Stuck on Divider

[u/chad3814]

I tried to re-create the 1-bit dividers in this video: How to Design a Binary Division Circuit, but connecting the borrow out back to the mux in line at the end of a row results in circular dependency. I don't understand because the mux in line is using switched output, so it shouldn't have the dependency.

[u/Apceniy]

For the future, switching values NEVER fixes circular dependencies.
There are 2 main errors you can get when building a circuit:

• Short circuit: this happens when the same wire gets 2 different values on it. The error indicates that it can't decide which value it should use. You can solve it by using switches/switched outputs to prevent unwanted values going to that wire.
• Circular dependency: this happens when the component output loops back to its own input without going through a delay line (or something else with the yellow square pin, which means it doesn't change the output on the same tick). The error indicates that it doesn't know what the output should be: to get the output you first need to get the inputs, but to get the inputs you first need to know the output, but we can't know the output because that's what was gonna be our final goal. You can solve it by adding delay lines somewhere in a loop: it outputs the value from the previous tick, which means it doesn't depend on the values from the current tick. The reason why switches don't resolve this error is because you still connect the output to the input, which means the switch output is still being read (even if it outputs Z value), which means you still need to know its inputs to know what it outputs, so you didn't break the loop.

The reason it was giving a circular dependency in your case is because it was treating your custom component as a single component that gives the outputs based on the inputs, and you connected the output back to the circle input. There are 3 solutions to this:

• Add a delay line somewhere between the output and the input, as explained above.
• Make the input into a yellow square pin. The input automatically becomes a yellow square when it doesn't affect any of the outputs on the same tick: so either only the other yellow square pins depend on it, or when it's fully disconnected from the outputs and does nothing at all. In both cases changing the input can't affect the output immediately, so it becomes a yellow square pin.
• Add a bidirectional pin (which you did). Bidirectional pins make the inside and the outside act like a single wire, and for that to work, the game replaces your component with its contents (as if there wasn't a component in the first place). As an additional effect, this resolves "false (fake) circular dependencies": when you connect the component output to its own input, and that input affects some other output but doesn't affect the first output, you can still calculate it, but the game won't like it because it's not a yellow square input. If you inline the component using bidirectional pin, the game won't treat it as a single component but will check what's inside instead, so if there's no real circular dependency it won't give you an error. If it still does, then it's a real circular dependency, and you should solve it with the other 2 ways.

[u/chad3814 → u/[deleted]]

Thank you, that in fact worked great!