Logisim Circuit prob

Thread Starter


Joined Aug 12, 2022
hello everyone.
I am a newbie in the world of logisim.

My prof asked me to copy this circuit, but i already spent 2 days trying to make it work so i can determine the answers.

To copy:


My work:

O RED.jpg

I wonder what is it that im doing wrong?

I'm meant to fill up a truth table:

Screenshot 2022-08-11 162406vvv.jpg
1. determine the relationship between 'D and Q' AND 'D and NOT_Q'

Im utterly confused.

Id appreciate some guidance here.



Joined Mar 30, 2015
Welcome to AAC!
i already spent 2 days trying to make it work
In those two days, did you read the manual pages?

Im utterly confused.
You have a wiring problem.

The blue wire indicates you don't have the clock connected correctly. Note the little green mark on the east border. That's where you need to connect the wire. If you want to connect on the south side, you need to change the attributes for that component.

You messed up something with the red wires. Delete them and re-enter.



Joined Mar 31, 2012
I think that the red wires are fine. The problem is that the simulator can't determine a value for them. The output of the bottom-left NAND gate is red because, with the bottom input 1, the output depends on the value of the other input. But that is a blue wire and so the state of that input is unknown. Similarly, with one input to the latch portion 1 and the other unknown, the values of the outputs of both NANDs that make up the latch are unknown.

Fix the issue with the clock signal and everything will likely work fine.

Thread Starter


Joined Aug 12, 2022
Hey Dennis, Thank you. I got it to work. The pin was so small for my eyes. But i saw the what was wrong eventually. Thanks for pointing it out.