Electronics > Projects, Designs, and Technical Stuff
Experimenting with TTL Cpu, 74LS chips, old vs New? Retro style switches?
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jfiresto:

--- Quote from: T3sl4co1l on June 04, 2020, 05:49:01 am ---
--- Quote from: jfiresto on June 04, 2020, 05:37:27 am ---The old 4000-series CMOS was a lot easier to work with. I think I would use that if I were building a discrete logic computer. It would be a little slow, but you could probably power it off bits of paper towel, lemon juice and some spare change.

--- End quote ---

Just about SFA at 5V, yup.  Plus you can overclock it to a massive 15, 18 volts even. Hold onto your hats we're cranking this baby up to TWO MEGAHERTZ! :-DD
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You could probably manage around 6 mhz at those voltages and be perhaps four times slower than the LSTTL equivalent. These days, I bet you could trounce a computer made with either, simulated in Python on a Raspberry Pi.
rwgast_lowlevellogicdesin:
@duak, Thanks a lot for that surplus link, the (SWT) 8V10128 model a quarter way down the page is exactly the kind of thing i was looking for and is WAY cheaper than a expected, but now looking at that page im wondering if the toggle switches with rollers on the end would be a cooler idea!

I have seen plenty of people breadboard pretty big 74LS projects with out any issues, most of the stuff I do is pretty low noise RF mixed with digital and hi power, so im pretty use to figuring out noise issue's, dealing with ringing etc. The thing is I don't want to deal with any of that crap while learning, hence why im not starting with the fastest logic chips I can. I would assume from some of the messy TTL projects I have seen that a good star grounding and decoupling rules of thumb like a .1uF on every chip along with a 1uf and 10uf for every 5 or 10 chips should be fine.

Still not sure if dumping the on hand 74LS and ordering everything in 74HC is worth the $50 bucks it will cost.
jfiresto:

--- Quote ---Still not sure if dumping the on hand 74LS and ordering everything in 74HC is worth the $50 bucks it will cost.

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With 74LS, you might have to think about fanout, but beyond that, I bet you can tend to everything else with a little thought and little fuss.
tggzzz:

--- Quote from: rwgast_lowlevellogicdesin on June 04, 2020, 06:29:38 am ---I have seen plenty of people breadboard pretty big 74LS projects with out any issues, most of the stuff I do is pretty low noise RF mixed with digital and hi power, so im pretty use to figuring out noise issue's, dealing with ringing etc. The thing is I don't want to deal with any of that crap while learning, hence why im not starting with the fastest logic chips I can. I would assume from some of the messy TTL projects I have seen that a good star grounding and decoupling rules of thumb like a .1uF on every chip along with a 1uf and 10uf for every 5 or 10 chips should be fine.

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"Ringing" isn't an appropriate concept, since that is associated with second (and higher) order filters.

If you are used to RF, you will know about transmission lines. Improper termination causes problems. The maximum wire length for which you can ignore transmission line effects depends solely on the transition time. For a quick intro, one place to start is https://www.edn.com/category/blog/bogatins-rules-of-thumb/

Power supply decoupling is required to deal with current transients due to changing voltage across capacitors and (with TTL, HTTL, STTL, LSTTL, FTTL) inputs consuming different current in the high and low state.

Decouplers need to have very short leads; you used to be able to buy flat capacitors that fitted under ICs and sockets with a built in capacitor under the IC.

Ideally you would have a solid ground plane and Vcc plane. On a two-sided board that would only be possible if you hand-wire all the signal connections.

For LSTTL an acceptable alternative is to have wide Vcc/GNd traces running under a row of ICs on the topside, and these should both be connected at both ends (don't have two interlocking fingers, one from each end). Put the 100nF decouplers on those traces by each IC. Add occasional "extra" grid grounds between the rows of ICs, to approximate a ground plane.

Wirewrap is OK for LSTTL but you have to be careful with faster families, and it fails for modern logic.

IDC is better than wirewrap, but I don't know if you can get the boards anymore.
T3sl4co1l:
Honestly I'd stick with the TTL.  You have it, you can breadboard it today.  You may have more special functions on hand than are available in HC.  Do try to design some if you can, inventory what you have and make sure you have enough of various types to do it.  And you can always interface to HC and such with just a little buffering.

Tim
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