Reverse-engineering a 1960s hybrid flip flop module with X-ray CT scans
righto.com
righto.com
This paragraph caused chills to run up my spine. The fact that they used AC coupling on the clock line seemed clever because it saved a couple of transistors, but the fact that they depended on J and K always being "slow" was cringeworthy. If J and K were somehow not slow, the device would become "not a proper flip flop." And yet it went to the Moon, so I guess they knew something I don't.
One other thought: When Ken grounded the J line, he was attaching it to essentially zero impedance to ground. The clock line will never have zero impedance, but it's reasonable to expect it to have lower impedance than regular signal lines. The sensitivity on J and K might be more a function of signal impedance than rise/fall time per se. Of course the two things are not unrelated. Potato/potahto.
I also will note that even the much vaunted Apollo guidance computer was a case of worse is better. The Saturn 5, now that had a proper flight computer(the LVDC), designed by IBM, redundant everything, A computer that could not fail. The AGC in contrast not only had no internal redundancy, it was designed to fail (in case of error the system could very quickly reboot and resume running it's program where it left off). However the trade off was that the AGC was half the weight and twice the speed as the LVDC and they could carry two of the things to get the reliability they wanted.
I eventually moved to software at which point I discovered that it's even worse here. It's at least 10^6x more difficult to kill people though and you usually don't have to get off your chair to undo the carnage.
Um, but what if someone does something outside of the tests.
"Well, then it breaks".
Yes, but this is software, how does it break?
"Hopefully not badly and insecurely"
The reason for this is that it saved much more than a couple of transistors.
Most flip-flops with relaxed timing requirements are of the so-called master-slave type, and the most frequent implementation variants need either 4 times or 3 times more transistors than are needed for an AC-coupled flip-flop, for which 2 transistors may be enough in its simplest variant.
Even the first integrated flip-flops have used schematics similar to the earlier discrete flip-flops, until they were replaced by later models, using more transistors, such as the TTL 54/7472, 54/7473, 54/7474, 54/7476.
I never knew AC coupled clocks happened before DC coupled clocks. Thanks!
By the way, this modules wasn't used in flight; it was part of a test box that was used on the ground. The Updata Link box onboard the spacecraft was built with different technology. Just want to avoid confusion :-)
This scan is online at: https://app.lumafield.com/project/afa60fd5-308d-41da-a0c6-14... You can manipulate the scan yourself after creating an account.
Anyway, thanks for the link, nice piece of technology.
So indeed the word "hybrid" could have been used only after the appearance of the first "monolithic" integrated circuits, to distinguish between the 2 types of integrated circuits.
I do not remember now if this is true or not, but the term "integrated circuit" could have been used before the first monolithic integrated circuit, to designate such modules assembled from various discrete components, which were then used as components themselves.
A few years later, the term "hybrid integrated circuit" began to mean specifically a device made with a substrate, usually ceramic, on which 1 or more dies of monolithic integrated circuits were attached, together with some discrete components, e.g. transistors, resistors, capacitors, inductors etc., and all were interconnected using thick-film or thin-film technology, before being packaged for environmental protection.
A device made in the same technology, but without any dies of monolithic integrated circuits, would have been named simply as a "thin-film integrated circuit" or "thick-film integrated circuit", as it was not a hybrid.
The flip-flop module described here is definitely an "integrated circuit", but it uses none of the more modern interconnection technologies used in the more recent integrated circuits, i.e. it is neither monolithic nor hybrid nor thin-film nor thick-film.
During the last decades, most integrated circuits have been monolithic, because that is the cheapest interconnection technology per component device, so now people presume when hearing just "integrated circuit" that it is a monolithic integrated circuit.
Such an old integrated circuit, for which none of the later specific terms are applicable, might be called now as a "non-monolithic integrated circuit" or just as a "flip-flop module".
Paying possibly hundreds of thousands of dollars for a machine and still not being able to operate it independently of the producer because a significant part of the software is “on the cloud” is not a good thing.