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Help with logisim

alice  crushalice crush wrote 12/04/2020 at 03:06 • 1 min read • Like

help with logisim

i need it.  While messing around i designed a simple memory unit.  It's bassed on an or gate with feed back.  This is so simple , but it doesnt work.  place an and gate which feeds an or gate.  put two user controlled inputs.  One to the and gate one to the or.  the out put of the or gate feeds back to the and gate.  the two user controled inputs are named latch (the or input) and /zero (the and input)  The system should work like this...

/zero  latch output

   1          1         1      and it latches in so when you change to

   1          0        1     stays as the out put.  so far so good, what should happen

   0         0       0    when you lower the /zero input to 0 is the output should drop to 0, right?  well logisim instead goes into this state

   0          0       Error     huh? whats going on here?  that's my question...

                                   Help!  I'm confused and lost for what's happening.

Please, give me a hint what's going on.  Two simple logic gates....  I'll upload the .circ file if you need to see it...

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Yann Guidon / YGDES wrote 12/12/2020 at 00:59 point

I'm late to the party, sorry...
https://hackaday.io/project/27280-ygrec8/log/182585-a-tale-of-flip-flops examines some considerations that you might find useful.

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alice crush wrote 12/07/2020 at 17:45 point

thankyou thankyou thankyou!

it does work like i imagined it!  just goes to proove... 2 heads are better than 1.

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Dr. Cockroach wrote 12/07/2020 at 18:44 point

:-D

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alice crush wrote 12/06/2020 at 00:01 point

I feel somewhat calmed down, if even you question logisim's correctness, then I'm not crazy... two gates!  I've uploaded the circ and added it to trixy's pages.  i'd enter a url if i knew how...  go have a look at my Trixy project...  It's the only file.  I'm dieing for your feed back...

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Dr. Cockroach wrote 12/06/2020 at 01:30 point

Well, I got rid of the error.... Your OR gate has a small open floating wire dangling at the bottom input and Logisim sees it as a floating connection and forces a error. Delete the stub and the error is taken care of :-)   That is one thing that bugs me about Logisim :-D

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Dr. Cockroach wrote 12/06/2020 at 01:47 point

When you delete connections in Logisim you would think that the entire line would be deleted but noooooo, sometimes a little piece stays behind and if missed, it messes up the whole simulation ;-)

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Dr. Cockroach wrote 12/05/2020 at 01:01 point

Yes. Please upload the .circ file. I think I understand how you have it set up but as I have had a lot of errors with Logisim that actually work with my real Light Logic gates I sometimes question Logisim even though it is my main simulator.

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alice crush wrote 12/13/2020 at 03:25 point

uploaded and fixed, yay!  thankyou dr cockroach.

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