interesting stuff. Michael


Well, there was one-bit hot glued to a popsicle stick. Built from the trash bin.
Regularly had to thump the benchtop to unstick it. Using majority logic then,
rather than truth table logic now. So the relay count wasn't quite as efficient.
Wasted one extra DPDT, yet didn't offer quite as many functions...

Some of the sticking could have been micro-welds from undamped coil flyback.
By the time I found MOVs to deal with that, I had new relays and a better plan.

I look back at this old drawing with few clues what could I have been thinking?
Majority3 of X,Y,Z is Carry. MAJ3 of X,Y,1 makes OR. MAJ3 of X,Y,0 gives AND.
Something like that. Further specifics I've totally forgot. Not worth it.

"Easy to make MAJ3 from MUX4. Hard to make MUX4 from MAJ3.", or
"Easy to glue junk to sticks. Much harder to unstick."
Might be other morals to this story.


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Thu Sep 22, 2022 6:14 am
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