woodelf wrote: If the difficulty with flip-flops is coming up with an edge-triggerred design, or regardless, you might be interested in a scheme used in (many) Japanese SSI calculators from the late 60s: - All flips flops are a master-slave form, but each section (M & S) is a basic, dead-simple, gated flip-flop. - The clock presents two phases to the system, the phases being *non-overlapping* pulses. - All slave sections are gated *directly* by one phase of the clock (call it the update phase). - Master sections are gated by the other phase (call it the capture phase), but not (necessarily) directly: typically, intervening logic controls whether a given master section is gated or not, as per the desired function of the flip-flop. Because the slave section outputs are all modified simultaneously, but asynchronous to the master sections, the master section inputs are guaranteed to be stable when the master sections are gated (as long as the longest logic propagation path is accounted for). Advantages: - simple flip-flop design, no need for edge-triggerring. - no concern about setup or hold times. - fully synchronous at the system level, no worrying about propagation glitches, etc. Disadvantages: - every 'system flip-flop' or 'bit of state' is actually two (gated) flip-flops. (Another cheap trick in the SSI IC era was to front a basic 2-gate flip-flop with discrete capacitors and resistors to get edge triggerring.)

This talk of making flip-flops brings to mind a topic not mentioned much at all any more--that of AC-coupled logic. Does anyone own any CPUs constructed using this logic type? I realize it was more common when thermionic devices (tubes/valves) were used, but I do recall seeing some transistor and tunnel diode circuits using AC coupling. Cheers, Chuck

Chuck Guzis wrote: Are you referring to AC-coupled/triggerred flip-flops (where the clock trigger is applied thru 2 capacitors to the input of each side of the FF) or to logic where all signals (gate inputs, etc.) are AC-coupled?

Chuck Guzis wrote: It's before my time, so I'm no expert, but I'm unaware of any 'full' systems made using such techniques. What I've run across about such stuff seemed to talk about it in-principle but with little or limited/specialised practical appplication. Core-logic, which was inherently AC-coupled, didn't go very far. The parametron circuit was AC-coupled wasn't it? .. read a little bit about it some years ago, but not in much depth. ..haven't heard of that one before.

I stumbled on this document: http://klabs.org/mapld04/papers/g/g233_alonso_p.doc while wondering about AC transformer-coupled logic and discovered that the original idea for the Apollo guidance computer was to use AC- coupled (core-transistor) logic. How's that for tying two threads together? :) Cheers, Chuck

Brent Hilpert wrote: Doing a bit of googling on the AGC, I found that it uses electroluminescent displays.

On 2 Jan 2007 at 22:18, Brent Hilpert wrote: I recall a Popular Science (IIRC) article of around that same time gushing about how EL was going to revolutionize the world and one of the applications shown was a large 7 segment display. Work with EL generated quite a bit of interest back in the 60's, including light amplification for radiography (make a sandwich of dots of EL cells with CdS photoresistors and apply an AC voltage. The dark cells will tend to stay dark, while those that fluoresce under bombardment will form a feedback loop.) Reminds me of making a code practice oscillator by sandwiching a carbon mic with an earphone. I don't know if the technology ever made it to prime time. So that it used EL doesn't surprise me. The only other alternatives (incandescent, plasma, mechanical) were probably too power-hungry and/or fragile. Cheers, Chuck

Brent Hilpert wrote: I don't see why. I've seen early 1970s guitar amplifiers that use a large EL strip for the control panel backlight. It's not a huge stretch to imagine that NASA would make a display for a spaceship computer out of them a few years previously. Gordon

At least one Philips valved radio (1960's, I think) used an EL panel as the base for the tuning dial (rather than the more conventional filament lamps to illuminate said dial). And I seem to remember reading about EL panels in photogrpahic books of the late 1950s (they were proposed as a darkroom safelight). Of course all these applications ued plain panels, not divided up into segments. -tony

I have a Japanese parametron logic trainer. I think there are 12 parametrons in it, so it is not too useful. I think parametrons died out fast because all other logic forms were much easier to implement as speeds increased. Once the things get up into the MHz region, tuning and phase shifting became real issues. Nobody wants to tune logic - leave that to the radio guys. -- Will

I would bet there is some sort of Nyquisteque formula for figuring out how fast a parametron could work, using frequency F. Obviously, for the parametron to go fast, the frequency (or pulse duration) needs to be really quite high (or short). And as the F goes up in HF and VHF, all the gremlins come out that all the radio guys know about. -- Will

All my (very few) documents (yes, Al), are in Japanese. with inputs feeding the core. With an odd number of inputs (required with majority gates), and sine signals of either phase applied (0 degrees is zero, and 180 degrees is one, for example) to the inputs, the phase in the majority saturates the core, and is fed out to the amplifier (12AX7s, in this case) to be normalized. At least I think that is how they work. The more important thing about this logic trainer, and the NEAC, is that it shows us Westerners that the Japanese were indeed able to make quality goods in the late 1950s. -- Will

On 2 Jan 2007 at 20:24, Brent Hilpert wrote: What's changed is that software methods can now be patented. But not that long ago, the best you could hope for was to publish your algorithm in CALGO or one one of the other journals (say, NYU Courant Institute) and hope someone noticed. I think that a number of software patents currently granted could be undermined with some scholaraly research. Nothing like omitted "prior art" citations to mess over a patent. Cheers, Chuck