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D flipflop design I am trying to build a D flip-flop but I can´t get rid of those red wires. Is there a way to solve this?

EDIT: I was able to fix it manually through step-by-step simulation, but I still would like to know if there is a way to avoid this problem.

D Flip Flop, no red wires

Math Keeps Me Busy
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dedelli_kun
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1 Answers1

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Depending on the circuit you build, you cannot avoid this situation.

Commonly you get into it, if you close a feedback loop that already has a signal in error.

The menu "Simulate" has the command "Reset Simulation", the keyboard shortcut is Ctrl-R.

Logisim might also decide to disable its simulation in certain situations. You will see this in the same menu at the command "Simulation Enabled" (Ctrl-E). If there is no check marker, the simulation is disabled. You can toggle by this command.

One good way to avoid this situation as much as possible is to build your circuit from the inputs to the outputs. First connect inputs, only then close loops. If you see a signal in error, which you are going to use as feedback, take a break and strive to change input signals to bring that signal to some non-error value.

the busybee
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  • Thanks for the tip on building it, very much appreciate it. By the way, do you have some software recommendations for simulating this kind of circuit? It really would make things a lot easier for me if I knew a platform on which I could test asynchronous sequential circuits logic. – dedelli_kun Jul 17 '23 at 14:17
  • Recommendations are off-topic here on SO. However, what do you mean by "_simulating_"? Logisim **is** a simulator, and you can test your circuit at least manually. It even has simple support for automatic verification, see chapter "Command-line verification" of the documentation. – the busybee Jul 17 '23 at 14:25
  • My goal is to build vhdl components using only boolean structural achitecture (which benefits from comportamental architecture in processing speed). With that in mind, I was looking for an easy way to test if the components are behaving as intended. That´s why I wondered if you had any tips on tools I could use that would prevent this error from happening. I didn´t know recommendations were off-topic, but it makes sense since the focus of the discussions should be on electronics problems themself, and not on which software is better/software advertising. – dedelli_kun Jul 17 '23 at 16:59
  • @dedelli_kun The problem with recommendations is that they are opinionated. They _can_ lead to fruitless discussions. -- However, as you are kind of used to Logisim, you might want to try its successor, [Digital](https://github.com/hneemann/Digital). It is based on Logisim and can use some VHDL via GHDL. – the busybee Jul 17 '23 at 17:23
  • @dedelli_kun Or [Logisim Evolution](https://github.com/logisim-evolution/logisim-evolution) if you are more comfortable there. Neemann's Digital is really nice and I tend to like it better. But Logisim Evolution is another good option. It's worth trying out your ideas on these other simulators as they may be able to handle situations others cannot. Try them both and see. – periblepsis Jul 17 '23 at 22:08