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Hello, guys.
I'm reading Charles Petzold's book "C.O.D.E" and there is an adding machine example that uses 8-bit latch to save the sum for further addition. Here's the circuit image from book: https://i.imgur.com/aVF9Rwp.png.
I've built this circuit in program, but it throws the error "Oscillation" when I try to add some numbers.
I attached project below, find category "14. Feedback and Flip-Flops" and circuit named "Adding Machine (2)" if you want to help me.
There is no error if I don't set first number by switches, which means adding 00000000 and latch contents.
"Add" button is actually the Clock input of the flip-flops.
I even tried to test components of the circuit separately (e.g. checked if the adding machine works properly or 8-bit latch saves data as it should) and they seem to work well.
But when I wire them like in the example in the book I'm getting error. I think the connection between latch output and adder's B input (it's the single 8-bit wire that goes back to adder) causes the problem, but I don't understand what exactly going on, because circuit is too complex for me, there is so much components.

Hi,
First of all if you have not yet read about the oscillation please read it here: https://logiccircuit.org/oscillation.html
In your circuit you are using flip-flops with clock that is working by level. So when the Add button is pressed each flip-flop is storing the data its receiving on it’s input. So now let’s see what is going to happened when you set the A0 to 1 and press the Add button. The adder will produce result 1 that will be sent to latch, which store it and send to adder. Now adder will add 1 from buttons and 1 from latch, so it produce 2 and send it to latch which store it and send back to adder which will add 1 from buttons and 2 from latch, and so on. The process will never end.
In order to fix it you will need to change you flip-flops to controlled by edge, not level. You can find such flip-flops in samples or build them yourself. For more details see: https://www.electronics-tutorials.ws/se ... seq_2.html
Having JK flip-flop you can build D flop flop.
Hope this helps,
Eugene

But why circuit cycles as you described? I'm just pressing "Add" button instantly and by that supplying voltage to Clock only for a moment. So after releasing button loop shouldn't even start, because when Clock becomes 0 latch output doesn't change. Maybe loop starts too fast before I release button and program catches it?

Precisely, your circuit can't get to any stable state while your add button is pressed down.

Thank you very much for help!

Did not look at your circuit,but anything that uses SR flip flops WILL oscillate
Don't use them.Use a master-slave JK flip flop.(jk flip flops just dont oscilate.and they can accept 1-1 inputs)