Fibonacci circuit that automatically stops

Thread Starter


Joined May 11, 2017
I can't do the part where the circuit stops automatically. I copy the wording and then tell what I've done.

We will create a sequential circuit that generates Fibonacci numbers.

\(F_0 = 0;\ F_1 = 1;\ ....;\ F_n = F_{n-1} + F_{n-2}\ for\ n = 2, 3, 4\ldots\)

Specifically, the size of the records should be 6 bits.
When (at the end) the design works, let's turn it into a real circuit that knows how to "take off and land". For this we need as input signals
  • A "reset" signal, which leaves the circuit at the initial values
  • A "start" signal to read the number n and start the computation of the number of
  • The number n encoded with 4 bits.
The circuit must end automatically when you have calculated the Fibonacci number and give as output
  • The number "Fn" coded with 6 bits
  • A "halt" signal saying that computing is over
What I've done is a basic fibonacci circuit with two registers. Then I added a counter that takes the number from the constant when the START signal is 1 or from the subtractor when its 0. I've tried to make the circuit stop automatically when the counter reaches 0 so I used an AND with the clock signal and the inverted of the subtractor output. The prroblem is the subtractor keeps working after it reaches 0, so the AND doesn't work to stop fibonacci from summing.

I gave my best shot at it. The deadline has passed so please give it your best shot.


Joined Mar 31, 2012
I can't read your schematic -- the resolution isn't good enough. Also, be sure that it is very clear what each of the components in the schematic is.

Plus, keep in mind that we will not just work the problem for you -- WE don't know that the deadline has passed, and we've had plenty of folks make claims like that in an attempt to trick people into doing their homework for them. So we have pretty rigid guidelines on how we approach homework help.

But you've shown your best attempt -- at least once you get a good image posted -- and so we should be able to make some observations or provide some hints.


Joined Mar 31, 2012
It's definitely more readable physically, but how are we supposed to know that a box that has four ports, only two of which are labeled and those two are labeled only as "b in" and "b out" does? Don't force people, that you are asking for free help from, to exercise mind reading skills or dust off their crystal balls.


Joined Mar 31, 2012
Perhaps the fact that no one else has even deigned to reply is an indication that you haven't given nearly enough information for anyone else to figure that you are worth their time to even bother with. So far, I'm the only one that has taken enough interest to even attempt to tease out of you the needed information . The onus is on YOU to communicate your thoughts clearly and completely. I'm trying to help you learn how to do that by pointing out things that you presently are not communicating well.

But since you apparently believe that the burden is on everyone else to figure out what you are trying to do with a circuit containing several undefined black boxes and lots of unlabeled I/O ports, I'll be more than happy to leave you to it.