
7400 Quad 2-Input NAND Gate: Neglected Survivor from a Pre-Microprocessor World - sohkamyung
https://hackaday.com/2018/12/28/the-7400-quad-2-input-nand-gate-a-neglected-survivor-from-a-pre-microprocessor-world/
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VLM
Surprising they didn't mention the PO74G00A and its friends.

[http://www.potatosemi.com/datasheet/PO74G00A.pdf](http://www.potatosemi.com/datasheet/PO74G00A.pdf)

Note before you try to make a 1 GHz CPU using 1970s design with those chips,
for current limit reasons those chips can only switch in the GHz range with
output capacitance below the input capacitance of a single gate input, so your
redesigned PDP-11 is only gonna run at a mere 500 MHz not in the GHz range.

I'm a little unclear where you buy their products other than their ebay store.
Digikey doesn't seem to stock. They DO seem to be real, not a meme.

I've never screwed around with the PotSemi products but I've seen the youtube
videos where some dude makes a classic ring oscillator out of an inverter that
runs at some high UHF frequency like seven hundred MHz or so. I thought I was
pretty cool making ring oscilators running at 20-something MHz back in the
80s. If you're really bored or don't have a tape measure you can measure a
length of cable by inserting it into a ring osc and recording the resulting
frequency and applying some correctional math based on the speed of the
inverter... I suppose with a GHz class inverter the correction factor would be
round to zero for any cable longer than a couple feet and could be ignored.
You can also make a toy TDR using what amounts to a ring osc and a very fast
(expensive) o-scope.

Power supply noise decoupling caps must be "fun" with those chips, what
happens if you put a very old 0.1 uF cap that self-resonates at a freq lower
than the switching freq of the chip? Nothing good, I imagine. I know you can
buy 0402 SMD caps that resonate in the higher GHz range so thats OK, but you
know some goofball is going to try an 0.1 uF electrolytic for decoupling LOL.

In the "Old Days" you used strange fast high power logic sparingly to
eliminate race conditions, obviously the 74F would always latch up before the
74LS or whatever so careful use of ttl family could eliminate race conditions.
I would imagine that, and strange interfacing tricks, would be the purpose of
modern TTL. If you wanted a slow arduino to intelligently monitor a 30 MHz
signal, a little TTL support might make it possible in certain very limited
cases.

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al2o3cr
That datasheet is unclear about what exactly is required to get that 1GHz+
performance; my naive reading is that the CL=2pF case is _half_ of another
gate's input capacitance, which seems implausible.

OTOH, if CMOS compatibility isn't a problem you can go waaaaay faster with
things like this:

[https://www.analog.com/en/products/hmc746.html](https://www.analog.com/en/products/hmc746.html)

Single gate per package, but supports 10+Gbps data rates. 290mW per gate power
consumption o_O

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totoglazer
If you want to get experience with 7400 series, i had a great time building an
8bit computer following this YouTube series
[https://eater.net/8bit/](https://eater.net/8bit/)

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rwmj
I've had a lot of fun over Christmas assembling a Gigatron TTL - a computer
built almost entirely out of 74-series chips. It's amazingly easy to follow
exactly how it works just by looking at the schematics. (More build photos
coming on my blog in a few days:
[https://rwmj.wordpress.com/](https://rwmj.wordpress.com/))

~~~
jacquesm
I looked over the few solder joints that are visible and I think your
soldering technique needs some work. First make sure your iron is actually hot
enough, a hotter iron works quicker and the result is less, not more heating
of the joint. Then, try to work like this: first heat up the joint with just a
tiny bit of solder on the tip of the iron, much less than you need for the
joint, just enough to transfer heat, do that for 1 to 2 seconds, then feed in
_just_ enough solder from the spool to make the joint, withdraw the spool and
then the iron and let it cool without moving at all. That way your joints will
flow nicely instead of beading above the PCB and you won't have too much
solder in the joints. Good luck!

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rwmj
Yup I'm totally sure my soldering sucks. In fact I started out my career as a
hardware engineer, and there's a few reasons why I'm a software engineer now
:-)

(Edit: To be fair the picture shows the first few joints where I was basically
getting into the swing of things. Things improved after that.)

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gumby
I'm delighted to see this make the front page. A couple of years ago I
submitted "50 years of TTL" and several comments were about confusion of "time
to life" with the logic. Which is _not_ to make fun of anyone; what I found
interesting as the primary technical plaything of my early teen years has long
been displaced.

It's easier than ever before to get started playing with circuits, but in many
cases why would you? Just whack a mpu or even a RPI or Arduino and get going
It's a similar issue with ham radio: this is a great time in many ways to be a
ham, but there are so many alternative and less fiddly ways to talk to others.

~~~
jacquesm
> there are so many alternative and less fiddly ways to talk to others.

That's the main reason I never became a ham, there was a ton of interesting
tech and a couple of very knowledgeable people around the place where I lived
as a teen but the majority of them were engaged in hour long chat sessions
with their buddies rather than to work on even more interesting tech.

So, now with the internet you can chat to people halfway around the globe
without even knowing what EME or Heaviside layer means.

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raverbashing
Neglected? Not so much I'd say

It's the basic component for digital electronics experiments (pre
microprocessor ones)

~~~
totoglazer
Agreed. I think it’s probably more famous than anything mentioned, except
maybe the 555.

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gumby
741\. When I was starting it was easier to make simple waveforms with the 555
so I have a warm spot in my heart for it and the SSI TTL parts, even if the
741 has ended up handier over the years.

There was a nice front page post on the 555 a couple of months ago:
[https://news.ycombinator.com/item?id=18190765](https://news.ycombinator.com/item?id=18190765)

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smartinstot
Discrete logic chips are still in use all over the place, I've seen them in
reset circuitry. Modern versions come in smaller packages like 4-pin bgas, or
sot-23 and are available on Digikey.

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bogomipz
The caption under the picture of the Xero Alto states:

>"We could have featured a minicomputer such as a DEC PDP-11 as an example of
a CPU built from 74 series logic. But the 74-driven Xerox Alto makes a greater
point about 74 logic as the progenitor of modern computing devices."

Can anyone say how many discrete logic chips the CPU for the PDP-11 or the
Alto used in the design of their CPUs?

Might anyone have some links or suggested literature regarding these pre-
microprocessor CPUs?

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mepian
Plenty of literature, including schematics, can be found here:

[http://www.bitsavers.org/pdf/dec/](http://www.bitsavers.org/pdf/dec/)

[http://bitsavers.org/pdf/xerox/alto/](http://bitsavers.org/pdf/xerox/alto/)

~~~
bogomipz
Wow this is a real treasure trove, thanks!

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IWeldMelons
O yeah, good old K155LA3 (the Soviet clone of 7400). Was very popular among
the electronics enthusiasts.

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madengr
TI and Fairchild make a 6 pin “tiny logic” part that can be configured for any
gate. I use them frequently for glue logic.

