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Ben Eater's 8-Bit Computer project calls for 8 "4-bit D-type register". Is it ok to use the CMOS version, the CD4076BMTE4?http://bg-electronics.de/datenblaetter/Schaltkreise/CD4076B.pdf

I have heard that sometimes the voltage varies too much. The orignal design asks for the 74LS173. http://www.ti.com/lit/ds/symlink/sn54173.pdf

Also, can you use a bidirectional register, like the 74S194, and set it to go one way? http://www.ti.com/product/SN74LS194A

Lastly, can an 8 bit shift register IC, like the 74hc595, be used with four bits or does the chip require 8 bits to work properly? http://www.ti.com/lit/ds/symlink/sn74hc595.pdf

Sorry, for asking so many questions at once.

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    \$\begingroup\$ Post a link to a schematic. TTL outputs do not always play well with CMOS inputs -- that's why 74HCT was invented. So plopping a CD4000-series part into the middle of a TTL design is probably not a good idea. \$\endgroup\$
    – TimWescott
    Apr 11 '19 at 22:56
  • \$\begingroup\$ But you haven't posted a link to the schematic of the board you're trying to build. Not everyone here knows of Ben Eater, much less his 8-bit computer project. \$\endgroup\$
    – TimWescott
    Apr 11 '19 at 23:29
  • \$\begingroup\$ I added it, but its a huge project. If you don't want to wade through it can you just go over the differences in those chips in general? \$\endgroup\$
    – Putvi
    Apr 11 '19 at 23:32
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Anytime you consider making a change to something that someone else has spent ... not hours but months and perhaps years making sure it works right ... you need to be prepared to evaluate your change ideas, closely. And that means you need to understand how it works.

Ben Eater has gone to some length to reach out and teach the ideas he's applied, taken to a level almost anyone serious about the topic can follow even without much prior background. In your link to his web page, if you click on the "registers" link there, it will take you to five separate videos that take about an hour to listen to. Just on the topic of his register design.

He starts out talking about using 7474 D-type FFs but then points out that there's a need for tristating buffers, so he trots out the 74245 and a bunch of AND, OR, and NOT gate chips as well, all of which he has discussed in other (older) videos. However, in these videos he's discussing a much simpler approach using the 74173, which is actually designed from the start to operate as a register attached to a bus. It not only includes four D-type FF, but it also includes the AND/OR and enable logic required and it also includes the tri-stating ability for its outputs, as well. So it's pretty much everything all bundled into a nice, easy to use part.

The 74194 does NOT have the tri-stating outputs and it's not designed as a register for a bus, but for an entirely different purpose. You can't just poke around like that. Even if you could get the 74194 to hold values for you, you still wouldn't have the tri-stating capability. And you need that, as well. So you'd now have to change his logic involved in using the part, entirely. It's just wrong on its face.

One thing is sure. You aren't prepared to make your own decisions about swapping parts around like this. So don't.

You already have Peter's recommendation about the two families that kind of "hang together" in acceptable ways. But even then you still need to be wary. Stick with a single family unless you feel competent to do otherwise. Taking into account Peter's answer, you should read at least some of An Introduction to and Comparison of 74HCT TTL Compatible CMOS Logic where you will find the following two tables in "easy to read" comparison format:

enter image description here enter image description here

HCT was designed to meet the TTL level standards at its inputs and do so with lower input current, but you can see that there are differences in the output voltage and current compliance specifications. It's not likely to bite you. But for example, the HCT output current compliance is symmetrical while the LS isn't. You need to be able to evaluate if this matters in some situation you are considering.

You might want to skim over the above intro-doc I linked above to see if anything catches your attention. Other than that? I'd stick to the plan. There's a lot of work ahead and it will be enough already just getting that much done and working right.

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  • \$\begingroup\$ I wanted you to know that I thank both of you for your time in answering this and am especially glad you pointed out the tri-stating outputs part. \$\endgroup\$
    – Putvi
    Apr 12 '19 at 18:26
  • \$\begingroup\$ @Putvi I'm just happy you are engaging a project like this. I did almost this same thing (not the exact same thing, of course) in 1974 using wire-wrap boards when I was quite a bit younger. It's a very educational (and for me frustrating at times, of course) project and the experience will inform you in many different ways. Just make sure you have a very good power supply with adequate current compliance. (If you use the HCT family, it's likely you won't need quite so good of a supply.) Despite the LS family being lower power than their predecessor, they still draw current. \$\endgroup\$
    – jonk
    Apr 12 '19 at 18:29
  • \$\begingroup\$ @Putvi This may not directly apply to you (I've no idea what options are available in your location), but Digikey sells (if you buy only one at a time and live in the US) the HCT173 at about 1/3rd the price they want for the LS173: USD 0.64 vs USD 1.55. You should check out your own supplier options and see which direction may be better for you. \$\endgroup\$
    – jonk
    Apr 12 '19 at 18:42
  • \$\begingroup\$ I live in the US (IL) , but I ordered some of this stuff online and it took a long time to get and was broken when it arrived. I really do thank you for saying you are happy I am trying this, but I get frustrated when it takes a long time to get the parts and then spend hours putting things together to find the part didn't work. \$\endgroup\$
    – Putvi
    Apr 12 '19 at 18:51
  • \$\begingroup\$ @Putvi I'd probably do the same thing and get the same results, if I tried today. Back then, by the way, the prices took my breath away as it cost entire months' worth of salary to buy them. Relatively speaking, these are still cheaper than when I was buying them for this. Digikey won't send you broken or poorly packaged parts. Neither will Mouser. And I noticed that Jameco sells a kit that probably includes most of what you need: 420 pcs kit of 74LS. You also need lots of jumper wire! \$\endgroup\$
    – jonk
    Apr 12 '19 at 18:56
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In that project, I saw several 4 bit parallel-in/parallel-out registers - the '595 definitely won't work for those, as it is serial in/parallel-out. The '194 probably would work, as it has parallel in and out - just ignore the shift capability.

That project seems to be designed with 74LS family parts. You should stick with 74LS, although 74HCT should also work.

74HC and CD4000 parts will not work reliably with 74LS, as the input and output high levels for 74LS are lower than for 74HC and CD4000 CMOS parts.

74HCT has lower input thresholds so it should work with 74LS parts.

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  • \$\begingroup\$ I wanted to thank both of you for taking the time to answer. I really do appreciate it. \$\endgroup\$
    – Putvi
    Apr 12 '19 at 18:28

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